Planet Arduino

Hello readers

Today we are going to examine a new kit from the people at Evil Mad Scientist Laboratories – the Diavolino. In English this means “little devil”. This little devil is a low-cost Arduino Duemilanove compatible board – with a few twists.

This is sold as a bare-bones kit, so you really need to plan ahead with regards to how you want to use it. It does not include a USB interface, nor power socket, header sockets, IC socket, nor a voltage regulator. This may sound like a bad thing – but it is not This kit is perfect for those who wish to make a permanent project using the Arduino system, without spending the extra on a whole board, and without the hassles of making your own barebones PCB version.

So let’s have a look… the kit ships in a nice reusable anti-static bag:

and upon turfing out the contents, one receives:

Which is just enough to have a basic setup. The instructions on their web site mention the inclusion of some zero-ohm resistors to be used as jumpers, but these were not included. However that is a non-issue, some resistor lead clippings will do the job. EML have gone to a lot of trouble with the printed-circuit board. It certainly is different to the normal green or blue ones out there. It is very well detailed with component position labels, and all components are through-hole. The other side of the board is also printed this way:

There is also a nice instruction laminated card included in the bag which has enough information to get your started. Furthermore, there is an excellent instruction manual available for download here (10 MB). Finally, this is an open-source hardware product, so the designers have also made available the gEDA CAD files.

Now for assembly. Normally I would photograph each step, however the instructions available for download are so good, I won’t need to Eleven out of ten for the instructions. Soldering it together is quite easy, however I did supply my own IC socket – I am just not a fan of soldering expensive parts (I get the shakes sometimes), however if you are confident, go for it.

Before deciding to permanently solder in that microcontroller, you will first need to take into account how you will be programming it. As the board does not support the usual native USB interfacing, you can’t just plug in the cable like a normal board. The Diavolino does have an interface for a TTL-level cable – so if you have (for example) a USB FTDI cable, you can program it via the USB port. But considering an FTDI cable is around $20, you might as well just buy a normal board like a TwentyTen instead.

It only took around fifteen minutes to get to this stage:

For my personal use as another bench-based board  (that sounds a little odd…) I will power it from the FTDI cable, so a link is required behind the TTL input pins – as well as adding the  6-pin and 8-pin header sockets. The easiest way to solder those in is to turn the whole thing upside down and plug it on top of an existing shield, as such:

However if you don’t want to buy an FTDI cable – and you already have another Duemilanove board, the cheapest way to program the microcontroller is to just insert it into a  Duemilanove-type board, upload the sketch, then drop the chip into the Diavolino.

You also need to decide on how to power the board. If you supply 4.5~5.5V, all you need is to feed in the power wires. If you are going to use more than 7V, you will need a 78L05 power regulator, 10uF electrolytic capacitor and a DC socket to use a plug-pack if necessary (see the instructions). However, a 78L05 can only supply 100 mA of current (see the data sheet.pdf), so you won’t be able to use some products like a MAX7219 LED driver and many LEDs. Unfortunately there isn’t enough space for a TO-220 sized 7805 1 amp regulator, so you will need to introduce 5V using an external supply hard-wired into the board if you need more than 100mA of current. Or you can power it from the USB FTDI cable for desktop use.

So there you have it – another successful kit build. This was an interesting alternative to the Duemilanove, and a great solution for a permanent project, or for someone who wants another board on the cheap. If you can work with the power supply current restrictions, all is well. So get one or more, have fun with it, and give one  to someone else to get them cooking as well My Diavolino came from Little Bird Electronics.

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. High resolution photos are available from flickr.

Otherwise, have fun, stay safe, be good to each other – and make something!

[Note - this kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

This is part of a series titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Welcome back fellow arduidans!

This chapter we will examine piezo buzzers, continue with our alarm clock, and then spend more time with the wireless radio modules by creating some remote control systems and sending various data over the airwaves. So let’s go!

Sometimes you would like to make some noise. For warnings, fun, or to annoy people. A very simple and inexpensive way to do this is with a piezoelectric buzzer. In simple terms, it contains a disc of metal that can deform when a current is applied to it. If you apply an alternating current at a high enough frequency, the disc will move fast enough to create a sound wave, something we can hear.

This is an example of a small piezo buzzer:

bzzzzz

This example was very cheap, less than $2.  Here is the data sheet: PS1240.pdf. It can run from between 3 and 30 volts AC – which thankfully the output from our Arduino falls between. But how do you output AC from an Arduino? There are several ways, however the easiest is using pulse-width modulation (PWM). If you look at your Arduino’s digital output sockets, some are labelled PWM. Using the function analogWrite(); you can send a PWM signal to the buzzer. For example:

/*

Example 13.0

Drive a piezoelectric buzzer with Arduino

http://tronixstuff.wordpress.com/tutorials > Chapter 13

*/

void setup()

{

     pinMode(11, OUTPUT);   // sets the pin as output

}

void loop()

{

     analogWrite(11,128);

     delay(500);

     digitalWrite(11, LOW);

     delay(500);

}

The sketch above will beep the piezo on and off, and be somewhat annoying. Perfect. However with the analogWrite(); function it is impossible to use the full frequency range of the piezo buzzer. With a value of 254 for the duty cycle, the frequency generated is around 1500 Hz:

Later on we will explore ways to create a better range of sounds. But now to use that buzzer in our alarm clock to help wake people up.

Continuing on from exercise 12.1, this chapter we will add some more features to the clock. First of all is the piezo buzzer. As we just discussed above, using it is quite simple. On the hardware side of things, we can replace the resistor and LED connected between digital pin 6 and ground with our piezo buzzer. On the software side of things, instead of digitalWrite(6, HIGH); we use analogWrite(6,128);. Very easy. And here is a short video – with sound!

Moving on, it’s time to clean up the alarm function in general. Most alarm clocks have a snooze function, so let’s add one as well. When the alarm sounds, the user presses button four to turn off the buzzer, and is then asked if they want to snooze. Button one is yes and four is no. If yes, add ten minutes to the alarm time and carry on as normal. When adding the ten minutes be sure to check for increasing the hour as well, and also take into account the jump from 2359h to 0000h (or 2400h). If the user presses no, the alarm is switched off and the user warned with the flashing “OFF”.

