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Dic
29

Ardupod scratch built hexapod squat and rotate code using analogue joystick

analogue, arduino mega, hexapod, scratch build Commenti disabilitati su Ardupod scratch built hexapod squat and rotate code using analogue joystick 

Round variant much simpler made fro two plastic plates



Ardupod scratch built hexapod squat and rotate code using analogue joystick




Lug
02

Tutorial – Arduino and the TI ADS1110 16-bit ADC

ADC, ads1110, analogue, arduino, converter, digital, i2c, instruments, texas, TI, tronixstuff, tutorial Commenti disabilitati su Tutorial – Arduino and the TI ADS1110 16-bit ADC 

Learn how to use the TI ADS1110 16-bit ADC with Arduino in chapter fifty-three of my Arduino Tutorials. The first chapter is here, the complete series is detailed here.

Updated 02/07/2013

Introduction

Moving on from the last chapter where we explained an 8-bit ADC, in this instalment we have the Texas Instruments ADS1110 – an incredibly tiny but useful 16-bit analogue-to-digital converter IC.  It can operate between 2.7 and 5.5 V so it’s also fine for Arduino Due and other lower-voltage development boards. This is a quick guide to get you going with the ADS1110 ready for further applications. Before continuing any further, please download the data sheet (pdf) as it will be useful and referred to during this tutorial. The ADS1110 gives you the option of a more accurate ADC than offered by the Arduino’s 10-bit ADCs – and it’s relatively easy to use. The only block for some is the package type – it’s only available in SOT23-6:

So unless you’re making a customised PCB, some sort of breakout will be required. One useful example is the Schmartboard we reviewed earlier:

ads1110schmartboard

The ADS1110 uses the I2C bus for communication, so if this is new to you – please review the I2C tutorials before continuing. And as there’s only six pins you can’t set the bus address – instead, you can select from six variants of the ADS1110 – each with their own address (see page two of the data sheet). As you can see the in the photo above, ours is marked “EDO” which matches to the bus address 1001000 or 0x48h. And with the example circuits we’ve used 10kΩ pull-up resistors on the I2C bus. You can use the ADS1110 as either a single-ended or differential ADC –  But first we need to examine the configuration register which is used to control various attributes, and the data register.

Configuration register

Turn to page eleven of the data sheet. The configuration register is one byte in size, and as the ADS1110 resets on a power-cycle – you need to reset the register if your needs are different to the defaults. The data sheet spells it out quite neatly… bits 0 and 1 determine the gain setting for the PGA (programmable gain amplifier). If you’re just measuring voltages or experimenting, leave these as zero for a gain of 1V/V. Next, the data rate for the ADS1110 is controlled with bits 2 and 3. If you have continuous sampling turned on, this determines the number of samples per second taken by the ADC.

After some experimenting with an Arduino Uno we found the values returned from the ADC were a bit off when using the fastest rate, so leave it as 15 SPS unless required otherwise. Bit 4 sets either continuous sampling (0) or one-off sampling (1). Ignore bits 5 and 6, however they’re always set as 0. Finally bit 7 – if you’re in one-off sampling mode, setting it to 1 requests a sample – and reading it will tell you if the returned data is new (0) or old (1). You can check that the value measured is a new value – if the first bit of the configuration byte that comes after the data is 0, it’s new. If it returns 1 the ADC conversion hasn’t finished.

Data register

As the ADS1110 is a 16-bit ADC, it returns the data over two bytes – and then follows with the value of the configuration register. So if you request three bytes the whole lot comes back. The data is in “two’s complement” form, which is a method of using signed numbers with binary. Converting those two bytes is done by some simple maths. When sampling at 15 SPS, the value returned by the ADS1110 (not the voltage)  falls between -32768 and 32767. The higher byte of the value is multiplied by 256, then added to the lower byte – which is then multiplied by 2.048 and finally divided by 32767. Don’t panic, as we do this in the example sketch below.

Single-ended ADC mode

In this mode you can read a voltage that falls between zero and 2.048 V (which also happens to be the inbuilt reference voltage for the ADS1110). The example circuit is simple (from the data sheet):

singledemoDon’t forget the 10kΩ pull-up resistors on the I2C bus. The following sketch uses the ADS1110 in the default mode, and simply returns the voltage measured (download):

// Example 53.1 - ADS1110 single-sided voltmeter (0~2.048VDC)
#include "Wire.h"
#define ads1110 0x48
float voltage, data; 
byte highbyte, lowbyte, configRegister;
void setup() 
{ 
 Serial.begin(9600); 
 Wire.begin(); 
}
void loop() 
{ 
 Wire.requestFrom(ads1110, 3); 
 while(Wire.available()) // ensure all the data comes in 
 { 
 highbyte = Wire.read(); // high byte * B11111111
 lowbyte = Wire.read(); // low byte
 configRegister = Wire.read(); 
 } 

 data = highbyte * 256; 
 data = data + lowbyte;
 Serial.print("Data >> "); 
 Serial.println(data, DEC); 
 Serial.print("Voltage >> "); 
 voltage = data * 2.048 ;
 voltage = voltage / 32767.0; 
 Serial.print(voltage, DEC); 
 Serial.println(" V"); 
 delay(1000);
}

Once uploaded, connect the signal to measure and open the serial monitor – you’ll be presented with something similar to:

singledemosm

If you need to alter the gain of the internal programmable gain amplifier of the ADC – you’ll need to write a new byte into the configuration register using:

 Wire.beginTransmission(ads1110);
 Wire.write(configuration byte); 
 Wire.endTransmission();

before requesting the ADC data. This would be 0x8D, 0x8E or 0x8F for gain values of 2, 4 and 8 respectively – and use 0x8C to reset the ADS1110 back to default.

