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A DIY Square Wave Signal Generator with Pulse Width Modulation

This circuit is very simple and has a fantastic range of potential uses. The two potentiometers (variable resistors) allow the frequency and pulse width to be varied independently and without affecting each other like in the super simple signal generator.

By incorporating a rotary switch, the value of the timing capacitor (C1) can be adjusted. This allows the frequency to be adjusted over the full range that the 555 timer can support.

A separate chip (LM393) is used to control the pulse width so that it will not effect the frequency. The LM393 is a 'Low Power Low Offset Voltage Dual Comparator' The pot (VR2) is used as part of a voltage divider so that the voltage on the inverting input of the comparator can be smoothly varied. This voltage determines the pulse width of the final output signal.

Like this circuit? Check out our range of Pulse width modulation circuits.

Pulse Width Modulated Signal Generator

IC1 LM555
IC2 LM393
R1 10k
R2 10k
R3 2.2k
R4 10k
VR1 1M
VR2 10k
C1 47nF
C2 4.7nF
C3 470pF
C4 47pF
SW1 4 Pole Rotary

Since the pulse width is relative to the input voltage on the this input, it is possible to use the circuit in conjunction with a multitude of robotic interface boards. This signal can be used to drive a H-Bridge or power transistor which is ideal for varying the speed of a DC motor. We have some circuits based on this idea on the Cyber Circuits page. We also have a simple DIY version of this device here


Potential Uses Might Include:
DC Motor Speed Control Control
Boosting or Variable Dimming for LED's and Light Bulbs
Transformer or Ignition Coil Driver

This circuit was used in the Power Pulse Generator project as part of the Ignition Coil Driver

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