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Project Notes

#120 Simple Peak Detector

The basic diode-RC peak detector.

Notes

Afrotechmods and w2aew both have some nice, clear videos on youtube explaining peak detector circuits.

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The most basic circuit uses a diode to rectify an incoming AC signal, and a capacitor to charge and hold the peak value. The RC pair holds the peak for a period governed by the RC time constant (𝛕).

Time to fully discharge is approximately 5𝛕, or in this case, about 5 seconds.

Appropriate values for the RC network depend on the signal frequency being sampled (higher frequencies will be better served by a shorter time constant).

The main problem with this circuit is the fact we lose the diode forward voltage from the output, resulting in offset measurements and an equivalent minimum input voltage sensitivity.

Here’s a sample trace recorded using LEAP#090 PlotNValues (a simple Processing sketch)

  • upper trace is the output of the peak detector
  • lower trace is the signal input (a rough triangle wave source in this test)

processing trace

Construction

Breadboard

The Schematic

The Build

Credits and References

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

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - 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
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.