Racking up miles on a bicycle odometer

[jonh] religiously tracks the miles he rides on his bicycle. When his odometer’s battery started getting low, he wanted a way to run the miles up to where they were before, since replacing the battery resets everything to zero. [jonh] used an Atmel microcontroller to run up the miles on his bike computer so he could pick right back up where he left off. There is definitely a Ferris Bueller’s Day Off joke in here somewhere.

The bike computer itself is designed to plug into a base that connects to a magnet-triggered reed relay. It uses a wheel-mounted magnet to count the number of revolutions made and thus the distance traveled. [jonh] hooked up a simple microcontroller-driven circuit to these connectors to trick the bike computer into thinking it was moving, and moving fast! Since he knew the number of miles he wanted to sandbag onto the odometer, he was able to program it to run up the proper amount of miles and then stop. There’s no source code listing for the project, but this shouldn’t be too hard to reproduce. He provides a pencil-drawn schematic for the connection to the cyclometer from the microcontroller. At the end, there’s also some sage advice for those of you who are interested in building a decent hardware hacking lab on the cheap.

Building a 555 timer from discrete components

The 555 Design Contest shook a whole bunch of really creative circuits out of the trees, hence the 555-heavy content lately. While not technically part of the contest, [esalazar] wanted to know what made the 555 tick, literally! He started working on the project in a circuit simulator, then ultimately ended up building the three main logic blocks inside the familiar timer on pieces of copper-clad board. He’d built a 555 using discrete components.

While this isn’t 100% compatible with the classic 555 IC, it covers the basics pretty well, and [esalazar] gets extra-credit points for embracing the hacker spirit of seeing for himself how stuff works while documenting it well and citing his references.

Digital Wavetable Oscillator

The tabulaRasa is a digital wave table oscillator, and features control of frequency, wave table selection, and interpolation. The device is split up into 2 parts. One is a pcb with a healthy amount of resistors, 3 potentiometers, ST TL074 JFET op amp, atmega328 and a SD socket.

The second part is software for your computer that allows you to edit or create your own waveforms. There are 3 different modes of control. Breakpoints, which allows you to set the waveform points and allows up to sixteen. Harmonic allows amplitude control over 16 harmonically-related sine waves, finally, the third mode lets you load in short sound clips.

Once you’re happy, save to a SD card and pop it into the board, and you’re ready to make some noise. The project page states at the end “tabulaRasa is in the last stages of development, and will be available soon.” so you cant get your hands on one just yet, but if you’re interested [Greg] has a kickstarter page setup where you can find out details on pricing.

Hear that? It’s a 555 Timer AM radio


[Eric] recently built an AM radio based on a 555 timer, and posted a few pictures to the Hack-a-Day Flickr pool. He used the 555 timer as an AM demodulator and power amplifier in order to drive the speaker. A hand-wound inductor is used to tune the signal which is then superimposed over the ramp signal produced by the circuit he built. [Eric] points out that he chose a CMOS 555 timer because of its superior performance in this particular application since the timer is used in a bit of a nontraditional manner. He shared his circuit diagram as well as a great video walking through each part of his design, finishing off with a demonstration of the radio, which can be seen below.

This is yet another great project that will be entered in the 555 Design Contest – simple and elegant. We love seeing these, so keep them coming!

If you want to see more cool projects made by Hack-a-Day readers, be sure to check out our Flickr pool as well as the forums.

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