CB-028 12-Bit D/A Converter Module - Jameco Electronics · Arduino Uno. A voltmeter can then be...

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r e v . 1 . 0 1 145 Rt. 46 West E‐mail: sales@electro‐set.net Wayne, NJ 07470 Web: www.Electro‐Set.net

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CB-028 12-Bit D/A Converter Module

September 04, 2014

Introduction

This application note will show two minimal code set ups to operate the 12-bit D/A converter module CB-028 one with an Arduino board and the other with Cardinal’s CB-026 Microchip microcontroller module.

The CB-028 has two output terminals, ground and the D/A output to which can be connected to a voltmeter or oscilloscope to observe the module’s output.

Arduino

The Arduino example will take consecutive values from an array and output them to the D/A converter. The array is initialized as a sine table. These values are also be presented to the Arduino serial monitor port.

Before proceeding any further, please have the Arduino software install to your computer. Visit Arduino’s user setup guide at http://arduino.cc/en/Guide/windows for step-by-step instructions.

Hardware

Parts List:

Arduino Uno USB type B connector CB-I-022 Cardinal Interface Board CB-028 D/A converter module

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Connect the components as shown in the picture below

Plug the CB-I-022 interface into the Arduino Uno board and the CB-028 D/A module into the interface’s Electro-Set 6 pin connector. Connect the USB cable between the computer and the Arduino Uno. A voltmeter can then be connected to the two terminals of the CB-028 module.

The computer will supply 5 volts through the USB cable which will be regulated on the Arduino interface board to 3.3 volts to run the CB-028 D/A module. The D/A module has an onboard 2.5 volt reference regulator which we will configure the D/A to use.

Two jumpers on the CB-028 can be used to change the slave address of the D/A. For this code we are using 0x10 as the 7-bit slave address so the two jumper should be populated towards the boards male connector as shown in the picture above.

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The Software

#include <Wire.h> // Wire I2C library

#define DA_ADDRESS 0x10 // 7-bit I2C DA_ADDRESS of D/A converter

byte da_MSB, da_LSB;

static int sine[] = { // 120 values from the sine table

0x7ff0, 0x86a0, 0x8d50, 0x93f0, 0x9a90, 0xa110, 0xa780, 0xadd0, 0xb400, 0xba10,

0xbff0, 0xc5a0, 0xcb20, 0xd080, 0xd590, 0xda70, 0xdf10, 0xe360, 0xe770, 0xeb40,

0xeec0, 0xf1f0, 0xf4d0, 0xf770, 0xf9a0, 0xfb90, 0xfd20, 0xfe50, 0xff30, 0xffc0,

0xfff0, 0xffc0, 0xff30, 0xfe50, 0xfd20, 0xfb90, 0xf9a0, 0xf770, 0xf4d0, 0xf1f0,

0xeec0, 0xeb40, 0xe770, 0xe360, 0xdf10, 0xda70, 0xd590, 0xd080, 0xcb20, 0xc5a0,

0xbff0, 0xba10, 0xb400, 0xadd0, 0xa780, 0xa110, 0x9a90, 0x93f0, 0x8d50, 0x86a0,

0x7ff0, 0x7940, 0x7290, 0x6bf0, 0x6550, 0x5ed0, 0x5860, 0x5210, 0x4be0, 0x45d0,

0x3ff0, 0x3a40, 0x34c0, 0x2f60, 0x2a50, 0x2570, 0x20d0, 0x1c80, 0x1870, 0x14a0,

0x1120, 0x0df0, 0x0b10, 0x0870, 0x0640, 0x0450, 0x02c0, 0x0190, 0x00b0, 0x0020,

0x0000, 0x0020, 0x00b0, 0x0190, 0x02c0, 0x0450, 0x0640, 0x0870, 0x0b10, 0x0df0,

0x1120, 0x14a0, 0x1870, 0x1c80, 0x20d0, 0x2570, 0x2a50, 0x2f60, 0x34c0, 0x3a40,

0x3ff0, 0x45d0, 0x4be0, 0x5210, 0x5860, 0x5ed0, 0x6550, 0x6bf0, 0x7290, 0x7940

};

int index = 0;

void setup()

{

Serial.begin(9600); // initialize serial monitor to 9600 baud

Serial.println("CB-028 Test"); // welcome message

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Wire.begin(); // initialize I2C port

Wire.beginTransmission(DA_ADDRESS); // start of I2C transmission to D/A

Wire.write(0x70); // first byte is a command byte, 0x70 selects to use the external reference

Wire.write(0x00); // dummy ignored by D/A

Wire.write(0x00); // dummy ignored by D/A

Wire.endTransmission(); // Complete the I2C transmission

}

void loop()

{

da_MSB=(sine[index]&0xff00)>>8; // select out the MSB part of the 16-bit hex sine value

da_LSB=(sine[index]&0x00ff); // select out the LSB part of the 16-bit hex sine value

Wire.beginTransmission(DA_ADDRESS); // start of I2C transmission to D/A

Wire.write(0x30); // command byte, 0x30 causes a data write and updates D/A output

Wire.write(da_MSB); // write the MSB

Wire.write(da_LSB); // write the LSB

Wire.endTransmission(); // Complete the I2C transmission

Serial.print(da_MSB,HEX);

Serial.print(da_LSB,HEX);

Serial.print(" ");

delay(200); // slow the update rate so a DVM attached to the D/A output can respond

if(++index >= 120) // increment the index, last array index is 119

index = 0; // wrap index back to first array location

}

Code Operation

The D/A module has a 7-bit I2C slave address as 0x10 which we make a #define.

