This is the second of three articles that will examine the LM391x series of LED driver ICs. The first covered the LM3914, this will cover the LM3915 and the LM3916 will follow. The goal of these is to have you using the parts in a small amount of time and experiment with your driver ICs, from which point you can research further into their theory and application.
Although these parts have been around for many years, the LM3915 isn’t used that much however for the sake of completeness we’re writing the tutorial. The LM3915 offers a simple way to display a logarithmic voltage level using one or more groups of ten LEDs with a minimum of fuss. If you’re wanting to make a VU meter, you should use the LM3916 which we will cover in the final instalment of this trilogy.
Instead of having each LED represent a voltage level as with the LM3914, each LED connected to the LM3915 represents a 3 dB (decibel) change in the power level of the signal. For more on decibels, check out Wikipedia.
To display these power level changes we’ll run through a couple of examples that you can use in your own projects and hopefully give you some ideas for the future. Originally by National Semiconductor, the LM391X series is now handled by Texas Instruments.
Getting Started
You will need the LM3915 data sheet, so please download that and keep it as a reference. First – back to basics. The LM3915 controls ten LEDs. It controls the current through the LEDs with the use of only one resistor, and the LEDs can appear in a bar graph or single ‘dot’ when in use. The LM3915 contains a ten-stage voltage divider, each stage when reached will illuminate the matching LED (and those below it in level meter mode).
Let’s consider the most basic of examples (from page two of the data sheet) – a simple logarithmic display of voltage between 0 and 10V:
After building the circuit you can connect a signal to measure via pin 5, and the GND to pin 2. We’ve built the circuit exactly as above on some stripboard for demonstration purposes, with the only difference being the use of an 8.2kΩ resistor for R2:
To show this in action we use a signal of varying AC voltage – a sine wave at around 2 kHz. In the following video, you can see the comparison of the signal’s voltage against the LEDs being illuminated, and you will see the logarithmic voltage increase represented by the LEDs:
We used the bar display mode for the voltage increase, and the dot display mode for the voltage decrease. Did you notice that during the voltage decrease, the LEDs below the maximum level being displayed were dim? As the signal’s voltage was varying very quickly, the change in the LED’s location is a blur due to the speed of change. In the video below, we’ve slowed the frequency right down but kept the same maximum voltage.
Well that was a lot of fun, and gives you an idea of what is possible with the LM3915.
Displaying weaker signals
In non-theoretical situations your input signal won’t conveniently be between 0 and 10 V. For example the line level on audio equipment can vary between 1 and 3V peak to peak. For example, here’s a random DSO image from measuring the headphone output on my computer whilst playing some typical music:
Although it’s an AC signal we’ll treat it as DC for simplicity. So to display this random low DC voltage signal we’ll reduce the range of the display to 0~3V DC. This is done using the same method as with the LM3914 – with maths and different resistors.
Consider the following formulae:
As you can see the LED current (Iled) is simple, however we’ll need to solve for R1 and R2 with the first formula to get our required Vref of 3V. For our example circuit I use 2.2kΩ for R2 which gives a value of 1.8kΩ for R1. However putting those values in the ILED formula gives a pretty low current for the LEDs, about 8.3 mA. Live and learn – so spend time experimenting with values so you can match the required Vref and ILED.
Nevertheless in this video below we have the Vref of 3V and some music in from the computer as a sample source of low-voltage DC. This is not a VU meter! Wait for the LM3916 article to do that.
Again due to the rapid rate of change of the voltage, there is the blue between the maximum level at the time and 0V.
Chaining multiple LM3915s
This is covered well in the data sheet, so read it for more on using two LM3915s. Plus there are some great example circuits in the data sheet, for example the 100W audio power meter on page 26 and the vibration meter (using a piezo) on page 18.
Conclusion
As always I hope you found this useful. Don’t forget to stay tuned for the final instalment about the LM3916. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.
In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.
This is the first of three tutorials that will examine the LM391x series of LED driver ICs. In this first tutorial we cover the LM3914, then the LM3915 and LM3916 will follow. The goal of these tutorials is to have you using the parts in a small amount of time and experiment with your driver ICs, from which point you can research further into their theory and application.
