PI-SPI-8AI16B channels mirror output signal

[Cesar-AlKaisy]

Hi, I need help troubleshooting an issue with the Widgetlords PI-SPI-8AI16B module.

I'm using it to read two 4–20 mA signals:

Channel 0 is connected to a configurable output (simulated signal)

Channel 1 is connected to a CO₂ sensor

The problem is that both channels return the same value which is whatever is set on the configurable output, even though the CO₂ sensor is connected and active. It seems like the output signal is bleeding into the other channel, and the sensor reading is being overridden.

from widgetlords.pi_spi import *
from widgetlords import *
import time

init()

input_module = Mod8AI16B()
input_module.set_channel(0)  # Configurable output

input_module2 = Mod8AI16B()
input_module2.set_channel(1)  # CO₂ sensor

while True:
    ad_30 = input_module.read()
    ad_100 = input_module2.read()
    print("Channel 0:", ad_30)
    print("Channel 1:", ad_100)
    time.sleep(1)

I also tried using just one instance of Mod8AI16B() and switching channels between reads:

input_module = Mod8AI16B()

while True:
    input_module.set_channel(0)
    ad_30 = input_module.read()

    input_module.set_channel(1)
    ad_100 = input_module.read()

    print("Channel 0:", ad_30)
    print("Channel 1:", ad_100)
    time.sleep(1)

But the result was the same

[optlink]

First, you should use only one instance of Mod8AI16B per module.

Second, can you verify that each channel works separately:

input_module = Mod8AI16B()
input_module.set_channel(0)

while True:
    ad_30 = input_module.read()

    print("Channel 0:", ad_30)
    time.sleep(1)

and

input_module = Mod8AI16B()
input_module.set_channel(1)

while True:
    ad_100 = input_module.read()

    print("Channel 1:", ad_100)
    time.sleep(1)

[Cesar-AlKaisy]

Thanks for the suggestion. I’ve tested each channel separately as you described, using only one instance of Mod8AI16B per module.

Here’s what I’m seeing:

Both channels are only reading what’s being changed on Channel 0, which is connected to the configurable output.

Even when I run the code for Channel 1 only, it still returns the same count value as Channel 0.

If I change the output on Channel 0 while the code is reading Channel 1, the reading on Channel 1 updates to match whatever Channel 0 is set to, even though the CO₂ sensor is connected to Channel 1 and Channel 0 isn’t being read at all.

To rule out hardware issues, I’ve also tested this with another PI-SPI-8AI16B board, and I’m seeing the same behaviour.

[optlink]

Do you have a second RPi to test with? Sometimes a damaged Pi can cause this behavior.

Do you have anything else connected to the RPi header, such as another SPI device?

[Cesar-AlKaisy]

I've tried using another Raspberry Pi to rule out hardware issues, but I'm still seeing the same problem. There are no other SPI devices connected to the Pi. I also tested with a third ADC converter board and managed to get it working by setting up SPI communication directly, rather than using the Mod8AI16B module. I followed the code example from the website that interfaces with SPI directly. So it looks like the issue might be with the Mod8AI16B module itself.

[optlink]

We have reproduced the issue locally and are working on a fix.