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

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.


My understanding is that the noise is coming from the power I.e. the VCC and not the signal line. The filter works on the signal line so unfortunately will not work. I tried it as well just to make sure and the noise remains. Without making the filter, I think the only option to eliminate the noise is to create a separate circuit.

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Love your R2D2, @shultis! I like your sound effects and the number module display. :slight_smile: Will you be adding more MP3 sound effects?

BTW your R2D2 is awesome! ;D

Hi @shultis!

Very nice your R2D2. I’m glad to had inspired you and brought you into the force :smile:
Keep inventing, sharing and count on me and this community if you need any support!
About the noise, @chris101 and @alexpikkert can help you better, but in my HW experience the noise can come from signal, power and ground lines (for audio is even worst to keep it clean) and it’s better to try cleaning it at the source (in servo bit), maybe anyone made some hack adding a capacitor or decoupling ground of the servo bit.
I just figured out another issue that confuses me sometimes, servo drain a lot of current, check your battery, maybe the other bits are shutting down or failing due to low voltage (the border line is unknown).Its weird but sometimes the power seems ok but when the servo (or fan) turn on some other bit fails. Try a new battery, USB power ou DC outlet to be sure, I always double check that. Also clean the conector contacts, dust can increase the resistance and drop the voltage when the load increases.




thank you diego. so happy i saw your pr2d2 project on the littlebits web. my 7 year old and i had a great time getting started into the little bits world.

You were correct, the 9v battery was down to 7.5 volts. I added a new 9v and the static is mostly gone. Also, changing the servo that powers his head from “swing” to “turn” helped too.

thank you for your comments, please keep posting your new projects, I enjoy your inspiring work!


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@alexpikkert Thanks for the instructions for creating a low pass filter. I ordered the following resistor and capacitor from digikey that @expresso2222 posted:

CAP ALUM 220UF 50V 20% RADIAL (P5183-ND)

I’m new to the proto bit, and it took me a bit to make sure everything was put together correctly. I attached a photo of the proto bit to help others… (It also needs to go right before the speaker…a fact I missed.)


Hi @Ben,
Great !
Indeed the only disadvantage of this filter is the fact that you cannot add any other bit after the speaker, because of the loss of power due to the 100 Ohm resistor…
But it minimizes the noise…
btw can you show us some details of your project please ?

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First, I should say that my LittleBits partners are a four-year old and two-year old.

This project started as a railroad crossing gate. It was very popular with the train set:
power --> slide dimmer -> servo

To upgrade, we uploaded some sounds (railroad crossing bells) from onto an SD card. I left out the correct parts, and let the four-year old assemble an addition:

power -> split 1-> slide dimmer -> servo
split 2 -> button -> mp3 player -> proto -> synth speaker


There were other solutions, but this wasn’t the first time we had this speaker/servo problem, so I appreciate the solution.

I’ll try to upload some more of our creations elsewhere. None will win a beauty contest, but they get used a lot, and the four-year old loves building a toy with dad.


@Ben this is super sweet! Can you share this on with a video of it working? :grinning: