Relay Wiring

Other Hardware General Electronics
1

I just bought this on ebay to turn a power supply on and off. Then, I saw some reviews online saying that they are reverse from normal relays in that you must pull the pins low to switch them, not high.

I could be wrong, but isn't this relay (well, all relays) SPDT? Meaning that whether it is NC or NO is dependent on how you hook the darn thing up? Therefore, whether you have to turn the pin high or low to turn it on all depends on how you hook it up. I've never worked with relays, so I could be wrong, but looking at the schematic, it seems as if this is the case.

Am I right, or are they?

Thanks

2

Then, I saw some reviews online saying that they are reverse from normal relays in that you must pull the pins low to switch them, not high.

There is no way of telling from the link what way the drive has to be in order to energise the relay.

Meaning that whether it is NC or NO is dependent on how you hook the darn thing up?

That is right. However, that is something different from the first point.

3

Grumpy_Mike:
There is no way of telling from the link what way the drive has to be in order to energise the relay.

Oops, my bad. I updated the link to the one with the schematic.

4

If that is the schematic then you do energise the relay by putting a logic low on the output and turn it off by putting a logic one ( HIGH ) on it.

5

With a transistor "on" is with the base pulled away from the potential of the emitter.

For an NPN transistor that would be a positive voltage WRT emitter (usually ground). For a PNP, the emitter is usually connected to Vcc, so it would be a negative voltage WRT Vcc, so anything below Vcc (i.e., VOL, or "logic low").

6

majenko:
With a transistor "on" is with the base pulled away from the potential of the emitter.

For an NPN transistor that would be a positive voltage WRT emitter (usually ground). For a PNP, the emitter is usually connected to Vcc, so it would be a negative voltage WRT Vcc, so anything below Vcc (i.e., VOL, or "logic low").

Right....but that doesn't affect whether its NC or NO, right?

7

but that doesn't affect whether its NC or NO, right?

Correct.
There is a difference between turning your load on and off an energising the relay.