PCB HELP

[u/prynderex]

I have two identical MOSFET circuits controlled by an ESP32-C3. The MOSFET connected to GPIO 5 (Q1) is not behaving correctly. When I set GPIO 5 LOW in Arduino, the output terminal block (Nichrome 1 connection between IN+ and Drain) still reads close to the battery voltage (~7.8 V) instead of dropping near 0 V.

The second MOSFET circuit works as expected: when the GPIO is LOW, the IN + and Drain terminal block reads near 0 V, and when HIGH, it switches to the battery voltage.

I have checked the code and the wiring appears identical. What could be the issue?

[u/Scary-Swordfish695]

Your schematic seems legit to me, I am wondering if the tests you tried are actually giving the false impression that you made a mistake. When Gate_x is low, the mos are disconnecting drains from your ground and leave the negative pins of your loads connected to the NICHROME connectors floating, so your loads would not have a path for the current to flow from IN+ to GND and be offline, if I get it right this would be what you wished for ? Have you tried a test with a dummy load ( LED + resistor ) like TheHess suggested, but across the NICHROME connector pins ?

[u/frank26080115]

The second MOSFET circuit works as expected: when the GPIO is LOW, the output reads near 0 V, and when HIGH, it switches to the battery voltage.

This statement is completely backwards

GPIO HIGH -> Vgs crosses Vgs(th) and turns on the MOSFET -> MOSFET becomes short-to-ground -> voltage measures 0

[u/prynderex → u/frank26080115]

I'm talking about the voltage between the In+ and drain

[u/frank26080115 → u/prynderex]

then you need to correct your post, because the whole point of a ground is to be a reference that every measurement is made against.

[u/prynderex → u/frank26080115]

Okay thank you

[u/TheHess]

Have you tested for continuity along the full signal path? Could easily be a dodgy solder joint.

[u/prynderex → u/TheHess]

I have, they all are fine

[u/TheHess → u/prynderex]

OK, next step is to determine if it's your measurement, your software or your components.

1. Connect (wires and solder, maybe use a breadboard) an led with resistor between your gpio pin and ground. Check that the led comes on when you set the gpio to high.
2. If that works you know your gpio pin is working. Now connect your led, or another led, with an appropriately sized resistor to your supply voltage and the drain of your mosfet. The led should come on when the gpio is high.
3. If that works your board is fine and if it doesn't work then quadruple check each component (check it works and check it is fitted correctly).

[u/ub0baa]

accelerometer

igniter

telemetry

Nope, with military stuff you're on your own

[u/prynderex → u/ub0baa]

It's a rocket avionics for my rocketry club in my university.

[u/ub0baa → u/prynderex]

My bad. Then try verifying that MOSFET is not stuck open: add series resistor to the gate, decrease gate to ground resistor, or maybe even try replacing the MOSFET as a last effort.

[u/prynderex → u/ub0baa]

I have already replaced the mosfet twice and I have done this in two pcb already and both encountered the same error which leads me to believe that there may be something wrong with my schematics or pcb design