Question for the group: I built a DIY Bluetooth speaker for my son, and right now it s powered by...

[G+_Shooter_FPV (Shooter_FP]

Question for the group: I built a DIY Bluetooth speaker for my son, and right now it’s powered by a 12v/5A power cord like you’d use for a laptop. I’d like to add a battery to it so he can take it out with him.

 

Being I’m a drone builder, I have a few handful of LiPo batteries hanging around. Could I wire up something where a 14.8V LiPo runs to a voltage regulator and drops the power to 12V? If it’s a big project i don’t need the battery to charge while plugged in, but it would be easier.

 

As you can see by the video, it’s actually a simple project. I have it working, but I get crazy hum from the Bluetooth module that mounts on top. I ordered a new one thinking the current one is defective somehow.

 

So... thoughts on the battery???

 

Thanks everyone!!!

[G+_Paul Hutchinson]

Assuming the 12V power input already regulates the voltage down to 5V or 3.3V to power the system, then it's likely the 12V input will work with a wide input range e.g. 16V to 9V. Check the specs for the power input to see if it can handle the slightly higher voltage directly and keep working down to the minimum from the battery.

[G+_Shooter_FPV (Shooter_FP]

Paul Hutchinson The power supply I use is a 12V/5A power supply that you’d use for a laptop or such. It has a brick, with a barrel connector that plug into a power socket. It gives 12V to the amp that everything is plugged into. So was hoping I could use a battery with 12V, or a higher voltage battery with a regulator that brings power down to 12V before it hits the amp.

 

I’m not too hip on where I want to go, so I hope I make sense... ?

[G+_Paul Hutchinson]

OK I'm a bit confused, you said you built a DIY Bluetooth speaker but now it seems you bought a Bluetooth speaker and perhaps added a DIY housing?

 

If you built it then you should know the part number of the power supply you built into the speaker system. Based on that part number you lookup the spec sheet and see what range of voltages are allowed while still producing the required output voltage & current that the speaker needs.

 

If on the other hand you bought a Bluetooth speaker then the spec sheet for the Bluetooth speaker should show the range of voltages that it can accept at its 12V power input. For automotive 12V systems (13.8V nominal) the range should be at least 10 to 14 but more often is 9 to 16. For consumer electronics 12V input power systems (12V nominal) the safe input range could be 11.75 to 12.25, or 7 to 28, only the manufacturer knows for sure.

[G+_Shooter_FPV (Shooter_FP]

See... I knew I didn't make sense... sorry for the confusion. I found a video to make a simple Bluetooth speaker. I should have attached the video, but I was using my phone, and I was having YouTube issues. The setup consists of a 100w amp, a module that lets you do Bluetooth, AUX IN, FM radio and SD card music... mounted in a box made from 1/2" MDF, and using 4" car speakers as speakers. Now that I am on my PC I can attach the link to the video, that will help to understand. I can't explain well sometimes..

 

So you'll see it's powered by a 12V power adapter. All I want to do is add a battery somehow so my son can take it with him. Right now it's only AC powered.

 

Here is the video:

 

[G+_Shooter_FPV (Shooter_FP]

David Peach It is the same, exact same. Problem is... the bluetooth "module" says it will run on either 5V or 12V, that's why he has the resistor there. But when I connect it like he does, the bluetooth module doesn't turn on at all. Even with a multimeter I see 5V going to that module. If I get rid of it and connect it directly to the 12V power, it works, although I do get a very annoying hum when bluetooth is selected. So in the long run I'd need no more than 12V going to that bluetooth module.

 

Any easy way to rig up any battery to have it charge when plugged in?

[G+_David Peach]

Shooter_FPV, I was looking at the amp not the bluetooth module. Sorry. Let me do some looking. Since my amp and bluetooth module are one unit, I made a quick assumption that the board on top of the speaker was just USB input to everything.

 

BRB with some possible answers.

[G+_Shooter_FPV (Shooter_FP]

David Peach No rush... my end goal is to just add a rechargeable battery so my son can take it with him, and hopefully rigging it so that the battery charges when plugged in at home. But yes, that bluetooth module runs at 12V. If the amp would run better at 20V I can get another power cord, then reduce voltage to 12V for the bluetooth module...

