Error when used with MCP3008 #605
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Can you post the code you're using? (please use fenced code blocks) I have seen other people report of SPI not working on Stretch but I can't reproduce. The following works fine for me: from gpiozero import MCP3008
pot = MCP3008()
while True:
print(pot.value) |
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Ben,
This is part of my Solar heating and pool manager system, I use the MCP3008 to read the thermistors on the solar array and the water temperature as it passes through the filter.
The code for the MCP3008 part is very simple
I load the libraries
```
from gpiozero import MCP3008
# Constants
vref = 3.3
# Variables used for the ADC channels
pool_channel = 0 # A0
solar_channel = 1 # A1
```
The code that reads the ADC, calls the sub-modules to convert it and store the values in an array is below, this is run every 30 seconds as part of the main loop that controls the pump speeds and diverter valves, reports values back etc.
```
# Read the Pool temperature sensor data
adc = MCP3008(channel=pool_channel)
pool_volts = vref * adc.value
pool_res = ConvertResistance(pool_volts,0)
pool_temp = ConvertTemp(pool_volts)
# Enter the reading in the next position in the array
np.put(a_p,a_index,pool_temp)
# Read the Array temperature sensor data
adc = MCP3008(channel=solar_channel)
solar_volts = vref * adc.value
solar_res = ConvertResistance(solar_volts,0)
solar_temp = ConvertTemp(solar_volts)
# Enter the reading in the next position in the array
np.put(a_s,a_index,solar_temp)
```
Nothing special at all about what I am doing here.
The error messages come from the gpiozero code.
Regards
Dave
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I have a similar problem in my project. When the application stops I get three exceptions: I wrote a basic application to reproduce the problem: mcp_adapter.py: monitor.py: worker.py: If it is less complex the exception doesn't appear. Environment: Package: python-gpiozero |
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gpiozero==1.4.1 from gpiozero import MCP3008
m = MCP3008(channel=3, clock_pin=21, mosi_pin=16, miso_pin=20, select_pin=1)
print(m.value)
m = MCP3008(channel=2, clock_pin=21, mosi_pin=16, miso_pin=20, select_pin=1)
print(m.value)
0.0004885197850512668
0.0004885197850512668
Exception ignored in: <bound method GPIOBase.__del__ of <gpiozero.MCP3008 object using <weakproxy at 0xb6180660 to NoneType at 0x3e5788>>>
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/gpiozero/devices.py", line 122, in __del__
File "/usr/lib/python3/dist-packages/gpiozero/spi_devices.py", line 37, in close
ReferenceError: weakly-referenced object no longer exists |
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What's happening is you're creating a reference to an SPI object, and then throwing it away by creating another with the same name. They're supposed to be connected, as they use a shared bus. But if you throw one away you have problems. You need to use separate variable names (e.g. m1 = MCP3008(channel=3, clock_pin=21, mosi_pin=16, miso_pin=20, select_pin=1)
m2 = MCP3008(channel=2, clock_pin=21, mosi_pin=16, miso_pin=20, select_pin=1)
while True:
print(m1.value, m2.value) |
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Thanks for the answer! from gpiozero import MCP3008
sensors = []
for i in range(0,6):
sensors.append(MCP3008(channel=3, clock_pin=21, mosi_pin=16, miso_pin=20, select_pin=1))
for s in sensors:
print(s.value) |
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OK, another mistake not using the variable 'i'! from gpiozero import MCP3008
sensors = []
for i in range(0,6):
sensors.append(MCP3008(channel=i, clock_pin=21, mosi_pin=16, miso_pin=20, select_pin=1))
for s in sensors:
print(s.value) |
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I have the same issue when I stop a script which reads multiple MCP3008 devices. It only gives the error when using non SPI pins, for example: for i in range(4):
device1[i] = MCP3008(channel=i, clock_pin=21, mosi_pin=20, miso_pin=19, select_pin=7)It works using default SPI pins (gpio8, gpio9, gpio10, gpio11) device1[i] = MCP3008(i) |
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Re-opening and assigning to @waveform80 , as he wrote all the SoftwareSPI stuff 🙂 |
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Yup, looks like there's definitely something iffy in the life-span of stuff using I'll dig into this... |
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Ben,
I have a couple of PIs with MCP3008 analogue devices, both are throwing the following exception.
Python 3.5 running on Stretch.
Any suggestions on how to stop this?
Regards
Dave
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