relay board for arduino

I purchase a 16 channel relay board and it works good. It has a connection for a power supply of 12 volts. I want to get another 4 channel. I see some are labeled 5v and some 12v. On the 5v do each of the 4 relays just work off the pins on the arduino. or on the 5v do you have to supply external 5v.
Thanks
Rick

ok this one on ebay has a pin for gnd and voc
It does not say what the voltage is on the board but the description is 12 volt
is this the pin for the external power supply

Those boards come with drivers for the relay, so little current per pin is required...

The link you posted is opto controlled, requiring a low/gnd signal to trigger it off, the relay breakouts vary..

So if I cut power to the arduino then the relay turns on

Providing the trigger pin goes low and you're supplying power to the relay board, then it should yeah...

If you happen own this http://www.amazon.com/SainSmart-16-CH-16-Channel-Relay-Module/dp/B0057OC66U one of the most common 16-channel 12v relay boards around and don't already know, after supplying it with 12v power it requires, the board itself supplies 5v from its 2 5v pins, which you could use to power other 5v devices.

For the 4 channel relay you posted, the diagram showing the relay connected to the 5v pin on the arduino seems to be contradictory. I believe the vcc on the relay board requires 12v, not 5v.