I found a circuit online that refers to a QST
article in 1999, that shows a CW zero beat decoder. It uses a LM567 that
converts the audio signal and switches on a LED to show the operator has
achieved a zero beat. The project has a variable resistor that can be used to
tune or “swing” the centre frequency – This was a good start for me, and I
created the following schematic for the build and set to work constructing it
on the breadboard.
As you can see its very simple indeed. I
did differ from the published design and found that I could use a single .22uF
capacitor across the output pins. So here is a breakdown of the build :
C1 0.1µF
C2 0.1µF
C3 1µF
C4 0.22µF
C5 0.47µF
VR1 10kΩ
R2 470Ω
IC1 LM567
LED1
Arduino Uno – Rev 3 (or any suitable
Arduino copy etc)
20x4 LCD display ( Im using a I2C display.
This takes up less wiring to achieve the same result)
Once I had built the electronics, and
before I tested it on the Arduino it was time to feed the circuit with some
audio. Luckily I have a audio output from the FT-2000 which had enough volume
to trigger the IC.
After some adjustments on the potentiometer
the LED was flashing in time with the tones being received on the 20m band at
750Hz audio frequency, This was great, with no mistakes and on the 1st
attempt the circuit burst into life. here is the breadboard layout of the 1st attempt. It is laid out subtly different - for ease of understanding only. (also be aware I'm using an I2C display - and in this version I was using a 2 line display)
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