High pitch screeching coming from a board

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Hey all,

I recently picked one of these I2C keyboard expansion modules: NeoKey 1x4 QT I2C - Four Mechanical Key Switches with NeoPixels - STEMMA QT / Qwiic Australia

It’s working perfectly and if anyone wants my code or some explanation around it just reply!

I just noticed there is an audible high pitch screech/hum coming from the board and wondering what it could be?
Here’s a link to the schematic and learn page on Adafruits site:

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Hi Liam,

Was there anything connected to this module or just the power supply? Try to isolate the noise as much as possible so you can find out what part or combination of parts causes it.

My initial hunch would usually be coil whine, where an inductor is vibrating ever so slightly due to the frequency of the signal passing through it, there is a good demo of what that sounds like here:

Sometimes you can prove what is causing the noise by probing around with a plastic tool and seeing if touching a component changes the noise.

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Hey Trent,

Its just the power supply through the I2C bus on the Pico. I tried probing around with my fingers but to no avail.

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Hey Liam,

Just set up one of these in the workshop last week with a MX Cherry Switch and haven’t run into that whining issue, was it only as you triggered the switch/es, or was the hum continuos. Also, what’re you using to communicate with the NeoKey? I’m assuming it’d be an ESP32 or Pico (quite sure a see a Pico in the picture), the voltage level should be correct but I2C often uses either 5V or 3.3V as standard.

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Hey Bryce,

It was a continuous hum, not super loud but the high pitch allowed the sound to seep through my headset.
Yeah it was a Pico soldered directly in using a cut down PiicoDev proto cable at a logic level of 3.3V.

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Hi Liam
Ah, in the headset so it is not mechanical. How are you powering this audio system. Hum is usually used to describe mains power 50 or 100Hz in the background. You describe a high pitch so could it be switching artefacts on your power source.
Cheers Bob

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Hi Bob,

I meant to say that I can hear it through the padding on my headset.

The system in question is a Neokey board from Adafruit and a RPi Pico running of my PC’s USB power(Also tested with a USB power bank but that also has a SMPS in it).

The ringing only occurs when the Neokey is plugged in (I’m using the STEMMA port) - I’m not sure why though as it features a linear regulator there. Once the world opens up again I’ll bring it into the uni and probe a few of the bits to try and see where it comes from.

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Hi Liam

So it still could be mechanical. I think you need to establish this one way or another. An oscilloscope would be pretty handy here. If it is Audio sometimes the shape and frequency of the interfering signal is a clue.

Just had a look at what a Neokey is. How that make an audible noise when it is plugged in is beyond me. Have you monitored for any changes in current requirement when you plug it in. If here is some sort of insidious fault on this board causing excess current it could pull a power supply down and if it recovers then goes down again rapidly it would not be picked up with a DMM, they are too slow. This sort of thing is where an oscilloscope is really a requirement. It will respond to rapid changes in power supply etc behaviour where nothing else will. There seems to be nothing else on that board but 4 switches, is that correct. There could be a problem with the board itself that got past testing, or a minute solder bridge under a switch, anything. But high speed monitoring of the power source could tell you a lot.
Cheers Bob

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