Servo generates much noise on Synth speaker -solved with HDK bit-

When I use a servo in combination with the mp3 player connected to the synth speaker in a project, the servo generates a lot of noise when used as a waving servo. I have connected my own amplifier and speakers and then there is no noise at all.
So I think the synth speaker bit does not suppress the incoming noise enough…
How can I solve this , any suggestions ?

Did you try placing a Filter immediately after the Servo bit? (with cutoff and peak turned all the way down)

Hello Goncalofsilva,
Thanks for your answer, a filter is a good idea.
But I have no filter available, I am using the speaker from the smart home kit. I did not buy the synthesizer kit (yet)…
Could I make my own filter with a connection bit from the HDK set and some R and C components ?

@alexpikkert Can you please detail your circuit? Is it power + mp3 + speaker + servo? What mode is the servo using, and what type of power module are you using?

Hello JackANDJude,
This is my circuit I am working on:
USB power+light sensor+servo turn mode+servo swing mode+motor+mp3+synth speaker.

@alexpikkert THAT is a funky fun circuit. I tried replicating it with my own external MP3 player as input to the space kit o22-speaker. Link to replicate your circuit:
I also tried it with the speaker you have, o24, tacked onto the end as an extra speaker, and the noise is pretty noisy!

I am working on a “money grabber” with musical reward.
See my draft prototype with the noise in the i25 mp3 part connected to the o24 speaker. at

when finished I will publish it.

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HAHAA - I love it! … I’ve tried placing all sorts of modules before the speaker to try and absorb the servo noise, but no luck. I’m grasping at straws here, but what if you put a threshold before it? I can’t test this theory, myself. In any case, I don’t notice your speaker noise because the servo itself is noisy.

No noise with the 022 speaker on my end.

Good luck troubleshooting & I can’t wait to see the whole sha-bang! :smile:

I tried a lot of bits to eliminate the noise. No luck until now.
I will change my project, using the servos not in swing mode. Then the noise is short.
Thanks for now.

That’s odd (and a little too noisy…) maybe the guys at littleBits will know exactly what’s happening here.

Did you try with different power sources? (battery, USB-to-computer, USB-to-wall adapter)
I’ve noticed on some of my synth experiments that USB-to-computer picks up very small amounts of noise from the computer it’s connected to.

Hello Goncalofsilva,
I think the noise is sent from the servos into the o24 amplifier/speaker through the VCC power connections.
I tested the project with disconnected signal line and the noise was still there…
I also tried all types of power supplies, usb via pc, usb via wall adapter, battery and my own wall adapter power supply.
No difference noticed.
JackANDJude tried a different speaker (from the space kit) and this one shows no noise.
Also my own speaker/amplifier bar from Creative works fine, no noise.
So my conclusion is : speaker o24 is very sensitive for noise via VCC.
Thanks for your remarks !

After a lot of tinkering I found a solution. I think the servo noise is coming through the VCC power connection.
So I made a VCC low-pass filter using a HDK bit and all the noise was gone…
See the result on
I realise a 100 Ohm resistor in the main VCC line is not in accordance with the Littlebits design rules,but maybe this solution could be integrated into the 024 speaker bit internally?
My recent project with servos and mp3 is working fine now.


Thanks for sharing your solution. Any chance you could also provide links to where you purchased your resistor and capacitor. I’d like to replicate your solution for my LB set-up that is also giving me unacceptable noise in the LB speaker (power -> cloudbit -> mp3 player -> LB speaker). Thanks!

Hello expresso2222,
I am from the Netherlands and I bought my electronic components from a local store that does not sell abroad. And I have stuff in my own dungeon too.
But I found the same components at radioshack,

Look for a 100 ohm 1/8 Watt resistor and a 220 microfarad electrolytic capacitor. These will work fine. I solved the noise from the servo with this filter, I wonder if you have the same type of noise in your setup with the cloudbit. I hope it works for you.
Please realise that due to the 100 ohm resistor sitting in the VCC line you cannot connect more bits behind the speaker. They will not get enough power anymore.
Let me know the result of your experiment if you want.

Thank you for your design…it works great. I was able to filter out the noise on the VCC line. This noise came from my Cloudbit and caused my speaker to pop and hiss quite a bit. In addition to the proto bit I used the following parts for the filter:

  • RES 100 OHM 1/8W 1% AXIAL (RNF18FTD100RCT-ND)
  • CAP ALUM 220UF 50V 20% RADIAL (P5183-ND)

…which I got from

Now the doorbell on my main house is connected to my garden room office.with the following set-up.

main house door bell
existing plain old door bell > small light bulb

…in an enclosed dark container with…

USB power > light sensor > Cloudbit

garden room office

USB power > Cloudbit > Long LED light > MIDI player > low pass filter > speaker

The two Cloudbits are connected via IFTTT.

Thanks again!

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Hello @expresso2222,
Great solution !
I am happy to see your doorbell design is working ok now.
Thanks for sharing this nice result, maybe other bitsters can use this also !

Just posted a description of my project. Thanks again for your help.


@alexpikkert Hello Netherlands! I am having the same signal noise issues here in NYC. I have the servo coming off one of the 3 channels on the wireless receiver, then the MP3 off of that. The MP3 has lots of noise when the servo runs (turn or swing). If I remove the servo from the system, the MP3 sounds just fine.

You sound like a smarter user than I, inventing your own filter was genius. @goncalofsilva had an "off the shelf " idea about using the littlebits Filter bit, do you think this will work to reduce the noise??, i dont know much about signals


@shultis, your machine looks awesome!

thanks! this is our first project here with little bits so…here is a vid that I am eager to over share!

also, this was completely inspired by the R2 bit bot as posted by @drthuler he made it easy to get started.