{"id":604,"date":"2011-12-27T00:32:27","date_gmt":"2011-12-27T05:32:27","guid":{"rendered":"http:\/\/blog.red-bean.com\/sussman\/?p=604"},"modified":"2012-02-15T15:28:39","modified_gmt":"2012-02-15T20:28:39","slug":"connecting-android-to-my-ham-radio","status":"publish","type":"post","link":"http:\/\/blog.red-bean.com\/sussman\/?p=604","title":{"rendered":"Connecting Android to my Ham Radio"},"content":{"rendered":"

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.<\/p>\n

The Problem<\/u>: 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.<\/p>\n

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”?<\/p>\n

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.<\/p>\n

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.<\/p>\n

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As you can see in the circuit, we take the ~.5V signal from the phone’s audio output jack and transform it into about ~5V. From there, we use a full-wave rectifier to convert the AC into DC, then eventually send that current into the transistor. The capacitor is there to smooth things out.<\/p>\n

The other half of the project, of course, was writing an Android app to act as a versatile memory keyer. The open source code is available on Google Code<\/a>, and the application is freely downloadable from Android Market<\/a>.<\/p>\n

In the video below, you can see a live demo of the prototype hardware & software in action:<\/p>\n

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