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[on:]

I am thinking of using relay to power up the USB host shield on specific intervals and then turn it off. Therefore I would be using the VCC of the Arduino for power of the Relay, and a set bit to turn on or provide current through the relay. Can anybody share the circuit for such a setup. I guess I would be using transistor and ofcourse a relay. Can any body share the specific information and circuit digram.

[Reply #1 on:]

I don't know anything about the USB host shield, but I think like most shields it pulls power from the arduino power pins.  The only way to turn it on/off would be to cut a trace and install a switch maybe?

[Reply #2 on:]

I am thinking of installing a relay so that it gets the current from the power pins only on specific intervals when the bit is set.

I am also looking to switch the current to another device (USB Host Shield )  using relay functionality. And the relay would be turned on once the microcontroller comes back to sleep. I have checked out the basic circuits one given in the arduion play ground. I am unable to guess where would I place the positive and ground connection of the device which i need to run from the relay.

[Reply #3 on:]

Any Suggestions ???

[Reply #4 on:]

Well it is hard to give any suggestions because it is hard to understand what you want to do and why.
Cutting off power to a shield is not a wise thing to do if the chips on that shield have connections to the arduino. Feeding a signal into an unpowerd chip is a good way to destroy it or cause what is called a latch up where nothing functions when the power is restored to half the circuit and you need a power down of everything.

I am also looking to switch the current to another device (USB Host Shield )

First you switch voltage not current. Next are you talking about two USB shields?

I am unable to guess where would I place the positive and ground connection of the device which i need to run from the relay.

Guessing is never a good idea in electronics. Look at this page to see how to wire up a relay.
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html