[Quick tip] Be very careful if you use a buck converter with a Bluetooth module

[Stephen37]

Today I have been playing with a CSR8635 Bluetooth audio module powered by a Mini-360 buck converter and discovered that a buck converter from eBay will cause serious interference with WiFI and Bluetooth.
Unless I put a 220uF capacitor on the input of the Bluetooth module my Wi-Fi would simply die in the house and the Bluetooth would not work but it would connect. Strangely before I tried to connect a large capacitor on the output of the converter both Bluetooth and wifi worked IF I powered them from my computer's USB slot, but not with a power bank or isolated power supply.



The lesson is that if anyone is trying to use any simple buck converter to get 3.3V to run such a Bluetooth module ONE MUST use a rather sizeable capacitor on the inputs.

[Andrey_irk]

Hi!
Did you look at the output of the buck with a scope? What was there?
Which controller is used in this buck?

I'm sorry, but your post is useless.

[Stephen37]

It's not too useful, but probably I am not the only one person on the planet who wondered why one can't use wifi and Bluetooth at the same time with such a module. My reason was that these cheap converters from ebay are too noisy and cause some interference in combination with the module.  I don't have a scope at hand.

Theoretically the converter should work without any extra capacitors, yet one needs to add more filtering.
https://www.monolithicpower.com/DesktopModules/DocumentManage/API/Document/GetDocument?id=583 is the regulator IC. (MP2307)

[Andrey_irk]

It's not too useful, but probably I am not the only one person on the planet who wondered why one can't use wifi and Bluetooth at the same time with such a module. My reason was that these cheap converters from ebay are too noisy and cause some interference in combination with the module.  I don't have a scope at hand.

Theoretically the converter should work without any extra capacitors, yet one needs to add more filtering.
https://www.monolithicpower.com/DesktopModules/DocumentManage/API/Document/GetDocument?id=583 is the regulator IC. (MP2307)

I don't think this buck can interfere with wi-fi.
But it might be a stability issue. The sixth pin of the IC is used for compensation and who knows which capacitance can be connected to the output of the buck with that RC network. What you did with connecing a large capacitor to the output is you've changed the main pole of the loop so it became stable (maybe!).
But it's only my guess. And if you want to figure out what is going on there you have to use a scope.

[SeanB]

LC filters at both input and outpu will do a lot to attenuate the switching noise, and will make for a more stable supply from the module. A lot of these modules use only the minimum of capacitance on the input and output, and no extra filtering, so adding some will help.

[Kilrah]

It's not too useful, but probably I am not the only one person on the planet who wondered why one can't use wifi and Bluetooth at the same time with such a module. My reason was that these cheap converters from ebay are too noisy and cause some interference in combination with the module

This particular one you got seems to with that particular BT module, but there are dozens of similar but different modules on the bay. If at least you included a link to the 2 items that don't work together... becasue it's very likely that a different BT module with the same supply and/or another similar supply with the same module work fine.

I guess that the thread can be summarized as "random power supplies when used with random modules may cause trouble"... which is to be expected and why things should be characterized and measured so that you know what you're getting into when putting random parts together.

[eda8039]

Thank you Stephen37  for such a well written and informative post.   I have been trying out various mini Buck converter boards to use in modules I hope to make many of and will be suspicious of these boards you mentioned.

[Beamin]

It's not too useful, but probably I am not the only one person on the planet who wondered why one can't use wifi and Bluetooth at the same time with such a module. My reason was that these cheap converters from ebay are too noisy and cause some interference in combination with the module.  I don't have a scope at hand.

Theoretically the converter should work without any extra capacitors, yet one needs to add more filtering.
https://www.monolithicpower.com/DesktopModules/DocumentManage/API/Document/GetDocument?id=583 is the regulator IC. (MP2307)

I don't think this buck can interfere with wi-fi.
But it might be a stability issue. The sixth pin of the IC is used for compensation and who knows which capacitance can be connected to the output of the buck with that RC network. What you did with connecing a large capacitor to the output is you've changed the main pole of the loop so it became stable (maybe!).
But it's only my guess. And if you want to figure out what is going on there you have to use a scope.

What do you mean by this? Or can you see the numbers on the chip and looked up it's data sheet?
So this is more advanced then: noisy output; put on a filtering cap? You are saying the converter functions differently with this cap? Can some one read those chip numbers so I can solve the mystery? 

Need more info with the first post but since your new: the people here like data sheets and are thorough and take things literally not much reading between the lines or assumptions. But I have been amazed at the effort some people put in looking up data sheets and even trying to recreate the problems. If I taught students electronics I would consider them cheating if they used this site on a project. Many, many, hours of frustration have been cut down into mere minutes when I have asked a question here.

[RadioNerd]

Wireless modules can draw short but surprusingly high current peaks.
Using regulators that are either too slow or too weak to provide the necessary peak current will lead to supply voltage drops... which in turn can lead to all sort of weird behavior of the digital circuits... I dont think that noise is the primary problem here

[Mechatrommer]

https://www.monolithicpower.com/DesktopModules/DocumentManage/API/Document/GetDocument?id=583 is the regulator IC. (MP2307)

The sixth pin of the IC is used for compensation and who knows which capacitance can be connected to the output of the buck with that RC network.

What do you mean by this? Or can you see the numbers on the chip and looked up it's data sheet? Can some one read those chip numbers so I can solve the mystery? 

as the link provided above in your quote... MP2307 the datasheet, MP2307 the ebay although i have almost similar module but it uses MP1584 the ebay clearly not pin compatible...

but since your new:

he is not newer than you are he just made less post

[janoc]

Strangely before I tried to connect a large capacitor on the output of the converter both Bluetooth and wifi worked IF I powered them from my computer's USB slot, but not with a power bank or isolated power supply.

This makes me think your problem is likely not the buck converter causing interference but either the power supply being underpowered and unable to handle the large current peaks the radios typically need when transmitting or your wifi module has some other issues.

Also be aware that many combined Wifi/Bluetooth devices can use both protocols but not at the same time - they interfere with each other. E.g. my Lenovo E31 has such combo BT+wifi card and it requires a specific driver support if you want Bluetooth - basically it needs to turn the wifi transmitter off when you want to transmit BT packets and re-enable it afterwards again. Without that the Bluetooth is extremely flaky/doesn't work at all.

[T3sl4co1l]

Necroposting aside, yeah, that module doesn't have enough capacitance on it, quite possibly the datasheet recommends more external capacitance.  As mentioned, radios can draw quite a lot of peak current, so you need adequate filtering, to a low enough impedance, and well damped, to ensure stable power.  A power supply is a filter network like any other, just usually a pretty low impedance.

Tim