3V Dark Detector Circuit

S

Suraj143

Active Member

• Oct 11, 2019

• #1

Can somebody Give me a circuit diagram of a Dark detector using discrete components with a snap ON, OFF ( built in Small Hystersis ) which can operate from two AA cells.

Thanks

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 11, 2019

• #2

Here is my Dark Activated LED circuit with two transistors, a low supply voltage and an LDR. But it has no hysteresis since it switches fairly quickly:

 

Attachments

• dark activated LED.PNG

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Pommie

Well-Known Member

Most Helpful Member

• Oct 11, 2019

• #3

Could a resistor be added from the PNPs collector to the NPNs base to introduce some hysteresis?

Mike.

 

alec_t

Well-Known Member

Most Helpful Member

• Oct 12, 2019

• #4

How much load current must the detector source/sink?

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 12, 2019

• #5

Pommie said:

Could a resistor be added from the PNPs collector to the NPNs base to introduce some hysteresis?

Mike.

Click to expand...

I think that will cause the transistors to turn on but never turn off, unless the new resistor value is very high.