My NTX2 (434.075) was wired up to the rest of the flight computer. Using Rob Harrisons code at http://www.pegasushabproject.org.uk/wiki/doku.php/ideas:notes?s[]=ntx2 it was a quick job to insert this into my code and pass the telemetry string too it. This was the easy bit The theory is fairly simple.
By adjusting the voltage on the TXD pin between two values (“MARK” and a “SPACE”) you can effectively make the 1’s and 0’s data which can then be decoded by DL-FLDIGI. Normally the carrier shift should be about 425Hz. The NTX2 has a range of 6000Hz over the input voltage range of 0 to 3V. So in theory 425Hz should be a modulation of about 0.2125v between the MARK and SPACE.
The sample circuit above was using 3.3V however on my Arduino the digital high voltage is 5V so I had to amend the voltage divider circuit. After alot of experimentation and alot of silly errors I managed to get the desired carrier shift of 425Hz. One thing to note is make sure you set your pinMode to output or you will get silly errors ( if you don’t set pinmode to output the low voltage isn’t 0v it’s 2v ish).
This is what I’ve come up with. Having tested it with my shiny new FT-817 I can confirm it’s all working
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