Dual power for SX

R.Miner

I am building a controller with an SX proto board, that will keep time·and drive servos.· I am concerned that when the batteries run low, moving the servos will cause brown-outs, which will cause the device to lose track of the current time.· My thought is to drive the SX with a 9V battery and the servos with·four AA cells.

It looks like I can connect both (-) of the batteries to Vss, connect the (+) of the 9V to Vin, and the (+) from the AAs to the servo middle contact (where the jumper usually connects the servos to either Vin or Vdd).· In this way, I hope to provide continual power for the time-keeping function, even after the servos have exhausted their battery power, and allow the batteries for the servos to be replaced while the "clock keeps ticking."

Is this an appropriate solution?


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Richard Miner

Thingmaker

JonnyMac

Yes, it is. You might want to drop big caps on both power supplies to keep any noise from the servos from having an ill effect on SX circuit. Also, enable the brown-out detector so that if the SX voltage does go low you can get a clean reset.

R.Miner

Thanks for the quick reply.· What would constitute a "big cap?"

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Richard Miner

Thingmaker

Bean

at least 1000uF with a voltage rating at least 2x the applied voltage.

Bean.

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R.Miner

Thanks.

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Richard Miner

Thingmaker