Differential ADC mode

In this mode you can read the difference between two voltages that each fall between zero and 5 V. The example circuit is simple (from the data sheet):

diffcircuit

We must note here (and in the data sheet) that the ADS1110 can’t accept negative voltages on either of the inputs. You can use the previous sketch for the same results – and the resulting voltage will be the value of Vin- subtracted from Vin+. For example, if you had 2 V on Vin+ and 1 V on Vin- the resulting voltage would be 1 V (with the gain set to 1).

Conclusion

Once again I hope you found this of interest, and possibly useful. 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 twitterGoogle+, 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.


Lug
02

Tutorial – Arduino and the TI ADS1110 16-bit ADC

ADC, ads1110, analogue, arduino, converter, digital, i2c, instruments, lesson, texas, TI, tronixstuff, tutorial Commenti disabilitati su Tutorial – Arduino and the TI ADS1110 16-bit ADC 

Learn how to use the TI ADS1110 16-bit ADC with Arduino in chapter fifty-three of my Arduino Tutorials. The first chapter is here, the complete series is detailed here.

Updated 02/07/2013

Introduction

Moving on from the last chapter where we explained an 8-bit ADC, in this instalment we have the Texas Instruments ADS1110 – an incredibly tiny but useful 16-bit analogue-to-digital converter IC.  It can operate between 2.7 and 5.5 V so it’s also fine for Arduino Due and other lower-voltage development boards. This is a quick guide to get you going with the ADS1110 ready for further applications. Before continuing any further, please download the data sheet (pdf) as it will be useful and referred to during this tutorial. The ADS1110 gives you the option of a more accurate ADC than offered by the Arduino’s 10-bit ADCs – and it’s relatively easy to use. The only block for some is the package type – it’s only available in SOT23-6:

So unless you’re making a customised PCB, some sort of breakout will be required. One useful example is the Schmartboard we reviewed earlier:

ads1110schmartboard

The ADS1110 uses the I2C bus for communication, so if this is new to you – please review the I2C tutorials before continuing. And as there’s only six pins you can’t set the bus address – instead, you can select from six variants of the ADS1110 – each with their own address (see page two of the data sheet). As you can see the in the photo above, ours is marked “EDO” which matches to the bus address 1001000 or 0x48h. And with the example circuits we’ve used 10kΩ pull-up resistors on the I2C bus. You can use the ADS1110 as either a single-ended or differential ADC –  But first we need to examine the configuration register which is used to control various attributes, and the data register.

Configuration register

Turn to page eleven of the data sheet. The configuration register is one byte in size, and as the ADS1110 resets on a power-cycle – you need to reset the register if your needs are different to the defaults. The data sheet spells it out quite neatly… bits 0 and 1 determine the gain setting for the PGA (programmable gain amplifier). If you’re just measuring voltages or experimenting, leave these as zero for a gain of 1V/V. Next, the data rate for the ADS1110 is controlled with bits 2 and 3. If you have continuous sampling turned on, this determines the number of samples per second taken by the ADC.

After some experimenting with an Arduino Uno we found the values returned from the ADC were a bit off when using the fastest rate, so leave it as 15 SPS unless required otherwise. Bit 4 sets either continuous sampling (0) or one-off sampling (1). Ignore bits 5 and 6, however they’re always set as 0. Finally bit 7 – if you’re in one-off sampling mode, setting it to 1 requests a sample – and reading it will tell you if the returned data is new (0) or old (1). You can check that the value measured is a new value – if the first bit of the configuration byte that comes after the data is 0, it’s new. If it returns 1 the ADC conversion hasn’t finished.

Data register

As the ADS1110 is a 16-bit ADC, it returns the data over two bytes – and then follows with the value of the configuration register. So if you request three bytes the whole lot comes back. The data is in “two’s complement” form, which is a method of using signed numbers with binary. Converting those two bytes is done by some simple maths. When sampling at 15 SPS, the value returned by the ADS1110 (not the voltage)  falls between -32768 and 32767. The higher byte of the value is multiplied by 256, then added to the lower byte – which is then multiplied by 2.048 and finally divided by 32768. Don’t panic, as we do this in the example sketch below.

