Using a Transistor to power Technic Servo (with PWM)

Hey everybody I’m an electronics student working on a final project for graduation. I am trying to learn the basics of the Arduino Uno and I was able to drive a small Technic continuous running servo using the write functions out of pin 9.

I want to begin driving multiple servos and want to begin using transistors to turn them on, my only confusion lies in the PWM of the servo control module. There are 3 pins on the servo control – orange, white, and black.

-Orange: Power
-Black: Ground
-White: PWM for control

I am using 3904 NPN transistors. My question is, should I be using the 3904 as common collector or common emitter? And can i drive the PWM (white) pin of the servo control directly from the arduino (pin 9)? If so I imagine orange (power) pin of the control module would go to the transistor?

I wanted to use say pin 10 to turn on or off the servo, and pin 9 as the PWM control pin to control servo direction and speed.

This is what I am envisioning (attached schematic).

Is there an easier way to accomplish this? Any information or advice is greatly appreciated.



Have a link to servo data sheet? Why do you think you need to disconnect power line, save a battery?

I have: -2x - 5292's -2x - 47154

I am most likely going to stick with the 47154's because of they consume a fraction of the amount of current - and the amount of power I need them dissipate is minimal.

I am using a VEX 3-pin servo control module ( to control the servo's. The schematic i posted previously does NOT work as described. I am going to try common emitter.

The point was to remove the stress of powering the servos off of the arduino and power them using a battery or other supply.

Just to clear, so you hack a servo and replace a motor? Control module isn't continuous rotation .