Serial1 with resistor

photon
Tags: #<Tag:0x00007fe22315bfa0>

#1

Hi!

I would like to use a resistor on TX and RX pin two avoid damage when pins are misconfigured.
I used to use 1kohm, but in some case I see that there is a noise on the RX.
What is the proper value of the resistor?

Thanks!


#2

In my experience, there is no “right” value as this has many dependancies. My rule of thumb to crudely protect I/O is to use 100R in series - its not perfect. It WILL NOT prevent damage from incorrect voltage levels - in this case you should use a level shifter or a buffer of some sort.

Perhaps post more detail or even a circuit sketch of what you are trying to achieve ?


#3

Just to add a bit to @shanevanj helpful post. Noise on the signal line might mean that there is an AC wire running near to it. There are various components you can add as protection typically from voltage spikes (zener diode) and a small resistor in series to limit the current. Also, a buffer IC. Any filter needs to be carefully designed so as not to filter out the signal! You also need to look at using shielded serial cable with a ground on the MCU end and making sure there is no interference being induced in your signal lines.


#4

Great thanks to both of you for the tips! I will take them into account and I check one more time where could be the problem!