It seems the cat protector project documentation has a small gap. There is just a hint that you have to use some scripts to prepare the SD card to play the audio files, but no details about this.
To use the scripts you need some knowledge how to use a command line interface on your operating system. The scripts are very simple to use on Linux and Mac OS X, but on Windows it is very tricky. I strongly advice you to use either Linux or Mac OS X. If you are working on Windows, just use a free virtual machine application and install a Linux (I suggest Ubuntu) or a Linux live CD where you don’t have to install anything.
Why? …. Why … that … complicated
The used microcontroller is not very fast, if the software on the microcontroller also has to deal with a complicated filesystem, no sequential blocks and other obstacles, changes are small to produce sound output in a good quality. Therefore I prepare the samples in a very simple format and instead of a complicated file system, I just store the blocks with the audio data sequentially onto the SD card.
The LM386N-1 I used before worked well, but has some disadvantages. There was a hearable distortion in the sound and I needed more amplification to create the required loudness.
I found the TDA 7052 chip, which was formerly produced by Philips, but now by NXP semiconductors. It contains everything required for an amplifier. You just have to supply power, the input signal and there are two outputs to connect the 8Ω speaker.
The updated schema looks like this:
I also added a trimmer to adjust the volume of the output. The value of the trimmer is missing in the schema. I used a 47kΩ trimmer, but a 10kΩ trimmer will work fine as well.
If you own a cat, you know even if your cat is well brought-up, laws are only valid as long you are at home or even in the same room. The goal of this project was to create a small device, which detects movement in protected areas (e.g. tables) and speak your usual phrases in your voice to the cat.
I documented a working prototype of the project in the hope to share some knowledge and give some ideas how certain details can be solved. It contains schemes for all hardware parts and a detailed description of all software parts, including a minimal implementation of a SD card access.
Please feel free to ask, if you do not understand a part, or if you have any suggestions where to extend the documentation or clarify parts.