Bluetooth Speaker Build Advice

[Josh6066]

 

Bluetooth Speaker Build

Hello everyone, I’ve recently watched a DIY Bluetooth speaker build on youtube https://youtu.be/a43LXqRwQC8 and am going ahead and trying making my only build inspired by it and have a lot of questions that I would like someone who knows a little more than me opinions on. Thanks in advance. 

 

I plan on building something like this:

 

 

In this post I’m just going to be considering electronics, I will work on building the housing later but feel free to put any comments, ideas or questions you have about the housing below.

Components

So far I’ve bought most of the components for it from eBay which I’ve listed below

2 x Dayton Audio ND65-8

 

https://www.ebay.com.au/itm/Dayton-Audio-ND65-8-6-4cm-Aluminium-Cone-Full-Range-Driver-8-Ohm-Huge-Saving-/322835667559?epid=1469751185&hash=item4b2a815a67:g:3TkAAOSwZlZZ51dS

 

30w Mini Amplifier (30w times 2 channels)

http://www.ebay.com/itm/OEP30Wx2-Audio-Module-Class-D-Digital-Power-Amplifier-Board-Replace-TDA8932-/182474865752?epid=593221892&hash=item2a7c597c58:g:LHgAAOSwx6pYt1BR

 

Bluetooth Module

http://www.ebay.com.au/itm/Bluetooth-4-0-Audio-Receiver-Board-Wireless-Stereo-Sound-Module-for-Car-LN-BT02-/282595837490?hash=item41cc064632:g:Dz0AAOSwoFxZga~G

 

Potentiometer

http://www.ebay.com/itm/B50K-50K-Ohm-Dual-Linear-Taper-Volume-Control-Potentiometer-Switch-T1-/252592538746?epid=1787033900&hash=item3acfb0447a:g:4J4AAOSwCGVYBsy7

(I might not use this, I’ll probably just use the buttons that come with the Bluetooth module)

 

The only parts I believe I still need to order are the batteries and charger, the ideal voltage would be 24V as that’s the amps max, and anything that goes with that which is where I’m a bit lost with what to do.

 

Drivers

The first problem is that the drivers arrived yesterday and when I opened them one was a ND65-8 (8 Ohm resistance) and one was a ND65-4 (4 Ohm resistance), from what I can tell only difference between the two is the resistance. I’ve contacted the seller and they said they could replace the ND65-8 with a ND65-4 so that I would end up with two ND65-4s. I’m wondering if this would work or do I need to get them to get me a second ND65-8. The amps specs on the back of it say you can use 4R speakers at 16V and 12V. I presume at 24V the wattage would be too high. How much of a difference would there be between using 4R drivers at 16V and 8R at 30W. The only problem is I bought what were meant to be the last ND65-8s but I guess if that is what I paid for they would have to work out a way to get me another one. Just as an afterthought I presume I couldn’t just use what I have and use one of each as I would get different volumes from each. This is the most urgent problem at the moment as I need to respond to the seller.

 

Power

The other issue is power, the Ideal situation would be to have the batteries fully contained in the speaker and it self balance (if that is necessary, which from what I’ve been looking at is very important). I would then just plug in a charger brick (e.g like a laptop size power adaptor) and it would charge up all the cells. The last part that I’m not sure is possible but would be really nice to have is a way to see how much battery is left like a little lcd display on the side. All minimum and maximum cutoffs voltages would be taken care of and all I would need to see is the percentage just like a phone but I don’t know if this is feasible or not.

 

Option 1

Use the method in the video of using 5, 6 or 7 individually protected 18650 cells. This method would mean I would have to take each cell out individually and charge them all before putting them back in. I’m thinking this would be a bit impractical. Also all of the protection circuits I’ve been looking at have a minimum cutoff voltage of around 2.5V whereas I’m pretty sure you weren't meant to discharge a cell past about 3.5V. Would this mean I would have to monitor all the cells manually making the over discharge protection a bit pointless but I guess still nice to have.

