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Topic: Emergency Shutdown Power Source (Read 736 times) previous topic - next topic

ximfinity

Aug 15, 2012, 03:29 pm Last Edit: Aug 15, 2012, 03:39 pm by ximfinity Reason: 1
Hi,

Apologies as I'm fairly new to electronics work.

I'm trying to figure out a good way to have a project turn a servo in the case of a power failure and run through a really quick 3 signal shutdown sequence.  I'm currently thinking this would require battery backup and a charging circuit, but I'm curious if anyone has worked with maybe a capacitor circuit that would be simpler to just send a write and power a servo to a specific position if the main board power were to fail.

Thanks for any thoughts.

I've found this: http://ruggedcircuits.com/html/circuit__13.html
using a "Super Capacitor" which seems like a simpler method than battery backup.  I'm not sure if 35 ma for 3 seconds would be enough to power a servo.

PaulS

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I'm not sure if 35 ma for 3 seconds would be enough to power a servo.

For the purposes of commanding the servo, yes. For powering it, no. The Arduino shouldn't be powering the servo, anyway.


ximfinity

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For powering it, no. The Arduino shouldn't be powering the servo, anyway.
What would be the correct method for powering the servos?  can it still be pulling power from the same plug power source so long as its rated for sufficient amperage just not through the +5V off the arduino?  This project will be stationary with a wall wart plug. 

Thanks,

spruce_m00se

it might be worth mentioning that i have read about arduinos going corrupt when they dont receive a good voltage supply,
the cap would assumedly give low volts as it discharges, and might cause a problem.

to power the servo, you need to know that its ok to power with 5v i assume it is, i would power it from the 5v that powers the arduino, and then control the pwm wire of the servo with the arduino ,

as a general rule, a pwm of 1000 gives one movement extreme, 1500 gives center and 2000 gives the other extreme, all points inbetween are slectable with the appropriate value,

PeterH

There is an Arduino clone that includes the hardware to charge and manage a LiPo battery, which would make it fairly simple to run your device for as long as you wanted. You'd need to supply power for the servo too. Perhaps it would be possible to run this directly off the LiPo too?
I only provide help via the forum - please do not contact me for private consultancy.

spruce_m00se

peter,

have you got the name of that clone,
im interested in that,

thanks,

Chagrin

Seeeduino Stalker has a LiPo management circuit. If you pick one up also grab one of the solar panels they sell; nice panels and good prices too.

ximfinity

Thanks for this, I think im going to avoid the lipo batteries though as they tend to fail over a long period of time, I intend for this project to rarely need the backup power and only need power for about 1/2 second to shut down.  I'm going to try and build the supercap circuit and see how that goes, it seems to be the cleanest solution i can find.

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