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A few months ago I made a schematic to allow a 5 V Arduino to control indicators + RGB LED strip on my electric scooter.

I've managed to get everything working when I'm dealing with 5 V, however - I just cannot wrap my head around using MOSFETs correctly as a relay for a 12 V circuit (lights).

I know how I've wired the MOSFET completely wrong. This is a problem I've been trying to solve for months, I'm sure it's quite simple - but I'm completely out of my depth. (programmer, not electrical engineer)

D3 is where I am controlling the gate's logic level from. The 1,2 headers is where I intend to plug the light/device, if that's correct.

Thank you!

(Blue circle indicates where my wiring to be wrong) enter image description here

Is this how it should be wired? enter image description here

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  • \$\begingroup\$ It doesn't look wrong inside the blue box - why do you think it is? Also, do you have a question? \$\endgroup\$
    – Andy aka
    Feb 14, 2022 at 10:42
  • \$\begingroup\$ Is the GPS connected anywhere else for signaling? If yes, it will be very problematic to switch it on the low side. \$\endgroup\$
    – winny
    Feb 14, 2022 at 10:45
  • \$\begingroup\$ @It doesn't look wrong inside the blue box. Here is a message I got from the Arduino forums. Unfortunately I'm unable to seek further clarification there. I'm not sure what he means by 'potential divider' and it sounds like he wants me to combine the 10k + 100R resistors which seems strange? "On your MOSFETs you have the 10k resistors in the wrong place, they should to to the output pin, not to the MOSFET gate. For example R6 should be between ground and D3. As you have them they form a potential divider with the 100Ω resistors (yes, I know, it does not make much difference)." \$\endgroup\$ Feb 14, 2022 at 10:49
  • \$\begingroup\$ @Is the GPS. Sorry, the GPS doesn't have anything to do with signaling. It's the same circuit, I actually circled it as it's the first. The idea is to power the GPS device when it's in a locked mode. Is this a bad way for me to power it? \$\endgroup\$ Feb 14, 2022 at 10:50
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    \$\begingroup\$ If you take away GND from your GPS with other signals still being referenced to ground, you will back drain current though them. Consider switching Vcc on the high side instead. \$\endgroup\$
    – winny
    Feb 14, 2022 at 13:33

1 Answer 1

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The schematic looks fine. Maybe there's an issue somewhere else (bad part, pins incorrectly assigned to footprint etc.). If the 12V supply is separate, the grounds have to be common, of course.

As to whether you put the 10k on one side or the other, the purpose is to pull the gate down should the connection be open for some reason. Putting it at the MOSFET gate is more 'sure' than putting it on the other side, but it drops a tiny bit of voltage. Since the parts are all on the same board (until you get to the connectors for the Arduino) it doesn't much matter which side you put it on. So don't worry about it.

If it's not working and the pinouts check out, then make some measurements and tell us exactly what you are observing. Just the facts. Image from the datasheet (tab is D as well).

enter image description here

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