Fullscreen HTML5Med Res (??MB)HTML4

Adding shuffle feature to low-cost MP3 player module I had a few friends over during Christmas, and to provide background music, I had my stereo amplifier connected to a CD player. After a while, I got sick and tired of getting up to put on a new CD. I decided that I wanted a way to play at least 10 CDs worth of music with reasonable quality so that each track was randomly played. I came across the Jaycar XC3748 MP3 audio module at $14.95, which plays audio files on a TF/SD card. It also has a serial communication interface (UART) that can be used to control which music tracks are played and in what order, plus six pushbuttons to control the basic functions like play, pause, previous, next track and level adjustment. There is also a USB interface to enable you to add music files from your computer. Its headphone jack provides a stereo output at the right level to directly connect it to an amplifier. It uses the YX5200-24SS processor, which provides reasonable music playback quality and, at 77 x 33 x 8mm, it can be mounted in a small utility box. Looking at the data sheet, I found that if you sent the serial code “7E FF 62 Silicon Chip 06 18 00 00 00 FE E3 EF” (hexadecimal) at 9600 baud, the module would play the tracks in a random order, as I wanted. All I needed was a simple microcontroller circuit to generate the code. The accompanying circuit diagram shows what I came up with. The unit is powered from a standard 12V or 9V DC power pack. This feeds linear regulator REG1 to produce 5V DC for the Jaycar module and the microcontroller. To start playing music in a random order, the Random start button must be pressed, taking input pin 5 (GP2) of the PIC12F617 micro high. The 100nF capacitor across the switch eliminates contact bounce. This positive level causes the random playback code listed above to be sent to the Jaycar module’s RX input. If you look at the data sheet for the module, you will see many other commands that can be sent. For example, you could ask it to play a particular track. If you are into coding, this would be a simple modification. After converting my CDs to MP3 format and copying them onto a FAT32 card, which I inserted into the module’s socket, I mounted the playback Australia’s electronics magazine module and my circuit in a small plastic utility box. I fitted three pushbuttons to the top of the box: random start, next track and previous track, plus an on/off toggle switch and a power indicator LED. On the side, I added a socket for the 12V power input and a hole for the jack plug lead connecting it to the stereo amplifier. On the side next to the USB socket, I cut a rectangular hole so that a USB cable can be plugged into the Jaycar board. This enables you to add or erase music files from the micro SD card without having to open up the box. The next track and previous track switches on the utility box are wired in parallel with the associated switch on the Jaycar board. These switches can also be used to adjust the volume. Holding down the previous button reduces the volume, while holding down the next track button increases it. Note that the random play button always cases the first track to be played. If that annoys you, jump to the next track by pressing the next button. Les Kerr, Ashby, NSW. ($80) siliconchip.com.au