Tuesday, May 28, 2013
I won the LayerOne Conference badge hacking contest... again!
Prior mention and details of the badge here:
Clearly, the Xprotolab option was the way to go! http://www.gabotronics.com/development-boards/xmega-xprotolab.htm
I didn't install any of the blinky-bling LED's that came in the kit.
(Since this IS my blog, I'd like to take a moment to announce that I am not a fan of blue LED's. I find them to be the visual equivalent of fingernails on a chalkboard. Maybe I'm just weird, but I'll be glad when that fad ends and we all go retro back to the original red LEDs ;) Better yet, why don't those optoelectronics engineers develop a new and improved funky new color that isn't such a retina-puncturing abomination???)
I took a lot of Saturday to get the thing built, and debugged. Sorry to those whose talks I missed!
But, before dinner, I had a working scope, but the signal generator required the PC to be connected.
I then took some time off the project to assist with Ham Radio exams, (is it clear yet that I'm obsessed with all things RF??) I was part of the Volunteer Examiner team, and when the dust settled, there were 6 new hams and one license upgrade. Woohoo! Congrats!!!
After a late evening, I headed home, as I live near enough to where the con was held that shelling out the $ for a room would have been rediculous.
That, and I don't drink like a hacker. ;)
Got up early, and started on Plan A, a voltage-controlled oscillator, (abbreviated VCO) which fortunately worked well, so plan B wasn't needed.
I'd never built a VCO before, but by about 8:30 am, I had a working one. Had a little problem with the badge, mainly an issue as to how the Arbitrary Waveform Generator was supposed to work, but once I got back to the con and asked Charlie a few questions, spent a few seconds with a "real" oscilloscope, everything started coming together.
The circuit is a "classic" TV (when it was analog) and FM radio "jammer" circuit. Just a toy, as it has a range of about 15 feet. (And notice I clearly marked it as a Part 15 device!!!) I built an Elenco kit version of this circuit way back in college. (Back when the Internet was all text, no pictures. Vax VMS, 2400 baud modems, and Telix on a 386sx, baby!) Back then, we used it as a dorm pirate radio station, but we were making more AM than FM with it, using an audio transformer between the transmitter and the stereo, as the modulation method.
Now that I'm a lot older and just a little wiser, and a heck of a lot better informed due to the addition of pictures to the Internet, I added what I correctly guessed would be a varactor modulator, a reverse-biased LED acting as a varacter diode. More details of this concept here:
The idea was that the output of the badge's waveform generator, using a traingle wave, would be put into the varactor, and hilarity would insue.
Not so much, but not only did it work, it sounds pretty clean. A "swept" VCO is essentially an FM transmitter, as is seen functioning in the video.
The completed project unfortunately did not end up as a self-contained, wearable item. First, the output op amp for the signal generator was not active when the badge was powered by the 3V battery, only when 5V from the USB adapter was attached. This caused me to abandon solving the other nagging issue, how to attach the VCO PCB to the badge in a removable, non-ugly manner.
It didn't seem to matter, I was awarded a Beaglebone Black. ;)
Things I would like to try next with the VCO:
*Add a microphone and a preamplifier to the VCO input, instead of the sweep gen. This would give "Mr. Microphone" functionality.
*Maybe add another LED in parallel, this might give more "pull" to the frequency range. It'd be neat to lash up a PLL chip to this and attempt to make a synthesized VHF transmitter.
The VCO board was constructed using what is called "Manhattan Style Construction." a bare unetched copper board is used as a ground plane, grounded part leads are soldered directly. All else is soldered to little interconnect pads, also punched out of unetched .060 FR4 with a Harbor Freight hand punch. These pads are glued down with gel CA glue, and then soldered to. Quick and easy.
The two coils are just three turns each of bare 18 ga. copper wire from the hardware store, used for hanging pictures, etc. Its not even magnet wire.
Wind three times around a pencil eraser, then use a razor blade or a guitar pick to spread the windings out a little bit, so they aren't touching each other.
They are also part of the "coarse" frequency adjustment, pushing them closer together (but making sure they don't touch) will raise the output frequency, spreading them apart will lower it.
Gotta love pre-WWI technology!
Last year, the radio transmitter was included in the badge, it was a controller for a toy RC car. One cut trace, one jumper wire, and some new Arduino code, and my badge became a CW (Morse Code) Radio beacon that sent a brief message to a nearby receiver.
A big Thank You for the folks who put on LayerOne, their sponsors, and Null Space Labs!