Help designing dark sensor circuit.

Thread Starter

jeffereyf98

Joined Feb 15, 2018
3
Hi,

I am trying to create a project that turns on an led when there is little to no light across the photodiode. The only parts we can use are 1 or 2 9 volt batteries, NJM4556A op amp, TL9741N op amp, a photodiode (resistance with light - 300k ohms, resistance when dark - 15M ohms), various resistors and a basic led. I have researched dark-sensing circuits online and have tried to emulate those circuits, but I am unable to do this with the 9v battery supply. If somebody could offer me a solution or draw a circuit diagram, that would be appreciated. And I have tried making a voltage divider, however, when i supply the op amp with the voltage from the voltage divider, the voltage drops to less then .1V. Thanks for any help.
 

Dodgydave

Joined Jun 22, 2012
10,033
Here is a circuit to detect light/dark using a photo cell, if you are using a photodiode these give out voltage under daylight and are more sensitive, if the led is coming on when in daylight, then connect the led between the opamp output and +V supply.

FOLN41XHD4VPZHS.LARGE.jpg
 
Last edited:

Reloadron

Joined Jan 15, 2015
5,995
Would this be schoolwork? Next you mention:
a photodiode (resistance with light - 300k ohms, resistance when dark - 15M ohms),
You reference a photodiode but seem to be describing a LDR (Light Dependent Resistor)? This is a data sheet for one of several pretty common photo diodes. This is a data sheet for some fairly common LDRs or photocells. Note the difference in the specifications. Which did you want?

Ron
 
Hi,

I am trying to create a project that turns on an led when there is little to no light across the photodiode. The only parts we can use are 1 or 2 9 volt batteries, NJM4556A op amp, TL9741N op amp, a photodiode (resistance with light - 300k ohms, resistance when dark - 15M ohms), various resistors and a basic led. I have researched dark-sensing circuits online and have tried to emulate those circuits, but I am unable to do this with the 9v battery supply. If somebody could offer me a solution or draw a circuit diagram, that would be appreciated. And I have tried making a voltage divider, however, when i supply the op amp with the voltage from the voltage divider, the voltage drops to less then .1V. Thanks for any help.
This 2 transistors and photo resistor LDR simple circuit may give you an idea.

 
Top