Dark / Light sensor

C

conntaxman

New Member

• May 3, 2013

• #1

I have tried about all of the cir. on the net/ lol. and I cant get one to work with the "Cadmium sulfide Photocells from Radio shack. I just tested one and the readings were 80.00 and down to 7.5 ohms. I used the cir with the 547 tran and the one with the 555 timer. What could be going wrong?i mean their is only about 6 parts. H E L P.
John.

 

davenn

Active Member

• May 3, 2013

• #2

Hi John

show us one of the circuits that you have tried. its a bit difficult for anyone to make any specific reccomendations without seeing at least one of the circuits you have tried
It can then be commented on as to if it will work or not. If the circuit will work, then we need to look at your construction methods and see if you are making an error there

Dave

 

alec_t

Well-Known Member

Most Helpful Member

• May 4, 2013

• #3

I just tested one and the readings were 80.00 and down to 7.5 ohms.

Click to expand...

Presumably those are the 'totally dark' and 'as light as possible' readings? If so, they are much lower than many CdS cells give. It's possible that the circuits you tried were intended for higher-resistance cells. As Dave says, show us the circuits. I'm sure we can come up with a solution.

 

C

conntaxman

New Member

• May 4, 2013

• #4

here is one cir. the top,this is with the 547 tran, and like i said their is one with a 555.
https://www.buildcircuit.com/darklight-sensor-using-transistor/
tks
John

 

alec_t

Well-Known Member

Most Helpful Member

• May 5, 2013

• #5

As I suspected, that circuit is intended for a higher resistance cell than the one you have. Try replacing the 100k resistor with, say, a 330 Ohm resistor. The downside is that by reducing the resistor value the current drawn from the battery will be higher.

 

JoeJester

Active Member

• May 6, 2013

• #6

The five pack photoresistors from radio shack p/n 276-1657 has five different photoresistors in them

https://www.electro-tech-online.com...cds-photoresistor-radio-shack-276-1657.85782/

None of the resistances on that sheet match what you described.