REL1101 buzzing/humming when DigitalOutput channels are opened, even with no load connected

[pkokoras]

Hello,

I am using a Phidgets REL1101 16x Isolated Solid State Relay Phidget connected to a HUB0002 VINT Hub.

I am hearing a noticeable buzzing / humming sound from the REL1101 board. At first I thought it might be caused by my Max/MSP patch or by the connected loads, but I have now done several tests and the sound seems to come from the REL1101 itself.

Here is what I tested:

- The REL1101 is connected to VINT Hub Port 3 (hub 4 slightly softer sound?).
- I disconnected all external loads from the relay outputs.
- The buzzing still happens with no load connected.
- When I close Max/MSP, the buzzing stops.
- When I open the same DigitalOutput channels in the official Phidget Control Panel, the buzzing also happens.
- In the Control Panel, the board is quiet before opening the channel.
- When I open an on/off relay output channel, the board starts buzzing.
- When I use the PWM slider in the Control Panel, it produces a very similar buzzing sound.
- I originally used channels 0, 1, 2, 3, then changed to channels 10, 11, 12, 13, but the buzzing continues.

So it does not seem to be caused by the load or by my Max patch. It seems related to opening/activating the DigitalOutput channels on the REL1101 itself.

Is it normal for the REL1101 board itself to make an audible buzzing/humming sound when DigitalOutput channels are opened, even with no load connected?

Thank you for any advice.

[burley]

How loud are we talking? There is definitely some coil whine from the inductor used in the isolation. It's there as soon as you plug the board in, though the pitch does tend to change a bit when the board is active so it might be more noticeable.

It's very quiet though. I can't hear it unless the board is very close to my ear (<6"). I can't detect any measurable noise beyond ambient in a quiet office with an SND1000 even right up next to the inductor. Unless your environment is unusually quiet I wouldn't expect it to make any discernable noise.

[pkokoras]

The REL1101 is currently about 12 inches away from my left ear, and I can hear the sound continuously. I am also using it as part of a music project, so even a relatively quiet buzz becomes noticeable in this context.

I do not have another REL1101 available to test side by side, but I do not recall hearing this kind of noise in previous projects...

I have attached a spectrogram of the noise, recorded with my phone starting approximately 1 inch from the REL1101 and then gradually moving away to about 16 inches. You can also listen to an MP3 recording of the noise here:
https://drive.google.com/file/d/1vRNBTz ... share_link


On a related note, perhaps this is a question for the Max library developer: when I open my Max patch with a [PhidgetDigitalOutput] object, there does not seem to be a way to stop the whining sound, even if I set DutyCycle to 0 and State to 0. It seems that as long as the object has opened communication with the REL1101, the board produces the noise. It would be useful to have a message to fully close the device communication when the relay is not being used, so that the relay can remain quiet until it is needed.

[burley]

Based on the clip provided I would say that this is most likely the inductor as I initially thought.

Unfortunately this is an intrinsic property of inductors and there isn't much that can be done about it. The changing magnetic field that an inductor uses to store energy can cause the wires in the coil to vibrate at an audible frequency. Your best bet is to simply add something around the hardware to dampen or muffle the sound. It shouldn't be too difficult as it is not very loud, perhaps some foam or even just a small box/enclosure.