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Iain-S / sentry-bot

Autonomous Nerf turret
MIT License
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Find a MOSFET replacement #37

Open Iain-S opened 1 year ago

Iain-S commented 1 year ago

The 3.3v GPIO output from the Pi does not seem to be enough to turn on our MOSFET. Some options seem to be

  1. Use transistors (in particular, a Darlington Pair) in place of the MOSFET
  2. Use a "logic level" MOSFET, which can be activated with a 3.3V gate voltage (a.k.a. Vgs(th))
  3. Use a transistor to drive a MOSFET

See this electronics.stackexchange answer for an overview of the options.

Iain-S commented 1 year ago

I have ordered two TIP110 Darlington Pairs. ETA 16th-17th Nov. They have a forward voltage drop of ~0.7V when on so we can expect to waste 1/2W through each. It's a convenient solution as they still work as a low-side switch so I don't need to change the motor wiring and they also use 10k resistors, which we have plenty of.

The transistor-driving-a-mosfet solution is probably better but that requires ordering transistors and mosfets and some motor rewiring (or else having the wrong wiring colours). We can fall back on this if we find that the DPs are getting too hot.

Iain-S commented 1 year ago

The current plan (subject to change)

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