So I'm building a "logic probe" for automotive diagnostics and am needing a little help with short circuit protection. I got the idea (and most of the circuit) for this from here.
In short, it's a voltmeter that is powered from the cars battery. The test lead/probe has three states. High, Low, (12v positive and ground right from the battery, used to directly power a headlight or fan or something) and a floating state that when probing a wire will tell you if the wire is high or low.
My version adds a meter to display the voltage read from the probe, a ground probe connected to the meter that can be isolated from the vehicles ground, and a switch that shorts the regular probe and the ground probe through a hefty resistor to load test the faulty circuit.
Here is my main schematic:
My question is, what do you think would be the best way to replace the big automotive relay. This is supposed to be a handheld device and it's really hard to cram everything into a tiny box with the relay taking up almost half of it.
This is the portion of the circuit I would like to replace/shrink:
The idea is that you hit the switch to initially latch over the relay, and the voltage at the zener diode is enough to hold it closed, but not enough to latch it over again if the relay turns off for whatever reason, e.g., I probed a ground wire with the probe set to "High".
This device has the possibility to see about a 30amp draw when powering something with the probes "High" state, hence the beefy relay.
I'm hoping someone here can point me in the right direction to using a mosfet or optocoupler (things I've never used) or just anything smaller that can still have this short circuit protection.
Any help is really appreciated, thanks for reading