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shobley
01-06-2009, 08:44 AM
Hi,

I've been following the recommendations to add a battery to an ATX PSU when using the Sabertooth to provide a current sink.

If I connect up the Arduino to the same 12v PSU is there any risk that the 'regenerative' current sent out from the Sabertooth will damage the Arduino, instead of going into the battery?

The nature of my project precludes me from putting the lead acid battery before the Arduino.

Steve

Adrenalynn
01-06-2009, 02:00 PM
Hey Steve! LTNS!

What recommendations where?
Anything more about how you're hooking what up to who? Some kinda diagram would be preferable to us guessing in the dark that you will or won't kill anything. ;)

shobley
01-06-2009, 03:19 PM
Hi,

Yes it's been a while, still trying to work out how to be a Dad and fit all the other stuff into my life. :veryhappy:

The recommendation on the Sabertooth (2x10) was given here:
http://www.robotshop.ca/dimension-engineering-sabertooth-2x25-6.html
The battery is acting as a current sink.

I'm building a Dome controller for my Dalek:

Dalek:
http://www.geocities.com/dalektimeline/NewDalek1.jpg

My Dalek:
YouTube - Dalek Eye - Arduino powered
YouTube - Arduino single wire controller
YouTube - Arduino Sound FX and Dome Controller

Now, as you can see in the first video I have a Arduino + servo controlling the iris. That pulls more current than the Sabertooth puts out on it's 5v line for control devices. So I have to connect the Arduino directly to the 12V supply.

My concern is that the current being pushed back into the battery (from the Sabertooth when the motors brake), might 'upset' the Arduino connected to the 12V supply.

I need to keep the dome as light as I can, so battery has to be outside.

Adrenalynn
01-06-2009, 03:30 PM
I think that might be a valid concern given that scheme. The Arduino's (assuming Diecimila or Deumilinove) regulator seems more than a bit touchy. I'm not terribly happy with its range or the results of pushing it.

How about hanging something like a 7809 regulator off the 12v battery in front of the Arduino? That gives you ~1.5A of clean 9v with an input range from a bit under 10v up to 25v+ *

It's cheap and easy and readily available, toss a couple caps in there, and any noise the Sabertooth puts on the wire gets filtered off (and I've found the Sabertooth to be noisy)

* Absolute max assumes heatsinking the regulator well. I wouldn't push it un-heatsinked beyond 1A and 17v max. Still inside the design parameters.

shobley
01-06-2009, 03:38 PM
I think I have one of those around here somewhere. I only need about 200ma to keep the servo and Arduino happy. I'll give it a shot.

Originally I was going to use Limor's Motor shield, but the job of moving the eye stick around proved too much like hard work and I had to upgrade to the Sabertooth + wiper motor.

Eventually this thing should be trundling around on 12v batteries, but while I'm tinkering the ATX supply seemed to be the easiest way to go.

Thanks for your help!

Steve

shobley
01-07-2009, 07:57 AM
Quick video update on the project:

YouTube - Moving the Dalek Eye stick...

What value for the bypass caps would you suggest for the Sabertooth?

jes1510
01-07-2009, 08:10 AM
Adrenalynn may know more since she has actually used the Sabertooth and I haven't but typically 0.1uF caps placed close to the device you want to protect will do the job for high frequency stuff.