Although these parts have been around for many years, the LM3914 in particular is still quite popular. It offers a simple way to display a linear voltage level using one or more groups of ten LEDs with a minimum of fuss.
With a variety of external parts or circuitry these LEDs can then represent all sorts of data, or just blink for your amusement. We’ll run through a few example circuits that you can use in your own projects and hopefully give you some ideas for the future. Originally by National Semiconductor, the LM391X series is now handled by Texas Instruments.
Getting Started
You will need the LM3914 data sheet, so please download that and keep it as a reference. So – back to basics. The LM3914 controls ten LEDs. It controls the current through the LEDs with the use of only one resistor, and the LEDs can appear in a bar graph or single ‘dot’ when in use. The LM3914 contains a ten-stage voltage divider, each stage when reached will illuminate the matching LED (and those below it in level meter mode).
Let’s consider the most basic of examples (from page two of the data sheet) – a voltmeter with a range of 0~5V:
The Vled rail is also connected to the supply voltage in our example. Pin 9 controls the bar/dot display mode – with it connected to pin 3 the LEDs will operate in bar graph mode, leave it open for dot mode. The 2.2uF capacitor is required only when “leads to the LED supply are 6″ or longer”. We’ve hooked up the circuit above, and created a 0~5V DC source via a 10kΩ potentiometer with a multimeter to show the voltage – in the following video you can see the results of this circuit in action, in both dot and bar graph mode:
Customising the upper range and LED current
Well that was exciting, however what if you want a different reference voltage? That is you want your display to have a range of 0~3 V DC? And how do you control the current flow through each LED? With maths and resistors. Consider the following formulae:
As you can see the LED current (Iled) is simple, our example is 12.5/1210 which returned 10.3 mA – and in real life 12.7 mA (resistor tolerance is going to affect the value of the calculations).
Now to calculate a new Ref Out voltage – for example we’ll shoot for a 3 V meter, and keep the same current for the LEDs. This requires solving for R2 in the equation above, which results with R2 = -R1 + 0.8R1V. Substituting the values – R2 = -1210 + 0.8 x 1210 x 3 gives a value of 1694Ω for R2. Not everyone will have the E48 resistor range, so try and get something as close as possible. We found a 1.8 kΩ for R2 and show the results in the following video:
You can of course have larger display range values, but a supply voltage of no more than 25 V will need to be equal to or greater than that value. E.g. if you want a 0~10 V display, the supply voltage must be >= 10V DC.
Creating custom ranges
Now we’ll look at how to create a lower range limit, so you can have displays that (for example) can range from a non-zero positive value. For example, you want to display levels between 3 and 5V DC. From the previous section, you know how to set the upper limit, and setting the lower limit is simple – just apply the lower voltage to pin 4 (Rlo).
You can derive this using a resistor divider or other form of supply with a common GND. When creating such circuits, remember that the tolerance of the resistors used in the voltage dividers will have an affect on the accuracy. Some may wish to fit trimpots, which after alignment can be set permanently with a blob of glue.
Finally, for more reading on this topic – download and review the TI application note.
Chaining multiple LM3914s
Two or more LM3914s can be chained together to increase the number of LEDs used to display the levels over an expanded range. The circuitry is similar to using two independent units, except the REFout (pin 7) from the first LM3914 is fed to the REFlo (pin 4) of the second LM3914 – whose REFout is set as required for the upper range limit. Consider the following example schematic which gave a real-world range of 0~3.8V DC:
The 20~22kΩ resistor is required if you’re using dot mode (see “Dot mode carry” in page ten of the data sheet). Moving on, the circuit above results with the following:
Where to from here?
Now you can visually represent all sorts of low voltages for many purposes. There’s more example circuits and notes in the LM3914 data sheet, so have a read through and delve deeper into the operation of the LM3914. Furthermore Dave Jones from eevblog.com has made a great video whcih describes a practical application of the LM3914:
Conclusion
As always I hope you found this useful. Don’t forget to stay tuned for the second and third instalments using the LM3915 and LM3916. Full-sized images are on flickr. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.
In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.
Controlling motors with an Arduino is a fun and generally integral part of the learning process for most up-and-coming embedded electronics enthusiasts. Or quite simply, using motors is fun ’cause you can make robots, tanks and stuff that moves. And thanks to Freetronics we have their new HBRIDGE motor shield for Arduino to review, so let’s check it out and get some things moving with it.
