This is a low cost project is based on the Dial-a-Speed design. This is a pulse-width modulation (PWM) speed controller, using a 555 timer IC wired in astable mode to control an N-channel power-enhancement MOSFET that actually switches the motor on and off. This circuit is cleverly designed to offer a wide range of control, and can produce square waves with duty cycles ranging from less than 5% to more than 95%, depending on where you set the dial.

I originally built the design exactly as shown in the Make article however I found all of the jumpers required on the board left the design rather messy. I opted to design a board for this project so I could just solder on the components and forget about all of the jumper wires.I am using the PWM to control the speed of a small DC motor that spins a magnet for a stir plate.


The schematic for this design can be seen in the Make Magazine Dial a Speed article, and the background details of the circuit can be found on the Dallas Personal Robotics Group page.


Parts list: (a slightly modified list from the Make Article)

  • Project Enclosure RadioShack 270-1805 (This is the enclolsure I used something different might work better for you)


  1. Procure circuit board
  2. Procure components
  3. Solder components to PCB
  4. Connect J1 to 5-12 VDC Power Supply
  5. Connect J2 to  Load (DC motor, LED, etc)
  6. Connect potentiometer (R1) to J3 and J4
  7. Adjust potentiometer to enjoy variable speed intensity ect.