Automation HAT, spurious signals on empty ADC channels

Spurious signals on empty ADC channels

Hello friends at Pimoroni and users everywhere.

I just installed an Automation hat to read 24V
digital signals from out Fanuc robot.
It works like a charm, excellent.

HW: Automation HAT, Raspi 3, latest raspbian updated & upgraded.
Used the easy curl-installation script.

My setup:

  • three digital 24vdc robot output lines connected to
    automation hat input lines
  • HAT GND plane connected to robot signal ground
  • everything works perfectly

Mystery part:

  • I connected the raspi 5V from screw terminal to
    ADC line 1 and got the voltage ok.
  • however I get spurious readings from empty lines
    (with led flashes) ADC 2 & 3


  • this is not an issue, I’m super happy with digital
    input, very nice!
  • I must be missing something fundamental here?

So comments would be extra nice, please?

all the best
Pete (Pekka) Kyrenius
Aalto University FINLAND

An unconnected ADC channel would be floating and subject to environmental noise or coupled-in signals, I wouldn’t worry about it.

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Gadgetoid: Thank you very much for the super-fast help. Must be coupled-in signals, as the “blips” disappeared as soon as I removed the jumper wire. All is fine. Very happy with Pimoroni products and support. br Pete

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You’re welcome- you could use a pull-down resistor on the channels you’re not using if you want to keep them in check, but for the most part you can just ignore them. Granted the lights flashing on and off is probably annoying!

It seems that even if I ground the the ADC pin I still get spurious spikes.This happens when I am polling the pin frequently. If the polling speed goes down this happens less.
Any ideas why polling the pin frequently would cause the spikes?