How to segregate arduino from other power sources?

Hi all,

I've had a look around but I'm still not 100% on this so I'd like some confirmation. I'm planning to run a robot with 4 ultrasonic sensors ( HC-SR04, staged to avoid interference ), 2 Sharp IR sensors, 2 continuous rotation servos, several pressure sensors and 3 normal servos.

My plan at the moment is to have 2 x 4 AA batteries in a parallel circuit for the servos and sensors and a 9v battery for the Arduino, however I'm worried that any sort of problems might result in a power feedback to the Arduino resulting in a melted board. My main concern is if I misfire my ultrasonic sensors during testing so that they all ping at once and create a spike on the power supply.

Is this a possibility or am I being paranoid? If this is a possibility is there a way to protect the arduino from unintentional spikes through the digital pins?

liomry:
however I'm worried that any sort of problems might result in a power feedback to the Arduino resulting in a melted board. My main concern is if I misfire my ultrasonic sensors during testing so that they all ping at once and create a spike on the power supply.

If the sensors are powered independent of the Arduino, then there should be no worry with regards to any power spikes. However, the Arduino is a 5v devices, and all inputs need to be 5v max as well. I'm not sure what a 2 x 4 AA battery config is exactly, but if it's 6v, you don't want that going to any of the Arduino's inputs.

Also - forget about using a 9V (PP3) battery; all you'd be doing is wasting money, those things don't have anywhere near the current capacity you need. If you really want to do this robot right, use a 7.2 volt NiMH R/C pack. Connect that to a y-adaptor, with one side powering the Arduino directly via the barrel jack (you might also want a 1/2 amp fuse in between). Hang a 5 volt BEC (battery eliminator) off the other end of the y-adaptor to power your servos, sensors, etc (or feed power from the BEC to the Arduino bypassing the regulator - but -only- if you are using a 5V regulated output BEC!).

A 7.2 volt pack will give you all the current you'll need (and if you need more, parallel another in), plus they are easy and cheap to get; you can pick them up almost anywhere. Feedback "spikes" aren't likely to be an issue (now, if you were running some large relays or brushed DC motors, then you might want some protection and isolation - but not for what you are running).

cr0sh:
... Hang a 5 volt BEC (battery eliminator) off the other end of the y-adaptor to power your servos, sensors, etc (or feed power from the BEC to the Arduino bypassing the regulator
...

If you're not familiar with those terms, they are from Radio Controlled Aircraft/Boats etc. Very good low-cost power solutions have been developed because of the high volumes of these products.

Thanks all, I was away for a week so apologies for the late replies. I'll research the suggested methods and see if I can source some Ni-MH packs. I'm in Ireland and R/C shops are pretty thin on the ground, can anyone recommend a good supplier in the UK?

(I was recently looking for Balsaloc to finish off a really old plane project and could only find some small garage-based shops that seemed to stock the stuff)

I've been looking for a Y adapter but all I can seem to find are the types which connect 2 battery packs in series or parallel, is there another term for the splitter adapter you are referring to?