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CIRCUIT NOTEBOOK
Interesting circuit ideas which we have checked but not built and tested. Contributions will be
paid for at standard rates. All submissions should include full name, address & phone number.
Portable amplifier built from modules
One of the things I like about Silicon
Chip is that some of the articles published give me ideas for future applications. A good example of this is the
El Cheapo article on Class D amplifier
modules (May 2019; siliconchip.com.
au/Article/11614). Several problems
about the particular amplifier described
were identified in that article.
I searched online for a better unit,
and found a TPA3116D2-based 2x50W
+ 1x100W power amplifier for less
than $20, including delivery. The layout of the components on the board
was different from the one shown in
the article; I suspect it is an improved
version. It seems to have none of the
problems described in the article.
The specifications for this amp quote
a working voltage of 12-24V, but the
data sheet for the TPA3116D2 IC shows
that it will work down to 4.5V. I could
80
Silicon Chip
not find a voltage regulator chip on the
board, so I tested the amplifier at lower
voltages and found that it worked without any apparent problems.
With that in mind, I used this amplifier board, in conjunction with two
other modules, to make up a radio,
Bluetooth and MP3 player that is powered from a nominally 11.1V Li-ion
battery pack. The pack I used contains nine 18650 cells arranged in a
3S3P configuration (three sets of three
paralleled cells connected in series).
I bought this second-hand, and it has
built-in cell protection and equalisation modules. It can be charged using
a standard 12V DC, 1A regulated plugpack. That charges each cell to 4.0V,
which is close enough to full charge
voltage (4.2V) for my needs.
Australia’s electronics magazine
The other two modules I used are a
12V-powered MP3 decoder board with
Bluetooth, USB, SD card and FM radio
support. It also came with a remote
control, and cost just $6. The remote
control allows for input selection and
volume control.
Earlier versions of these MP3
decoder boards were sold as running
from 5V, so would need a regulator in
my circuit. But later ones are rated to
run from a voltage as high as 12V, and
still work well at lower voltages.
I also bought an 18650/26650 Li-ion
battery tester, which shows the battery
voltage and load current, for just $10.
I decided to incorporate it in my unit
to make checking the status of the battery pack easy.
I mounted all these components
(battery, amplifier, MP3/Bluetooth/FM
module and voltage display) inside a
large ABS plastic box I bought from
Jaycar.
I added speaker connectors stripped
from a dead amplifier so that external
speakers could be easily connected. I
sourced some speakers from my local
op shop for $2 each, and the sound
isn’t too bad. With the battery between
9-11V most of the time, it can be wound
up far too loud for an average room.
Larger (and better) speakers can be
connected to improve the sound quality, making it into a portable outdoor
unit with a lot of grunt.
I sourced the on/off switch and
5.5mm DC charging socket from Jaycar.
The internal wiring is quite straightforward, as you can see from the circuit diagram. I used hot-melt glue and
a mixture of nuts and machine screws
for a quick and straightforward build.
I gave the finished device to my
granddaughter as a Christmas present in 2019. It has worked flawlessly
for the last eight months, and she has
only had to charge the battery four
times! She tells me she charges the battery when it stops working. She usually connects her mobile phone using
Bluetooth, but occasionally uses other
input methods.
Sid Lonsdale,
Whitfield, Qld. ($100)
siliconchip.com.au
The MP3 decoder/FM module ►
incorporates the display. While most
current versions of this module are
powered from 12V, earlier versions
used 5V and so a separate regulator
is needed. The amplifier controls
(below the display) are from left-right:
left/right channel volume; subwoofer
adjustment; total volume control.
The amplifier is the smaller device
sitting below the twin JVC speakers.
Larger speakers (up to 50W) can
easily be used if needed.
►
A close-up of the display of the ►
18650/26650 Li-ion battery tester
module. It displays the battery voltage
and load current.
The internals of the portable amplifier are shown above at larger than actual size. The power amplifier module measures
approximately 100 x 85mm and is sold for about $20 including postage online. Note that this TPA3116D2-based module
has a power-on artifact which induces a pop noise on all speakers even when muted.
siliconchip.com.au
Australia’s electronics magazine
August 2021 81
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