Sunday June 12, 2016
We realized that Bit would not work in direct sunlight. It appears that the BitReceptor circuit has too high of a gain in the initial transimpedance stage. Direct sunlight is railing the op amp at the first gain stage removing the AC component of the BitBeacon. Initially when we designed the BitReceptor circuit, we had a simple transimpedance stage with a very small feedback resistor. The small feedback resistor provided gain in the first stage, but too much as to not saturate the op amp. The next gain stage has a high pass filter which filters out DC which ends up being from background light (sunlight, nearby lamps, other random IR emitters, etc.). This is our solution to make our photosensor circuit immune to ambient light. Although, it appears we made the gain of the first transimpedance stage too high by using a 22.6k resistor. A few simple tests show that a 1k or 2k resistor would be fine though.
Also, Shadman is starting to work on the PCB for the new BitBeacon circuit. Should be fun!