Example 13.1 – Here is a demonstration of what I came up with:

and the accompanying sketch: example13p1.pdf. The hardware is the same as exercise 12.1, except the LED and resistor from digital pin 6 to GND has been replaced by the piezo buzzer as described earlier. You will find the snooze function is controlled in the checkalarm(); function in the sketch.

In chapter eleven we started to examine the inexpensive serial data transmitter/receiver pairs. In this chapter we will continue working with them, to create the backbone of various remote control and data transmission ideas for you to use.

Example 13.2

First of all, a simple remote control with four channels. That is, it has four buttons, and the transmitter will send out the state of the four buttons, high or low. This would be useful for a remote control toy or a perhaps robot. The sketches are quite simple. The transmitter reads the buttons with digitalRead(); then transmits a single letter a~h – which is code for a button and its state. For example, a means button 1 is low, h means button 4 is high. The receiver just decodes that a~h code and sends the result to the serial monitor window. Here is the sketch for the transmitter – tx.pdf and receiver – rx.pdf.

To save time I will use the button board created in example 12.3. Here are the schematics for the transmitter and receiver sections:

And set up:

And finally a video of the serial monitor showing the button states:

Now that we have the data being sent across, let’s get some switching happening.

Example 13.3

Using the same transmitter system as example 13.2, we will turn on or off four LEDs at the receiving end. Of course you could use relays, transistors, 74HC4066s, etc instead. Our sketch (ex13.3rx.pdf) decodes the transmitted data once more, but sets the digital pins high or low depending on the received code. Here is the schematic for the new receiver:

… and the board laid out:

And again a quick demonstration video:

Now that you can turn the LEDs on or off with a push of a button, there are a few other ways of controlling those digital outputs with the remote control rig without altering the hardware.

Example 13.4

This time, we will control two digital outputs with the four buttons, as each output will have an on and off button. Consider this sketch; and the following demonstration video:

So there you have various ways to control digital outputs and send basic data across a wireless radio serial data link. In the coming chapters we will examine sending more detailed data, such a numbers, and more complex variables using a faster and more reliable hardware link.

Well that is another chapter over. However, as usual I’m already excited about writing the next instalment… Congratulations to all those who took part and built something useful!

Please subscribe (see the top right of this page) to receive notifications of new articles. High resolution photos are available from flickr.

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. If you would like to showcase your work from this article, email a picture or a link to john at tronixstuff dot com. You might even win a prize!

Don’t forget to check out the range of gear at Little Bird Electronics!

So have fun, stay safe and see you soon for our next instalment, hopefully by 7th August 2010.

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Hello readers

Today we are going to examine the Texas Instruments TLC5940 16-channel LED driver IC. My reason for doing this is to demonstrate another, easier way of driving many LEDs as well as LED display modules that are common-anode. If you have a common-cathode display module, you should have a look at the Maxim MAX7219. Moving along, here is the IC:

Another nice big DIP IC. Also available in HTSSOP and QFN packaging. What can this IC do for us? It can control 16 LEDs per IC, and also be cascaded to control more and more, with the display data arriving via a serial line in the same manner as a 74HC595 shift register. Furthermore, another benefit of this IC is that you don’t need matching current-limiting resistors for your LEDs, as this IC is a current sink, in that the current flows from the 5V rail, through the LED, then into the IC. However, it can control the brightness of the LEDs using pulse-width modulation over 4096 steps via software, or using a single resistor.

What is pulse-width modulation? Normally an LED might be on, or off. But if you switch it on and off very quickly, it does not look as bright (as it is not on 100% of the time). If you alter the period of time between on and off, you can alter the perceived brightness of the LED. Here is an example, compare the brightness of the LED bars against the display of the CRO – as the brightness increases, the voltage (amplitude [vertical thickness]) spreads across the entire time period (horizontal axis); as the brightness decreases, the voltage spread across time retreats:

Using the IC is very easy on the hardware front. Here is the data sheet: TLC5940.pdf. The pinout diagram is quite self-explanatory:

Pins OUT0~OUT15 are the current-sink pins for each LED. When one is selected they allow current to flow into the IC from the 5V rail, with the LED in between – turning it on. However it is easier to understand with a practical example, such as this (click to enlarge):

Here we have our Arduino board or compatible sending serial data to the TLC5940 to control sixteen LEDs. The 2k ohm resistor is required to set the maximum current available to flow through the LEDs, thereby adjusting their brightness. Using software you can adjust the brightness with PWM for each LED by itself. Very important: this circuit will need external power into the Arduino or a separate 5V power supply. The circuitry on the breadboard draws up to ~318 mA by itself – running the Arduino from USB only made it somewhat flaky in operation. Here is the circuit in action with an ammeter between the breadboard and 5V out on the Arduino:

Anyhow, let’s get moving once more - here is the assembled demonstration circuit:

For our example, we will be using the Arduino way of doing things. Thankfully (once more) there is a library to make controlling the IC exponentially easier. The library page and download files are available from here; the documentation page is here.  If you need guidance on installing a library, please visit here. However the commands to control the IC are quite simple with the Arduino library.

First of all, include the TLC5940 library, as such:

#include “Tlc5940.h”

Then in void setup(); you create the object using the function:

Tlc.init();

You can insert a number between 0 and 4095 to set the starting PWM (LED brightness) value, however this is optional.

Setting an output for display requires two functions, first Tlc.set(l, p); where l is the output (0~15) and p is the PWM brightness level – then execute Tlc.update(); which sends the command to the IC to be executed. The sketch below is easy to follow and understand the process involved.

Moving forward with the demonstration, here is the sketch  - TLC5940demo.pdf, and the video clip of operation:

When the LEDs are glowing from dim to bright and return, we are altering the PWM value of the LEDs to adjust their brightness. This also occurs during the last operation where the LEDs are operating like the bonnet of KITT.