 

But as I said, just want to add a battery... :) Thanks for the help everyone... :)

[G+_David Peach]

Shooter_FPV , To do some testing, I would find a 12V battery (pop the hood on the car if necessary) and make sure the hum goes away when on battery and not wall plug. I suspect it will. But, if it doesn't, then you may have a different problem than what a battery will solve.

 

"says it will run on either 5V or 12V, that's why he has the resistor there" That is a voltage regulator putting out 5V, not a resistor (unless I missed something in the video). That should put out a consistent 5V and everything should work. Obviously it isn't working. So...

 

[What I'm outlining below is for the purpose of being able to keep the 12-20V input of the system and still give you 5V out to the Bluetooth. This keeps things simpler to add any size battery within the 12-20V range.]

 

I would find another 5V supply (USB phone charger maybe?) and hook that up to the Bluetooth module and see if it even really works with 5V. The specs say 3.7V to 5V. If your new 5V supply still doesn't work, try 3.7V (I suspect you have many batteries with that output capacity).

 

I'm going to make a guess that the Bluetooth module isn't going to work with 5V. It is more likely that something is wrong with the Bluetooth module than the 7805 being bad.

 

If the alternate 5V supply works, then I would put some smoothing capacitors onto the 7805 regulator to see if that works. I'll explain that with a picture. Basically you are smoothing out any kind of power fluctuations from your input power supply and making the 5V output of the 7805 a smooth 5V. It may take out the hum, but I'm not certain of that.

 

In my attached picture you see 12V (or up to 35V) input voltage on the left. Ground is in the middle. 5V output on the right. You want to solder (or pinch in your power connector block) a capacitor that connects the input and ground legs that is between .33 uF and 47 uF. (I know that is a huge difference, but from what I've read the bigger the better up to 47 uF).

 

Then, between ground and the 5V output side solder a .1 uF to 10 uF between the legs. Again, bigger is better supposedly.

 

Recap: If the alternate 5V supply works on the Bluetooth module, then go through the mess about adding the smoothing capacitors to see if that makes the original setup work as expected.

 

Concerning charging a battery at the same time as making it work I have to leave that idea to better minds.

[G+_David Peach]

Forgot my picture in the above comment.

[G+_Shooter_FPV (Shooter_FP]

I think the bluetooth board/module has a problem, because I don't get hum when it's unplugged, and when the module is plugged in and bluetooth is picked from the options, the hum is crazy. but then I switch it to either FM or AUX, and it's fine. I ordered a different one from Amazon and should be delivered today.

 

Oh yea, I guess it's a voltage regulator... sorry, still learning about resistors/regulators and stuff... and I don't think the 7805 is bad, I tested it with a multimeter and it's at 5V on the nose.

 

And in thinking about this, I did a Raspberry Pi project early last year making a Gameboy-type thing, and part of it was adding a rechargeable battery. I think there was some kind of charging module in the mix, I'll have to look that up, maybe I can get a starting point from that.

[G+_John Sullivan]

It would be helpful if you could provide make and model of your amp and the replacement bluetooth module you just bought.

In the video, he is supplying 12 volts to his amp board, and using the regulator in parallel to step it down to 5 volts to supply the bluetooth module.

If your module says it will run on 12 v or 5v, and it runs ok at 12 v, but not 5v, then there is more to the story (or it's defective, as you already suspect). You may need to make a jumper connection or select the input voltage some other way, but we'll see what the new module says.

As for the battery, the 12volt 5amp power brick that you are now using supplies 12 volts, but UP TO 5 amps.

The amplifier is rated at 100 watts at 12 volts, so that would be 8 amps output power. Assuming that it is less that 100% efficient, it might require 12 to 16 amps input power or more in order to achieve the full 100 watts out (50 watts per channel)

As your brick is only supplying 5 amps, you are only getting 60 W input, so maybe 30 w output ( 15 per channel).

 

LiPo batteries have a "C" rating, which gives an approximation of how quickly you can discharge them.

This article gives a pretty good explanation:

https://www.tested.com/tech/502351-rc-battery-guide-basics-lithium-polymer-batteries/

They show a calculation of a 2200 mah LiPo battery with a 20C rating supplying up to 44 amps of current.

We can reverse that formula and calculate that a 1000 mah battery supplying 5 amps of current would need at least a 5C rating.