Arriving in retail-friendly packaging, the HBRIDGE can be stored with the included reusable packaging, and also has a quick-start guide that explains the technical specifications and URLs for tutorials:
The shield is compatible with the latest R3-series Arduino boards including the Leonardo and of course the Freetronics Eleven board:
Specifications
The HBRIDGE shield is based on the Allegro A4954 Dual Full-Bridge DMOS PWM Motor Driver. For the curious, you can download the data sheet (pdf). This allows very simple control of two DC motors with a maximum rating of 40V at 2A, or one bipolar stepper motor. Unlike other motor shields I’ve seen, the HBRIDGE has a jumper which allows the power supply for the motor shield to be fed into the Arduino’s Vin line – so if your motor power supply is under 12V DC you can also power the Arduino from the same supply. Or you can run the motors from the Arduino’s power supply – if you’re sure that you won’t exceed the current rating. Frankly the former would be a safer and this the preferable solution.
The motor(s) are controlled very simply via PWM and digital logic. You feed the A4954 a PWM signal from a digital output pin for motor speed, and also set two inputs with a combination of high/low to set the motor direction, and also put the motor controlled into coast or brake mode. However don’t panic, it’s really easy.
The chassis is pretty much a standard tank chassis with two DC motors that run from an internal 9V battery pack. Search the Internet for “Dagu Rover 5″ for something similar. Connection is a simple manner of feeding the power lines from the battery and the motor wires into the terminal block on the HBRIDGE shield.
Next, take note of two things. First – the slide switches below the jumpers. Using these you can select the maximum amount of current allowed to flow from the power supply to each motor. These can be handy to ensure your motor doesn’t burn out by drawing too much current in a stall situation, so you can set these to the appropriate setting for your motor – or if you’re happy there won’t be any issues just leave them both on 2A.
The second thing to note is the six jumpers above the switches. These control which digital pins on your Arduino are used to control the motor driver. Each motor channel requires two outputs and one PWM output. If you leave them all on, the Arduino pins used will be the ones listed next to each jumper, otherwise remove the jumpers and manually wire to the required output. For the purposes of our demonstration, we’ll leave all the jumpers in. A final word of warning is to be careful not to touch the A4954 controller IC after some use – it can become really hot … around 160 degrees Celsius. It’s the circled part in the image below:
So back to the DC motors. You have two digital outputs to set, and also a PWM signal to generate – for each channel. If you set the outputs to 1 and 0 - the motor spins in one direction. Use 0 and 1 to spin the other way. And the value of the PWM (0~255) determines the speed. So consider the following sketch:
Instead of chasing the tank chassis with a camera, here it is on the bench:
Now to try out a stepper motor. You can control a bipolar motor with the HBRIDGE shield, and each coil (pole) is connected to a motor channel.
Hint – if you’re looking for a cheap source of stepper motors, check out discarded office equipment such as printers or photocopiers.
For the demonstration, I’ve found a random stepper motor from a second-hand store and wired up each pole to a channel on the HBRIDGE shield – then run the Arduino stepper motor demonstration sketch by Tom Igoe:
/*
Based on example by Tom Igoe included in Arduino IDE
at File -> Examples -> Stepper -> stepper_oneRevolution
Modified to suit pinouts of Freetronics HBridge Shield
*/
#include <Stepper.h>
const int stepsPerRevolution = 240; // change this to fit the number of steps per revolution
// for your motor
// initialize the stepper library using the default pins on the HBridge Shield:
Stepper myStepper(stepsPerRevolution, 4, 7, 3, 2);
void setup() {
// set the speed at 200 rpm:
myStepper.setSpeed(200);
// initialize the serial port:
Serial.begin(38400);
}
void loop() {
// step one revolution in one direction:
Serial.println("clockwise");
myStepper.step(stepsPerRevolution);
delay(1000);
// step one revolution in the other direction:
Serial.println("counterclockwise");
myStepper.step(-stepsPerRevolution);
delay(1000);
}
With the following results:
Considering it was a random stepper motor for which we didn’t have the specifications for – it’s always nice to have it work the first time! For more formal situations, ensure your stepper motor matches the power supply voltage and so on. Nevertheless it shows how easy it can be to control something that appears complex to some people, so enjoy experimenting with them if you can.