Well once again that’s enough blinkiness for now, again this is another useful IC that helps simplify things and be creative. As always, avoid the risk of counterfeit ICs  – so please avoid disappointment, support your local teams and buy from a reputable distributor. Living in Australia, mine came from Farnell (part number 1226306). So have fun!

Remember, if you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. High resolution photos are available from flickr.

Otherwise, have fun, stay safe, be good to each other – and make something!

[Note - the TLC5940 was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

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Hello readers

Today we are going to examine the 74HC238 decoder/demultiplexer IC. My reason for writing this was to examine another way to get more output pins when using an Arduino or compatible board. However you can use any combination of three logic lines to turn on or off eight mutually exclusive outputs. How? Let’s find out…

First of all, here is the IC:

It is also available in SO16, SSOP16,  TSSOP16 and DHVQFN16 packages. What? Here is a good list of various SMD packaging types. Although my sample is from NXP, a quick search shows it is also made by Texas Instruments and ST Microelectronics. Here is the NXP data sheet.

The pin layout is very simple, apart from +5V and ground, you have six pins that control the outputs, and eight output pins, however in reality you only need to control three from the microcontroller or other logic lines. Here is the pinout diagram:

To get the output pins high, you use a combination of levels on pins A0~A2 and possibly E3. If you leave E3 low, no outputs can be set to high. The input combination required for each output is described in this table from the data sheet (click to enlarge):

Notice that columns with an X can be set either high or low, but you must not leave them floating, so always connect or set an X to high or low. If you need to have active low outputs (that is, outputs are high instead of low), there is the 74HC138. So now to do this in real life! Here is a demonstration schematic to use the 74HC238 with an Arduino Duemilanove or 100% compatible board:

… and in real life:

And here is a demonstration video, using this arduino sketch: 74HC238Arduino.pdf

Question: In real life, in which country is the Hoff a popular singer?

As with most other ICs of this type, you can only source 25 milliamps of current from each output, so if you need more you will have to consider the use of a switching NPN transistor etc. Although only one output can be high at a time, if you scan them quick enough, you can create the illusion that all are on at once (as in the video). Apart from LEDs and other items, you could use this IC to control stepper motors or even create a safeworking environment on a model train layout.

To conclude, the 74HC238 offers one of several ways to control more things with less control pins. Ideal for mutually exclusive outputs, however if you needed more than one high at once, the 74HC595 shift register would be the better solution. (See here for a 74HC595 tutorial).

As always, avoid the risk of counterfeit ICs and get yours from a reputable distributor. Living in Australia, mine came from Little Bird Electronics.

Once again, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our new Google Group. High resolution photos are available on flickr.

Otherwise, have fun, be good to each other – and make something!

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In this article you can follow the process of making another LCD shield for the Arduino Duemilanove or compatible boards. In the past (which explains the word another in this title) I made a 16 x 2 character LCD shield, however it was not backlit, nor large enough. Recently I acquired a 20 x 4 character backlit LCD for use in my Arduino tutorials, therein making this project necessary. To refresh your memories, here is the original shield:

However this time, I cannot mount the display on the shield, it is just too large. Furthermore, it is preferable to be able to stack other shields on top of the new LCD shield. Therefore the display will be external and connected with lengths of wire. So time to get cracking. The first step was to assemble all the parts together. The new LCD has a standard 16-pin  HD44780 interface, and is very easy to connect:

What we have: one 20×4 character backlit LCD, a Freetronics basic protoshield, some stacking pin headers, a button, 10k ohm trimpot for contrast adjustment, and some spacers and matching screws to give the LCD some legs. Afterwards I got some 0.1uF ceramic capacitors as well, to smooth supply current on the 5V rail of the shield. Here is the data sheet for the LCD: 2004 LCD.pdf.

As usual the first thing to do was to make a plan. The LCD interface is easy enough, but I still like to have something on paper to refer to:

The next step is to breadboard it – to make sure it works. However I did solder in the wires to the LCD at this stage:

And after assembling the circuit, a brief test:

Success. The demonstration sketch is the example provided with the Arduino IDE, modified for a 20×04 LCD – 2004LCDdemo.pdf. During the test above, I used an external 5V power supply for the breadboard. Remember to connect the ground line from the Arduino to the ground line of your breadboard, otherwise it will not work. At this point I was wondering how much current the LCD used by itself. The data sheet claimed it was five milliamps… I think not. Mr Multimeter had a different opinion:

Now it was time to finish the soldering work. Instead of trying to jam all the wires together along the digital pins, I used some wire jumpers to spread out the landing points for the wires from the LCD.

Furthermore, I decided to install a power LED and 560 ohm resistor – you can never have too many LEDs. The rear of the protoshield was also quite neat, dollops of solder easily bridged pads when required. Then after a visual inspection it was time to solder in the header pins. The easiest way to do this is to use an existing shield:

After soldering in the pins, the first attempt of using the display was unsuccessful. I had confused a couple of wires, but some reprogramming of the sketch fixed that. (It was Saturday night and my eyes were tired). But once the error had been fixed – success!

If this shield/display needed a name, I would call it the Dog’s breakfast. Now, hardware is only half of the solution – there are one or two things to take into account when writing your sketch. If you do not have the latest version of the Arduino IDE (v18), upgrade so you will have the new LiquidCrystal library. Also, when using .setCursor(x,y); to position the cursor, the top left position on the LCD is 0,0; and the bottom right is 19,3. For example, the image below was created by:

lcd.setCursor(0, 0);
lcd.print("A");
lcd.setCursor(1,1);
lcd.print("B");
lcd.setCursor(2,2);
lcd.print("C");
lcd.setCursor(3,3);
lcd.print("D");

Now to make something slightly more useful to take advantage of the screen area – another clock! (I like clocks) using my DS1307 real time clock shield. Here is the sketch: worldclock.pdf, (doesn’t allow for DST) and an action shot:

Question – from which organisation did my LCD module come from?

So there you have it. Another way to use an LCD with an Arduino, and show how you can do things yourself.

