Sometime last fall my son got a kid's toy which would play this really annoying 10 second bleep bloop loop (anybody with kids know what I'm talking about). After torturing the family with it for a few weeks I decided drastic measures would be in order. So I devised a plan to replace the electronics inside the toy with a SD card player of my custom design.
Basically the design consist of a SD card adapter, an ATmega328P microcontroller (I love using these chips), R-2R resistor DAC, op amp for buffering and low pass filtering and a TDA7052A power amplifier (see the schematic at the end for details). The design itself is quite simple, but making the PCB for this one was quite tricky because I'm making my own PCBs and they have to be single-sided. Also in this case, the space inside the toy was quite tiny and the PCB had a lot of rounded shapes.
Instead of a lengthy write up I'm going to present this project as a series of images. Here we go!
|The toy opened showing the original PCB
|Paper prototype of the new PCB. I wanted to be extra sure that everything fits
nicely inside the cramped enclosure.
|Exposure mask printed on a transparent sheet
|UV exposure process in progress. I made the UV exposure box myself a few years ago.
|Etched PCB before cutting. I had to do some manual fixes using a pen before
etching because I made some errors during UV exposure process :)
|Cut, drilled and painted PCB. It fits, huzzah!
I used a Dremel to cut the board. I had this idea of painting the PCB with a matte grey spray
and I really like the result so I'm probably going to use it in future projects too.
|PCB with all components soldered in place. There was no room for the LED and
SD card adapter (right) so they are on separate boards sandwitched on top of the main PCB.
|Schematic made in Eagle CAD
Finally here's how it looks and sounds in action. The 8 GB micro SD card is currently loaded with 50 songs with plenty of space left for more songs! Anyone recognize the song? :)