Arduino DC motor and rangefinder Power regulation

Hi guys, I'm hooking my arduino up to two dc motors, an ultrasonic rangefinder from SeeedStudio, and have a 7.4V Lithium Ion Battery attempting to power both the motors and the rangefinder, now I know that the rangefinder only runs on 5v, and the arduino board can regulate 5v out, my question is should I just use a 7805 regulator outside of the arduino board and power the rangefinder, and then use the Vin pin on the arduino to supply the dc motors?

Thanks, Chris

Also Im attempting to power the entire unit using the 7.4 V lithium ion battery so how should I go about the actual hook-up? I guess I'm going to need to get a 2.1mm jack and hook the connecters up directly to the battery and then use both the 5v and Vin pins on the arduino; the 5v pin for the rangefinder, and the Vin for the motors?

Chris

I'm hooking my arduino up to two dc motors,

Which ones? Typically, motors need a motor driver shield.

an ultrasonic rangefinder from SeeedStudio

Link?

I guess I'm going to need to get a 2.1mm jack and hook the connecters up directly to the battery

Yes.

then use both the 5v and Vin pins on the arduino; the 5v pin for the rangefinder, and the Vin for the motors?

No. You need a motor shield for the motors. Connect the battery to the battery/power in terminals on the shield and the motors to the outputs on the shield.

The range finder can probably be connected to +V and Ground.

search for motor driver shelids on you favourite elsectonic kits shop or use a motor driver ic or h bridge the above things are well described here http://en.wikipedia.org/wiki/H-bridge but as paul said it depends on what sort of motors ( i assume you are trying to make a obstacle avoiding robot so normal motor drives ics like l298 should suffice unless the thing is really huge