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. High resolution photos are available from flickr. This article is a guide – always check your own work before committing to construction.

Otherwise, have fun, stay safe, be good to each other – and make something!

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Today we are going to examine the Maxim MAX7219 LED display driver IC. The reason for doing so is to show you how something that used to be quite complex can be made very simple – and that is what all this technology is for, isn’t it?

If you have ever tried to control lots of LEDs, or more than two or three 7-segment displays, or even an LED matrix, you realise that there is quite a lot of work to do on the software and hardware side of things. It usually involves lots of shift registers, switching transistors, and some nifty coding to get everything working. And then your code is too large, so the resulting display scans slow enough to see it flicker, etc.

Not any more! The MAX7219 combined with a great library (well for Arduino anyway) solves all the headaches in no time. After using it for the first time today I was briefly angry for not finding out about it sooner… better late than never.

First of all, let’s have a look:

Yes, at first glance you may think that it takes a lot of real estate, but it saves some as well. This chip can completely control 64 individual LEDs, including maintaining equal brightness, and allowing you to adjust the brightness of the LEDs either with hardware or software (or both). It can refresh the LEDs at around 800 Hz, so no more flickering, uneven LED displays. You can even switch the display off for power saving mode, and still send it data while it is off. And another good thing – when powered up, it keeps the LEDs off, so no wacky displays for the first seconds of operation.

Interfacing the MAX7219 is also very simple, you only need three digital output pins from a microncontroller, 5 volts and ground. Up to eight ICs can be cascaded to control up to 512 LEDs at once – from only three data pins. Wow. However, controlling all these LEDs will require a power supply that can allow 330 mA just for the IC, so you can’t just run this off your Ardiuino – you will need external power. Nothing an LM7805 regulator cannot fix.

For more technical information, here is the data sheet: MAX7219.pdf. Now to put it to work for us – this article will demonstrate using an 8 x 8 LED matrix, as well as 8 digits of 7-segment LED numbers. First of all, let’s examine the hardware side of things. Here is the pinout diagram for the IC:

At this point I should mention it is designed for common-cathode display systems.

One example would be an LED matrix, such as:

Normally you would have to program to switch on individual rows and columns, and repeat those commands in software, as well as using switching transistors or a 74HC4066 to control the cathodes.

Another example is a multi-digit 7-segment LED module – current flows in through the anode pins, and each digit is illuminated only when its cathode is connected to ground. Such as this unit:

It has input pins for each of the eight LED elements, and four cathode pins, one for each digit. We can use two of these displays with the MAX7219 very easily, as you will see below.

An example circuit to demonstrate using the matrix is below. Note the lack of resistors and transistors:

When using with (for example) an arduino-type board, you would connect serial data in, clock, and load to three digital pins. The resistor is the hardware control via limiting current to the LEDs. My examples use a 1k0 1/4-watt value. If you are going to experiment with this value, refer to page 10 of the data sheet first. Furthermore, ensure the ground of the MAX7219 is connected to the ground of the microcontroller. The capacitors are used to reduce supply current ripple. And here is the demonstration circuit on the breadboard:

In the above photo, the five wires on the left are connected to the Arduino board (5V, GND, load, clock, data). The two wires from the terminal block head to my DIY 5v power supply.

Now it is time to examine the software aspect, or how to control the MAX7219. My knowledge of microcontrollers is currently only Arduino, so we will use that for this review. Thankfully there is an excellent library that has been specifically written for the MAX7219 – the LedControl library. You will need to download and install the library from the LedControl page. If you need guidance on installing a library, please visit here.

The author has done a marvellous job of documenting his library, so I will briefly describe the basic functions you need to get things blinking. Here is a very basic demonstration sketch:

#include "LedControl.h" //  need the library

LedControl lc=LedControl(12,11,10,1); // lc is our object
// pin 12 is connected to the MAX7219 pin 1
// pin 11 is connected to the CLK pin 13
// pin 10 is connected to LOAD pin 12
// 1 as we are only using 1 MAX7219
void setup()
{
// the zero refers to the MAX7219 number, it is zero for 1 chip
lc.shutdown(0,false);// turn off power saving, enables display
lc.setIntensity(0,8);// sets brightness (0~15 possible values)
lc.clearDisplay(0);// clear screen
}
void loop()
{
for (int row=0; row<8; row++)
{
for (int col=0; col<8; col++)
{
lc.setLed(0,col,row,true); // turns on LED at col, row
delay(10);
lc.setLed(0,col,row,false); // turns off LED at col, row
delay(10);
}
}
}

Using the lc.setLed() saves a lot of code, as the chip will hold the display on until it is told otherwise, you don’t need to program in a delay loop. You can just enter X and Y coordinates for the LED to switch on.

To switch off the display to save power, use lc.shutdown(0, true); - replace true with false to switch it back on again.

The video clip below is more of a detailed demonstration, using the schematic above, and this sketch:

Notice how altering the brightness up and down causes a nice “breathing” affect. However, don’t run that type of thing for too long, the MAX7219 does warm up nicely after about ten minutes of running all LEDs at once at full brightness…

Question – What was the manufacturing week and year for my MAX7219?

