Bare Bones Photovore

BBPV -- Grant McKee

From Grant McKee's Beam Circuits Page: "The voltage is read from the mid point of a voltage divider crated by two reverse bias photodiodes. As the light changes between the photodiodes the mid point voltage basically slams from + to - with little deadband. Conveniently the AC series has a threshold voltage of very close to half the supply voltage. Also given the tight tolerance on photodiode this usually makes tuning unnecessary."

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BBPV V2 -- Wilf Rigter

From Wilf Rigter's Beam post: "The BBPV is a little vulnerable to damage if a motor with too low resistance is connected to the first driver stage. That can cause the logic level on the second driver paralleled inputs (connected to first driver outputs) to be near the switching threshold. That can cause up to 200ma to flow through the second stage output stage and the circuit can self destruct from internal thermal overload."

"A slightly different design uses two inverters in series to process the photo input stage and uses the first and second inverter outputs to drive the respective parallel inputs of 2 groups of 3 inverters used as motordrivers. A small layout drawing is attached."

"The addition of the cap changes behaviour in different light conditions like the BeamANT."

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Wiring Diagram:

Breadboarded: