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Project Notes

#336 Comparator-based Relaxation Oscillator

Test a classic comparator-based relaxation oscillator, modified for single-supply LM358 OpAmp.

Build

Notes

The comparator-based relaxation oscillator is similar to the astable opamp oscillator - see LEAP#039 - but is a more straight-forward and symmetrical circuit, one that is easy to intuit.

OpAmpHystereticOscillator

Rather than use dual (+/-) supply, I’m using a voltage divider and buffer to provide a half-supply reference.

The theoretical frequency f = 1/(2ln(3)RC)

I tried a few combinations, and performance was remarkably close to the theory:

R C f (actual) f (theoretical)
100kΩ 10µF 437mHz 455mHz
100kΩ 100nF 44.8Hz 45.51Hz

Here’s the 100kΩ/100nF combo on the scope. Channels connected per the schematic, clearly showing the hysteresis of the capacitor charging curve as it battles the positive feedback.

scope_100k_100n

Construction

Breadboard

Schematic

Build

Credits and References

About LEAP#336 OpAmpOscillators
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.