Need suggestion for RAK3172 Input Pin Pullup/Pulldown Value for push button

LPWAN Modules / EVBs RAK3172
#1

Hello,

I am using RAK3172, in noisy environment, I need to be pull up/down values for an Interrupt GPIO.
Currently I have tested below 2 configurations.

active High or low
active High or low1702×676 61.2 KB

I need to make sure that no false trigger occurs.

There are some query I want to clear:

  1. which value of pullup should be choose in Active Low configuration, whether to use 10k,4.7k, or other?
  2. Any other suggestion of values and components need to add or remove or value change, taking consideration of noisy environment and ultra low power.

Thank you

#2

Hi @gokat ,

For the pullup resistor, the lower you have the better. The only drawback is the current drawn. Also, your 1uF is high I think. It depends on the noise you are trying to suppress. In my experience before we put 2 parallel capacitors in different capacitance to target different resonant frequencies. I am not sure why you select 1uF but putting a lower value 0.1uF might help. For higher freq noise 0.01uF could be even helpful. Also remember that putting capacitor will create a time constant so make sure that the trigger for your interrupt is long enough than that.

For really really noisy environment like factories with heavy machineries, you will most likely need to isolate your input to have a very robust IO. 24V lines are common in factories, but if you’ll look that DC supply signal in a scope, you’ll see real chaos.