Digitally controlled threshold detector

Posted on Feb 6, 2014

This circuit uses small switching transistors. The maximum motor drive current is limited to about 250mA maximum at 5V. I`ve tested the circuit on voltages from 3V to 21V. With some component changes it should be usefulto 63V in a 36V PV panel system although I haven`t tried this yet. With higher voltage and the use of heat sinks on the bridge transistors much higher currents should be possible. (View)

Digitally controlled threshold detector
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Circuit 1 tends to chatter the relays under certain lighting conditions as there is no built in hysteresis. This version uses a Schmitt trigger hex inverter circuit to eliminate the chatter. It works better but is more complex. Note! R4 and R5 are used to force parking when it gets dark. If parking is not desired don`t use R4 and R5. Parking may not be desired in low power consumption applications. Also, the parking resistors, R4 and R5, reduce sensitivity a bit. (View) I have been looking for truly low cost and yet accurate conventional solar trackers. The CdS tracker is pretty good but lacks accuracy and sensitivity. I was thinking about using PV cells as the sensor. I was experimenting with LEDs and noticed they generate voltage in sunlight. Bingo! This got me to thinking. They generate quite a bit of voltage. The green ones generate about 1. 65V, some as much a 1. 74V. Not the piddley. 55 volts of a silicon PV cell. How is this so Well, it turns out green LEDs are made from Gallium Phosphide, a semiconductor with a much higher bandgap voltage. I thought I had invented the use of LEDs as PV cells as I had never heard of this effect before. Well, after some investigating I found a number of references to this. The guys that had done the most work in this area were the people form the BEAM project. They make tiny solar powered robots and some used LED photo sensors. I had been using a very low threshold MOSFET in a TO-92...

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