Now it is time to examine how the MAX7219 deals with seven-segment LED display modules. It can handle up to eight digits, so I have two four-digit display modules to use. The anodes will be connected, so they behave as one single eight -digit unit. Here is the schematic:

And here is the demonstration circuit on the breadboard:

Now to examine the functions to control these displays. Once again, be sure to have the LedControl library as used with the matrix. Here is another simple sketch:

#include "LedControl.h" //  need the library
LedControl lc=LedControl(12,11,10,1); // lc is our object
// pin 12 is connected to the MAX7219 pin 1
// pin 11 is connected to the CLK pin 13
// pin 10 is connected to LOAD pin 12
// 1 as we are only using 1 MAX7219
void setup()
{
  // the zero refers to the MAX7219 number, it is zero for 1 chip
  lc.shutdown(0,false);// turn off power saving, enables display
  lc.setIntensity(0,8);// sets brightness (0~15 possible values)
  lc.clearDisplay(0);// clear screen
}
void loop()
{
  for (int a=0; a<8; a++)
  {
    lc.setDigit(0,a,a,true);
    delay(100);
  }
  for (int a=0; a<8; a++)
  {
    lc.setDigit(0,a,8,1);
    delay(100);
  }
  for (int a=0; a<8; a++)
  {
    lc.setDigit(0,a,0,false);
    delay(100);
  }
  for (int a=0; a<8; a++)
  {
    lc.setChar(0,a,' ',false);
    delay(100);
  }
  for (int a=0; a<8; a++)
  {
    lc.setChar(0,a,'-',false);
    delay(100);
  }
  for (int a=0; a<8; a++)
  {
    lc.setChar(0,a,' ',false);
    delay(100);
  }
}

Once again, the use of the LedControl library certainly makes things easier. The difference between setChar() and setDigit is that the former can also write A~F, space, and a few other letters that are legible when used with a 7-segment display. Here is a video of the above sketch in action:

As you can see, driving all those LED digits is now a piece of cake. To think twenty years ago we used to muck about with various 4000-series ICs, decimal to BCD converters and so on. The MAX7219 just does it all. Now that I have learned how to make a nice huge display – there is only one thing to do… make another clock! It uses an arduino board, and my RTC shield. Here is the sketch: maxclock.pdf, and the clock in action:

Well that’s enough blinkiness for now, I could spend a week making displays with the MAX7219. In all honesty, I can say that it makes life exponentially easier when trying to control more than one LED with a microcontroller. Therefore it really is highly recommended. The only catch is the MAX7219 isn’t the cheapest IC out there. eBay seems to be full of counterfeit versions – just compare the Maxim Direct 1000+ price against the eBay price – so please avoid disappointment, support your local teams and buy from a reputable distributor. Living in Australia, mine came from Little Bird Electronics. So have fun!

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. High resolution photos are available from flickr.

Otherwise, have fun, stay safe, be good to each other – and make something!

[Note - the MAX7219 was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

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This is part of a series titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.

Welcome back fellow arduidans!

This chapter we will spend some more time with the rotary encoder by using it to control a clock, look at ways of driving a common-anode LED display with Arduino, and make a usable alarm clock with which we can start to move from the prototype stage to an actual finished product – something you would be proud to give to someone.

So off we go…

In chapter eleven, we looked at getting some values from the rotary encoder. Not the easiest way of receiving user input, but certainly interesting. This week I have an example for you where the encoder is used for setting the time of a digital clock.

Example 12.1

This example is basically two previous projects mashed together. It consists of the LED digital clock from exercise 7.1, and the rotary encoder sketch from example 11.2. The sketch was quite simple in theory, but somewhat complex in execution. The idea was to read the decoder, and after every read, display the time. However, if the encoder’s button was pressed, the time set function would be activated. At this point, you turn the encoder in one direction to set the hours, and the other direction to set the minutes. Then press the button again to set that time and return to normal operations.

To recreate it you will need:

• Your standard Arduino setup (computer, cable, Duemilanove or 100% compatible)
• Seven 560 ohm 1/4 watt resistors
• Four 1 kilo ohm 1/4 resistors
• Four BC548 NPN transistors (if you cannot find these, you can use 2N3904)
• Two 74HC595 shift registers
• DS1307 timer IC circuit components (see this schematic from chapter seven) or a pre-built module
• Solderless breadboard and connecting wires

Here is the sketch for your perusal: example 12.1.pdf, and the matching schematic (sorry, I forgot to add the DS1307 module – see example 12.2 schematic below for how to do this):

… in real life:

and a video clip:

After watching that clip you can soon see that there is an issue with the encoder. As a normal switch can bounce (turn on and off very very quickly in the latter part of operation), so can a rotary encoder. That is why it would sometimes return a result of clockwise, instead of anti-clockwise. Furthermore, they are right little pains when trying to use in a breadboard, so if you were going to use one in greater lengths, it would pay to make up your own little breakout board for it. Therefore at this stage we will leave the encoder for a while.

You may also have noticed the extra shield between the real time clock shield (yellow) and the TwentyTen arduino board. It is the Screwshield for Arduino – reviewed here. It is very useful to making a stronger connection to the I/O pins, or using normal multi-core wires.

Next on the agenda is the common-anode LED display. Normally the LED display we have demonstrated in the past has been common-cathode, and very easy to use. Current would flow from the power supply, through the shift register’s outputs (for example the 74HC595), through current-limiting resistors, into the LED segment, then off to earth via the cathode. Current flows through a diode from the anode to the cathode, and finally back to earth/ground. For a refresher on diodes, please read this article.

The other month I found this useful LED display:

Absolutely perfect for our clock experimentations. A nice colon in the middle, and another LED between the third and fourth digit which could make a good indicator of some sort. However the one catch (always a catch…) is that is was common-anode. This means that current starts from the power supply, through the common anode pin for the particular digit, then the LED segment, the LED’s individual cathode pin, through the current-limiting resistor and then to ground. With the current flowing in the opposite direction via a common anode, we can’t just hook the display up to our 74HC595 shift register.

Therefore, we will need the shift register to control switches to allow the current to flow through each segment, just like we have done previously controlling the cathodes of a common cathode display (see example 12.1). So to control the digits of this new display, we will need twelve switches (eight for the segments of the digit, and four to control the anodes). That would mean twelve BC548  transistors and 10k ohm resistors, and a lot of mess.

Example 12.2

Instead we will now use the 74HC4066 quad bilateral switch IC. I have reviewed this chip being used with Arduinos in a separate article here. The 74HC4066 is quite a common chip, available from many suppliers including: Farnell/Newark (part number 380957), Digikey (part number 568-1463-5-ND) or Mouser (771-74HC4066N). If you cannot find them, email me and I can sell you some at cost plus postage. Once you have a understanding of this IC, please consider the following circuit:

Most of this should be easily understood. One shift register is controlling the anodes, turning them on and off via a 74HC4066. In past examples this shift register would have turned off common cathodes via a 10k resistor and an NPN transistor. The other shift register is controlling the individual LEDs for each digit via a pair of 74HC4066s (as they only have four switches per IC).