Single-ended ADC mode

In this mode you can read a voltage that falls between zero and 2.048 V (which also happens to be the inbuilt reference voltage for the ADS1110). The example circuit is simple (from the data sheet):

singledemoDon’t forget the 10kΩ pull-up resistors on the I2C bus. The following sketch uses the ADS1110 in the default mode, and simply returns the voltage measured:

// Example 53.1 - ADS1110 single-sided voltmeter (0~2.048VDC)

#include "Wire.h"
#define ads1110 0x48
float voltage, data;
byte highbyte, lowbyte, configRegister;
void setup()
{
 Serial.begin(9600);
 Wire.begin();
}
void loop()
{
 Wire.requestFrom(ads1110, 3);
 while(Wire.available()) // ensure all the data comes in
 {
 highbyte = Wire.read(); // high byte * B11111111
 lowbyte = Wire.read(); // low byte
 configRegister = Wire.read();
 }

 data = highbyte * 256;
 data = data + lowbyte;
 Serial.print("Data >> ");
 Serial.println(data, DEC);
 Serial.print("Voltage >> ");
 voltage = data * 2.048 ;
 voltage = voltage / 32768.0;
 Serial.print(voltage, DEC);
 Serial.println(" V");
 delay(1000);
}

Once uploaded, connect the signal to measure and open the serial monitor – you’ll be presented with something similar to:

singledemosm

If you need to alter the gain of the internal programmable gain amplifier of the ADC – you’ll need to write a new byte into the configuration register using:

Wire.beginTransmission(ads1110);
Wire.write(configuration byte); 
Wire.endTransmission();

before requesting the ADC data. This would be 0x8D, 0x8E or 0x8F for gain values of 2, 4 and 8 respectively – and use 0x8C to reset the ADS1110 back to default.

Differential ADC mode

In this mode you can read the difference between two voltages that each fall between zero and 5 V. The example circuit is simple (from the data sheet):

diffcircuit

We must note here (and in the data sheet) that the ADS1110 can’t accept negative voltages on either of the inputs. You can use the previous sketch for the same results – and the resulting voltage will be the value of Vin- subtracted from Vin+. For example, if you had 2 V on Vin+ and 1 V on Vin- the resulting voltage would be 1 V (with the gain set to 1).

Conclusion

Once again I hope you found this of interest, and possibly useful. 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.

LEDborder

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, 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.

The post Tutorial – Arduino and the TI ADS1110 16-bit ADC appeared first on tronixstuff.

Giu
17

Learn how to use the NXP PCF 8591 8-bit A/D and D/A IC with Arduino in chapter fifty-two of my Arduino Tutorials. The first chapter is here, the complete series is detailed here.

Updated 17/06/2013

Introduction

Have you ever wanted more analogue input pins on your Arduino project, but not wanted to fork out for a Mega? Or would you like to generate analogue signals? Then check out the subject of our tutorial – the NXP PCF8591 IC. It solves both these problems as it has a single DAC (digital to analogue) converter as well as four ADCs (analogue to digital converters) – all accessible via the I2C bus. If the I2C bus is new to you, please familiarise yourself with the readings here before moving forward.

The PCF8591 is available in DIP form, which makes it easy to experiment with:

pcf8591

You can get them from the usual retailers. Before moving on, download the data sheet. The PCF8591 can operate on both 5V and 3.3V so if you’re using an Arduino Due, Raspberry Pi or other 3.3 V development board you’re fine. Now we’ll first explain the DAC, then the ADCs.

Using the DAC (digital-to-analogue converter)

The DAC on the PCF8591 has a resolution of 8-bits – so it can generate a theoretical signal of between zero volts and the reference voltage (Vref) in 255 steps. For demonstration purposes we’ll use a Vref of 5V, and you can use a lower Vref such as 3.3V or whatever you wish the maximum value to be … however it must be less than the supply voltage. Note that when there is a load on the analogue output (a real-world situation), the maximum output voltage will drop – the data sheet (which you downloaded) shows a 10% drop for a 10kΩ load. Now for our demonstration circuit:

pcf8591basic_schem

Note the use of 10kΩ pull-up resistors on the I2C bus, and the 10μF capacitor between 5V and GND. The I2C bus address is set by a combination of pins A0~A2, and with them all to GND the address is 0×90. The analogue output can be taken from pin 15 (and there’s a seperate analogue GND on pin 13. Also, connect pin 13 to GND, and circuit GND to Arduino GND.

To control the DAC we need to send two bytes of data. The first is the control byte, which simply activates the DAC and is 1000000 (or 0×40) and the next byte is the value between 0 and 255 (the output level). This is demonstrated in the following sketch (download):

// Example 52.1 PCF8591 DAC demo
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
void setup()
{
 Wire.begin();
}
void loop()
{ 
 for (int i=0; i<256; i++)
 {
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x40); // control byte - turn on DAC (binary 1000000)
 Wire.write(i); // value to send to DAC
 Wire.endTransmission(); // end tranmission
 }

 for (int i=255; i>=0; --i)
 {
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x40); // control byte - turn on DAC (binary 1000000)
 Wire.write(i); // value to send to DAC
 Wire.endTransmission(); // end tranmission
 }
}

Did you notice the bit shift of the bus address in the #define statement? Arduino sends 7-bit addresses but the PCF8591 wants an 8-bit, so we shift the byte over by one bit. 

