I have a laser on my MPCNC that I use for engraving. When I added the laser to the machine, I installed a separate on/off toggle switch for the laser power. What I’d really like is something like a momentary switch that latches when 12 volts is present, then disengages when the power goes off. It’s just a bit of extra safety I’d like, so the laser isn’t powered up when it doesn’t need to be. Anyone using anything like this?
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Are you thinking of something like this maybe? When you turn on the main switch, the laser stays off because it gets powered through the relay and the relay isn’t energized until you push the momentary switch, after which the relay is self energizing so both the relay and laser stay on until you turn off the main switch.
For something like this an inexpensive automotive relay would do nicely.
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That is a neat circuit Rocco
@Rocco85 Yes, that’s pretty much what I was thinking of. After reading your suggestion, I Googled around to find a suitable relay (not quite as simple as I thought it would be 
) and I came across a DPDT latching circuit that I’d like to try. Hopefully, this will allow me to disengage the coil without powering down the controller board. Thanks for your help Rocco.
Here’s a slightly different version of that circuit with an extra push button switch, the top one is normal open and serves as a start button, the bottom one is a normal closed switch and serves as a stop button.
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@Rocco85 I finally got hold of the components and put the circuit together (on a breadboard). It works just like I hoped, thanks Rocco. I don’t have much electronics experience, but after reading around I thought it would be a good idea to add a flyback diode. I had a 1N4004 diode left over from a previous project, so added that in parallel with the relay coil.
Before I go ahead and install it in my MPCNC, I’m wondering if relays interfere with other components, and whether I need to locate it away from the controller board or certain wires?
I’m no electronics expert either but I’m pretty sure the relay won’t cause any interference, especially with the addition of the flyback diode, I think adding that was a good call.