Competition
Thanks to Freetronics we have a shield to give away to one lucky participant. To enter, clearly print your email address on the back of a postcard and mail it to:
H-Bridge Competition, PO Box 5435 Clayton 3168 Australia.
Entries must be received by the 20th of September 2013. One postcard will then be drawn at random, and the winner will receive one H-Bridge shield delivered by Australia Post standard air mail. One entry per person – duplicates will be destroyed. We’re not responsible for customs or import duties, VAT, GST, import duty, postage delays, non-delivery or whatever walls your country puts up against receiving inbound mail.
Conclusion
As demonstrated, the HBRIDGE shield “just works” – which is what you need when bringing motorised project ideas to life. The ability to limit current flow and also power the host board from the external supply is a great idea, and with the extra prototyping space on the shield you can also add extra circuitry without needing another protoshield. Very well done. For more information and to order, visit the Freetronics website. Full-sized images are on flickr. And if you made it this far – check out my new book “Arduino Workshop” from No Starch Press.
In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.
Note – The motor shield used in this article was a promotional consideration supplied by Freetronics.
Learn how to use MC14489 LED display driver ICs with Arduino in chapter fifty-one of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.
Updated 12/05/2013
Introduction
Recently we’ve been looking at alternatives to the MAX7219 LED display driver IC due to pricing and availability issues (stay tuned for that one) – and came across an old but still quite useful IC – the MC14489 from Motorola (now Freescale Semiconductor). The MC14489 can drive five seven-segment LED numbers with decimal point, or a combination of numbers and separate LEDs. You can also daisy-chain more than one to drive more digits, and it’s controlled with a simple serial data-clock method in the same way as a 74HC595 shift register. Sourcing the MC14489 isn’t too difficult – it’s available from element14, Newark, Digikey, and so on – or if you’re not in a hurry, try the usual suspects like Futurlec.
For the purpose of the tutorial we’ll show you how to send commands easily from your Arduino or compatible board to control a five-digit 7-segment LED display module - and the instructions are quite simple so they should translate easily to other platforms. Once you have mastered the single module, using more than one MC14489 will be just as easy. So let’s get started.
Hardware
Before moving forward, download the data sheet (pdf). You will need to refer to this as you build the circuit(s). And here’s our subject in real life:
For our demonstration display we’ll be using a vintage HP 5082-7415 LED display module. However you can use almost any 7-segment modules as long as they’re common-cathode - for example, Sparkfun part number COM-11405. If you’re using a four-digit module and want an extra digit, you can add another single digit display. If you want a ruler, the design files are here.
Connecting the MC14489 to an LED display isn’t complex at all. From the data sheet consider Figure 9 (click the image to enlarge):
Each of the anode control pins from the MC14489 connect to the matching anodes on your display module, and the BANK1~5 pins connect to the matching digit cathode pins on the display module. You can find the MC14489 pin assignments on page 1 of the data sheet. Seeing as this is chapter fifty-one - by now you should be confident with finding such information on the data sheets, so I will be encouraging you to do a little more of the work.
Interesting point – you don’t need current-limiting resistors. However you do need the resistor Rx – this controls the current flow to each LED segment. But which value to use? You need to find out the forward current of your LED display (for example 20 mA) then check Figure 7 on page 7 of the data sheet (click image to enlarge):
To be conservative I’m using a value of 2k0 for Rx, however you can choose your own based on the data sheet for your display and the graph above. Next – connect the data, clock and enable pins of the MC14489 to three Arduino digital pints – for our example we’re using 5, 6 and 7 for data, clock and enable respectively. Then it’s just 5V and GND to Arduino 5V and GND – and put a 0.1uF capacitor between 5V and GND. Before moving on double-check the connections – especially between the MC14489 and the LED display.
