To interface a LDR with a relay

[sharat]

I want to activate a relay by a LDR. The relay's output is connected to a h-bridge IC which moves the motor in forward or reverse direction. Is there some IC which is used to activate a relay by a LDR

 

[Reloadron]

You could likely start using the LDR in conjunction with a comparator like the LM311 chip. Scrolling down on this page there are some LDR circuit examples.

As to driving the relay coil it depends on the relay coil specifications? How much current is needed and what voltage? In some situations using a transistor like a 2N2222 works fine between the comparator and the relay.

Ron

 

[MikeMl]

Why drive a relay which drives an H-Bridge which drives a motor. Either drive the H-Bridge directly from the LDR electronics, or use the LDR to switch a relay (or two relays if the motor must reverse) which then drives the motor?

 

[sharat]

I think I am not able to explain my problem correctly.

 

[sharat]

I want to use a relay as a switch which switches according to the output of a LDR. I am not been able to figure out how this can be done.Someone told me that it can be done using an IC but I havent been able to find out about this IC. So please help me in finding about this IC or is there any other way to switch the relay by LDR

 

[MikeMl]

Since you said nothing about available power supply, which relay, which LDR, I had to assume everything.

LDR is this one. (Available from DigiKey)
Relay is 12Vdc with coil resistance of ~120Ω
Supply is 12V
Relay pulls-in in daylight.
Adjustable over varying light levels.

X-axis is resistance of the LDR

 

[sharat]

What about IC ? Isn't there any IC which can be used to connect LDR and relay?

 

[Reloadron]

What about IC ? Isn't there any IC which can be used to connect LDR and relay?

Mike gave you a rough circuit that would allow a LDR to operate a relay. That circuit would work just fine and allows LDR sensitivity adjustment. I gave you a link for using a comparator IC as a start. You have been asked for details about your existing LDR and Relay and have not provided any information like the relay coil specifications (voltage and current). Everything depends on what you have and without any information from you it is impossible to answer your question(s). Without more information this is as good as it gets.

Ron

 

[sharat]

I want to activate a SPDT relay with the help of a LDR. The resistance of LDR is 900 Mohm in dark and around 9 ohm when max amount of light falls on it. I have a dc supply of 6V. Please give some circuit ideas on how to solve the above problem?

 

[Reloadron]

Mike gave you a circuit to do exactly as you ask. It doesn't get any simpler. Do you understand the circuit that Mike posted for you? The posted circuit even allows you to adjust the sensitivity of the LDR and at how much light the relay will energize. What part of what Mike posted do you not understand? Far as I can see it will do very nicely exactly what you are asking.

Ron

 

[sharat]

Thanks guys for helping me. I will try this circuit and will come back with results or doubts,if any

 

[heinzehtet]

thanks a lot Mike! Now I get a answer for my project.