Votlage Supplies (kinda BS2 "?" )

tahlorn

I will be soon posting a "OMG help me" thread, but for now, I have a basic question about voltage supplies. Apologies if this is too off-topic.

I need to run the BS2 with its voltage source. I am using this to control a servo, and then a stepper motor. I can't run the servo off of the board due to the current draw and reseting the stamp. The stepper needs 12V. So I have 3 devices to power, but I have a small space.

Is there a way to double-team a power supply so it can give the 5volts and 12 volts, so I don;t have to cram 3 battery packs or power supplies into this thing? Servo and Stepper will never run at the same time.

Also, if I have a pin outputting a constant voltage (signal turned high), will that affect at all signal output for a servo or stepper motor?

Thank you all for any help.

-Newbie

Mike Green

You would run the stepper directly off the 12V supply. The servo needs to run off a supply that provides somewhere between 4.8 and 7.2V. The Stamp's regulator works fine with voltages between 6 and 9V. The "sweet spot" is between 6 and 7.2V and I'd suggest closer to 6V since the servo motor lasts longer around 6V. You need a regulator to drop the 12V to 6V. The LM7806 is simple and straightforward to use (www.fairchildsemi.com/ds/LM/LM7806.pdf) and is available from many sources. You could even have one for just the servo and one for the Stamp. Be sure to provide a heatsink for the regulator supplying the servo motor. It will be dissipating several Watts, as much as 6W at peak and 2-3W average when the servo is operating.

Franklin

Mike, just for clarification, the stamp will run at from 5 to 15 volts (if you don't require too much from the pins as outputs)

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- Stephen

Mike Green

The unregulated input to the Stamp (and some of the Stamp development boards) requires a minimum of about 6V for proper operation. I know it will often operate down to 5V, but it's not designed for that nor will it behave reliably. The maximum voltage is usually specified as 9V although the parts used will work at over 12V. The limiting factor (as you mentioned) is power dissipation and, at 12V, this goes up pretty quickly with seemingly small amounts of current. I don't like to make recommendations to someone who's inexperienced to push the limits of what's recommended. They may not understand the boundary considerations and it's easy to break things there.

tahlorn

Alright, so what I am getting from this is that the Servo, as I have read elsewhere, can not run with the stamp on the same supply. And I will either need to regulate down the stepper supply to go to the stamp, or perhaps if I get fancy, regulate the stepper down to the servo. I would rather put the mechanical parts all on one supply (being a mechanical engineer, I feel safer like that), and give the BS its own supply.

thanks for the feedback, y'all.

Franklin

I think what Mike and I are saying is you only need one supply. 12vdc for the stepper, then you regulate down from there to the other voltages using 'voltage regulators' of sufficient power handling capacity for the devices you plan to power.

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- Stephen

tahlorn

Ah, alright. That I can work around with then. May ask my robotics friend about correctly wiring that up so I don't fry anything. Thanks!