I want to read an RFID tag using an Arduino, which controls some relais. This is easy.
For me the more complex part is to build it fault-tolerant. So I thought I could use the watchdog. The tricky part is, my relais module should keep a certain state (change of state is rare), no matter what happens to the Arduino.
My first thought was to put some condensators to the relais. Calculate the RC component so it can last the watchdog timeout plus booting up.
Now there is the problem, that the relais module is keeping its state while booting. I guess I can't use a pull up/down resistor, since the state of the relais can be low or high at random.
My second thought was using a latch relay. But this has the disadvantage, that it probably can hide problems. For example if the arduino died, and the latch relay holds a certain state, it masks the problem. In that case it's not possible to notice a faulty Arduino.
Those are the reasons I tend to think condensators are better?
Are those ideas feasible? Are there easier ways to accomplish this?
Are there more problems to think about?
(I was already reading about millis at gammon's page. Apparently it's not a problem after all.)