there are actually 2 types of relays, -1- the normal have one input that must be energized to operate the relay -2- but there are relays with 2 inputs, where a puls on each input does a switch over. that one would survive a powerfail, but your problem would be to find out what position its in. I se...

For the actual project... If it were me, I would make the manual override a manual key-switch. The person with the key can just walk up and unlock the door with a key and it will stay unlocked until the key-switch is re-engaged. Oh I didn't know there were key-switch addons! Unfortunately I have to...

There are relay boards with 1, 2, 4, 8, or 16 relays etc. If you want 2 relays search for 2 channel relay board. You probably want relay with 5V coil so you can power it from the RPi. What is the point of running 2 relays in series? Thanks for the reply! I just figured that if the relays, or I supp...

Hey everyone! I've got a project I'm undertaking for work, and I was running into a problem while trying to figure out if the goal I have in mind is a feasible way to go about doing this, or if its even possible at all. Any help or advice would be greatly appreciated to a beginner like me! The main ...