How to Make a DC Motor Speed Controller




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Previously I made a DC motor Speed Controller, the design was good but it could be used with only 12 V motors.
Soon I needed to control 24 V motors, so I had to come up with a design I can use for the work. I saw it would be easy to use a 7812 with the 555 or a zener, but I wanted something very versatile, then decided to use lm317 as a voltage regulator.

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Step 1: Components

Lm317 :

Heat sink :

10 k Pot :

10 k Pot Knob :

220 Ohm resistor

Perf Board

Screw terminal:

22 AWG wire :

1N4007 Diode :


Btw if you are like me, you can salvage the most items from electronic boards

Step 2: Adding the Resistor

Start by soldering the lm317 to the Veroboard.I had already attached the heat sink to the Lm317 with the help of m4 nut and bolt.

There are three pins in the lm317

1 Adjust

2 V out

3 V in

Soldering the220 ohm resistor with Adjust and V out.A diode will be added parallel to the 220 Ohm resistor with the cathode toward the Adjust pin.Then take the 10 k pot and add it to solder it to Adjust and Ground

Step 3: Add the Capacitor

What are the capacitors for?

A 0.1 uF disc or 1.0 uF bypass capacitor is recommended to reduce the sensitivity to input line impedance.I have used 1 uF.

The adjustment terminal may be bypassed to ground to improve ripple rejection.A 10 F capacitor should improve ripple rejection about 15 dB.


The cathode of 1 uF capacitor connects to the V in and the anode to the Gnd

The cathode of 10 uF capacitor connects to the Adj in and the anode to the Gnd

Step 4: Add the Terminal and Flyback Diode

what is a flyback diode?

It is a diode used to eliminate flyback, which is the sudden voltage spike seen across an inductive load when its supply current is suddenly reduced or interrupted.


The cathode of the diode is connected to V in.

The anode of the diode is connected to V out.

Step 5: Lets Control

Adjusting the potentiometer changes the V out,

The minimum voltage will be 1.25V and the max will the applied voltage.The only drawback is the efficiency is not so great, Being a linear regulator it will change the voltage drop to heat, so you will need a good heat sink for higher voltages applied .

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8 Discussions


1 year ago

In the part where you connect the capacitors, u said the anode goes to ground, who meant the cathode (-) goes to ground


2 years ago

dude i need help with a 180V 4A 4000RPM dc motor .did u know how to run it or can u share a speed controller schematic for this type of motors ?


2 years ago

This is a variable voltage shunt type power supply. And while it can provide variable speed for a DC motor, it does that by turning any unused voltage and current into heat. And that is okay if you have a good power supply to feed it. But it does use up a lot of current into heat. Nice idea all the same.

1 reply

Reply 2 years ago


better use step-down or pwm, e.g., on 555 timer. line regulators is for low power and precise devices only nowadays, like adc, etc


2 years ago

Just a small technical tip: jumper the potentiometer center wiper to the unused lug, if the wiper fails, the pot will still deliver maximum resistance as a fail safe value.

1 reply

Reply 2 years ago

didnt really know that people use that as fail safe, nice tip


2 years ago

oh sorry, where is your schmatic?