The batteries you have are 14.7 v full charged and (depending on the make and model) that should be close enough for your amp.

I would say go ahead and plug in one of your LiPo batteries (once you get the new bluetooth board installed) and try it. Turn the volume (on your phone or whatever is feeding it) way down to start, then turn it up a bit and see if the battery is getting warm. If not, turn it up a bit more.

Obviously if the battery starts to feel hot, unplug it.

You may also want to install something like a 12 volt 5 amp automotive fuse inline from the battery, just for some protection from discharging the battery too quickly if someone decides to turn the volume all the way up.

You may find that LiPo batteries are not the best choice for this application. Maybe PadreSJ has a better suggestion?

[G+_Shooter_FPV (Shooter_FP]

John Sullivan Thanks for the info, I'm learning a lot from you guys...

 

So here is where I am at... I put in the replacement Bluetooth module, kinda the same as the other one, except it is straight 12V, which is fine. The only issue is the same problem I had with the other module: when switched to the Bluetooth setting, there is a very annoying whining noise... it doesn't get louder when you increase the volume, but you'd hear it during the silence between tracks or with soft music. And it happens whether a device is paired or not. I hate to say it's the amp, because if the bluetooth module is not powered it's quiet, except for a very faint hum that isn't an issue.... unless it actually is the amp... I'm frustrated at this point... I got the amp and older bluetooth module from China, and I hate returning it, or even spending more money than I already have... ugh....

[G+_David Peach]

Shooter_FPV, Try a 12V battery to feed the system and see if the hum goes away. I strongly suspect that the noise is from the power supply brick you are using. If it doesn't make the noise on battery power, then the power supply is definitely the issue.

 

If it still makes noise on the battery, then I would have to suspect the amp. But, I don't think that will be a problem.

[G+_Shooter_FPV (Shooter_FP]

David Peach I've tried 2 different power supplies, and they both do the same. I'll look around my shop to see if I can find another one to use. I don't have a battery with me here at work, so I'll have to try it at home tonight.

 

I do have an amp, a 7812 and a 24V power supply in my cart at Amazon, but I REALLY don't want to have to spend more if I don't have to...

 

I'll report back later... thanks :)

[G+_Shooter_FPV (Shooter_FP]

David Peach I found a 12v 1A power supply that I use to power an external hard drive, and I still get the hum... and when I put my fingers close to where the audio input goes in, the hum gets super loud... and this happens no matter what power supply I use... so I suspect that the amp is bad. Would you agree?

[G+_Paul Hutchinson]

I may have missed some info so first I'll state the conditions that I think exist based on my reading of this thread.

 

1. The system uses a speaker amplifier and a seperate receiver that has USB, SD, line, FM, and Bluetooth inputs.

 

https://www.banggood.com/TK2050-50W-50W-Audio-Amplifier-Board-T-Class-Dual-Channel-HIFI-Stereo-p-1070906.html?cur_warehouse=CN

 

https://www.banggood.com/DC-12V5V-MP3-Decode-Board-LED-USB-AUX-FM-Bluetooth-Radio-Amplifier-With-Remote-p-1130424.html?cur_warehouse=CN

 

2. When any input source except for Bluetooth is used it works fine.

 

3. When Bluetooth is used there is a background high pitched whine that does not vary with the volume setting.

 

Assuming I've understood the conditions correctly then the problem can not be the amplifier because the noise is only present when Bluetooth is used for an input. If the amplifier was the problem then it would make the same noise when other inputs are selected on the receiver since the amplifier has only one input. The problem must just be a poorly designed or constructed Bluetooth section in the receiver.

[G+_David Peach]

Another thing to try is a different wall plug or power strip. In fact, I would definitely not use a power strip while testing just to eliminate another variable.

 

I don't think there is anything wrong with the amp. This is a very common problem in audio circuits. There is just some kind of RF interference going on. It might be eliminated by replacing the speaker wires with something just a little shorter or longer. It might be taken care of by a high/low-pass filter (a simple capacitor/resistor combination that works miracles).

 

I'm convinced the problem is an electric supply problem and not the amp. It is probably a ground loop or something in the system is sending out an RF signal that is interfering with something else. It may not be solved by a battery, but I suspect it might.

