Home > Circuits > Bi-Directional Speed Controller
Modified:20:40, 22 October 2013
After building a Radio Control Speed Controller it seemed a natural progression to extend this into a stand alone Bi-Directional Speed Controller.
It is based entirely on the RC controller with the addition of a variable mark/space astable to simulate the RC input.
I am not sure on the uses for this but I am sure there are some!
This circuit uses most of the RC Speed Controller with the addition of an astable that produces the variable mark/space signal that simulates an RC receiver output. The PIC provides the signals to drive the 4 branches of the MOSFET driver correctly.

The PIC used is a 12F629 with a program written to convert the signals accordingly.



This section contains the voltage regulator RG1 which supplies the 5v required for IC1 and IC2. The only change from the RC Speed Controller is that the transistor inverter/buffer has been replaced with a 555 astable to provide the required pulse widths. The astable is configured to provide a low pulse width with a duration from 1-2ms exactly (or as exactly as you can with a 555). The PIC times the pulse using a timer TMR1 which is gated by pin 3 and is active low, thus the inverter from the RC Controller is not needed.


More information on this bridge driver can be found on the MOSFET Bridge Driver page

The PCB is a modification of the one used in the Radio-Controlled Speed Controller.
It measures 40mm x 55mm and is made from single sided board with no wire links.

The tracks that lead to the MOSFETs and connector TB1 had a liberal amount of solder added to increase their current carrying capacity.

Water soluble fluxed solder was used and the PCB was washed clean after soldering. Then a couple of layers of clear laquer applied to prolong the life of the tracks.


VR1 can be mounted directly to the PCB. The type used is 16mm PCB mount type as shown left.

The power and motor connections are via TB1 and are shown above. The circuit will work up to 18v. After that the 78L05 (RG1) might start to sweat a bit and will need to be uprated. The polarity of the motor connections will need to be trial and error. If the motor turns the wrong way then reverse the wires.

WARNING - The heatsink tabs of the TO220 MOSFETs and Diodes are NOT isolated and are connected to one of the terminals of each device. Take care adding any heatsink to them and ensure that any metal heatsink applied is insulated from all the tabs.

Available soon...

  • PCB LAYOUT using WORD - check size but it should be correct

Please note: Even though I have every faith in this project, I accept no responsibility for any damage occuring from you building or using the controller.

The pre-programmed PIC is available from our shop.

Designed and Written by Phil Townshend 2011
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