I've made a simple relay circuit to switch power to a small DC motor
Here is a diagram of what I got right now:
Is it possible to replicate that with a transistor. Which one would be a good choice?
Electronic – Using a transistor instead of a relay to control a DC motor
dc motorrelaytransistors
Related Solutions
Yes, you can use a relay for direction reversing of a brushed DC motor. It would use a DPDT relay as shown in the diagram below. And yes, at the same time you can use an N-Channel MOSFET transistor to control the speed of the motor by driving the MOSFET with a high speed PWM signal. The duty cycle of the PWM would control the motor speed.
With the proper selection of MOSFET you would be able to drive the MOSFET from the PWM output from your Arduino. The direction relay coil is shown as using the same voltage as that used to power the motor. If the relay coil was a different voltage it could be connected to a separate voltage rail.
You're asking your npn transistor to carry current from emitter to collector, which is opposite to how this transistor needs to work.
Best Answer
You can use a logic gate MOSFET, like the FDC855, and then your circuit will look like this:
A FET will give you a high current if needed (probably not necessary, since you're powering the motor from AA cells).
Or a BJT like the BC547, and then you would make it like this:
With the 1 kΩ base resistor you'll have minimum 100 mA current for the motor. If you need more I'd recommend the FET solution.
The diode can be a 1N4148.