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Project Notes

#164 Watson LED Ring

Test a Watson 3-LED Ring oscillator.

The Build

Here’s a quick video of the circuit in action:

WatsonLedRing

Notes

A neat and simple circuit that I found presented on the rustybolt blog.

It has three n-channel mosfets linked in a ring with an RC circuit controlling the gate of each. Each FET drives an LED. Once the circuit gets started, it oscillates indefinitely.

There is nothing inherent in the circuit that kicks off the oscillation - it is completely symmetrical - so I guess it relies on slight component variations and residual capacitor charge to get started. In practice I haven’t seen any issues getting the oscillation started.

This runs at 5V nicely, which is enough to exceed the LED forward voltage with sufficient headroom to turn on the FETs hard enough.

Construction

Breadboard

The Schematic

WatsonLedRing_bb_build

Here’s a quick video of the circuit running on a breadboard:

WatsonLedRing

Running at 3V

Since 5V is a bit inconvenient to package, it’s possible to run off a lower voltage by adding 22kΩ resistors in parallel with the LEDs. It also helps to switch to LEDs with a lower forward voltage.

I tested this configuration with green LEDs, and was able to get it running very nicely on a 3V coin cell.

Breadboard

The Schematic

WatsonLedRing3V_bb_build

Here’s a quick video of the 3V circuit running on a breadboard:

WatsonLedRing

Freeform Build

This is a quick freeform build that arranges the 3-LED ring in a circular frame that holds a CR2032 coin cell

WatsonLedRing3V_build_complete

The Build

Here’s a quick video of the circuit in action:

WatsonLedRing

Credits and References

About LEAP#164 Oscillators
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.