Frequency Meter (using a PIC 16F84)

This design was published recently in Amateur Radio, the journal of the world's oldest amateur radio association (we're rather proud of it ;-).

The Frequency Meter is made from recycled ideas and stolen source code. The original idea and some of the source code came from Eamon Skelton EI9GQ.

See his web page at

Microchip provided the binary to BCD code and the code for reading and writing the PIC EEPROM. The remainder of the code (the badly written bits ;-), I actually wrote myself.

The differences between the two design are:

  • Eamon's has a built in VFO stabiliser. Mine doesn't.
  • Eamon's has fixed IF frequencies (reprogram chip to change them).
    My design is self programming (just connect to your BFO and press a button.)
    You can reprogram it at least 10,000 times. You're bound to get it right eventually.
  • There are minor differences in the "counter" hardware and the "front end".
Thanks to Eamon for unwittingly getting me started on this project (it's not his fault and he probably doesn't know ;-).

I have had a mighty lot of fun building and testing it, and the end result has been rather useful.

Here's an article I had published in Amateur Radio magazine, the circuit diagram and the latest source code.
This version of the source code (27/11/2002) has, I hope, fixed a bug in the calculation of the displayed frequency. This bug caused wildly wrong frequencies to be displayed whenever the Intermediate Frequency was above the Local Oscillator frequency.

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