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Nov 08, 2013, 09:41 PM
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Death of a gadget








It finally had to be put down so its enclosure could be used to make a flashlight. The enclosure probably won't last long, anyway.

It was made during the rcgroups downtime in Feb 2011, before there was a phone which could do the job. It was a speedometer/distance tracker/odometer/stopwatch/GPS logger/GPS clock.

The LCD was driven with voltage dividers & ordinary logic pins from 0-3.3V. It took some doing to reverse engineer how a passive matrix LCD could be driven from logic pins. The result was very contrasty & more legible than the device the LCD originally came from, but if it got hot, all the segments went dark. If it was too cold, all the segments stayed clear.

The LCD flex cable was another failure point. Pressing it down enough to make good contact squeezed the liquid out of the display.

The 8 bit PIC spoke the current speed through headphones, using the PWM driver. It was made without the aid of an oscilloscope, which nowadays sounds incredible. Those headphones were lost in 2011 & never found again. The speedometer function was used to run fast, but it required holding the GPS module very steady.

The distance tracker didn't work as well as hoped, either. It glitched way off indoors & you had to remember to pause it to go indoors. Phones still have the same problem.

The stopwatch & clock just copied GPS, so the stopwatch was accurate to 1 second. It wasn't very useful. The voice synthesizer also spoke what mode it was in & spoke all the data on the screen.

The logging function never worked. The SD cards all got bricked. Writing to an SD card from a PIC was something that never worked.




There were some theories that it was condensation bridging the pins or bad contact. It's since gotten more popular for hobby electronics to write a flash chip directly than an SD card.

It needed a huge amount of power. Left a battery in it & it destroyed the battery.

Developing the LCD driver, the PWM voice synthesizer, running those few miles with the voice reading the speed, was still a fond memory.
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