CTCSS board.


I have yet to try this out, but a simple CTCSS board can be made with an Arduino Nano driving an R2R network.
Pins 2 detects the TX on, and 3-7 select what tone is to be used.
Later today I'll put one together to see if it works.
This will be a cheap board as the R2R network can be soldered directly to the Nano so no extra board is really needed. Just maybe a few Rs and Cs.
Of course, this can use the Basic VFO board I have if folks are interested. And a display could be added too.



I have a demo board running.
There is a push button for the "PTT" switch. The code expects a LOW for TX. But in real life, it may be a resistive divider from the TX power, and active HIGH. Or an opto isolator, or transistor......

Here is just to show how little is needed.
This uses discrete resistors for the R2R_DAC. It will be a lot neater to use the SIP resistor pack shown next to the board.

The series resistor network selects the channel

A 12 position switch is the selector for the required tone.
The tones are...
1 = 0.0Hz (no tone)
2 = 67.0Hz
3 = 74.4Hz
4 = 88.5Hz
5 = 91.5Hz
6 = 94.8Hz
7 = 103.5Hz
8 = 118.8Hz
9 = 123.0Hz
10 = 141.3Hz
11 = 179.9Hz
12 = 440.0Hz as a setup test tone.

These tones can be changed in the code if needed.

The tones could use a bit more filtering maybe, as they are only 5 bits.
Of course, a trim pot will be added, along with an isolating resistor and coupling cap to feed the tones to the mic circuit, but that may depend on the set in question.

CTCSS_20120304.zip is the working code as is shown above.
Feel free to modify it as you want.


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