Home > Circuits > Triangle Wave Astable
Modified:21:50, 22 October 2013
When producing sound waves for projects, square wave astables are easy to build but sound harsh when amplified through a speaker. Sine waves sound much more pleasant to the ear but are tricky things to produce accurately, especially if you want to vary the frequency. This Triangle wave astable is a good substitute as it is closer to a sine wave and the frequency can be varied.

This is a common circuit to produce a ramp wave based upon a ramp generator and a Schmitt trigger. As the ramp generator output - also the wave output - reaches the "upper trigger point" of the Schmitt trigger, the trigger output goes low, causing the ramp output to start falling. When it reaches the "lower trigger point" of the Schmitt trigger, its output goes low, causing the ramp output to start rising again. The process repeats itself creating a ramp output.

The Schmitt trigger and Ramp generator are made from op-amps. The ones shown are TL074 but this was only because this was part of another circuit (Drill Speed Controller. Any general purpose op-amp will do, some will perform better at high frequencies. The lower the output slew rate the better for high frequencies.

VR1 controls the frequency of the wave by altering the rate of charge on the ramping capacitor.

This of course can be altered by changing the trigger points of the Schmitt trigger. By increasing R3, the output amplitutude will be increased since the trigger points are further apart. If R3 is greater than R4 then the astable will cease functioning.

Red trace: Ramp
Blue trace: Square

This is the output directly from the op-amp. Since it is not working on a split power supply the output ramps from 3 to 6 volts. There is also a square wave output but again its amplitude will depend on the saturation limits of the op-amps

Red trace: Ramp
Blue trace: Square

with the addition of a capacitor can be converted to AC. This is done by opening SW1. The output will oscillate around 0v but will take a few milliseconds to do so as C4 initially charges.

Simulation of Triangle Wave Astable

Designed and Written by Phil Townshend 2007
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