I'm trying to cobble together a circuit which will play back a digitised sample (for use as a doorbell).
Do any of you know of any circuit designs or kits or ideas that might be of use? The best idea I can come up with is a DAC chip fed by an EEPROM clocked by a couple of counter ICs, but I'd rather not reinvent the wheel if I don't have to.
I've done quite a bit of searching (Googling) and checked quite a few hobbyist sites for circuit diags but no luck yet.
To make it sound good, you need significant filtering on the output from the DAC. There are quite a few chips that will do this for you (including the control for the memory, DAC, and filtration all in one package). Some are designed for both recording and playback, while others are designed to use ROM, and playback only. Have a look at:
These use CVDS encoding, which gives better storage use for speech, and software is available to encode a sample from an PC audio card into this format. Harris used to do a sound playback chip, but I don't if this is now available from anyone. Yamaha do some synthesiser chips like this, but they are rather 'up-market'. There are a number of recent chips that do this from MP3 encoded deta, giving much higher efficiency for storage use. Winbond, does a unit called the 'ChipCorder', which is a single chip solution (has it's own internal memory), and is the basis of many units like the audio recording 'pens'.
I had a look at the various ICs, some of them look pretty good and I can get them locally (although the fidelity looks a bit low - they keep talking about "voice optimised".)
I had a think about using a PIC but I know bugger-all about them and I'm not set up with the programmers or anything, maybe I should actually look into this a bit more because some of the projects I've seen with them are so much easier to do than discrete logic.
Your comment about mp3 set me thinking... maybe I should just look for a junky old 2nd-hand mp3 player (say a Rio 600 32MB) and wire that in. I guess the start-up delay might be the killer there... a 5 second delay after pressing the doorbell ain't gonna cut it.