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switching noise when powering microcomputer ?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author switching noise when powering microcomputer ?
thetechnobear
hi

Im very new at creating DIY modules, and have a small issue...

Im powering a Beaglebone Black directly from the 5v line on the modulars ribbon connector - and im finding im getting noise (esp as the microprocessor starts up, but then turns into a high pitched whine) from other modules outputs.

(this happens with just the BBB connected, ie. no connections to audio/cv IO)

Im assuming this is something to do with the processor load, so switching, that then is being passed down the power lines?

is there a simple solution for this?
preferably with some simple schematics, given im a beginner at this smile


thanks for any help/pointers, as Im really not sure where to look for a solution.

Cheers
Mark
guest
you can try splicing in some ferrite beads or inductors on the power and ground lines to the beaglebone. is it all modules, or just ones that use the 5V power as well?
thetechnobear
guest wrote:
you can try splicing in some ferrite beads or inductors on the power and ground lines to the beaglebone. is it all modules, or just ones that use the 5V power as well?



thank you.

its not on Eurorack, but an AE modular, which is all 5v, and yeah its all modules connected to the same ribbon with that 5v..


Im connecting the 5v directly into the gpio, so using 22awg wire to connect.

is there some kind of component I can add, as ive no idea what size ferrite bead to use (id have to order something)


------
note:
I tried to look at the MI clouds schematics to get some inspiration, but that seems to just use a voltage regulator (as far as i can see), but that is taking the voltage down from 12v to 3.3v
is it also stabilising/isolating it to?
is there a voltage regulator i can use to go 5v to 5v, but just for this purpose?
guest
perhaps another thing to check, is to run the beagle off of its own powersupply, and see if the noise goes away. that will rule out other forms of interference that could be going on.

whats the powersupply for the ae modular like? does it come in as 5V or is it stepped down from 9V or something like that.
thetechnobear
guest wrote:
perhaps another thing to check, is to run the beagle off of its own powersupply, and see if the noise goes away. that will rule out other forms of interference that could be going on.


yes, if I run the beagle off (separate) USB power the noise disappears entirely.


Quote:

whats the powersupply for the ae modular like? does it come in as 5V or is it stepped down from 9V or something like that.


its a 9v 1.3A , stepped down to 5v - should have plenty of spare mA to cope with the beagle.


----

I noticed the terminal tedium has a 10uH inductor on its BOM
(mouser # 542-78F100-RC) , but as i can't find the schematic, im not sure how its used, or if its used in conjunction with a capacitor (etc)

(Im thinking it must be a similar issue, assuming the TT runs the rPI off the +5v supply - but again, without schematics im unsure)
guest
if you want to use the capacitor/inductor method you would cut the power line, put in a capacitor between the lines, then an inductor in series with each line, and then another capacitor between the lines. something like this:

https://wiki.analog.com/_media/university/courses/electronics/text/chp tr6-f13.png?w=500&tok=d806c9

except with another inductor on the ground line as well.

another option is to stick a 7805 on the input 9v to make a seperate 5v for the beagle.
mskala
If the Beaglebone interfaces with anything else in the system via standard unbalanced connections, then you may not want to put an inductor (or any other impedance) into the 0V, because it'll make the switching spikes more visible on the inputs and outputs.
Graham Hinton
thetechnobear wrote:
Im assuming this is something to do with the processor load, so switching, that then is being passed down the power lines?

is there a simple solution for this?
preferably with some simple schematics, given im a beginner at this smile


No. The onus is on you to fully describe and give a diagram of what you are doing, only then can people tell you what you are doing wrong. It may also focus your mind on what the problem really is.

You need to describe the modules that have the hum on them and what you are listening to that hum on and how they are interconnected. They are all part of the problem.
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