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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