Home :: DIY Speed Control Instructions

DIY Speed Control Instructions

Stir Plate Speed Control Assembly Instructions

DIY Stir Plate Speed Control Kit

DIY Stir Plate Speed Control BOM
Part Qty


S1 1 SPST Toggle Switch
R3 1 10K Speed Adjust Pot
HS1 1 TO220 Heat Sink
J1 1 2.5mm DC Power Jack
IC1 1 LM317T Voltage Regulato
C2 1

.1uF 25V Filter Cap


1 5K ohm High Speed Trimmer Pot
KB1 1 Adjustment Knob
PCB 1 Stir Plate Printed Circuit Board
C1 1 .01uF Disc Filter Cap
LED1 1 Blue Power Indicator LED
H1 1 3-pin Male Header
R1 1 10K ohm Resistor (Brn/Blk/Org)
SO1 2 1/2" Stand Off
NUT 2 4-40 Hex nut
WASHER 2 4-40 Washer

4-40 X 1" Mounting Screw



1) Make Sure Your DIY Stir Plate Speed Control Kit Came with Everything.

Take a look at all the parts you received and compare them with the picture and list above and familiarize yourself with the parts. Before you solder anything, it's a good idea to use the blank circuit board as a template to drill the holes in the face plate of your case. The two inner holes need to be 1/4" and the outer screw holes 1/8". The access hole for the plug should be 1/2". Due the the availability of the various components, some of the parts may not look exactly like the photo, but should be the same general shape and configuration.

2) Solder the small parts first.

Like any circuit board assembly, when assembling this DIY Stir Plate Speed Control , solder the smaller parts first so they are not in your way. This circuit is pretty simple and easy to solder, but since there are components on both sides of the board, care should be taken to follow the order in these instructions. All of the components are placed on the side they are shown in the silkscreen and soldered on the opposite side.

I find it easiest to start by soldering in the H1 Header. Insert the header from the silkscreen side or omit the H1 altogehter and solder the wires from your fan directly to the board (last). Laying the circuit board on a flat table against the header holds it in place nicely while you solder it. Next solder in the Power Jack, J1. Be careful not to bend the pins when inserting it. Once it's soldered in place, apply a drop of super glue or epoxy to the pin protruding from the board. You can also melt the pin too for a flat disk which is the best way to do it, however, take great care not to melt it off. A soldering iron is too hot for this! Allow the glue to dry.

Once those two components are in, go ahead and place R1, R2, C1 & C2 on the board as shown. Pay careful attention to the polarity of C2, there is a stripe on the negative side. C1 does not have a polarity. Bending the leads helps hold the components in place while you solder them. Once all the small parts have been soldered, trim all the leads to the board. Here is an image of the back of the board, fully populated: NOTE: R1 is not shown in this image, but is placed just above R2.  R1 is the 10K ohm resistor used to drop the brightness of the LED.

DIY Stir Plate Circuit Rear View

Now turn the board over and thread the LED into its holes. The longer lead is the positive side, make sure you get the orientation correct here too. Rest the board on top of the LED and solder only one lead in place. Check to make sure the LED is flush with the board, reposition it if neccesary. Once you're happy with the placement, solder the second lead and trim the leads even.

3) Move on to the bigger parts.

Snap the main speed control pot, R3 onto the board. It's easiest to align the pins with the holes first, then snap the lugs down into the board. It takes a little pressure. Next, find the switch and take a look at it.  The current switch is momentary in one position and latches in the other. Flip it back and forth a few times to ID the latched side and insert that side up, towards the letters on the board. Make sure you watch the solder mask since the switch, speed control and LED are all mounted on the opposite side of the board compared to the rest of the components.

To solder the switch in, rest the board against the switch and solder in just the top lead. Before the solder cools, position the switch so it is straight, even and as low to the board as you can get it. Re-melt the solder and reposition the switch as needed. Once you're happy with it, solder the other two leads. Solder the leads on R3. Here is an image of the front of the board fully populated:

DIY Stir Plate Front

4) Now for the part that makes it all work.

Take the LM317T and using a pair of needle nose pliers, very carefully bend the leads 90* backwards, about 1/8" from the case. Backwards is towards the heatsink tab. Slide the LM317T into the heat sink HS1. Insert it into the board and solder in place. Finally trim the leads to the board.

5) Congratulations!

OK!, that's all there is to it!

6) Testing and Adjusting

To test the circuit, clip a voltage meter to the output pins. Turn the main speed adjustment pot, R3 full counter-clockwise. Plug in the power supply and switch the DIY Stir Plate speed control on. The LED should light and at full counter-clockwise, the circuit should will still output about 1.3VDC. Turning the main speed control, R3 full clockwise should bring the output all the way up.

Important! Trimmer R2 is used to tune the top speed of your fan, but it must not be set below 850 ohms.  Setting R2 below 850 ohms will cause too much current to flow through R3, burning it out.

Solder your fan to the header or solder your fan leads straight to the board if you omitted the H1 header.  The fan gound is the outer most pin and fan + is the inner most pin.  The center pin is not attached to anything.

7) Finish It Up and Make a Starter.

Mount it up in your enclosure, make a starter and brew some beer!