Cannot communicate with MCP4725 with smbus or Adafruit_MCP4725 library

Bhaskar · April 23, 2019, 5:07pm

looks like everything is working as it should. may be your read DAC value function is not working.
if i were you i will run the dac values from 0 to 4000 and read the output on meter.

jgatzemeier · April 23, 2019, 5:16pm

My DMM still reads 6.33 when I iterate through.

I changed the lines set_voltage(1024) and time.sleep(DELAY)

to
i = 0
while i < 4001:
set_voltage(i)
time.sleep(DELAY)
i = i + 1

Bhaskar · April 23, 2019, 5:20pm

set the value to 2096 and see if it changes.

jgatzemeier · April 23, 2019, 5:27pm

The reading the on the DMM did not change. It still reads 6.3 VDC. however, the reading from the dac changed. the data is [192, 48] causing a voltage of 0.02.

Bhaskar · April 23, 2019, 6:13pm

Hi,
i will recommending sending it back for further inspection.

Thanks

adamada · April 23, 2019, 6:45pm

This library is really easy to use. The one you linked to is deprecated.
https://github.com/adafruit/Adafruit_CircuitPython_MCP4725/blob/master/examples/mcp4725_simpletest.py

jgatzemeier · April 23, 2019, 6:48pm

I have looked at that one but was confused by the “circuit-python” board because I do not have one of those.

adamada · April 23, 2019, 6:52pm

It doesn’t matter; as long as the IC is the same, you can use any library for these boards. In fact, if you look inside that library, it ultimately just puts several layers on top of smbus.

Here is how I ultimately used it in my project:

github.com

adamrubock/laser-reflow/blob/5d0a1e6fc4d04487bb9ba1bbaf33f0814cb92fac/laserline/ldm/scripts/ioprocess.py#L139


self.y_dac.normalized_value = float(self.r.get('y_axis'))

durations = [float(duration)

             for duration in self.r.lrange('durations', 0, -1)]

levels = [float(duration)

          for duration in self.r.lrange('levels', 0, -1)]

self.digital_out.set_output(0, False)  # on!

logging.info('laser on!')

prevtime = datetime.now()

for duration, level in zip(durations, levels):

    try:

        self.power_dac.normalized_value = level

        currtime = datetime.now()

        logging.info('actually waited milliseconds: ' +

                     str((currtime - prevtime) / timedelta(milliseconds=1)))

        prevtime = currtime

        logging.info('power set to: ' + str(level))

        logging.info(

            'planning to wait ms:' + str(duration))

    except OSError:

        logging.error(

            'unable to write power level', exc_info=False)

adamada · April 23, 2019, 6:54pm

setting normalized_value sets the output to the specified fraction of the maximum, which for this board is 10V.
Proof this works:

jgatzemeier · April 25, 2019, 10:41pm

My pi won’t even let me install that library. It gives me a TypeError.

jgatzemeier · April 25, 2019, 11:54pm

@Bhaskar would I be able to get a new one overnight? I have been working on it for over a month.

adamada · April 26, 2019, 11:32am

Are you using Python 3?