Controlling the MC14489
To control the display we need to send data to two registers in the MC14489 – the configuration register (one byte) and the display register (three bytes). See page 9 of the data sheet for the overview. The MC14489 will understand that if we send out one byte of data it is to send it the configuration register, and if it receives three bytes of data to send it to the display register. To keep things simple we’ll only worry about the first bit (C0) in the configuration register – this turns the display outputs on or off. To do this, use the following:
digitalWrite(enable, LOW);
shiftOut(data, clock, MSBFIRST, B00000001); // used binary for clarity, however you can use decimal or hexadecimal numbers
digitalWrite(enable, HIGH);
delay(10);
and to turn it off, send bit C0 as zero. The small delay is necessary after each command.
Once you have turned the display on – the next step is to send three bytes of data which represent the numbers to display and decimal points if necessary. Review the table on page 8 of the data sheet. See how they have the binary nibble values for the digits in the third column. Thankfully the nibble for each digit is the binary value for that digit. Furthermore you might want to set the decimal point – that is set using three bits in the first nibble of the three bytes (go back to page 9 and see the display register). Finally you can halve the brightness by setting the very first bit to zero (or one for full brightness).
As an example for that – if you want to display 5.4321 the three bytes of data to send in binary will be:
1101 0101 0100 0011 0010 0001
Let’s break that down. The first bit is 1 for full brightness, then the next three bits (101) turn on the decimal point for BANK5 (the left-most digit). Then you have five nibbles of data, one for each of the digits from left to right. So there’s binary for 5, then four, then three, then two, then one.
To demonstrate everything described so far, it’s been neatly packaged into our first example sketch – Example 51.1:
// Example 51.1
// Motorola MC14489 with HP 5082-7415 5-digit, 7-segment LED display
// 2k0 resistor on MC14489 Rx pin
// John Boxall 2013 CC by-sa-nc
// define pins for data from Arduino to MC14489
// we treat it just like a 74HC595
int data = 5;
int clock = 6;
int enable = 7;
void setup()
{
pinMode(data, OUTPUT);
pinMode(enable, OUTPUT);
pinMode(clock, OUTPUT);
displayOn(); // display defaults to off at power-up
}
void displayTest1()
// displays 5.4321
{
digitalWrite(enable, LOW); // send 3 bytes to display register. See data sheet page 9
// you can also insert decimal or hexadecimal numbers in place of the binary numbers
// we're using binary as you can easily match the nibbles (4-bits) against the table
// in data sheet page 8
shiftOut(data, clock, MSBFIRST, B11010101); // D23~D16
shiftOut(data, clock, MSBFIRST, B01000011); // D15~D8
shiftOut(data, clock, MSBFIRST, B00100001); // D7~D0
digitalWrite(enable, HIGH);
delay(10);
}
void displayTest2()
// displays ABCDE
{
digitalWrite(enable, LOW); // send 3 bytes to display register. See data sheet page 9
// you can also insert decimal or hexadecimal numbers in place of the binary numbers
// we're using binary as you can easily match the nibbles (4-bits) against the table
// in data sheet page 8
shiftOut(data, clock, MSBFIRST, B10001010); // D23~D16
shiftOut(data, clock, MSBFIRST, B10111100); // D15~D8
shiftOut(data, clock, MSBFIRST, B11011110); // D7~D0
digitalWrite(enable, HIGH);
delay(10);
}
Now that we can display numbers and a few letters with binary, life would be easier if there was a way to take a number and just send it to the display.
So consider the following function that takes an integer between 0 and 99999, does the work and sends it to the display:
void displayIntLong(long x)
// takes a long between 0~99999 and sends it to the MC14489
{
int numbers[5];
byte a=0;
byte b=0;
byte c=0; // will hold the three bytes to send to the MC14489
// first split the incoming long into five separate digits
numbers[0] = int ( x / 10000 ); // left-most digit (will be BANK5)
x = x % 10000;
numbers[1] = int ( x / 1000 );
x = x % 1000;
numbers[2] = int ( x / 100 );
x = x % 100;
numbers[3] = int ( x / 10 );
x = x % 10;
numbers[4] = x % 10; // right-most digit (will be BANK1)
// now to create the three bytes to send to the MC14489
// build byte c which holds digits 4 and 5
c = numbers[3];
c = c << 4; // move the nibble to the left
c = c | numbers[4];
// build byte b which holds digits 3 and 4
b = numbers [1];
b = b << 4;
b = b | numbers[2];
// build byte a which holds the brightness bit, decimal points and digit 1
a = B10000000 | numbers[0]; // full brightness, no decimal points
// now send the bytes to the MC14489
digitalWrite(enable, LOW);
shiftOut(data, clock, MSBFIRST, a);
shiftOut(data, clock, MSBFIRST, b);
shiftOut(data, clock, MSBFIRST, c);
digitalWrite(enable, HIGH);
delay(10);
}
So how does that work? First it splits the 5-digit number into separate digits and stores them in the array numbers[]. It then places the fourth digit into a byte, then moves the data four bits to the left – then we bitwise OR the fifth digit into the same byte. This leaves us with a byte of data containing the nibbles for the fourth and fifth digit. The process is repeated for digits 2 and 3. Finally the brightness bit and decimal point bits are assigned to another byte which then has the first digit’s nibble OR’d into it. Which leaves us with bytes a, b and c ready to send to the MC14489. Note that there isn’t any error-checking – however you could add a test to check that the number to be displayed was within the parameter, and if not either switch off the display (see example 51.1) or throw up all the decimal points or … whatever you want.
