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

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: