I have a Arduino board, connected to a relay. When the digital pin on the board is set to HIGH, the relay closes. If the digital pin is LOW, the relay opens.
Now that from time to time, I will have to (software) restart the Arduino. The digital pin refresh, and therefore if the relay is closed, it will bounce open. Untill the Arduino board sends out a signal again.
Should I add a switch/ other electric components before the relay? Such that the signal could be "memorized"?
I have thought of using a time-delay relay. But once it is invoked, you'll have to wait until the delay time have pass to turn it off…
Best Answer
I'm going to assume that the AVR controller on the Arduino board is similar to the Microchip PIC family in that the pins default to INPUT upon reset.
If that assumption is correct, all you need is a really simple sample-and-hold circuit for the relay driver. It also requires you to think about how you have your software structured.
First, I'll show the circuit. Then I'll talk about the software implications.
simulate this circuit – Schematic created using CircuitLab
Software is really easy.
1) Controller is just coming out of reset. Port pins are all currently set as Input.
2) Set port pin to desired level (Hi or Lo)
3) Change port pin(s) DDR to Output
Note that the above order is important if you want to avoid glitches. If you set the pin to Output first, then set the level, there can be a glitch.
Also note that the circuit introduces a delay of about 1 ms. I assume that is completely inconsequential if you are driving a relay.
You must choose a low-leakage capacitor for C1 but that's easy. Tantalum works pretty good.