You can download the demonstration sketch for the function – Example 51.2, and view the results in the following video:
You can also display the letters A to F by sending the values 10 to 15 respectivel to each digit’s nibble. However that would be part of a larger application, which you can (hopefully) by now work out for yourself. Furthermore there’s some other characters that can be displayed – however trying to display the alphabet using 7-segment displays is somewhat passé. Instead, get some 16-segment LED modules or an LCD.
Finally, you can cascade more than one MC14489 to control more digits. Just run a connection from the data out pin on the first MC14889 to the data pin of the second one, and all the clock and enable lines together. Then send out more data – see page 11 of the data sheet. If you’re going to do that in volume other ICs may be a cheaper option and thus lead you back to the MAX7219.
Conclusion
For a chance find the MC14489 is a fun an inexpensive way to drive those LED digit displays. We haven’t covered every single possible option or feature of the part – however you will now have the core knowledge to go further with the MC14489 if you need to move further with it. And if you enjoy my tutorials, or want to introduce someone else to the interesting world of Arduino – check out my new book “Arduino Workshop” from No Starch Press.
In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.
Learn how to use MC14489 LED display driver ICs with Arduino in chapter fifty-one of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – A tutorial on the Arduino universe. The first chapter is here, the complete series is detailed here.
Updated 12/05/2013
Introduction
Recently we’ve been looking at alternatives to the MAX7219 LED display driver IC due to pricing and availability issues (stay tuned for that one) – and came across an old but still quite useful IC – the MC14489 from Motorola (now Freescale Semiconductor). The MC14489 can drive five seven-segment LED numbers with decimal point, or a combination of numbers and separate LEDs. You can also daisy-chain more than one to drive more digits, and it’s controlled with a simple serial data-clock method in the same way as a 74HC595 shift register. Sourcing the MC14489 isn’t too difficult – it’s available from element14, Newark, Digikey, and so on – or if you’re not in a hurry, try the usual suspects like Futurlec.
For the purpose of the tutorial we’ll show you how to send commands easily from your Arduino or compatible board to control a five-digit 7-segment LED display module - and the instructions are quite simple so they should translate easily to other platforms. Once you have mastered the single module, using more than one MC14489 will be just as easy. So let’s get started.
Hardware
Before moving forward, download the data sheet (pdf). You will need to refer to this as you build the circuit(s). And here’s our subject in real life:
For our demonstration display we’ll be using a vintage HP 5082-7415 LED display module. However you can use almost any 7-segment modules as long as they’re common-cathode - for example, Sparkfun part number COM-11405. If you’re using a four-digit module and want an extra digit, you can add another single digit display. If you want a ruler, the design files are here.
Connecting the MC14489 to an LED display isn’t complex at all. From the data sheet consider Figure 9:
Each of the anode control pins from the MC14489 connect to the matching anodes on your display module, and the BANK1~5 pins connect to the matching digit cathode pins on the display module. You can find the MC14489 pin assignments on page 1 of the data sheet. Seeing as this is chapter fifty-one - by now you should be confident with finding such information on the data sheets, so I will be encouraging you to do a little more of the work.
