I’ve looked at references for similar projects driven by arduino, and a common setup is a TIP120 for controlling power to a solenoid. This diagram represents my current plan.
Looks workable!
Just need to be sure your USB power source is sufficient for the solenoid (< 500ma), unless you plan on using a separate charger which should be sufficient.
I don’t know the output logic on the PWM (source/sink current specs.) so you might need a pull up resistor on the base of that transistor (10k to +5v).
Ensure the mainboard can supply enough switching current to turn the tip120 on. Had these issues in the early days…
Almost two decades ago I quit using transistors for digital equipment and have used mosfets since. Many will allow a direct connect to the micro or computer. High input impedance means no real on current needed for it to switch… When on the junction resistance between drain - source is in milliohms. Generates less heat because of less resistance…
Good luck
Have fun 
I agree with the mosfets, but they have high input capacitance which means slow switching, I’d only use one if you are careful to use only 100% on / 0% off PWM to avoid switching losses. Too much time spent between fully on and off will cause them to heat up.
He’s switching a mechanical solenoid… think it’s slower than that?
No, that is fine, I was just thinking if his PWM is at 1KHz and he mistakenly commands a laser power of 50%.
The trick would be to use a device that is closely matched to the load.
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