Author Topic: Servos and micros and power isolation, oh my!  (Read 658 times)

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Offline rrinker

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Servos and micros and power isolation, oh my!
« on: December 24, 2016, 05:21:55 am »
 Cheap servos = electrical noise. Micros = noise is bad.
So - opinions on "is it isolated enough" if there is a common, say 12V DC unregulated power feed and one (for the sake of example, a nice jellybean part, the good old 7805 linear regulator) regulator circuit powering ONLY the servo, and another regulator circuit powering the micro - both sources from the same unregulated supply. Assuming the 7805's were wired up per proper practice with the recommended caps and all that.

 Would this be enough isolation to keep most of the servo noise out of the micro side of things, or do I really need to run two completely independent power supplies? Anecdotal evidence from a commercial product that I have used that is designed this way (input power goes to two different regulator circuits, one feeds just the servo power, the other feeds the micro, pushbuttons, and indicator LEDs) sees to indicate this type of design is definitely sufficient. The commercial product was and still is quite reliable, and I never had any issues with noise causing spurious operation of the circuit.

 

Offline SeanB

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Re: Servos and micros and power isolation, oh my!
« Reply #1 on: December 24, 2016, 06:13:43 am »
Better is to add some series resistance to the regulator inputs, so the RC filter is more effective at reducing noise. If your current is such that the R is low, then a small inductor ( well damped with a parallel resistor and some lossy ferrite core) will do as well. This adds impedance to the regulator supply, so that you do not have the decoupling capacitors handling the motor ripple current. on the input side you still need adequate decoupling capacitance, but this is more relaxed value and ESR wise then.
 


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