Power supply problems

Rob311

Im working with a bs2, BoE, eb500, h-bridge and servo controller. Im trying to get them all to run off 1 power supply without making smoke or reseting the bs2.
attached should be a quick schematic of what my setup looks like. If i have the system wired as in the schematic when i send my h-bridge the command to move both of my motors forwards my stamp resets. If i use a good ol' 9 volt for my bs2 all works out well.

what should i be using to buffer the BoE within my system so i can run from one power supply?

Steve Joblin

you should use two power supplies (one for your electronics; and one for things that consume high current like motors). Make sure that you tie your grounds together. The problem you are encountering is that your motors are drawing too much currrent causing your stamp to reset.

Mike Green

You have a combination of factors in your design all contributing to the resets.

1) The 6V supply leaves little "headroom" for surges. The Stamp's regulator requires an input voltage about 1/2V above the regulated output (5V). If the 6V supply sags more than 1/2V, the regulator stops regulating.

2) The startup surge current demand of the motor is probably way above the 800mA available from the wall-wart.

Suggestions:

1) Use 5 x AA NiMH rechargables as your primary power source with the wall-wart providing the charging current. You can get AA cells with a capacity of 2.4A and these will generally take a charging current of 1/10 that (or 240mA). When the servos are not actually running, the batteries will charge. You could use a 9V wall-wart and an LM7805 voltage regulator as a current source providing 200 or 240mA. There's an example near the end of this datasheet: pubpages.unh.edu/~aperkins/pdf/LM-devices/LM7805.pdf.

Rob311

I figured it was either a current drop or a voltage drop, but for simplicity's sake I want to run this bot off 1 supply. I have to be able to put something like a capacitor in the mix to keep the board on.

Thanks Mike, that looks like a good idea... now to find where i can throw all them AA's...

Post Edited (Rob311) : 12/29/2007 10:10:29 PM GMT

Phil Pilgrim (PhiPi)

It's best to use two supplies, but if you must use a single supply, try this: Connect a diode (e.g. 1N4001) from the wall wart positive supply line to the BOE's Vin terminal. From Vin, connect a large (3300uF+) electrolytic cap to ground. This will help to isolate the BOE from the low-going transients on the wall wart supply and provide a charge reservoir from which to draw current.

-Phil

Addendum: I missed the 6V part. The series diode might only make matters worse. However, most wall warts exceed their rated voltage by quite a bit when no current is being drawn, so it's not inconceivable that the added filter cap could charge to 9V or more. You'll just have to try it...

Post Edited (Phil Pilgrim (PhiPi)) : 12/29/2007 10:18:17 PM GMT