I stumbled across this little module which had everything you need to build a simple
Bluetooth module. So I got one and built this – which I think is the simplest Bluetooth
speaker that you can build for less than 7 dollars. In this video, I am going to show
you how I built it and we are also going to take a closer look at the modules themselves.
There are three variants available and if you plug a micro USB cable into two of them,
then you can use them as a USB sound card to play music from your computer – which
is an added bonus. I received the main PCB itself along with
two speaker cables and 2 connectors for the PCB which can be soldered in place. The PCB
design looks very simple and all the logic and operation is handled by this big IC that
is labelled MH-M38. The two smaller ICs are 5 watt amplifiers, one for each channel which
means that the total power output is 10W which again is not at all bad. I couldn’t find
the datasheet for the amplifier but the product listing gives us the information that we need.
It can drive speakers that have an impedance of about 2-8 ohms and that can handle 3-5
watts of power. Going back to the PCB, you have the Bluetooth
antenna, a 24MHz crystal, a micro USB port and 3 additional pins that are used for power.
You can power the module in 3 different ways: one using the onboard micro USB connector
which is the simplest way to go about with it. You could also connect an external 5V
supply directly to this pin here. The module can also work from a 3.7V lithium battery
which can be connected to the terminal marked VBAT. This diode is used to isolate the two
power supplies but as soon as you connect a USB cable to the board, the VBAT pin gets
a voltage of about 5V minus the diode drop which is too high for a lithium battery and
it could damage it. I would recommend using only one power supply at any given time to
avoid any conflicts. If you want to use a battery then make sure you use an additional
protection board like the TP4056. Now that you know more about the board, it
is time to test it so I started soldering the speaker connectors and also soldered the
wire to the speakers themselves. I am using these compact, 3w, 4ohm speakers that are
commonly available. Ideally, you should be using 5W speakers but I do not have them with
me and using smaller ones is going to be okay as long as you don’t turn the volume all
the way up. 6 watts is still loud enough for me so I am going to stick with these for now.
I then connected the speakers to the module and powered it ON using a USB power supply.
The first thing I noticed is that there was a bit of a thump as the module was powered
ON. You might be able to view the speaker drivers moving rapidly when power is applied.
This is not very healthy for the speaker and I would not use this with expensive speakers
but since this is a DIY project, it is acceptable. Most commercial amplifier use a relay to disconnect
the speakers and this is then activated after one to two seconds which gets rid of the thump.
The welcome chime was actually the best one I’ve heard from a Bluetooth speaker module
so far. There was a slight hiss in the audio and I am not sure if the mic is picking it
up right now. You might not notice this so it probably would not be an issue for you.
I tried using different power supplies and it’s been the same so I’m guessing it
has something to do with the module itself.
Moving on, and it showed up on my phone with no problems what so over and pairing was a
breeze as well. Once again, the tone was pleasant which is a nice touch. It was time to test
it out with some music and this is where things got interesting. Not only did it sound very
clear and much better than I expected, I noticed that it retained a lot of the low frequencies
which I definitely like. I am not sure if you can notice the speaker diaphragm bouncing
about with the beat but there is definitely a lot of movement there even at low volumes
which gives it a nice full sound. A speaker enclosure plays a huge role in enhancing the
final audio and that is why I would recommend adding one to it. We will look at this later
in the video. Now that the Bluetooth section was working,
it was time to test out the USB feature. All I had to do was plug it into a computer
and it immediately showed up as a new sound card. The Bluetooth feature is automatically
disabled when you connect it to your computer. There were no issues whatsoever when playing
audio from the computer and this means that you can build yourself some very nice computer
speakers with this module. Let’s talk about the three variants that
are available, they are called M18, M28 and M38. M18 is the bare minimum version that
only contains the Bluetooth chip and it is priced at one dollar, 23 cents. If you want
to embed this onto a PCB then that would be the one to get. You can also add a couple
of additional buttons to control the tracks and so on. They all are connected to a single
pin but use different series resistors which means that the chip is using some sort of
a voltage divider network to determine which button is pressed. This is very clever and
it can be useful for future projects. With the M18, you will need to connect an external
amplifier module, which means that you can use a high-powered amplifier like the OEP30W
to drive even bigger speakers if you like. The M28 is similar to the M18 module but it
adds a micro USB port along with a 3.5mm audio jack. This means that you can use it as a
USB sound card and also connect the audio output to headphones or another speaker system.
The M28 is available for about one dollar and 45 cents. The M38 is the one that I am
using and which costs one dollar and 64 cents. The reason I decided to use this one is because
it has the amplifier ICs which simplifies the entire build. I’ve already spoken about
the features of this module so let’s jump straight to building the actual speaker.
I built this modular speaker system a long time ago and that was pretty bulky as I used
the electronics from a kit. I still like the enclosure so I decided to use two of these
speaker enclosures and mount the module inside. Here’s what we will need for the enclosure
section – the speaker boxes, front plates, side panels and 17 M3x8 screws. I also wanted
to add a switch to the speaker so I would need a pushbutton switch, a micro USB breakout
board for power along with some wire to connect it all.
This was definitely one of the easiest builds on this channel. First, I soldered some wire
to the micro USB breakout board. Then, I had to wire the switch in place so I cut off the
additional pins that I would not be using. This is how it needs to be wired in place.
5 volts from the micro USB breakout board passes through the switch, before going to
the M38 module. You can use this reference diagram to view how everything comes together.
Once this was done, it was time to prepare the enclosure so I used an old soldering iron
to create two holes at the back – one for the USB port and the other for the pushbutton
switch. I created much bigger holes than needed so that I could push the board and switch
a bit further out to make it easier to access them. It was then time to glue the switch
first, followed by the micro USB breakout board. While this half was drying, I decided
to start assembling the other half. I first pushed the speaker in place, added the front
cover and then screwed in the 4 screws to hold it together. I then had to add the side
cover, and screw it in place using 3 screws. Once all that was done, this half was complete.
I then had to glue the board in place, so I held it down and applied some hot glue around
it. This is the end result after it dried and all that was left to do was connect the
two speaker and close it all. I first stacked the two halves together and used 3 screws
to attach them together. I then plugged in both the speakers, starting with the one that
was already attached to the unit. I then used the front cover and some screws to attach
the second speakers to the unit. This was then followed by attaching the side cover
to complete the build. The end result is a very compact and decent looking speaker. You
could probably do a much better job at attaching the switch and micro USB board. It was now
time to test it so I connected a micro USB cable and pressed the switch to hear the power
ON chime, followed by the successful pairing chime. The speaker definitely sounds much
better with the enclosure – this is both an improvement in the overall loudness and
tone.
And there you have it, a compact, cost effective and very easy to build DIY Bluetooth speaker
system. If you are looking to get started with electronics or if you want to encourage
someone else then I think building a Bluetooth speaker like this one is a nice practical
way to begin. I do hope this video was useful for you. Don’t forget to subscribe if you
haven’t already. Thank you for watching and I will see you in the next one!