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Purpose: to provide a working interface that can be used to connect a computer, phone or tablet that produces morse code tones from text, to a transmitter.
This enables you to send morse at higher rates than most humans can interpret and if used with a program like FLDIGI, will give very good results.
Why not just connect the PTT input of the transmitter to the computer via a serial port, USB or even parallel port (assuming you can find one of these)? The reason is that even some of the best programs do not allow you to do this and instead produce an audio tone output.
[The front (left most) part of this circuit is only there to simulate an interrupted tone that comes from the sound card.]
The op amp is set up as a comparator that allows the signal level to be set, using the 10K pot, for optimal response to the tone. This is best done by ear. The output of the comparator op amp is a squared-up version of the input tone. This is then filtered by the RC circuit which is then fed into the base of the transistor.
The transistor then switches current that is sent through the coil of the relay.
NOTE: If building this circuit, select a 12 volt signal switching relay if you use 10 - 12 volts supply.
[On the simulation, an LED is placed in the current path to show when the circuit has detected a tone. In reality, this LED is not really needed as this is where the CW or PTT connectors go to the radio. i.e. the relay contacts are in place of your morse key!]
The op amp functions might be translated to work using Schmitt trigger inverting buffers but EC has NO Schmitt input devices. Maybe one day???
ENJOY
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