I need some advice on How to reduce the sensitivity of the light sensitive switch shown in the attachment. Basically what is happening is the LED's are coming on way before they are needed.

I use the 741IC

 

hi,
A quick fix would be to change the fixed R3 resistor to a 10K potentiometer.
E

EDIT:
You must also add a clamping diode across the relay coil, in order to protect the transistor

 

Great Thank you very much for the advice

Regards

Rod

 

1. How about the Vf and If of the LEDs?
2. What does these LEDs used for ? (car,motorbike,bike,other)
3. How is the I_relay?
4. Maybe you can using bjt or mosfet to replace the relay?
5. Are you trying to do a delay to turn on/off the LEDs?

 

OK a couple of your questions I don't understand so just going to answer the ones I do.

The light sensitive switch is used to switch many things thus the 10 Amp relay, its a waste for the LED's however it is a standard PCB so I just use it. There is a delay switching on and off basically I call it cloud delay.

 

How about the Vf and If of the LEDs? (as 3V/20mA)

A 10 Amp relay, it could be a reed relay.

If you using the spec of LED is 3V/20mA, it better only using about 80% of 20mA that equal to 16mA, 16mA*4 =64mA, so you can using 2SC1384 to replacing the BC547, and take the relay away, just using 2SC1384 to drive the LEDs.

But if you doing this way, it will affecting the LEDs driving ability and delay time.

 

If R7 is for hysteresis, it should be connected to + input and should be much smaller, maybe about 100kohms.

 

a simple and cheap fix would be to put a piece of tape over the light sensor.