i am doing a project on room light controller using 8051..
i am using a pcb relay for controlling the light..
i have a doubt regarding the relay pins....





i have a doubt regarding which are the coil terminals and which terminals are nc ,no and common!!





pls help!!

 

Use an ohm meter to measure the resistance across the pins. The coil resistance should be in the 100's of ohms. Or if you can find the data sheet of the relay in question, you will find your answers there. I cannot clearly see the numbers/model of the relay in the picture.

 

@Bsomer it is a 5 terminal cube /pcb relay..
its specifications are
7a/240vac
7a/24vdc
coil 12vdc

 

Hard to see from the bottom picture but it looks like 1 side has 2 pins and 1 side has 3..
The side with 2 pins is the coil side. The contacts are the 3 pin side..
To verify use your ohmeter and measure the resistance across the 2 pins & like Bsomer said should be in the 100-4000 ohm area or so (thats the coil). Then measure the other pins .The open contact set should read open and the closed contacts should read very low resistance (sub 10 ohms for sure)

 

The specifications you list are just telling you the max current the contacts can safely handle and the coil voltage. They really are not helpful in identifying the coil pins.

mcgyvr's comment may very well be right. Although I have come across some relays where the coil was the two outside pins on the 3 pin side and the middle pin was the normally closed contact.

Generally the coil pins are on the side with a notch when looking at it from the top. However, this is not always the case. The best way to find out for sure is to measure it with a multimeter. If you do not have one, I would plan on buying one. Even a cheap analog multimeter would be beneficial to troubleshooting problems or just general testing of your projects.