I am trying to use the 4-20 mA current loop which uses the MCP4725, but I cannot get any output. I am using an I2C shield and the device is detected at address 0x60. I am following a Sparkfun tutorial, which uses the same chip. Here is the sample code they provide:
#include <iostream>
#include <errno.h>
#include <wiringPiI2C.h>
using namespace std;
int main()
{
int fd, result;
// Initialize the interface by giving it an external device ID.
// The MCP4725 defaults to address 0x60.
//
// It returns a standard file descriptor.
//
fd = wiringPiI2CSetup(0x60);
cout << "Init result: "<< fd << endl;
for(int i = 0; i < 0x0000ffff; i++)
{
// I tried using the "fast write" command, but couldn't get it to work.
// It's not entirely obvious what's happening behind the scenes as
// regards to endianness or length of data sent. I think it's only
// sending one byte, when we really need two.
//
// So instead I'm doing a 16 bit register access. It appears to
// properly handle the endianness, and the length is specified by the
// call. The only question was the register address, which is the
// concatenation of the command (010x = write DAC output)
// and power down (x00x = power up) bits.
result = wiringPiI2CWriteReg16(fd, 0x40, (i & 0xfff) );
if(result == -1)
{
cout << "Error. Errno is: " << errno << endl;
}
}
}
I understand this is being used for voltage output, but the value that it loops through should still give me some change in output in the current loop, but all I see is 0.