 

Wiggle wires around and see if any make it any worse or better. Also, check the solder joints on the audio input of the amp. The fact that 2 different Bluetooth modules display the same results makes me think that you should focus your attention on the power system and the amp circuit. (Again, not that I think the amp is bad, but something is interfering with what it does.

 

This is fun! (The fact that I have no skin in the game but get to play with the troubleshooting end of things).

[G+_Shooter_FPV (Shooter_FP]

Paul Hutchinson You are correct up to this point, but I tried 2 different Bluetooth modules and they both have the same hum/whine as described. But... there's also a very low-pitched hum coming from the speakers when I connect power WITHOUT the Bluetooth connected.... and with power connected, I put my finger near where the input of the Bluetooth module is, and the hum gets WAY louder. It's almost like back in the day with rabbit ears antennas when you grab them the picture magically gets better, then when you let go it's snow... so if I touch it where the input is, it gets super loud, when I take my finger off it gets soft.

 

This is why I'm getting so frustrated, because I don't know what the cause is. I've tried 3 different power cords and it's still the same. David Peach suggested a battery, but I can't do that until I get home tonight...

 

I ordered a different amp from Amazon, which was actually half the price of what I currently have, so we'll see...

[G+_Shooter_FPV (Shooter_FP]

David Peach I think it’s pretty fun too, but frustrating that I can’t seem to find out what the issue is. I’m learning a LOT from you guys, so thanks.

 

I tried just now plugging in to a wall outlet, and get the same hum. I am attaching a picture of the unit.

 

The red/black wires on the left is the power in. The thicker wires are direct from the power cord. The thin ones go to the Bluetooth module. The white wires are the speaker wires. The red/black/yellow wires are the audio in from the Bluetooth module.

 

So... right now it’s humming, softly, but loud enough to hear it. If I touch the amp where the 2 green boxes are on the lower right, the hum gets very loud, and sometimes pops. Also, if I hold onto the red/black/yellow wires the hum gets way loud as well.

 

In the beginning I thought that maybe the screw terminals were funky, so I soldered the audio out wires and Bluetooth power wires directly to the pins on the backside of the amp, but that didn’t make a difference...

 

I already ordered the new amp, I should get it Thursday.

 

But from what I’ve described, does that make a solution any clearer??

 

Also, I’m not sure what the blue boxes with the screws on them are, but I tried turning the screws and that didn’t help...

[G+_Shooter_FPV (Shooter_FP]

David Peach And this is the Bluetooth module... I cut a rectangle into the top of the enclosure and it fits right in. The green wire is the external antenna, I just soldered a wire into the board. The disc-type thing floating above it is a microphone, guess you can actually make phone calls with it...

[G+_Paul Hutchinson]

Shooter_FPV "You are correct up to this point, but I tried 2 different Bluetooth modules and they both have the same hum/whine as described"

 

That confirms that the high pitched whine is a design/construction flaw in the receiver module, when two examples of a product give the same result you've definitively identified the source of the flaw.

 

Since the hum is apparent with or without the receiver connected that flaw is in the amplifier. The hum is almost certainly 60Hz hum, it may be avoidable with proper audio quality sinlge point grounding and shielding of the wiring harnesses, or by adding 60Hz filtering on the DC output line of the AC power source. Note: even a $10,000 amplifier will give hum when the inputs are not properly shielded and single point grounded, or when you add a human 60Hz antenna connection to the input (humans are great 60Hz antenna's).

 

Both these situations are not at all surprising based on my experience with Chinese import audio products, in fact I'd be more surprised if one or both of these problems wasn't apparent with that gear.

[G+_Shooter_FPV (Shooter_FP]

Paul Hutchinson Any tutorials on adding a 60Hz filter? New ground for me (ground... lol... electrical joke...). And how do I go about grounding and shielding the wiring? I love learning about this stuff...

[G+_Paul Hutchinson]

Shooter_FPV I learned all that back in the 60's/70's based on books (e.g. Audio Cylopedia in the Oaklawn RI public library, paid a $100 for a personal copy around 1980) and "The Audio Amateur" magazine so I have never reviewed any online information sources.

[G+_Shooter_FPV (Shooter_FP]

Paul Hutchinson Rhode Island?? That's where I'm at... I'll do some Googling, but will post back here on any new revelations...