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Simplified Version of the Analog LED comparator circuit.
Instead of using dedicated voltage regulators, a 12v circuit divided 8 times is referenced against an alternating voltage source - much simpler.
This circuit was designed for O2 sensor output visualization for Air/Fuel mixture monitoring.
A standard O2 sensor outputs .1-.9Vdc. Unfortunately, the cheap ones (15-30$) only have a High, Stoic (14.7:1), and Low Air:Fuel output, so only 3 LED's can be used for these.
Wideband oxygen sensors output from 0-5 and run about double the cost for the cheapest version, but will give much more resolution for the tech to adjust air/fuel mixing via carburetor or PCM control.
Total cost of circuit is about 20$ including perf-board and housing. A 70$ sensor and wiring brings the total to about 100$ for wideband A/F monitoring - a fraction of the cost of manufacturer devices.
A simple voltage divider, or step-down op-amp circuit can regulate the battery-provided 12v to a 5v reference (divided by the # of lights desired) for monitoring.
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