PWM motor controller - through hole version

Pulse width modulated (PWM) controller for efficient speed control of DC motors.  When connected to a PP3 battery, this module provides very smooth control of the Scalextric car (or any other DC motor such as model electric train).   The circuit is based on the inexpensive, reliable and robust CD40106 integrated circuit and can operate at supply voltages of 3-18V. Further details of the circuit are given here.

PWM motor speed controller schematic

 

IC1a forms a schmitt inverter astable. Variable duty cycle is achieved using separate charge and discharge paths for C1 using diodes D1 and D2 and potentiometer VR1. The period is set by C1 and VR1, it can be approximately calculated by the product C1 x VR1. The astable output is buffered by IC1b which drives an autoprotected power MOSFET. D3 is also switched on and off by the astable.  It gives an approximate indication of average output voltage as the mark space ratio is adjusted by VR1. D4 and C2 provide a noise free power supply for IC1.

 

Connections

 

The PCB is connected to the Scalextric track via PL1.

 

When using the PWM controller, DO NOT use the normal Scalextric power supply or handsets. Instead, power is supplied via the PCB from a PP3 battery.

 

Pin 1 of PL1 (identified by the square PCB pad) is connected to the positive terminal of the battery and to one side of the Scalextric track via a 3.5 mm jack plug.

Pin 2 of PL1 (the middle pin) connects to the other side of the track (via the jack plug)

Pin 3  of PL1 connects to the negative terminal of the battery.

 

If you find cars drive the wrong way around the track, swap over the jack plug connections.

 

Controlling the Ecocar

 

The PWM controller can also control the speed of the Ecocar. No wiring changes are needed. When the Ecocar is put on the track, energy for driving the motor is supplied by the on-board supercapacitors via an autoprotected MOSFET. The car's brush pick-up connects to the PWM output supplied to the track via a bridge rectifier which controls the on-board MOSFET.  With this arrangement, the PWM controller only supplies a control signal (but virtually no energy) to the car.

PWM motor controller - Surface mount version

Surface mount version version of PWM controller listed above but with just over half the PCB area.

PICAXE based PWM motor controller

Pulse width modulated (PWM) controller for efficient speed control of DC motors.  This controller provides the same function as the controllers listed above except that the potentiometer setting is mapped to output pulse width using software.  This allows the user to create non liner controls e.g. make the controller less sensitive at slower speed settings.