The results of the sketch are shown below, we’ve connected the Vref to 5V and the oscilloscope probe and GND to the analogue output and GND respectively (click image to enlarge):

triangle

If you like curves you can generate sine waves with the sketch below. It uses a lookup table in an array which contains the necessary pre-calculated data points (download):

// Example 52.2 PCF8591 DAC demo - sine wave
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
uint8_t sine_wave[256] = {
 0x80, 0x83, 0x86, 0x89, 0x8C, 0x90, 0x93, 0x96,
 0x99, 0x9C, 0x9F, 0xA2, 0xA5, 0xA8, 0xAB, 0xAE,
 0xB1, 0xB3, 0xB6, 0xB9, 0xBC, 0xBF, 0xC1, 0xC4,
 0xC7, 0xC9, 0xCC, 0xCE, 0xD1, 0xD3, 0xD5, 0xD8,
 0xDA, 0xDC, 0xDE, 0xE0, 0xE2, 0xE4, 0xE6, 0xE8,
 0xEA, 0xEB, 0xED, 0xEF, 0xF0, 0xF1, 0xF3, 0xF4,
 0xF5, 0xF6, 0xF8, 0xF9, 0xFA, 0xFA, 0xFB, 0xFC,
 0xFD, 0xFD, 0xFE, 0xFE, 0xFE, 0xFF, 0xFF, 0xFF,
 0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xFE, 0xFE, 0xFD,
 0xFD, 0xFC, 0xFB, 0xFA, 0xFA, 0xF9, 0xF8, 0xF6,
 0xF5, 0xF4, 0xF3, 0xF1, 0xF0, 0xEF, 0xED, 0xEB,
 0xEA, 0xE8, 0xE6, 0xE4, 0xE2, 0xE0, 0xDE, 0xDC,
 0xDA, 0xD8, 0xD5, 0xD3, 0xD1, 0xCE, 0xCC, 0xC9,
 0xC7, 0xC4, 0xC1, 0xBF, 0xBC, 0xB9, 0xB6, 0xB3,
 0xB1, 0xAE, 0xAB, 0xA8, 0xA5, 0xA2, 0x9F, 0x9C,
 0x99, 0x96, 0x93, 0x90, 0x8C, 0x89, 0x86, 0x83,
 0x80, 0x7D, 0x7A, 0x77, 0x74, 0x70, 0x6D, 0x6A,
 0x67, 0x64, 0x61, 0x5E, 0x5B, 0x58, 0x55, 0x52,
 0x4F, 0x4D, 0x4A, 0x47, 0x44, 0x41, 0x3F, 0x3C,
 0x39, 0x37, 0x34, 0x32, 0x2F, 0x2D, 0x2B, 0x28,
 0x26, 0x24, 0x22, 0x20, 0x1E, 0x1C, 0x1A, 0x18,
 0x16, 0x15, 0x13, 0x11, 0x10, 0x0F, 0x0D, 0x0C,
 0x0B, 0x0A, 0x08, 0x07, 0x06, 0x06, 0x05, 0x04,
 0x03, 0x03, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01,
 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x03,
 0x03, 0x04, 0x05, 0x06, 0x06, 0x07, 0x08, 0x0A,
 0x0B, 0x0C, 0x0D, 0x0F, 0x10, 0x11, 0x13, 0x15,
 0x16, 0x18, 0x1A, 0x1C, 0x1E, 0x20, 0x22, 0x24,
 0x26, 0x28, 0x2B, 0x2D, 0x2F, 0x32, 0x34, 0x37,
 0x39, 0x3C, 0x3F, 0x41, 0x44, 0x47, 0x4A, 0x4D,
 0x4F, 0x52, 0x55, 0x58, 0x5B, 0x5E, 0x61, 0x64,
 0x67, 0x6A, 0x6D, 0x70, 0x74, 0x77, 0x7A, 0x7D
};
void setup()
{
 Wire.begin();
}
void loop()
{ 
 for (int i=0; i<256; i++)
 {
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x40); // control byte - turn on DAC (binary 1000000)
 Wire.write(sine_wave[i]); // value to send to DAC
 Wire.endTransmission(); // end tranmission
 }
}

And the results (click image to enlarge):

sine

For the following DSO image dump, we changed the Vref to 3.3V – note the change in the maxima on the sine wave:

sine3v3

Now you can experiment with the DAC to make sound effects, signals or control other analogue circuits.

Using the ADCs (analogue-to-digital converters)

If you’ve used the analogRead() function on your Arduino (way back in Chapter One) then you’re already familiar with an ADC. With out PCF8591 we can read a voltage between zero and the Vref and it will return a value of between zero and 255 which is directly proportional to zero and the Vref. For example, measuring 3.3V should return 168. The resolution (8-bit) of the ADC is lower than the onboard Arduino (10-bit) however the PCF8591 can do something the Arduino’s ADC cannot. But we’ll get to that in a moment.

First, to simply read the values of each ADC pin we send a control byte to tell the PCF8591 which ADC we want to read. For ADCs zero to three the control byte is 0×00, 0×01, ox02 and 0×03 respectively. Then we ask for two bytes of data back from the ADC, and store the second byte for use. Why two bytes? The PCF8591 returns the previously measured value first – then the current byte. (See Figure 8 in the data sheet). Finally, if you’re not using all the ADC pins, connect the unused ones to GND.