Interesting point – you don’t need current-limiting resistors. However you do need the resistor Rx – this controls the current flow to each LED segment. But which value to use? You need to find out the forward current of your LED display (for example 20 mA) then check Figure 7 on page 7 of the data sheet:
To be conservative I’m using a value of 2k0 for Rx, however you can choose your own based on the data sheet for your display and the graph above. Next – connect the data, clock and enable pins of the MC14489 to three Arduino digital pints – for our example we’re using 5, 6 and 7 for data, clock and enable respectively. Then it’s just 5V and GND to Arduino 5V and GND – and put a 0.1uF capacitor between 5V and GND. Before moving on double-check the connections – especially between the MC14489 and the LED display.
Controlling the MC14489
To control the display we need to send data to two registers in the MC14489 – the configuration register (one byte) and the display register (three bytes). See page 9 of the data sheet for the overview. The MC14489 will understand that if we send out one byte of data it is to send it the configuration register, and if it receives three bytes of data to send it to the display register. To keep things simple we’ll only worry about the first bit (C0) in the configuration register – this turns the display outputs on or off. To do this, use the following:
digitalWrite(enable, LOW);
shiftOut(data, clock, MSBFIRST, B00000001); // used binary for clarity, however you can use decimal or hexadecimal numbers
digitalWrite(enable, HIGH);
delay(10);
and to turn it off, send bit C0 as zero. The small delay is necessary after each command.
Once you have turned the display on – the next step is to send three bytes of data which represent the numbers to display and decimal points if necessary. Review the table on page 8 of the data sheet. See how they have the binary nibble values for the digits in the third column. Thankfully the nibble for each digit is the binary value for that digit. Furthermore you might want to set the decimal point – that is set using three bits in the first nibble of the three bytes (go back to page 9 and see the display register). Finally you can halve the brightness by setting the very first bit to zero (or one for full brightness).
As an example for that – if you want to display 5.4321 the three bytes of data to send in binary will be:
1101 0101 0100 0011 0010 0001
Let’s break that down. The first bit is 1 for full brightness, then the next three bits (101) turn on the decimal point for BANK5 (the left-most digit). Then you have five nibbles of data, one for each of the digits from left to right. So there’s binary for 5, then four, then three, then two, then one.
To demonstrate everything described so far, it’s been neatly packaged into our first example sketch:
// Example 51.1
// Motorola MC14489 with HP 5082-7415 5-digit, 7-segment LED display
// 2k0 resistor on MC14489 Rx pin
// John Boxall 2013 CC by-sa-nc
// define pins for data from Arduino to MC14489
// we treat it just like a 74HC595
int data = 5;
int clock = 6;
int enable = 7;
void setup()
{
pinMode(data, OUTPUT);
pinMode(enable, OUTPUT);
pinMode(clock, OUTPUT);
displayOn(); // display defaults to off at power-up
}
void displayTest1()
// displays 5.4321
{
digitalWrite(enable, LOW); // send 3 bytes to display register. See data sheet page 9
// you can also insert decimal or hexadecimal numbers in place of the binary numbers
// we're using binary as you can easily match the nibbles (4-bits) against the table
// in data sheet page 8
shiftOut(data, clock, MSBFIRST, B11010101); // D23~D16
shiftOut(data, clock, MSBFIRST, B01000011); // D15~D8
shiftOut(data, clock, MSBFIRST, B00100001); // D7~D0
digitalWrite(enable, HIGH);
delay(10);
}
void displayTest2()
// displays ABCDE
{
digitalWrite(enable, LOW); // send 3 bytes to display register. See data sheet page 9
// you can also insert decimal or hexadecimal numbers in place of the binary numbers
// we're using binary as you can easily match the nibbles (4-bits) against the table
// in data sheet page 8
shiftOut(data, clock, MSBFIRST, B10001010); // D23~D16
shiftOut(data, clock, MSBFIRST, B10111100); // D15~D8
shiftOut(data, clock, MSBFIRST, B11011110); // D7~D0
digitalWrite(enable, HIGH);
delay(10);
}
void displayOn()
// turns on display
{
digitalWrite(enable, LOW);
shiftOut(data, clock, MSBFIRST, B00000001);
digitalWrite(enable, HIGH);
delay(10);
}
void displayOff()
// turns off display
{
digitalWrite(enable, LOW);
shiftOut(data, clock, MSBFIRST, B00000000);
digitalWrite(enable, HIGH);
delay(10);
}
void loop()
{
displayOn();
displayTest1();
delay(1000);
displayTest2();
delay(1000);
displayOff();
delay(500);
}
… with the results in the following video:
Now that we can display numbers and a few letters with binary, life would be easier if there was a way to take a number and just send it to the display.
