Circuit Notes

*All of the circuits on the PCB are configured so that when the photosensors are dark, the output of the 556 timers will be HIGH.
*The release delay times of each 556 timer can be changed by selecting suitable combination values for the R7/C2, R8/C3, R9/C4 and R10/C5 pairs.
*The LM339 input detection voltage levels for the circuit as shown is set at 1/2 of the supply voltage. If a lower or higher detection level voltage is needed, the values of resistors R5 and R6 can be changed to suit.
*NOTE When power is applied to the circuit, the outputs of the 556 timers will be HIGH for 1 release delay time period. (Until the timing capacitors have charged to 2/3rds of the supply voltage.)
There are RESET inputs for each LM556. These inputs do not have terminal block connections but do have pads with holes to solder wires to if needed. The RESET inputs could be used to force the outputs of the 556 timers LOW until the timing capacitors have fully charged after power is applied to the circuit but an external timer would be needed to accomplish this.
*This circuit does not require a regulated power supply and can operate on supply voltages of up to 15 volts.
*For information on other light detector circuits, see Light Activated Detector Circuits at this site.
*For more general information on Voltage Comparators see the Voltage Comparator Information page at this site.
*For more general information on LM556 timers see the 555 Timer Information page at this site.
*WARNING - If the polarity of the power supply for this circuit is reversed or the circuit is connected to an AC or DCC source this circuit will be damaged. The maximum supply voltage for this circuit is 15 Volts.

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