The following example sketch simply retrieves values from each ADC pin one at a time, then displays them in the serial monitor (download):

// Example 52.3 PCF8591 ADC demo 
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
#define ADC0 0x00 // control bytes for reading individual ADCs
#define ADC1 0x01
#define ADC2 0x02
#define ADC3 0x03
byte value0, value1, value2, value3;
void setup()
{
 Wire.begin();
 Serial.begin(9600);
}
void loop()
{ 
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC0); // control byte - read ADC0
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value0=Wire.read();
 value0=Wire.read();
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC1); // control byte - read ADC1
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value1=Wire.read();
 value1=Wire.read();
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC2); // control byte - read ADC2
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value2=Wire.read();
 value2=Wire.read();
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC3); // control byte - read ADC3
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value3=Wire.read();
 value3=Wire.read();
 Serial.print(value0); Serial.print(" ");
 Serial.print(value1); Serial.print(" ");
 Serial.print(value2); Serial.print(" ");
 Serial.print(value3); Serial.print(" "); 
 Serial.println();
}

Upon running the sketch you’ll be presented with the values of each ADC in the serial monitor. Although it was a simple demonstration to show you how to individually read each ADC, it is a cumbersome method of getting more than one byte at a time from a particular ADC.

To do this, change the control byte to request auto-increment, which is done by setting bit 2 of the control byte to 1. So to start from ADC0 we use a new control byte of binary 00000100 or hexadecimal 0×04. Then request five bytes of data (once again we ignore the first byte) which will cause the PCF8591 to return all values in one chain of bytes. This process is demonstrated in the following sketch (download):

// Example 52.4 PCF8591 ADC demo 
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
byte value0, value1, value2, value3;
void setup()
{
 Wire.begin();
 Serial.begin(9600);
}
void loop()
{ 
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x04); // control byte - read ADC0 then auto-increment
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 5); 
 value0=Wire.read();
 value0=Wire.read(); 
 value1=Wire.read(); 
 value2=Wire.read(); 
 value3=Wire.read();
 Serial.print(value0); Serial.print(" ");
 Serial.print(value1); Serial.print(" ");
 Serial.print(value2); Serial.print(" ");
 Serial.print(value3); Serial.print(" "); 
 Serial.println();
}

Previously we mentioned that the PCF8591 can do something that the Arduino’s ADC cannot, and this is offer a differential ADC. As opposed to the Arduino’s single-ended (i.e. it returns the difference between the positive signal voltage and GND, the differential ADC accepts two signals (that don’t necessarily have to be referenced to ground), and returns the difference between the two signals. This can be convenient for measuring small changes in voltages for load cells and so on.

Setting up the PCF8591 for differential ADC is a simple matter of changing the control byte. If you turn to page seven of the data sheet, then consider the different types of analogue input programming. Previously we used mode ’00′ for four inputs, however you can select the others which are clearly illustrated, for example:

adcmodes

So to set the control byte for two differential inputs, use binary 00110000 or 0×30. Then it’s a simple matter of requesting the bytes of data and working with them. As you can see there’s also combination single/differential and a complex three-differential input. However we’ll leave them for the time being.

Conclusion

Hopefully you found this of interest, whether adding a DAC to your experiments or learning a bit more about ADCs. We’ll have some more analogue to digital articles coming up soon, so stay tuned. 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 twitterGoogle+, 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.


Giu
17

Learn how to use the NXP PCF 8591 8-bit A/D and D/A IC with Arduino in chapter fifty-two of my Arduino Tutorials. The first chapter is here, the complete series is detailed here.

Updated 17/06/2013

Introduction

Have you ever wanted more analogue input pins on your Arduino project, but not wanted to fork out for a Mega? Or would you like to generate analogue signals? Then check out the subject of our tutorial – the NXP PCF8591 IC. It solves both these problems as it has a single DAC (digital to analogue) converter as well as four ADCs (analogue to digital converters) – all accessible via the I2C bus. If the I2C bus is new to you, please familiarise yourself with the readings here before moving forward.

The PCF8591 is available in DIP form, which makes it easy to experiment with:

pcf8591

You can get them from the usual retailers. Before moving on, download the data sheet. The PCF8591 can operate on both 5V and 3.3V so if you’re using an Arduino Due, Raspberry Pi or other 3.3 V development board you’re fine. Now we’ll first explain the DAC, then the ADCs.

Using the DAC (digital-to-analogue converter)

The DAC on the PCF8591 has a resolution of 8-bits – so it can generate a theoretical signal of between zero volts and the reference voltage (Vref) in 255 steps. For demonstration purposes we’ll use a Vref of 5V, and you can use a lower Vref such as 3.3V or whatever you wish the maximum value to be … however it must be less than the supply voltage. Note that when there is a load on the analogue output (a real-world situation), the maximum output voltage will drop – the data sheet (which you downloaded) shows a 10% drop for a 10kΩ load. Now for our demonstration circuit:

pcf8591basic_schem

Note the use of 10kΩ pull-up resistors on the I2C bus, and the 10μF capacitor between 5V and GND. The I2C bus address is set by a combination of pins A0~A2, and with them all to GND the address is 0×90. The analogue output can be taken from pin 15 (and there’s a seperate analogue GND on pin 13. Also, connect pin 13 to GND, and circuit GND to Arduino GND.

