I finally conjured up an electronics project which scratched an itch of mine — while simultaneously allowing my buddy and I to design a custom hardware/software solution.
The Problem: ham folks use morse code ‘keyer’ devices to aid them. It’s basically a tiny computer that plays a morse code message in a loop. You program messages into a few memories on the device, then tell the device to play “CQ CQ CQ DE NN9S” in a loop while waiting for someone to hear your hail. Or maybe you program the device to give standard canned responses when you’re participating in a radio contest. Either way, I had this realization that the smartphone in my pocket was essentially a supercomputer; why on earth was I bothering to assemble little IC devices with 5 or 10 flash memories to do this job? My phone was infinitely more powerful.
So really, the question boils down to this: assuming we can write a phone app that plays any morse code we want, how do we convert a ‘beep’ sound into a signal that my radio thinks is equivalent to “pressing the straight key”?
The radio’s connector is quite simple: it sends a small current out of a jack. If the current comes back to it, it thinks you’re pressing down on the straight key (closing the circuit). The straight key is just a physical switch.
So Jack AI4SV (my mentor/elmer) designed a circuit below which uses a common NPN bipolar transistor as the switch; we simply need to tickle the transistor’s base with a bit of current from the phone’s audio, and poof, the transistor closes the radio’s circuit and the radio sends a ‘beep’ out the antenna.
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