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Topic: Pro Mini and Power (Read 443 times) previous topic - next topic

c131frdave

Forgive me, but I'm new, so this question might seem dumb, but what can you do...

I am working on a project that uses two large servos to move a Christmas decoration when someone approaches it.  It's hard to explain.  But I want to make it a permanent thing, so I was thinking of using a Arduino Pro Mini328 to run it.  The two servos are quite powerful, and use up to 400ma of current at 6 volts each.  I'm using a 2 amp, 12VDC tranformer that I have that used to power an old external disk drive to supply power to the device. 

What I was thinking was to build a voltage redulator circuit with two 7806CT regulators, caps, and diods to supply 6VDC of regulated power (I could use just one, but they are only $0.50, and redundancy seems prudent) to the project.  Can I run the servos and the Arduino off this circuit?  Would I get any issues from hooking up two large servos and the microcontroller together? 

The arduino schematic says that the arduino pro has a maximum voltage input of 16VDC.  Should I just run a wire straight off the 12V transformer to power the arduino separately?

Thanks.


CrossRoads

The promini won't take much power,  you don't have it driving lots of LEDs or anything. You can power it directly from 12V.
Or use a 5V regulator and provide 5V directly to the VCC pin. (vs 12V to the RAW pin). Don't forget caps on the regulator input & output.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

c131frdave

#3
Dec 05, 2012, 06:33 pm Last Edit: Dec 05, 2012, 06:49 pm by c131frdave Reason: 1
Okay.  I noticed that the transfromer I am using is actually supplying 13.2 VDC.  The schematic says it can take 16VDC, but the description on the Arduino Product page says 12V is max.  Which is correct?


Also, is it somehow better on the arduino if you supply 5V instead of 12V?


One more question to you gurus.  I noticed on youtube that a guy showing how to drive a HiTech servo (similiar to mine) used 12V to supply power directly to the servo- no regulation down to 5,6 or 7.2 VDC as the servo data sheet says it requires (actually the sheet just gives torque numers at those voltages).  Did he do that because there is no load on the servo, so no harm/no foul, or can you actually send 12V to a servo without burning it up? 

CrossRoads

If you can supply 5V vs 12 or 13, the un-heatsinked onboard regulator won't get all heated up trying to bring it down.

Servo's - I imagine at 13V they will be able to draw more current and accelerate faster, until they burn up.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

c131frdave

#5
Dec 05, 2012, 09:43 pm Last Edit: Dec 05, 2012, 09:45 pm by c131frdave Reason: 1
Thanks for the feedback.  It is very helpful.

This might not be the place for my next question, but can you just use Arduino bootloader-programmed chip (Atmega328P) by itself and send a regulated 5 volts to the VCC pin and then just run the rest of the project off this chip?  I could plug in the chip on my Uno board, program it, then  unplug it and put it in a PCB socket, no?  I guess the better question is, will this chip stand alone, or does it require some other components to drive two servos and sense input from an ultrasonic rangefinder?  Thanks. 

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