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The setup() function is called when a sketch starts. The setup code, initializes the serial monitor baud rate at 9600, outputs a welcome message and then initializes the I2C port as a master. The D/A is also initialized to use the external on board reference by writing 0x70 as the command byte, which is the first of 3 bytes in an I2C write to the D/A. See the chip datasheet for more information.

.

After setup has completed sketch causes the function loop() to be repeatedly called.

The variable ‘index’ is used to access through the sine array sequentially. The integer sine value retrieved is split into two byte which are written into the D/A with the command byte 0x30. This command byte causes the two data byte to be written to the D/A input register and the D/A output to be updated with the new value.

A delay of 200mS helps aloow the output from the D/A to be observed which will change between 0 volts for a data code of 0x000 to the reference voltage of 2.5 volts for a data code of 0xfff0.

The index is incremented each time around the loop and tested for a value of greater than or equal to 200, which indicated the index has passed the end of the array and is wrapped back to zero to repeat the sequence again.

As compiled on Arduino 1.0.5 r2 and with the delay(200) and Serial.print lines commented out, the loop function take 432uS to complete. With 120 data points in one sine cycle the output sinusoidal period will be 0.432*120mS or

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51.8mS.

Microchip Module CB-026

The CB-026 example in PICBASIC PRO will write digital values to the D/A converter to form a saw tooth waveform and also output the values via the serial port to a terminal emulator such as hyperterminal.

Before proceeding any further, please have the MicroCode Studio PICBASIC PRO suite installed on your computer.

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Hardware

Parts List:

Electro-Set module CB-026 microcontroller USB type mini connector CB-028 12-bit D/A converter module

Connect the components as shown in the picture below

The Software

INCLUDE "modedefs.bas"

#CONFIG __config _HS_OSC & _WDT_ON & _LVP_OFF & _CP_OFF

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#ENDCONFIG

DEFINE OSC 20 ‘ Set for 20 MHz oscillator

SCL var PORTC.3 ‘ Set I2C pins

SDA var PORTC.4

Soutpin var PORTC.6 ‘ Set serial port pins

Sinpin var PORTC.7

baud1 var byte ‘ for serial port baud rate

testword var word ‘ 16-bit variable, for D/A values

baud1 = 6 ‘ 38400 baud, no inversion

Write_DA:

i2cwrite sda,scl,$20,[$70],nodata ‘ initialize D-A & Checks if module is connected'

' if not connected, goto nodata

Serout2 soutpin,baud1,["Writing to D-A",13,10] ‘ welcome message

serout2 soutpin,baud1,["Creating a 0 to 3.3 volt ramp function",13,10]

pause 2000 ‘ wait 2 seconds

for testword = $0010 to $AF00 step $FF ‘ increase testword for each loop

i2cwrite sda,scl,$20,[$30,testword.byte1,testword.byte0],nodata ‘ write testword to D/A

serout2 soutpin,baud1,["Set for ",dec testword/13500,".",dec2 (testword /135)," Volts",13,10]

pause 100

next testword

serout2 soutpin,baud1,["Done",13,10] ‘ report completed for loop iteration

pause 1000 ‘ wait 1 second

goto Write_DA

NoData:

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Serout2 soutpin,baud1,["D-A Module Not Connected",13,10] ‘ report D/A not responding

pause 500

goto Write_DA

end

Code Operation

The line

“# CONFIG __config _HS_OSC & _WDT_ON & _LVP_OFF & _CP_OFF”

includes configuration for the programmer in the output hex file so it does not necessary to manually change the entries in the programmer configuration window every time you come to write a new version of your program to the microcontroller.

The port pins for the I2C interface are set on PORTC pins 3 and 4. The CB-026 board wires these to the Electro-Set 6 pin connector.

The microcontroller serial port pins are set on PORTC pins 6 and 7, these connect to the FTDI chip on the CB-026 which couples through to the USB and so when plugged into a PC producing a virtual COMM port where the microcontroller’s serial data can be seen on a terminal emulator such as hyperterminal. The terminal emulator should be set to connect to the virtual COMM port assigned to the FTDI driver and connect at 38400,8,N,1.

We declare the variable baud1 for use in the serout2 to set the baud rate. For a baud rate of 38400, baud1 is set to 6, see the MicroChip documentation for other rates and options.

The first parameters for the PicBasicPro functions i2cread and i2cwrite uses and 8-bit slave address which is a one bit left shift of the 7-bit slave address, so the D/A module’s 8-bit slave address is 0x20.

The line

i2cwrite sda,scl,$20,[$70],nodata

initializes the D/A to use its external reference pin, which is supplied by the 2.5 volt regulator on the CB-028 module.

Next the welcome messages are sent out the serial port.

The for loop causes the variable ‘testword’ to increase from low to high. On each iteration of the for loop the value of ‘testword’ is written to the D/A’s internal register address 0x30 causing the D/A’s output to change accordingly, rising from low to high.

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i2cwrite sda,scl,$20,[$30,testword.byte1,testword.byte0],nodata

Also on each iteration a decimal representation of ‘testword’ is output to the serial port.

A scope connected to the D/A output shows the saw tooth waveform.

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