problem driving relay through ULN2803

i have attached the circuit diagram. In this one part of coil of relay is connected to +12v and other is connected to output pin of ULN2803. ground is commonly connected to +12 volt and +5 volt supply negative. I have used two different power supplies for 5v and 12v.then too relay is not working

so how did you connect the relay? any schematic so that we can check what is wrong

see this how u can connect relay using ULN......

excellent mirza!!!

i have attached the circuit diagram. In this one part of coil of relay is connected to +12v and other is connected to output pin of ULN2803. ground is commonly connected to +12 volt and +5 volt supply negative. I have used two different power supplies for 5v and 12v.then too relay is not working

sam1789

Sounds like your wiring is okay.
Are you sure the Micro is driving the ULN2803 ?

What readings do you get if you put a meter on the input and output of the ULN2803.

hi sam1789
be sure ground of +5 volt and +12 volt is common

[quote]
hi sam1789
be sure ground of +5 volt and +12 volt is common
[/quote12993265
i connected both the power supply to common but then too its not working. every thing else is working right except that relay ..i mean to say when i connect led directly to AT89C2051 by sinking current from +5volt through led to port pin,then leds are performing according to program but when i connect relay through ULN driver then relay is not working

hi sam test your ULN alone by inputing 1 or 0 in ULN input to verify your ULN is okay..

you said everything is working except at ULN side then you must focus on that area..

test also the coil of your relay if not open..

silly but is your MCU programmed or have you checked sensor tsop1736/38 is okay ?

Topic moved to Electronics forum