optocoupler drive circuit 1

[abad]

I am trying to design a circuit using an optocoupler that would sense a light source and give an output which could be used to drive a DC motor.
can anyone help with the circuit design for the optocoupler, i would probably use a photo diode has any one got ideas of a simple circuit how i can test the photo diode to make sure it is giving an output.
it would be most appreciated.

 

[BrianG]

I think you need to clarify what you are trying to do. An opto coupler provides isolation between two circuits: it does NOT sense light. As you have mentioned using a photo diode I assume you are trying to respond to a source of light, if so the a photo diode is more like the sort of component to use.

You don't say if you require some sort of proportional response or just simple on/off detection at a certain light level. A photo transistor may be a better device to use here as it has gain; to get anything useful from a photo diode requires a separate op-amp circuit, and you will certainly need a power amplifier stage to drive your motor if you want proportional response. For simple on/off control a photo transistor as part of a switching circuit can be used. This would provide a power tarnsistor, or possibly a relay, to control the motor supply.

 

[abad]

yes BrianG i think i made myself unclear and you are right i am not looking for isolation i want detection.
first i wanted to build a simple circuit to make sure that either a photodiode or phototransistor are working correctly maybe if i make it drive an LED to start with so i can see the responce, then i want to use it to control the speed of a DC motor so i presume this will incoperate feedback. can you give me tips on circuitry or places to find more help because i am new at this and haven't a lot of experience in this field.

regards

 

[Lewish]

Look at the application notes on both National Semi and Linear Technology for circuits using photo diodes.

http://www.national.com

http://www.linear-tech.com