Should I use diodes???

[ihacker71]

I hope I'm not putting this in the wrong place, but I was wondering should I run diodes between the controller and solenoids, or relays because I hear if you don't it can fry your controllers? should I???

[JackMan]

Can you provide more details on exactly what you are using and how you intend to connect them?

[bsnut]

I am wondering if you mint putting diodes across the coil of the relay or solenoid coil. Is this what you are meaning? If this is what you mean to help protect the coils or solenoids from spikes it's up to you to do. But, the ULN that is on the board has this protection built-in into the ULN itself.

Another thing is to not use any relay or solenoid the is more than 200ma since the ULN is able to handle 500ma max overall. With one channel turned on and you are trying to turn on a relay or solenoid that is around or at 500ma and  you are trying to turn on another relay or solenoid with the same rating you are taking the chance of damaging the ULN with over current or better you may see some blue smoke. If you see the blue smoke its not good and means you will need a new one. That's why I like to use relays or solenoids less than 200ma, which allows you to operate more than one relay or solenoid at one time.

[JonnyMac]

If you're using the ULN2803 to activate the solenoids then you don't have to as they are built in. If, however, you are using an external power supply you can add them. Typcially, something like a 1N4001 is connected with the cathode (band) connected to the positive side, the anode (not marked) connected to the ground side.