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I want to create a circuit that will allow me to conveniently control a 3V electric motor - specifically I want to be able to control how fast it rotates and in which direction.

From usability perspective I thought that a knob would be nice. I have very little idea about electronics but a potentiometer came to my mind as a convenient element that already has a knob that I could use as the control knob. I then did some reading/listening about transistors - and it seems I can use them (n-p-n, specifically) to complete my circuit.

I am asking you to advise me whether this is a reasonable approach. I still need to define specific values of the resistors/potentiometer but before I do that I would like to make sure I am not doing something inherently silly.

The circuit:

schematic

simulate this circuit – Schematic created using CircuitLab

** Edit **

@Kyle, thank you but that example does not work for me - it uses 2 input components: a switch and a potentiometer if I understand correctly, and I would like to use just a single knob. However, I am now learning about MOSFEDs, since they look like something I might want to prefer here.

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@fghfgjfgjfdjfdjdjfgdfff, that circuit is not practical, as it does not turn off the the opposite pair of transistors when reversing the motor. A simulation shows the bridge drawing 286 mA from the supply while driving the motor with about 5 mA.

DC motor bridge simulation

It is possible to make a linear reversing H-bridge motor driver with discrete NPN and PNP transistors. This design will supply about +/- 2 volts into a 50 ohm load (38-45 mA) from a 5V supply and a control signal of 600 mV to 1.2 V.

Better DC motor bridge simulation

It bothered me that the circuit above did not provide anywhere near rail-to-rail output, so I added four more transistors and a few tweaks, to get what I think is a fairly useful and efficient circuit:

Even better circuit

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  • \$\begingroup\$ The first simulation contains another (worse) circuit because the low side base current paths do not crossover. \$\endgroup\$
    – Jens
    Jul 9, 2022 at 23:56

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