Tranquili-T


Idea: Peter Neufeld (Germany)

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 a Tranquili-T in action.

 
Tranquili-T circuit
Figure 1
 

We can be brief about the power supply: anything that supplies 4.5-5 VDC is usable. For example, three 1.5-V batteries are a possibility, but remember that the LED draws about 20 mA and the player draws about 50 mA at an average sound level. A USB power bank can provide good service; then you don't have to worry about dead batteries.

MP3 players with integrated Class-D amplifiers are preferred for simplicity. The author has had good experiences with the JQ6500 and the DFplayer Mini. These are available at decent prices from the usual suppliers in the Far East. Figure 1 shows two options for volume control in a box. The variant with S2 and S3 uses two digital inputs; the variant with S4 and S5 one analog input in combination with two different resistors. The values ​​drawn in the diagram apply to the JQ6500. Probably some experimentation is needed here, supported by information from the datasheet and the Internet.
 
Inside the design
Figure 2
Regarding the loudspeaker, use one 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 4Ω one.)
 
Tranquili-T in all its glory
Figure 3

Figure 2 shows the "guts" of a copy built around the DFPlayer Mini. Figure 3 finally shows a Tranquili-T in all its glory.
 

Want more? Check out these other small circuits.