Here is the sketch, this should be quite a familiar piece of code for you by now: example 12.2.pdf.

To recreate it you will need:

• Your standard Arduino setup (computer, cable, Duemilanove or 100% compatible)
• Seven 560 ohm 1/4 watt resistors
• DS1307 timer IC circuit components (see this schematic from chapter seven) or a pre-built module
• Two 74HC595 shift registers
• Three 74HC4066 quad bilateral switch ICs
• Solderless breadboard and connecting wires
• LED clock display module

And here is the result, with red and a blue display.

And the usual board layout:

Question – Do you think the time shown on the display was correct when I took the photo? Personally the blue looks really good in a dark background. You can also get them in yellow and green.

Moving along. Now and again, you often want to have a few buttons in use for user input, however the cheap ones don’t really like to sit in a breadboard. Naturally, you could make your own “button shield”, which would be very admirable, but then it would be preset to certain pins, which could interfere with your project. I had the same problem in writing this chapter, so came up with this example of an external “button panel” to make life easier.

Example 12.3

Here is the schematic, nothing complex at all – just four buttons and the required 10k ohm pull-down resistors:

and the finished product:

This was a quick job, as I will need to use a few buttons in the near future. Have also put some rubber feet on the bottom to stop the solder joints scratching the surface of the bench. Originally I was going to chop off the excess board at the top, but instead will add some LEDs to it after finishing this article. However using this button board will save a lot of frustration by not trying to jam the buttons into a breadboard.

Exercise 12.1

Now it is time for you to do some work. From this chapter onwards, we will be working on making a small alarm clock – something you could use. Just like the six million dollar man, we have the capability, the technology, and so on … except for Steve Austin. So this chapter, your task is to create and breadboard the  circuit and the underlying sketch. Using the LED display from example 12.1, your clock will have a menu option to set the time, alarm time, turn on and off the alarm, a snooze button – and also switch the display on and off (so you don’t stare at it when you should be trying to sleep).

You could either use a DS1307 module, or the raw parts. For an explanation of the circuitry, please see this post about making a RTC shield. You can always change it when we get to making a real prototype. The same with the Arduino – but for this exercise just stick with the normal board. Later on we will use a bare circuit the same as in chapter ten. With regards to user input, it’s up to you. A rotary encoder could be a real PITA, my example below just uses buttons. Anyhow, off you go!

Parts you will need:

• Your standard Arduino setup (computer, cable, Duemilanove or 100% compatible)
• Seven 560 ohm 1/4 watt resistors
• DS1307 timer IC circuit components (see this schematic from chapter seven) or a pre-built module
• Two 74HC595 shift registers
• Three 74HC4066 quad bilateral switch ICs
• Four normally open buttons or a board as described in example 12.3
• Solderless breadboard and connecting wires
• LED clock display module

Here is my interpretation of the answer to the exercise, the sketch: exercise 12.1.pdf. Although this is a particularly long sketch for our examples, it is broken up into many functions which are quite modular, so you can easily follow the flow of the sketch if you start at void loop(). All of the types of functions used have been covered in the past tutorials. In then next chapters we will add more functions, such an an adjustable snooze, selectable blinking colon, and so on. If you have any questions, please ask.

The buttons have several functions. In normal clock display mode, button one is for menu, two turns the alarm on, three turns it off, and four turns the display on and off. If you press menu, button two is to select time set, three for alarm set, and four is like an enter button. When in the time/alarm set modes, button one increases the hour, button two increases minutes in units of ten, and button three increases minutes in ones, and four is enter. When the alarm activates, button four turns it off.

The schematic is just example 12.2 and example 12.3 connected together, however the first button on the external board is connected to digital pin 8 instead of 1.

So here is a photo of our work in progress:

And a video clip showing the various functions of the clock in operation:

Well that is another chapter over. However, as usual I’m already excited about writing the next instalment… Congratulations to all those who took part and built something useful!

Please subscribe (see the top right of this page) to receive notifications of new articles. High resolution photos are available from flickr.

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. If you would like to showcase your work from this article, email a picture or a link to john at tronixstuff dot com. You might even win a prize!

Don’t forget to check out the range of gear at Little Bird Electronics!

So have fun, stay safe and see you soon for our next instalment, hopefully by 23rd July 2010.

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This is part of a series titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here

Welcome back fellow arduidans!

Finally it is wireless week here in the tiny tronixstuff lab, as we will start to investigate radio data transmission; then followed by starting to make sense of rotary encoders.

So let’s go!

As technology has marched along and generally improved on the past, things have been getting small and relatively cheaper. What was once jaw-droppingly amazing is now just meh. But as you are reading this, you know differently. We can now take control of this technology for our own devices. What has been in the past quite unapproachable is now relatively – the concept of wireless data transmission. But no just sending a signal, like a remote-control garage door opener – but sending actual,  useful data – numbers and characters and so on.

How is it so? With this pair of tiny devices:

Quite small indeed – the pins are spaced 2.54mm apart, and the graph paper is 5mm square. The transmitter is on the right. This pair operates at 315 kHz, over up to a theoretical 150 metres. The data transmission speed is 2400 bps (bits per second). These units are serial passthrough, that is they can replace a link of wire between the serial TX (pin 1) from one Arduino, and the RX of another Arduino (pin 0). They don’t need aerials for very short distances, but the use of one will extend the range towards the maximum. And finally, the transmitter needs between 2 and 10 volts; the receiver 5. Here is the data sheet for these modules: 315MHz.pdf. Normally they are sold individually, for example the transmitter and receiver. You can also find faster (data speed) modules, however we will use these ones today.

In preparation to use these modules, another library needs to be installed – the VirtualWire library. Download the latest revision from the following location: http://www.open.com.au/mikem/arduino/.