An example of a protection circuit I’ve found, most of them are similar to this. http://www.ebay.com.au/itm/1S-2A-3-7V-4-2V-Li-ion-18650-Battery-Cell-BMS-Circuit-Protection-Round-Board/112554179554?hash=item1a34c07be2:g:NfUAAOSwfcBZkrgQ

 

Option 2

Create a series set of 5, 6 or 7 18650s cells in series. I’m putting 7 in there because when discharging the cells down fully they will give 3.5V, so 3.5*7=23.5V, pretty close to 24V but not sure how important this is. My only worry with doing this is when fully charged at 4.2V so 4.2*7=29.4V it would be too much for the amp so I would have to get a voltage step down for this. Also with all of the protection circuits they all seem to have cut off voltages of around 2.5V per cell so again this seems to defeat the purpose of the over discharge protection for what I’m trying to do. The example below also has an overcharge cutoff voltage of 4.325V and I know you should only charge each cell to 4.2V. Does this all mean that the purpose of this circuit is more of a backup protection circuit and you still need to use a full on balancing charger as well as over discharge alarms to know when the cells are fully drained..

An example of a 7S protection cell I’ve found, most of them are similar to this.

https://www.ebay.com/itm/PCM-Protection-Circuit-Module-BMS-22A-7S-25-9V-Li-ion-Li-Po-battery-7S22W001-/321784266292?hash=item4aebd63e34 .

 

Option 3

Still using 5, 6 or 7 18650s cells in series and create my own cutoff circuit with adjustable voltages so I could set it to 3.5V, e.g https://youtu.be/1Fs4SfVSsLk. This seems quite complicated as I’m quite new to electronics but could probably give it a go and get some help from someone local. I would need to convert it to 5, 6 or 7 cells, whatever I use and may need a bit of help with that. I could use my Turnigy Accucell-6 50W 6A Balancer/Charger (which I already own for drone batteries) if I was using 5 or 6 cells to charge it (it doesn’t support 7S). This would work but whenever took the speaker somewhere like on holiday I would have to take the charger aswell, which could be a bit inconvenient. This method does have the advantage that I could use the cutoffs circuit display as a bit of a battery percentage monitor, though it wouldn’t mean anything to anyone else who looked at it and would probably confuse them a bit. So far I’m thinking this is the best method but not perfect.

https://hobbyking.com/en_us/turnigy-accucell-6-50w-6a-balancer-charger-lihv-capable.html?___store=en_us

 

I'm very open to other options like getting a 24V battery that has all of the electronics and everything done for me inside it but I can’t seem to find any that aren't massive and weigh multiple kg but please send me some links if you can. I swear I’ve seen some in videos before but can’t remember where.

 

Please comment on as much or as little as you know and I’ll keep everyone updated with how it goes.

 

A huge thanks to everyone who got this far and really looking forward to what you have to say.

 

Josh

[bob345]

For the drivers, id go with the 4 ohm ones. Lets you get a bit more power out of the amp at the expense of a bit of efficiency. for power i would just go with 4 18650's in series with a protection and charging circuit like this https://www.amazon.com/SMAKN®-Lithium-Battery-Charger-Protection/dp/B018JVE2FA

You dont want to run these tiny amps at the max rated power though, they wont last long pushed like that. Alternatively you could use a rc lipo pack, but you need to be more careful around those than your average 18650. Looks like you already have most of it figured out. Ive used those dayton audio drivers before and they are pretty great imo.

[Josh6066]

Ok thanks, I'll use the 4 ohm ones, if I go with 4 18650's in series or maybe even create a 4S2P for more battery life and that charging controller would I have to stop the discharge of the batteries at around 3.5V or do I just use the speakers until the charge controller kicks in at 2.5V. This doesn't sound like a good idea to me because I was pretty sure you had to stop at around 3.3V-3.5V. Also I presume I would just charge this with my balance charger. Thanks for your help

[DrowningFish]

This looks really cool. I am not good with working with audio components, are you going to make a post of how it turned out?

[Josh6066]

I can just post in here how it turned out if you would like or for anyone to see. Or do you think I should make a new forum.

[myselfolli]

8 minutes ago, Josh6066 said:

I can just post in here how it turned out if you would like or for anyone to see. Or do you think I should make a new forum.

Post it here, it should be fine ^^