Elektor_Mag_-_January-February_2021

lektor January & February 2021 53

idea: Peter Neufeld (Germany)

Tranquili-T
The big ideas and projects resulting from the
efforts of an electronics enthusiast are, unfor-
tunately, not noticed by friends and family —
that DIY oscillator or servo controller can’t
really be called a crowd pleaser. However,
the soothing Tranquili-T by Mr. Neufeld has
received much praise, resulting in him build-
ing several devices to give to friends and
acquaintances.

The circuit (see Figure 1) is built around a
cheap MP3 player loaded with soothing music
or, for example, the sound of surf or birds.
The soothing effect is then amplified with a
rainbow LED that provides subdued lighting
in a dark room. A video from the author shows
the Tranquili-T in action [1].

We can be brief about the power supply:
anything that supplies 4.5 to 5.0 V can be
used. For example, three 1.5 V batteries
are an option, but remember that the LED
draws around 20 mA and the player draws
a further 50 mA at an average sound level.
A USB power bank is a good option, as then
you don’t have to worry about dead batteries.

MP3 players with integrated Class-D ampli-
fiers are preferred for simplicity. The author
has had good experience with the JQ6500
and the DFplayer Mini. These are available at
reasonable prices from the usual suppliers in
the Far East. Figure 1 shows two approaches
for implementing the volume control outlined
in seperate boxes. The variant using S2 and S3
uses two digital inputs; the variant using S4
and S5 uses a single analogue input in combi-
nation with two different resistors. The values
drawn in the diagram apply to the JQ6500.

Some experimentation may be required here,

supported by information from the datasheet

and the Internet, with other MP3 players.

With respect to the choice of loudspeaker,

select a model that is as small and flat as

possible with a load capacity of at least 0.5 W

and an impedance of 8-32 Ω. (It turned out

that the volume was too high when using a

4 Ω speaker.) Figure 2 shows the ’guts’ of a

version built around the DFPlayer Mini while

Figure 3 shows a completed Tranquili-T in

all its glory.

Small Circuits Revival

From the Elektor suggestions box

Compiled by Eric Bogers (Elektor)

No appetite for tackling a big project? That’s fortunate because here we have a few more

small circuits that are easy to build and perfect for keeping those ‘January blues’ at bay...

mini projects

BAT

S1

R 3

150...220

4V5...5V

500mAh

D 1

LS1

500mW

R 1

3k3

R 2

6k2

S2 S3 S4 S5

V–, < V+, > V–, < V+, >

MP3

200557-001

4...32

PLAYER

Figure 1: The heart of the circuit is realized with an MP3 player (module).

Figure 2: The electronics can be built compactly

on a small piece of prototyping board.

Figure 3: The final Tranquili-T in all its glory.