There is also a guide to using the library in .pdf format as well. Please note the library author’s instructions with regards to licensing on the last page of the guide. For a refresher on how to install a library, please head back to chapter two. This library will save us a lot of time, it takes care of checking for errors, and only allows complete, correct data (i.e. what is received matches what is sent) to be used in the receiver’s sketch. However, as wireless is not 100% reliable, you need to take into account that transmissions may not be received, or erroneous ones will be ignored by the receiver’s sketch. You can reduce the data speed to improve reliability and range.

Therefore if you are using this for some important communications, have the transmitter repeatedly sent the message. Later on in this series we will investigate more powerful solutions. Anyhow, moving along …

Example 11.1

First of all, we will demonstrate the use of these modules with a basic sketch. It sends some text from one Arduino to another. The receiving Arduino sends the data to the serial monitor box. Of course you could always use an LCD module instead. In my own inimitable style the sketches are very simple, yet allow you to use their contents in your own work. Here is the sketch for the transmitter – tx.pdf and the receiver – rx.pdf.

When working with two sketches at the same time, you can have two Arduinos connected to your PC simultaneously,  just remember to select the correct USB port for the correct Arduino. Do this with the tools > serial port menu option in the IDE. Otherwise you will become very frustrated if you upload the rx sketch to the tx Arduino. Furthermore, you will need to remove the wire from digital 0 to the data pin on the receiving units before uploading the sketch. And finally, remember to set the serial monitor window at 9600 baud. Now I can laugh, but earlier I kept setting it to 2400 as that number was in my mind from the sketch.

Here are my two boards in action:

Although having both boards connected to the one computer is only useful for demonstration purposes, in real life this is obviously useless. Remember that once you upload your sketch the Arduino doesn’t need a computer, only a power supply. You can feed yours between 7 and 12 volts DC through the socket. A nice switchmode power pack will do nicely, or if you are a cheapskate like me, a PP3 battery and clip soldered to a DC plug:

You may find that when you use a battery powered Arduino that it basically does not work. Arduino genius Jon Oxer (co-author of Practical Arduino) has found a solution for this issue – place a 10k resistor between GND and digital 0 (RX), or between digital pins 0 and 1. The next thing to consider it improving the reception range. This can be done using two methods – the first by connecting an external antenna, either a length of wire, or perhaps a purpose-built aerial. The second method is to increase the supply voltage of the transmitter up to 12 volts.

Now it is your time to do some work:

Exercise 11.1

You now are able to send characters using the radio link from one Arduino to another. Now it is time to control things remotely. For the purpose of the exercise, we will just control three LEDs, turning them on and off. You already know how to control other things with digital output pins, so we just need to focus on getting the switching on and off. Hint – you can send characters via the wireless link, so create your own codes.

You will need:

• Two standard Arduino setups (computer, cable, Duemilanove)
• two breadboards and some connecting wire
• One transmitter and one receiver unit
• three LEDs
• 3 x 560 ohm 0.25 W resistors. They are to reduce the current to protect the LEDs

Here is the schematic of my interpretation:

… the transmitter:

… the receiver:

and the video:

So how did you go? Hopefully this exercise was easier than you had first expected. If not, here are the example sketches: exercise 11.1 tx.pdf and exercise 11.1 rx.pdf. A basic transmit/receive system like this would also be handy for testing the range that wireless modules can operate over, or testing a particular site to see if you could implement such wireless modules. It’s always better to test before agreeing to make something for someone.

If you are having trouble understanding the sketches, please feel free to ask for help via email, leaving a comment, or asking the question in our Google Group.

That concludes our work with radio wireless links – for now.

Next on the agenda is the rotary encoder. Recall how we used a potentiometer in the previous chapters as a dial, to select menu options using the readdial() function. It was simple, cheap and it worked, but some may say it was a kludge. There must be a better way! And there is, with the rotary encoder. A rotary encoder looks like a potentiometer, but it is a knob that can be rotated in either direction infinitely. Furthermore, the knob is also a normally-open button. The encoder we will be using in this chapter is a 12-step encoder, in that you can feel it physically resist rotation slightly twelve times over the 360 degrees of rotation.

Here is our example:

On one side there are three pins, and two on the opposing side. On the perpendicular sides are legs for strength, that is they are meant to be soldered into a PCB to lock it in nicely. The problem for us is that those legs interfere when trying to use the encoder in a breadboard, so I have bent them up and cut them off:

The pins are easy to understand. The two pins on one side are the button contacts, just like any simple button. The other side with the three pins – the centre goes to ground, and the outside pins are the forwards and backwards output pins. The data sheet for our encoder is here. After fooling about with this all afternoon, the quickest way to get a feel for how it works is with a simple demonstration. So first we will test it out, then see how we can use it in our user-interfaces.

Example 11.2

This example is very easy to assemble. You only need an encoder, and the usual Arduino setup. Here is the sketch: example 11.2.pdf; and the schematic:

and in real life:

and finally a snapshot of the output. Don’t forget to set the speed in your serial monitor box to 115200 baud:

So as you can see, this is a much better solution that then potentiometer that we used in the past. Plus having the button integrated in the encoder is very convenient, you can really create a user interface with only one control. In the next instalment of this series we will implement the encoder in an existing design.

At this point I would like to ask you for some feedback. Would you like shorter, weekly articles – or longer, fortnightly (every two weeks) articles? Please leave a comment with your opinion.

Subscribe (see the top right of this page) to receive notifications of new articles. High resolution photos are available from flickr.

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. If you would like to showcase your work from this article, email a picture or a link to john at tronixstuff dot com. You might even win a prize!

Don’t forget to check out the range of gear at Little Bird Electronics!

So have fun, stay safe and see you soon for our next instalment! (Hopefully the 10th of July)

Hello interested readers

Today we are going to examine a part that makes connecting external wires to an Arduino Duemilanove or 100% compatible board easier than trying to electrocute yourself – the Wingshield Industries ScrewShield. Is is such a simple and useful thing I am almost angry at myself for not getting one earlier. Better late than never!