So consider the following function that takes an integer between 0 and 99999, does the work and sends it to the display:
void displayIntLong(long x)
// takes a long between 0~99999 and sends it to the MC14489
{
int numbers[5];
byte a=0;
byte b=0;
byte c=0; // will hold the three bytes to send to the MC14489
// first split the incoming long into five separate digits
numbers[0] = int ( x / 10000 ); // left-most digit (will be BANK5)
x = x % 10000;
numbers[1] = int ( x / 1000 );
x = x % 1000;
numbers[2] = int ( x / 100 );
x = x % 100;
numbers[3] = int ( x / 10 );
x = x % 10;
numbers[4] = x % 10; // right-most digit (will be BANK1)
// now to create the three bytes to send to the MC14489
// build byte c which holds digits 4 and 5
c = numbers[3];
c = c << 4; // move the nibble to the left
c = c | numbers[4];
// build byte b which holds digits 3 and 4
b = numbers [1];
b = b << 4;
b = b | numbers[2];
// build byte a which holds the brightness bit, decimal points and digit 1
a = B10000000 | numbers[0]; // full brightness, no decimal points
// now send the bytes to the MC14489
digitalWrite(enable, LOW);
shiftOut(data, clock, MSBFIRST, a);
shiftOut(data, clock, MSBFIRST, b);
shiftOut(data, clock, MSBFIRST, c);
digitalWrite(enable, HIGH);
delay(10);
}
So how does that work? First it splits the 5-digit number into separate digits and stores them in the array numbers[]. It then places the fourth digit into a byte, then moves the data four bits to the left – then we bitwise OR the fifth digit into the same byte. This leaves us with a byte of data containing the nibbles for the fourth and fifth digit. The process is repeated for digits 2 and 3. Finally the brightness bit and decimal point bits are assigned to another byte which then has the first digit’s nibble OR’d into it. Which leaves us with bytes a, b and c ready to send to the MC14489. Note that there isn’t any error-checking – however you could add a test to check that the number to be displayed was within the parameter, and if not either switch off the display (see example 51.1) or throw up all the decimal points or … whatever you want.
You can download the demonstration sketch for the function – Example 51.2, and view the results in the following video:
You can also display the letters A to F by sending the values 10 to 15 respectivel to each digit’s nibble. However that would be part of a larger application, which you can (hopefully) by now work out for yourself. Furthermore there’s some other characters that can be displayed – however trying to display the alphabet using 7-segment displays is somewhat passé. Instead, get some 16-segment LED modules or an LCD.
Finally, you can cascade more than one MC14489 to control more digits. Just run a connection from the data out pin on the first MC14889 to the data pin of the second one, and all the clock and enable lines together. Then send out more data – see page 11 of the data sheet. If you’re going to do that in volume other ICs may be a cheaper option and thus lead you back to the MAX7219.
Conclusion
For a chance find the MC14489 is a fun an inexpensive way to drive those LED digit displays. We haven’t covered every single possible option or feature of the part – however you will now have the core knowledge to go further with the MC14489 if you need to move further with it. And if you enjoy my tutorials, or want to introduce someone else to the interesting world of Arduino – check out my new book “Arduino Workshop” from No Starch Press.
In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.
Planet Arduino is, or at the moment is wishing to become, an aggregation of public weblogs from around the world written by people who develop, play, think on Arduino platform and his son. The opinions expressed in those weblogs and hence this aggregation are those of the original authors. Entries on this page are owned by their authors. We do not edit, endorse or vouch for the contents of individual posts. For more information about Arduino please visit www.arduino.cc
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After building the circuit you can connect a signal to measure via pin 5, and the GND to pin 2. We’ve built the circuit exactly as above on some stripboard for demonstration purposes, with the only difference being the use of an 8.2kΩ resistor for R2:
