v = (chan.voltage) dies as a service

[smclaugh5]

I can get the voltage no problem with:

        chan = AnalogIn(ads, ADS.P0)   #channel 1 of 4 on 16 bit A2D ADS1115
        v = (chan.voltage) 

but I have the python program set up as a linux service so I can get my data acquisition program to execute automatically on boot. The (chan.voltage) kills the script. The program runs fine from the command line or the Thonny environment. Any suggestions?

[caternuson]

In general, you do not need the parans. I doubt that is the issue, but you can do:

v = chan.voltage

If your intent is to create a single member tuple, you would need to do:

v = (chan.voltage, )

Do you have a stack trace or any other kind of error message for what happens when the script fails to run?

[smclaugh5]

test_adc.service - test the adc as a service Loaded: loaded (/lib/systemd/system/test_adc.service; enabled; vendor preset: enabled) Active: activating (auto-restart) (Result: exit-code) since Wed 2020-01-29 14:21:47 CST; 6s ago Process: 1545 ExecStart=/usr/bin/python3 /home/pi/Documents/python_programs/adc_test.py (code=exited, status=1/FAILURE) Main PID: 1545 (code=exited, status=1/FAILURE)

---

Here is the code:

!/usr/bin/python3

from time import sleep import smbus import board import busio import adafruit_ads1x15.ads1115 as ADS from adafruit_ads1x15.analog_in import AnalogIn import Adafruit_MCP4725

class multiplex:

def __init__(self, bus):
    self.bus = smbus.SMBus(bus)

def channel(self, address,channel):  # values 0-7 indictae the channel, anything else (eg -1) turns off all channels

    if   (channel==0): action = 0x01
    elif (channel==1): action = 0x02
    elif (channel==2): action = 0x04
    elif (channel==3): action = 0x08
    elif (channel==4): action = 0x10
    elif (channel==5): action = 0x20
    elif (channel==6): action = 0x40
    elif (channel==7): action = 0x80
    else : action = 0x00

    self.bus.write_byte_data(address,0x04,action)  #0x04 is the register for switching channels 

bus=1
address=0x70
plexer = multiplex(bus)

plexer.channel(address,6) #multiplexer channel for 16 bit a2d i2c = busio.I2C(board.SCL, board.SDA) ads = ADS.ADS1115(i2c) ads.gain = 2/3

Create a DAC instance.

dac = Adafruit_MCP4725.MCP4725()

plexer.channel(address,6) #multiplexer channel for 16 bit a2d chan = AnalogIn(ads, ADS.P0) #channel 1 of 4 on 16 bit A2D ADS1115 v = (chan.voltage)
v = chan.voltage #works either way psi1115 = (chan.voltage / 5)*300 -15 #(correction for absolute) print("Voltage = ", v, "Pressure = ", psi1115)

while True: print("Voltage = ", v, "Pressure = ", psi1115) sleep(1)

---

here is the service:

[Unit] Description=test the adc as a service

[Service] Environment=DISPLAY=:0 Environment=XAUTHORITY=/home/pi/.Xauthority ExecStart=/usr/bin/python3 /home/pi/Documents/python_programs/adc_test.py Restart=always RestartSec=10s KillMode=process TimeoutSec=infinity

[Install] WantedBy=graphical.target

---

I can see the I2C bus activity on an oscilloscope every 10 second.

---

output from py program in editing environment: Voltage = 0.5242659993285927 Pressure = 15.375926999725333 Voltage = 0.5242659993285927 Pressure = 15.375926999725333 Voltage = 0.5242659993285927 Pressure = 15.375926999725333 Voltage = 0.5242659993285927 Pressure = 15.375926999725333 Voltage = 0.5242659993285927 Pressure = 15.375926999725333 Voltage = 0.5242659993285927 Pressure = 15.375926999725333 Voltage = 0.5242659993285927 Pressure = 15.375926999725333

[smclaugh5]

Sorry, some of that uploaded kinda weird....

[caternuson]

Based on that stack trace, what makes you think it's related to chan.voltage? Looks like all we know is it exited with a non-zero status:

Process: 1545 ExecStart=/usr/bin/python3 /home/pi/Documents/python_programs/adc_test.py (code=exited, status=1/FAILURE)

It could be something like an import error due to that process running in a different environment than when running via command line or Thonny.

[smclaugh5]

Comment out chan.voltage and the program runs.

[caternuson]

Where do you comment that out? It's used in several places. Can you recreate this with a more simple example that just uses the ADS1115?

You can also edit your post above with the code to clean up the code syntax.

[smclaugh5]

I am working on a simple set up. It is interesting to note that it won't survive a try / except either.

Standby for more information; To answer your prior question:

v = chan.voltage

The above commented out allows the code to run as a sub process or service.

[smclaugh5]

OK, looks like the problem is related to using the old TCA9548A multiplexer example python code and modules with the newer Circuit_Python modules for the ADC. I am going to close this (unresolved) thread and try to get some help with setting up the multiplexer and the DAC's and ADC's.

Still confused why the code works in then environment and not as a service or a sub-process.

[smclaugh5]

BTW, the ADC works fine as a stand alone connected to the PI i2c. Just not through the TCA9548A.

[caternuson]

Tested and seems to work. If you continue to have issues, please post in the forums with photos of your setup.

(blinka) pi@raspberrypi:~ $ python3
Python 3.7.3 (default, Apr  3 2019, 05:39:12) 
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import board
>>> import adafruit_tca9548a
>>> import adafruit_ads1x15.ads1115 as ADS
>>> from adafruit_ads1x15.analog_in import AnalogIn
>>> tca = adafruit_tca9548a.TCA9548A(board.I2C())
>>> adc = ADS.ADS1115(tca[0])
>>> chan = AnalogIn(adc, ADS.P0)
>>> chan.voltage
0.888277108066042
>>> chan.voltage
1.5059209570604573
>>> chan.voltage
2.4190738242744225
>>> chan.voltage
1.1637855159154027
>>>