Hi, this is Wayne again with a topic “Weekend Projects – Dial-a-Speed Motor Controller”.
Hi, I’m Sean Regan, I’m technical editor for Make Magazine if you’ve ever built a robot or other project that uses a small DC motor. You may have run into a speed problem off the shelf. Most of them just run too fast for so-called direct drive applications. That’S where you connect the load that you want to turn directly to the motor shaft. Sometimes you can use gears or pulleys or some other sort of mechanical drivetrain to slow down the motor output and solve your problem, and sometimes you can’t in those situations, you’ll need an electronic speed controller, which is where this comes in. We call it the dial speed, it can be used with almost any small DC motor or brushless fan that will run at 12, volts or less. The dial of speed uses a potentiometer, a 555 timer and a MOSFET to switch the motors power supply on and off.
At a set rate, the total power delivered in a given time is determined by the potentiometer setting. My design is based on a circuit posted by Rick Bickle of the Dallas personal robotics group, with a few minor modifications. You’Ll need to pick up the following parts to make this project, all of which can be found at your local RadioShack. You’Ll also need these basic tools.
Let’S get started with the build we’ll start by cutting down the potentiometer shaft use a hacksaw to make the cut. Then a file just move the edges. Next twist and solder, a pair of diodes and a small length of wire together to make a y-shaped junction note the orientation of the silver stripes. Now you can solder the free ends of the diodes, the potentiometers outer terminals and another length of wire to the center terminal, apply heat shrink tubing to make sure the diodes don’t short against the center terminal. The transistor that switches, the motor current may get a bit hot when running so we’ll attach a heatsink to keep it cool. First then, the three MOSFET legs up toward the transistor cut a piece of double: stick: foam tape to fit the front surface of the body and stick it in place strip the end of a length of wire grip on the uninsulated ring tongue, lug and solder.
It in place next attach the mosfet and the ring tongue lug to the heatsink, with a machines. Now we’ll start wiring up the circuit board, start by soldering all eight legs of the five five five timer into the PCB and attaching a piece of foam tape to the back. Now we can solder in the PC board terminals, one above and one below the five five. Five next we’ll add a diode right below the 555 timer, making sure that the silver stripe on the diode body is closest. Pin for this helps control the counter electro-motive force that occurs when motors are switched off.
The next two components are ceramic capacitors. The first is soldered between pen, five and ground, and the second one is soldered between pen, two and six and ground. Next, we’ll add the electrolytic filter capacitor, it’s soldered to the board, laying down on its side with its positive lead, connected to, pin eight and it’s negative lead to pin five connect, the wire from the potentiometer terminal to pin three on the five five five timer and The wire from the diode junction to pen to run the stripped leads in from the component side of the board, then bend and solder them on the copper sighs. Now we can add the MOSFET first remove the protective layer of foam tape from the MOSFET and the 555 timer.
It’S important that the MOSFET is aligned perfectly. The first lead should be aligned next to the five five five timers pin, seven, the second next pin six and the third next to pin five once aligned carefully guide the leads through the PCB hole and push the MOSFET in until the two pieces of tape. Stick together now bend the flange lead down and solder it in place then bend the transistors first lead away from the IC solder it in place and reflow the solder at pin number seven solder. The second transistor lead and cut off any excess metal. Finally solder.
The third lead into place and reflow the solder to connect it to the adjacent capacitor lead, we’re almost done, there’s just four more solder side connections; first, install a pull-up resistor between pin 7 and the top left terminal pen. Next install a red power jumper between the VCC terminal pin and the bottom right terminal pen then install a jumper between the MOSFETs flange lead and the bottom left terminal, pin finally install a jumper wire between the top right terminal pen and the MOSFETs third lead. Remember you can refer to the project page for detailed instructions on how all the components were electrical schematics and our troubleshooting guides.
Well, that’s it! The circuit is now complete. Let’S check it out. The potential applications for this circuit are many and varied. You could use it to build an adjustable magnetic, stir plate for your laboratory or an adjustable fan or fluid pump. You can even use it for non motor applications like dimming, incandescent or solid-state lighting, or for whatever else you can imagine. I’M going to use mine to upgrade my original optical tremolo box for better low-speed control. What will you do with yours? Please? Let us know in the comments on the project page .