To control the DAC we need to send two bytes of data. The first is the control byte, which simply activates the DAC and is 1000000 (or 0×40) and the next byte is the value between 0 and 255 (the output level). This is demonstrated in the following sketch:

// Example 52.1 PCF8591 DAC demo
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
void setup()
{
 Wire.begin();
}
void loop()
{
 for (int i=0; i<256; i++)
 {
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x40); // control byte - turn on DAC (binary 1000000)
 Wire.write(i); // value to send to DAC
 Wire.endTransmission(); // end tranmission
 }

 for (int i=255; i>=0; --i)
 {
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x40); // control byte - turn on DAC (binary 1000000)
 Wire.write(i); // value to send to DAC
 Wire.endTransmission(); // end tranmission
 }
}

Did you notice the bit shift of the bus address in the #define statement? Arduino sends 7-bit addresses but the PCF8591 wants an 8-bit, so we shift the byte over by one bit. 

The results of the sketch are shown below, we’ve connected the Vref to 5V and the oscilloscope probe and GND to the analogue output and GND respectively:

triangle

If you like curves you can generate sine waves with the sketch below. It uses a lookup table in an array which contains the necessary pre-calculated data points:

// Example 52.2 PCF8591 DAC demo - sine wave
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013

#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address

uint8_t sine_wave[256] = {
 0x80, 0x83, 0x86, 0x89, 0x8C, 0x90, 0x93, 0x96,
 0x99, 0x9C, 0x9F, 0xA2, 0xA5, 0xA8, 0xAB, 0xAE,
 0xB1, 0xB3, 0xB6, 0xB9, 0xBC, 0xBF, 0xC1, 0xC4,
 0xC7, 0xC9, 0xCC, 0xCE, 0xD1, 0xD3, 0xD5, 0xD8,
 0xDA, 0xDC, 0xDE, 0xE0, 0xE2, 0xE4, 0xE6, 0xE8,
 0xEA, 0xEB, 0xED, 0xEF, 0xF0, 0xF1, 0xF3, 0xF4,
 0xF5, 0xF6, 0xF8, 0xF9, 0xFA, 0xFA, 0xFB, 0xFC,
 0xFD, 0xFD, 0xFE, 0xFE, 0xFE, 0xFF, 0xFF, 0xFF,
 0xFF, 0xFF, 0xFF, 0xFF, 0xFE, 0xFE, 0xFE, 0xFD,
 0xFD, 0xFC, 0xFB, 0xFA, 0xFA, 0xF9, 0xF8, 0xF6,
 0xF5, 0xF4, 0xF3, 0xF1, 0xF0, 0xEF, 0xED, 0xEB,
 0xEA, 0xE8, 0xE6, 0xE4, 0xE2, 0xE0, 0xDE, 0xDC,
 0xDA, 0xD8, 0xD5, 0xD3, 0xD1, 0xCE, 0xCC, 0xC9,
 0xC7, 0xC4, 0xC1, 0xBF, 0xBC, 0xB9, 0xB6, 0xB3,
 0xB1, 0xAE, 0xAB, 0xA8, 0xA5, 0xA2, 0x9F, 0x9C,
 0x99, 0x96, 0x93, 0x90, 0x8C, 0x89, 0x86, 0x83,
 0x80, 0x7D, 0x7A, 0x77, 0x74, 0x70, 0x6D, 0x6A,
 0x67, 0x64, 0x61, 0x5E, 0x5B, 0x58, 0x55, 0x52,
 0x4F, 0x4D, 0x4A, 0x47, 0x44, 0x41, 0x3F, 0x3C,
 0x39, 0x37, 0x34, 0x32, 0x2F, 0x2D, 0x2B, 0x28,
 0x26, 0x24, 0x22, 0x20, 0x1E, 0x1C, 0x1A, 0x18,
 0x16, 0x15, 0x13, 0x11, 0x10, 0x0F, 0x0D, 0x0C,
 0x0B, 0x0A, 0x08, 0x07, 0x06, 0x06, 0x05, 0x04,
 0x03, 0x03, 0x02, 0x02, 0x02, 0x01, 0x01, 0x01,
 0x01, 0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x03,
 0x03, 0x04, 0x05, 0x06, 0x06, 0x07, 0x08, 0x0A,
 0x0B, 0x0C, 0x0D, 0x0F, 0x10, 0x11, 0x13, 0x15,
 0x16, 0x18, 0x1A, 0x1C, 0x1E, 0x20, 0x22, 0x24,
 0x26, 0x28, 0x2B, 0x2D, 0x2F, 0x32, 0x34, 0x37,
 0x39, 0x3C, 0x3F, 0x41, 0x44, 0x47, 0x4A, 0x4D,
 0x4F, 0x52, 0x55, 0x58, 0x5B, 0x5E, 0x61, 0x64,
 0x67, 0x6A, 0x6D, 0x70, 0x74, 0x77, 0x7A, 0x7D
};
void setup()
{
 Wire.begin();
}
void loop()
{
 for (int i=0; i<256; i++)
 {
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x40); // control byte - turn on DAC (binary 1000000)
 Wire.write(sine_wave[i]); // value to send to DAC
 Wire.endTransmission(); // end tranmission
 }
}

And the results:

sine

For the following DSO image dump, we changed the Vref to 3.3V – note the change in the maxima on the sine wave:

sine3v3

Now you can experiment with the DAC to make sound effects, signals or control other analogue circuits.

