Hi all,

I was wondering if someone would mind taking a look at my interfacing diagram to ensure I don't end up cooking my chip? To summarize my inputs and outputs, I have two TTL step inputs from a couple of hall-effect speed sensors, 1 relay input (relay is 12V control), and two PWM outputs controlling two solid state relays.

For the SSR outputs, a 1:1 opamp buffer and current limiting resistor is used to provide the current required by the SSR while ensuring I do not exceed the maximum current the port can source.

I have tested my SSR outputs off-board well beyond the expected maximum frequency using a function generator and on my eval. board when being controlled by software. A scope confirms they are working exactly as they should be but I have yet to test my inputs and want to be sure my board is safe before I do so.

I believe my resistor values are correct now thanks to Jan W. She informed me that a relay input is normally configured as "active low" and I also recently read that you don't want to use pulldowns so any advice you can provide to help me fix my inputs would be greatly appreciated!

Thank you in advance,
Brian

Diagram

MCU Datasheet Specs. start on p.3, Vdd=5V