1.2V Retro Chip Oscillator

Using an old microchip, it’s possible to build a simple low voltage oscillator.

In this case, i’m using an LM339N, a Quad Comparator.
Looking at the datasheet, quite often an equivalent circuit diagram will be shown. By tracing the inputs/outputs for transistors seen on the diagrams, the connections can be found to at least one of them. Sometimes they relate to the power pins, sometimes the pins will be inverted, depending on how the manufacturer is using the transistors within..
In this case, it was as easy as the regular power connections and 1 of the Comparator outputs. Pin 12 to the Negative of the battery, Piin 3 to one coil ending, Pin 2 to the other end of the coil winding.

The coil is wound bifilar, 300 turns and 150…in practice, the circuit will run with either coil output connected to either chip pin.
Also, the LED will light in either direction, but stronger one way around.

The high coil windings total enables the circuit to only draw approx 4mA, when the LED is lit brightly.

I built my first such oscillator by accident about 5 years ago. It used an Intel 8255 and would run as an electrostatic detector, flashing several LED’s in step with someone walking on a carpet nearby. Although the 8255 datasheet stated it required 12V, it was being driven with a 3.6V house phone battery pack.

Bit different 🙂

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