Simple FM Transmitter That Shows Off Its Own Circuitry

April 19, 2011 by Mike Szczys 8 Comments

[Sean Michael Ragan] built this FM transmitter which shows off its circuitry via a clear plastic dome. The device is electrically identical to one we looked at in September. That version championed a construction method that used small squares of copper clad as solder points which were each super-glued to a large copper-clad platform serving as a ground plane. [Sean] is using a printed circuit board that was laid out by Sonodrome. You can check out their own glass-jar transmitter build where the board artwork is available for download.

One of the tips we enjoyed from [Sean’s] step-by-step build is the coil wrapping. He used the threads of a 1/4-20 bolt to guide copper wire as he wrapped a total of four turns. Once the bending is done, just unthread the bolt to separate it from the coil and gently stretch the wire for a 12mm distance between the two leads. Not only is this visually pleasing, but it will help with transmission clarity.

Open Hacker Conference Badge Project Needs Your Help!

April 18, 2011 by Jeff Katz 18 Comments

[Aestetix] writes in to tell us that the OpenAMD (Attendee Meta-Data) project is working on a new revision of their hardware, to be debuted at CCC Camp this fall.

For the uninitiated, OpenAMD combines an Active RFID tracking system with social networking, and is completely open-source. You walk into the conference, put on the OpenAMD badge, and suddenly you can see yourself as a dot moving around on a map. Or you can log into the social networking site, create a profile, and watch as your personal information is pulled into the mesh, which then tells you talks you might like, people you might like, where those people are, and more. There’s even an open API where you can create your own ‘killer’ apps, which may include games or other interesting aggregates of the attendee information.

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DTMF Shield Aimed At Ham Controlled Arduino

April 17, 2011 by Mike Szczys 8 Comments

[Colin] wanted a way to reliably control an Arduino via ham radio. One of the easiest methods of automated radio control makes use of Dual-Tone Multi-Frequency signalling. To those who aren’t into amatuer radio you probably recognized DTMF as the touch-tone system for telephone communications. [Colin] built a shield that has an audio input and can decode DTMF signals.

The hardware is based around an MT8870 DTMF decoder chip. This is a popular choice for DTMF hardware because it does all of the decoding work for you. Whenever a valid tone is detected it outputs the associated value in binary on four output pins. There is a fifth pin that strobes after each new tone. [Colin’s] design offers a lot of feedback for what’s going on with the input signal. The DTMF value is displayed on a 7-segment display (controlled completely in hardware), the value is output on for Binary Coded Decimal pins, and mapped to a set of ten pins which pull to ground to match the digit received.

PIC-based Ham Radio Autotuner

April 7, 2011 by Mike Nathan 6 Comments

cw_autotuner

A few years back, [Floyd, K8AC] built a high frequency autotuner as an addition to his Ham radio setup. Based off a design he saw in QST magazine back in the early ’90s, he has been using the tuner almost daily for the last few years, on both the 3.5 MHz and 7 MHz bands.

Built into the wall in his radio room, it is a pretty impressive sight. His “L” circuit is controlled by a pair of mechanically coupled inductors which are driven in concert by a pair of two-way motors. The positioning of the C and L components are monitored by a PIC controller which stores the tuning data for up to 30 predefined frequencies. A couple of button presses on his controller’s front end sends the tuner into action, dialing in his unit’s inductors and capacitor to their proper settings. The PIC monitors the tuner’s progress, informing him when the proper frequency has been tuned in, or if the frequency can not be set, indicating issues with the equipment.

His setup has undergone several revisions over the years, with the most recent iteration being the most automated of the bunch. Check out his site for plenty more details, or keep an ear out for [K8AC] on 40 or 80 meters.

[Thanks, Rich V]

RC Override For Autonomous Hardware

March 22, 2011 by Mike Szczys 9 Comments

[Simon Inns] developed this board to act as a radio controlled override for autonomous hardware. It sits between some servo motors and two different sets of controllers for those motors. One set of hardware that can control the motors is a microcontroller programmed for autonomous tasks. In [Simon’s] case this enables a sailboat to navigate open water with out human intervention. But if that board fails, or if you just need to call the boat back to port, this module allows for a traditional RF vehicle controller to take command.

The board seen above, dubbed the Servo Switcher, uses a PIC 12F683 to monitor the incoming signal from the RF receiver. If that signal is not present it switches control of the motors over to a separate microcontroller board. This means that the override control is established simply by turning the handheld controller on. This will save you a swim to retrieve your boat, which is a nice convenience. But if you modify this for a plane or helicopter, it can save your aircraft from certain destruction. Check out the video walk through after the break.

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RF Range Finder Doesn’t Need To See To Calculate Distance

March 21, 2011 by Mike Nathan 35 Comments

radio_rangefinder

Instructables user [Jones Electric] has been quite busy lately, building a radio-frequency range finder. Built as part of a German youth science competition, he and his partner built a pair of transmitter/receiver modules that can be used to measure distances of up to a mile (~1.5km). Their argument for radio-based rangefinders is that laser rangefinders are obviously limited to line of sight, whereas their range finders are not.

To determine the distance between the two stations, the base station is triggered, which starts a counter and sends a 433 MHz signal to the second station. When the second station receives the signal, it in turn broadcasts an 868 MHz signal, which is received by the base station. The total distance between the points is then calculated based upon the round trip time of the two radio signals.

[Jones Electric] claims that the range finder is relatively accurate, with a deviation of up to 5 meters per measurement, and that the accuracy could be increased by adding a higher frequency crystal to the timing circuit.

We are pretty sure using these two frequencies in the US without a license is not allowed, though we are unsure of the usage laws in Germany, where this was constructed.

Frequency Counter For $10 Worth Of Parts

March 14, 2011 by Mike Szczys 10 Comments

[Scott] built this frequency counter using less than $10 in parts. It’s set up to meter frequencies in megahertz which is fitting since he’s planning to use it with his radio hardware experimentation. But we would find it useful too because our cheap multimeter only reads up to around 4 MHz.

He’s using an ATmega16 that he had on hand but it has features way beyond the specs for the device. He speculates that an ATtiny2313 would easily work in its place. The microcontroller is mostly used to drive the multiplexed 7-segment display after reading the frequency values from the 74LV8154 counter chip that he is using. He doesn’t have a full schematic for the device, but there is a hand drawn diagram for using the frequency counter; the rest should be easy to piece together. Looking at that circuit we don’t think it would be too hard to make this a manual-ranging frequency counter to give you more use out of the dedicated device. Check out [Scott’s] demonstration video which is embedded below the fold.

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