World’s Simplest PWM Motor Controller

Really Basic PWM Motor Controller

Well, I did it!

Knowing nearly nothing about electronics, I managed to finally build my own PWM (Pulse-Width-Modulation) DC Electric Motor Controller!

OK, that makes it sound way too fancy. At the beginning of the semester, I signed up for a non-credit electronics class at the local two-year technical college. I’ve been wanting to take that class for years, but it’s never worked out with my schedule. The instructor is an interesting guy, whose stories always illustrate electronic principles in a way that you won’t forget. He’s worked at Motorola when the cell phone division was only six people, patented EKG monitors for veterenary use, and worked on superconductors at General Electric. That’s right, he’s the Forrest Gump of electronics!

So, being in this class is really interesting to me. Mostly it’s just been learning the basics of DC electronic components, and now we are moving on to learning about waveforms and other aspects of alternating current.  Now, I’m not one to just sit around talking theory. I want to BUILD something!

Recently, I was using an LED light as part of a lighting setup for a product video I was working on. The LED light was so compact, I could put it right in the scene without a light stand or even really being noticed by the camera. This was a simple LED array designed for use as an under-cabinet light. They are very inexpensive (when compared to professional lighting equipment) but don’t have the accessories that pro lighting gear would have, such as barn-doors. The other tool that would have been really handy would be a DIMMER.

However, traditional dimmers don’t work with LEDs. Instead, the best way to dim an LED is just to turn it on and off really fast. On and off hundreds or thousands of times a second would be ideal. This is the EXACT same principal as how the speed of a DC electric motor is controlled. So, I thought I could build a basic dimmer box for my LED light, and use it to help me further understand the principals of how my electric car runs.

At the Milwaukee Makerspace, Thursday nights is the Electronics Club night. It’s a great time to work on circuit boards, robots, and more. But the most important part is that there are folks there that can help get you get started – Electronic Mentors if you will. I talked with a couple members, including Tom G., about the simplest way to build a basic PWM controller, and was referred to the “555 Timer” and a tutorial on the Dallas Personal Robotics Group web page. Many robots use small DC motors, with speed controlled by PWM, so it makes sense that robot builders would have all this figured out, and made into a handy teaching tool. (Tom’s been building robots for years.)

Having never really built anything like this before, I found it interesting and just exactly challenging enough. All the parts need – a 555 integrated circuit, a 100K potentiometer, a couple capacitors, a few resistors, were right there in the electronics parts library at the Makerspace. I grabbed a breadboard, Tom explained what holes were connected to what in it, and I got to work plugging in a few components and wires. I didn’t get very far on the circuit that evening, but felt like I now knew what I was doing.

Last night, I completed the circuit. Instead of the output driving an electric motor, it goes straight to a resistor and single red LED.

I connected the 12v power and VWALA! the red LED came on!

Rotating the potentiometer one way or the other would make the LED brighter or dimmer. Visually, this was really not very exciting. It’s just one little dim red light. The exciting part was knowing that the light was blinking at 1440 times a second, and that the same circuit could be used as the brains to dim a very large LED array or even drive an electric car!

PWM circuit, image care of DPRG

Here’s the diagram of the circuit I used. A resistor and LED was used in place of Q1 and M1 for testing the circuit.

Tagged as: controller, led, motor, PWM