Using the ADCs (analogue-to-digital converters)

If you’ve used the analogRead() function on your Arduino (way back in Chapter One) then you’re already familiar with an ADC. With out PCF8591 we can read a voltage between zero and the Vref and it will return a value of between zero and 255 which is directly proportional to zero and the Vref. For example, measuring 3.3V should return 168. The resolution (8-bit) of the ADC is lower than the onboard Arduino (10-bit) however the PCF8591 can do something the Arduino’s ADC cannot. But we’ll get to that in a moment.

First, to simply read the values of each ADC pin we send a control byte to tell the PCF8591 which ADC we want to read. For ADCs zero to three the control byte is 0×00, 0×01, ox02 and 0×03 respectively. Then we ask for two bytes of data back from the ADC, and store the second byte for use. Why two bytes? The PCF8591 returns the previously measured value first – then the current byte. (See Figure 8 in the data sheet). Finally, if you’re not using all the ADC pins, connect the unused ones to GND.

The following example sketch simply retrieves values from each ADC pin one at a time, then displays them in the serial monitor:

// Example 52.3 PCF8591 ADC demo
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
#define ADC0 0x00 // control bytes for reading individual ADCs
#define ADC1 0x01
#define ADC2 0x02
#define ADC3 0x03
byte value0, value1, value2, value3;
void setup()
{
 Wire.begin();
 Serial.begin(9600);
}
void loop()
{
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC0); // control byte - read ADC0
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value0=Wire.read();
 value0=Wire.read();
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC1); // control byte - read ADC1
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value1=Wire.read();
 value1=Wire.read();
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC2); // control byte - read ADC2
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value2=Wire.read();
 value2=Wire.read();
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(ADC3); // control byte - read ADC3
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 2);
 value3=Wire.read();
 value3=Wire.read();
 Serial.print(value0); Serial.print(" ");
 Serial.print(value1); Serial.print(" ");
 Serial.print(value2); Serial.print(" ");
 Serial.print(value3); Serial.print(" ");
 Serial.println();
}

Upon running the sketch you’ll be presented with the values of each ADC in the serial monitor. Although it was a simple demonstration to show you how to individually read each ADC, it is a cumbersome method of getting more than one byte at a time from a particular ADC.

To do this, change the control byte to request auto-increment, which is done by setting bit 2 of the control byte to 1. So to start from ADC0 we use a new control byte of binary 00000100 or hexadecimal 0×04. Then request five bytes of data (once again we ignore the first byte) which will cause the PCF8591 to return all values in one chain of bytes. This process is demonstrated in the following sketch:

// Example 52.4 PCF8591 ADC demo
// http://tronixstuff.com/tutorials Chapter 52
// John Boxall June 2013
#include "Wire.h"
#define PCF8591 (0x90 >> 1) // I2C bus address
byte value0, value1, value2, value3;
void setup()
{
 Wire.begin();
 Serial.begin(9600);
}
void loop()
{
 Wire.beginTransmission(PCF8591); // wake up PCF8591
 Wire.write(0x04); // control byte - read ADC0 then auto-increment
 Wire.endTransmission(); // end tranmission
 Wire.requestFrom(PCF8591, 5);
 value0=Wire.read();
 value0=Wire.read();
 value1=Wire.read();
 value2=Wire.read();
 value3=Wire.read();
 Serial.print(value0); Serial.print(" ");
 Serial.print(value1); Serial.print(" ");
 Serial.print(value2); Serial.print(" ");
 Serial.print(value3); Serial.print(" ");
 Serial.println();
}

Previously we mentioned that the PCF8591 can do something that the Arduino’s ADC cannot, and this is offer a differential ADC. As opposed to the Arduino’s single-ended (i.e. it returns the difference between the positive signal voltage and GND, the differential ADC accepts two signals (that don’t necessarily have to be referenced to ground), and returns the difference between the two signals. This can be convenient for measuring small changes in voltages for load cells and so on.

Setting up the PCF8591 for differential ADC is a simple matter of changing the control byte. If you turn to page seven of the data sheet, then consider the different types of analogue input programming. Previously we used mode ’00′ for four inputs, however you can select the others which are clearly illustrated, for example:

adcmodes

So to set the control byte for two differential inputs, use binary 00110000 or 0×30. Then it’s a simple matter of requesting the bytes of data and working with them. As you can see there’s also combination single/differential and a complex three-differential input. However we’ll leave them for the time being.

Conclusion

Hopefully you found this of interest, whether adding a DAC to your experiments or learning a bit more about ADCs. We’ll have some more analogue to digital articles coming up soon, so stay tuned. 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.

LEDborder

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, 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.

The post Tutorial – Arduino and PCF8591 ADC DAC IC appeared first on tronixstuff.