The ScrewShield allows you to connect wires to all of your Arduino I/O pins via PCB-mounted terminal blocks. And it is also designed as a shield, so you can stack more shields on top like any other. Now to save costs it comes unassembled, but that isn’t a problem. Here is the contents of the bag upon arrival:

The quality of the PCBs are very good:

And no instructions were necessary – so time to fire up the soldering iron and fume extractor (hi Kortuk).

The first thing to do was jig up the socket pins with the PCBs using my favourite method, a lump of blutac:

Then it was a simple matter to turn it over and solder away; then repeat the process for the other wing. Time for a quick break to see how they look:

Once the sockets have been soldered in, the next step was to connect the terminal blocks together for each appropriate line:

And then time for another soldering session:

And we’re done. Looks kind of like a Lego spaceship from my childhood:

You can never have too many Arduino shields:

Another use for the ScrewShield is to make it easy to connect multi-core wires to a breadboard. Using PCB terminal blocks is usually difficult as the pins are a fraction too large for the holes in the average breadboard. However you can only use the analogue shield to do this, as a reader has pointed out, the pin spacing for the digital side is a little off:

Nice one. It’s always great to have a product with more than one use.

So there you have it. Another inexpensive, interesting and very useful part for the Arduino fans out there. If you use an Arduino – you really should get one of these. They are available from the usual retail outlets, and I purchased mine from Little Bird Electronics here in Australia.

If you have any questions at all please leave a comment (below). We also have a Google Group dedicated to the projects and related items on the website – please sign up, it’s free and we can all learn something. High resolution photos are available from flickr.

Otherwise, have fun, stay safe, be good to each other – and make something!

[Note - these parts were purchased by myself personally and reviewed without notifying the manufacturer or retailer]

Hello readers

Today you can follow making a simple 5V DC power supply from initial idea to finished product. This is not an exercise in making a flash power supply, just solving a problem with the parts at hand.

When writing my Arduino tutorials, or generally experimenting with the breadboards – and more often both – I have needed 5V DC to power something, or in the case of working with two Arduinos at once, having to run USB cables all around the place just to power them. Some may say “Oh, just get another couple of wall warts/plug packs”. True, but good ones are over Au$20 here… and buying cheap ones have not been so successful in the past. However, I do have a collection of odd-voltage plug packs from old cordless phones and so on.. 12V AC, 15V DC etc. And to be honest, right now the bbbooost project is in pieces in a box as I’ve run out of breadboards at the moment working on other things.

So while at my desk I thought “How can I combine my need for 5V, my cheapness and use one of these plugpacks?”. Easy!

After perusing my stock database it turned out that all the parts were already around me to make a simple 5V supply using an LM7805 voltage regulator. It is quite versatile, can accept voltages up to 35V, and I have some in the drawer. Here is the data sheet: LM7805.pdf.

Following this it occurred to me that it would be nice to not have to worry about the type of current from the plug pack – AC or DC. So my circuit needs a bridge rectifier. That can be made with four 1N4004 diodes. And it would be nice to have a power-on indicator that isn’t a tiny speck of light. Thankfully I bought some 20mm red LEDs when Farnell had a crazy sale last year. Perfect.

And finally, a nice enclosure. Or anything really, to hold it all together. A small semi-opaque jiffy box was hiding in the cupboard with some veroboard, so they will be used. How? Here is my schematic: (click to enlarge)

Oh – the resistor is 560 ohms. And here are the participants in this project:

The black stuff at the top-right is heatshrink. The next though was how to mount the board in the box – I don’t have any standoffs, but the box does have some slots to hold the board. So this tells me how much space there is to use on the board, as I will trim it down to fit the space available:

But before hacking things up with the tinsnips, it pays to see if your circuit will actually fit in the board space available. (However my circuit was quite small, so I knew it would fit). This can be done by laying out your parts on a sheet of paper that has a grid of dots at 2.54mm intervals. Next was to measure the internal dimensions of the box in order to cut the veroboard. Then out with the tinsnips and chop chop chop. When using tinsnips or a saw of some sort, try and cut a little outside of the line – as the PCB material does flex a little .This means that you may lose 2~3 mm at the edges, so make allowances for that.

Moving on, I now have the board sized for the box and can start component placement:

The parts just fit in together nicely. I will have to drill the holes for the 7805 regulator so it can fit, however it doesn’t really leave room for the 0.1uF capacitor. However it is not really necessary, the output will be ok without it. The leads from the power socket, and to the switch and output lead will feed from the bottom of the PCB.

Now for one final visual check, and then to solder in the components.

After doing so, then it was time to put the link in and cut the tracks. I use a sanding bit on the drill to cut the tracks, completely removing the copper.

After cutting the tracks on the solder side, it was a good time to use the continuity function of the multimeter to check for shorts between tracks and other errors. The soldering proved to be fine, and the track cuts worked. Now it was time to position the DC socket and switch in order to wire them in, then drill their holes. The output wire is to come out of the top:

Now all there is to do is solder the connecting wires from the DC socket to the rear of the circuit board, and the output wire via the switch. At this point the unit was also tested. Naturally my eyesight had failed me and a short had appeared. However it was sorted out with the solder sucker:

Notice how I tied a know in the output lead before it passes through the lid – this is to stop accidental damage to the board caused by someone pulling the wire out. Here is the finished product, with a nice red glow for a power-available indicator:

Hooray – finished. What else was there to do on a Tuesday night? The LED indicates power is supplied to the box, and the switch just controls the load. Not too happy about that 5.05V reading… but then again, that meter was somewhat inexpensive.

I hope you enjoyed peering into my electronic life once again. The purpose of this post was more of a confidence-builder than anything, but hopefully someone out there read this and thought “Yes, I can do that”. So go for it!

As always, thank you for reading and I look forward to your comments and so on. Furthermore, don’t be shy in pointing out errors or places that could use improvement. Please subscribe using one of the methods at the top-right of this web page to receive updates on new posts. Or join our new Google Group. High resolution images can be found on flickr.

Otherwise, have fun, be good to each other – and make something!