Time to back up in the sewer and give a bit more explanation of how it is done. This is not about the 300-pound Mary Jo and the backseat of the 57VW Beetle, but the CW Transceiver project in progress.
Our DCR Receiver project of course used the Arduino Uno for the LO (CLK0) and provides a nice LCD display. But the thought of an Arduino still creates panic amongst many homebrewers. There is no reason why you can't use something like a Glue Stick PTO with the Receiver and similarly use Crystal Control for the Transmitter.
The net result in either form factor is that you have a CW transceiver. Fortunately, specific frequencies have been established for QRP CW operation and thus you can leverage those frequencies for a simplified design.
With that in mind the Transmitter portion has been envisioned as capable of operation without the Arduino, meaning it could be Crystal Controlled.
With that idea in mind one feature is not included in the Arduino Logic and will work in either scheme. Behold the PNP Keying circuitry which simply provides a mechanism to key the Voltage of a Buffer stage.
The Circuitry to be built on the Blank Squares
Ahead of that Buffer is either the CLK2 from the Si5351 which is offset from the Receive (CLK0) frequency by 600 Hz AND is only "ON" during the transmit cycle. Or a simple Crystal Oscillator which is manually turned on during transmit.
I ran a test with keying both the Oscillator (PNP Germanium) and the Buffer. Cleaner Signal and about 72 milliwatts output.
The Arduino sketch features a keyed pin (Pin6) which does the following.
1) Starts a two second timing Cycle.
2) Outputs Voltages on Pins 9 and 10.
3) Enables CLK2 which is CLK0 - 600
4) Disables CLK2 after the cycle is over
5) It is not involved in the keying of the Buffer
The Voltage on Pin 9 triggers a fast-acting Reed Relay via a BS7000 to supply 12VDC to the TR Diodes and the Bias to the IRF510. Pin 10 simply lights an LED to show you are in Transmit and could provide a source voltage for other controls.
Initially the delay was set to 2 seconds -- Having seen it work on the Mega 2560, I can envision that is too long so needs some tuning like about 1 second before return from transmit (maybe even less than that). But that part is working.
During the timing cycle (now set at 2 seconds) the Arduino sketch is locked on to just those functions designated in that sub-loop which by some is viewed as "bad", but I do not see that as an issue. Essentially it puts the TR Diodes in the transmit mode and supplies a constant Bias to the IRF51o while generating CLK2. Timing cycle over and that all goes away. The real keying of the transmitter is done with the PNP keying transistor which is now a 2N2905.
My tests of the Keying circuit show a bit of artifact garbage which will be evaluated. I will also look at the "back wave" phenomena.
Were you to directly utilize the Arduino for transmitter keying then my simple approach may need refinement -- but then you are locked into using an Arduino.
TYGNYBNT
73's
Pete N6QW