This is part of a series titled “Getting Started with Arduino!” by John Boxall – A tutorial on the Arduino microcontrollers, to be read with the book “Getting Started with Arduino” (Massimo Banzi).

The first chapter is here.

Welcome back fellow arduidans!

This week we will continue to examine the features of the DS1307 real time clock, receive user input in a new way, use that input to control some physical movement, then build a strange analogue clock. So let’s go!

Recall from chapter seven, that the DS1307 is also has an inbuilt square wave generator, which can operate at a frequency of 1Hz. This is an ideal driver for a “seconds” indicator LED. To activate this you only need to send the hexidecimal value 0×10 after setting the date and time parameters when setting the time. Note this in line 70 of the solution for exercise 7.1. This also means you can create 1Hz pulses for timing purposes, an over-engineered blinking LED, or even an old-school countdown timer in conjunction with some CMOS 4017 ICs.

For now, let’s add a “seconds” LED to our clock from exercise 7.1. The hardware is very simple, just connect a 560 ohm resistor to pin 7 of our DS1307, thence to a normal LED of your choice, thence to ground. Here is the result:

Not that exciting, but it is nice to have a bit more “blinkiness”.

Finally, there is also a need to work with 12-hour time. From the DS1307 data sheet we can see that it can be programmed to operate in this way, however it is easier to just work in 24-hour time, then use mathematics to convert the display to 12-hour time if necessary. The only hardware modification required is the addition of an LED (for example) to indicate whether it is AM or PM. In my example the LED indicates that it is AM.

Exercise 8.1

So now that is your task, convert the results of exercise 7.1 to display 12-hour time, using an LED to indicate AM or PM (or two LEDs, etc…)

Here is my result in video form:

and the sketch: exercise8.1.pdf.

OK then, that’s enough about time for a while. Let’s learn about another way of accepting user input…

Your computer!

Previously we have used functions like Serial.write() and Serial.print() to display data on the serial monitor box in the Arduino IDE. However, we can also use the serial monitor box to give our sketch data. At first this may seem rather pointless, as you would not use an Arduino just to do some maths for you, etc. However – if you are controlling some physical hardware, you now have a very simple way to feed it values, control movements, and so on. So let’s see how this works.

The first thing to know is that the serial input has one of two sources, either the USB port (so we can use the serial monitor in the Arduino IDE) or the serial in/out pins on our Arduino board. These are digital pins 0 and 1. You cannot use these pins for non-serial I/O functions in the same sketch. If you are using an Arduino Mega or compatible board (lucky you) the pins are different, please see here.  For this chapter, we will use the USB port for our demonstrations.

Next, data is accepted in bytes (remember – 8 bits make a byte!). This is good, as a character (e.g. the letter A) is one byte. Our serial  input has a receiving buffer of 128 bytes. This means a project can receive up to 128 bytes whilst executing a portion of a sketch that does not wait for input. Then when the sketch is ready, it can allow the data to serially flow in from the buffer. You can also flush out the buffer, ready for more input. Just like a … well let’s keep it clean.

Ok, let’s have a look. Here is a sketch that accepts user input from your computer keyboard via the serial monitor box. So once you upload the sketch, open the serial monitor box and type something, then press return or enter. Load this sketch, example 8.1.pdf. Here is a quick video clip of it in operation:

Notice in the line Serial.print(character, BYTE); that we force the display to byte, this is to show the value as the matching ASCII character; otherwise it would return the ASCII value of the character instead. For the young ones out there, please read this for an explanation of the ASCII table.

So now we can have something we already know displayed in front of us. Not so useful. However, what would be useful is converting the keyboard input into values that our Arduino can work with.

Consider this example – example 8.2.pdf. It accepts an integer from the input of serial monitor box, converts it to a number you can use mathematically, and performs an operation on that number. Here is a shot of it in action:

If you are unsure about how it works, follow the sketch using a pen and paper, that is write down a sample number for input, then run through the sketch manually, doing the computations yourself. I often find doing so is a good way of deciphering a complex sketch. Once you have completed that, it is time for…

Exercise 8.2

Create a sketch that accept an angle between 0 and 180, and a time in seconds between 0 and (say) 60. Then it will rotate a servo to that angle and hold it there for the duration, then return it to 0 degrees. For a refresher on servo operation, visit chapter three before you start.

Here is a video clip of my interpretation at work:

and the example solution sketch: exercise 8.2.pdf

So now you have the ability to generate user input with a normal keyboard and a PC. In the future we will examine doing so without the need for a personal computer…

Finally, let’s have some fun by combining two projects from the past into one new exercise.

Exercise 8.3

Create an analogue clock using two servos, in a similar method to our analogue thermometer from chapter three. The user will set the time (hours and minutes) using the serial monitor box.

Here is a photo of my example. I spared no expense on this one…

And of course a video demonstration. First we see the clock being set to 12:59, then the hands moving into position, finally the transition from 12:59 to 1:00.

If you had more servos and some earplugs, a giant day/date/clock display could be made… If you like different clocks, have a look at these kits.

Nevertheless, we have had another hopefully interesting and educational lecture. Or at least had a laugh

Another week over. I apologise for this chapter being a little shorter than usual, unfortunately we have some sickness in the family. 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!




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