Servo hum

Good evening,
I've made a physical hit counter. Every time my site gets a hit a servo is fired which clicks a counter along one.

When I've tested it without the ethernet stuff running (the ethernet function in my code, the shield was still connected), it's fine. It clicks the counter once every second, as I've told it to.

When I connect the servo it all works, it clicks the counter when I get a hit, but the servo hums almost constantly, but isn't moving. Or at least isn't moving observably, it could be making very fine back and forth movements.

I'm using the standard servo and ethernet libraries.
I've tried the servo on pin 8 and pin 9, there was no difference.
There is also enough slack in the connection between the servo and counter for their to be no strain on the servo when at 0 (which it goes to in setup().


It has calmed down, the hum seems mostly intermittent. I'd still like to know why though.

Do you have the servo connected to its own power supply of sufficient amperage (5-6V, > 1A is best)? An insufficient supply of power (ie, running the servo off the same regulator as the Arduino) can be a culprit of such humming...

No, it's running off the arduino.

It hums when it's got nothing to do though, when it's not being told to do anything. Is it still likely to be an insufficient power supply?

I run it in short bursts so it doesn't cause the arduino to reset.

Yeah, I think it is still possible, even in the dead band. Try a separate supply, see if that quiets it.

I'll have a rummage in the box of power supplies that don't match up to any devices that I've been keeping just in case. Glad I might've finally found a use for them!

Or a proper rechargeable/replaceable battery pack. Four AA batteries in series provides approximately 5VDC at 0.7 to 1.5 Amp/hour (depending on type of battery used) which is adequate for most standard size servos. Remember to common your grounds with your arduino power supply.

Why do I need to common the grounds?
(I'm new to this electronics malarky)

If you only hooked up positive and negative to the servo then connect the control line from the atmega chip, it would be possible for current to flow from the battery through the control line circuitry in the atmega chip to ground and if sufficient cause catastrophic damage. Providing an electrical connection between the battery ground and the atmega power supply ground is an effective way to prevent undesirable ground paths.

thanks for the info :slight_smile:

Why do I need to common the grounds?

Thanks grumpy mike, that's really useful.

"Most beginners do something like this:" is exactly what I did the other day. Might try again now!

And finally I can't resist any longer.

Why do servos hum?

Because they don't know the words.


And finally I can't resist any longer.

Why do servos hum?

Because they don't know the words.

What took you so long? You getting slower in your old age> ;D


No I'm just getting better at resisting. :wink: