• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need help with audio Bluetooth receiver and amplifier from the same DC source.

Status
Not open for further replies.
I am making a portable Bluetooth speaker with one 12v battery, and i have a Bluetooth receiver that is powered over usb, so i putted on a 12v to 5v car usb adapter and it works but it has a lot of noise, and when i put the Bluetooth receiver to power from another battery, i works perfect.

So i searched on the internet and find out that this is a common problem when using the same battery, and it is called ground loop, and that there are 3 solutions:
1 - use two battery
2 - use completely isolated dc-dc converter
3 - use a audio transformer isolator

So i think the best solution for me is a completely isolated dc-dc converter, and i found this 5v dc-dc converter but is this what i need ?


B0505S-1W 5 V/DC 5 V/DC 200 mA 1 W

--Data sheet

If this is what i need i would put it on the output of 12v to 5v car converter is that correct?
 

audioguru

Well-Known Member
Most Helpful Member
You did not describe the noise. Maybe it comes from the 12V to 5V car usb adapter.
The new converter might not block the noise frequencies since it is not listed in its spec's.
 
no it does not comes from the 12V to 5V car usb adapter, because i have put the same usb adapter on another 12v battery and works fine.
the sound is like in this video:

is the dc-dc converter that i linked isolated power source or not ?

what do you suggest i do to solve this problem?
 
Last edited:

Les Jones

Well-Known Member
Most Helpful Member
I suspect that the noise is due to a ground loop problem. With the audio lead plugged into the car power the blue tooth adapter from a battery. (Which you say does not produce the noise.) Confirm that it is working with no noise then connect the negative of the battery to to the negative of the socket that the usb power converter was plugged into. This will create the same ground loop that you had with it powered from the USB adapter. If the noise comes back when you do this then it is a ground loop problem. If the noise does not come back then the problem may be noise from the switching regulator in the USB adaptor.(12v to 5 volt converter.) Still with the same setup power the Bluetooth adapter from the USB adaptor but supply the USB adaptor from a separate 12 volt battery. (Not the car battery.) If you still have the noise problem then it is being caused by the switching regulator in the USB adaptor. You could solve this by building a linear regulator using an LM7805 (Or similar.)
The data sheet shows that the DC to DC converter is isolated (Up to 1000 volts isolation.) so if the problem is a ground loop then this should cure it. This converter has an oscillator running at 100Khz and although that is well above the audible range it is possible it could effect the Bluetooth module.

Les.
 

audioguru

Well-Known Member
Most Helpful Member
I heard a whistle when the USB was plugged into the silver right thing and the volume was turned up high.
I heard the same whistle when the USB was plugged into the player but there was also some buzzing. The buzzing modulated the whistle.

In a car, a ground loop would probably cause "alternator whine" which is a whistle that changes its pitch with engine RPM. I doubt that a ground loop in a car would cause the buzzing sound.
 
I suspect that the noise is due to a ground loop problem. With the audio lead plugged into the car power the blue tooth adapter from a battery. (Which you say does not produce the noise.) Confirm that it is working with no noise then connect the negative of the battery to to the negative of the socket that the usb power converter was plugged into. This will create the same ground loop that you had with it powered from the USB adapter. If the noise comes back when you do this then it is a ground loop problem. If the noise does not come back then the problem may be noise from the switching regulator in the USB adaptor.(12v to 5 volt converter.) Still with the same setup power the Bluetooth adapter from the USB adaptor but supply the USB adaptor from a separate 12 volt battery. (Not the car battery.) If you still have the noise problem then it is being caused by the switching regulator in the USB adaptor. You could solve this by building a linear regulator using an LM7805 (Or similar.)
i did as you suggested and the noise comes back as soon as i connect the negative side of the battery, what did you mean by effecting the Bluetooth module with dc-dc converter, you mean effecting it with noise or ?
 

Les Jones

Well-Known Member
Most Helpful Member
That would suggest that the problem is a ground loop and as "audioguru" suggested the source could be from the alternator. (If the engine was running.) It could also be noise from data communication between various computer modules in the car. Just out of interest was the test you are referring to the first on with the Bluetooth module powered by a 5 volt battery or powered from a 12 volt batter via the 12 to 5 volt converter. It is just a remote possibility that the 100 Khz inverter inside the DC to DC converter could cause noise on the Bluetooth module. I think it is worth trying as the power ground needs to be isolated from the signal ground.

Les.
 
I am not using it in the car, the video is not mine, i found it on youtube only to show what kind of noise i have.
i am making a portable Bluetooth speaker, so i don't have an alternator or car chips that can cause noise.

i only have a 12v battery, amplifier, loudspeaker, Bluetooth module powered by a 12-5v converter meant to be used in the car.
 

Les Jones

Well-Known Member
Most Helpful Member
I'm not clear about what works and what doesn't work.
Are you saying it only works without the noise is the amplifier is powered from a 12 volt battery and the Bluetooth module is powered from a 5 volts battery ? And that if you connect the negative of the 12 volt battery to the negative of the 5 volt battery the noise returns ?

Les.
 
no i don't use a 5v battery, i used two battery of 12v for testing with negative side connected and when i connect the negative side the noise returns.
the only way it works when i power the amplifier from one 12v battery and the bluetoth module with step down usb converter from another 12v battery, as soon as i connect the negatives of boat battery the noise returns.
 

Les Jones

Well-Known Member
Most Helpful Member
I think the 12 volt to 5 volt switching regulator is injecting noise between it's negative input and negative output connections. probably either the isolated DC to DC converter or the audio isolator will solve the problem. Before spending money on either of these items I would try using a linear regulator to drop the 12 volts down to 5 volts. Even if you do not have one in stock you should be able to buy one for less than £1.00. You will also need two capacitors. See the data sheet on the regulator IC that you choose for the recommended values of the capacitors.

Les.
 

audioguru

Well-Known Member
Most Helpful Member
Does the transformer pass very low and very high audio frequencies properly?
 
Does the transformer pass very low and very high audio frequencies properly?
i don't know this is the transformer from ebay
and i also added a 1000uf capacitor across the 12v input of the 5v usb converter, and the sound is now awesome.

I also have a question about the Bluetooth antenna, i have a Bluetooth 2.4 GHz antenna and where should i solder it at the beginning of the original antenna or the end?
and should i solder only the central wire or both central and the shielding wire of a coaxial cable ?

here is the picture:

 

audioguru

Well-Known Member
Most Helpful Member
ebay garbage usually has no spec's. "20hz-30Khz" does not mean anything because it does not say, "plus or minus 1dB" so it might be awful at plus or minus 60dB or worse.
I do not know if your antenna is a dipole or a single whip. A single wire 2.4GHz antenna is about 2.5" (6.3cm) long. Leave the center wire sticking out of the shield of the coax cable for that length and do not connect the shield to anything.
 

audioguru

Well-Known Member
Most Helpful Member
If there is an on board antenna then it is all that is needed. Do not connect two antennas together, disconnect one and use the other one.
 
there is an on-board antenna, this one:

so i am thinking to connect my external antenna where the blue arrow is, where the two printed leads join and to disconnect the rest of the on-board antenna am i right?
 
Status
Not open for further replies.

EE World Online Articles

Loading

 
Top