I’ve been designing a circuit to control 9 x 12v solenoids. I’ve have it working with a breadboard and a photon and I have started to move to a non-breadboard prototype. I started with perfboard, but have since moved on to protoboard. No real reason there, just my soldering was so bad on my first run I needed to start over and wanted to see how protoboard compared to perfboard.
Anyway, something that has troubled me since my first prototype is the diode. I understand that I’m using a 1N4001 blocking diode to prevent the discharge from the solenoid passing back into my circuit and blowing components, but even after reading several tutorials and playing with my multimeter, I’m still not really sure I understand. I want to make sure I fully understand being completing my current prototype. Not strictly a photon question, sorry.
In most of the diagrams I find, you see something like this…
The diode sitting between the two ends of the solenoid, stopping the power running back. But the diode isn’t actually “inline” with the rest of the circuit. What is to stop the power from the solenoid going straight past the diode and back into the circuit?
In my circuit, I have the middle pin of my tip120 connected to one end on my solenoid, and the 12v power going directly to the other end of the solenoid. If I put a multimeter on the solenoid I can see 12v on both ends. The 12v runs all the way back to the middle pin on the tip120. When I send current from my photon GIO pin, the current on the middle pin of the tip120 drops to 1.6v and then drops on one end of the solenoid, while the other stays at 12v, and the solenoid fires. All as expected. Nothing is actually broken here, I just don’t understand how the diode is protecting anything.
(I’ve only pictured the front, safe to assume the connections underneath between wires and components are complete, as the circuit is responding as expected)
If anyone has anything I can read or any pointers that would help me clear this up, it would be appreciated.