I have been spending the past couple of days prototyping up a new version of my Micro Pulse Rifle (uPR) counter board. This one has sound.
I had a brainwave the other day. Instead of designing a two-unit system as I had been planning - a really powerful sound board coupled with the less powerful counter board, I thought "Why don't I try and tweak the design of the existing counter board to make it give sound?" - so I did.
In some senses the new design is less capable than the old one. The main chip I am using on it now is of a family tier below that of the old chip. Before it was a meaty PIC32 chip (32 bit MIPS processor). Now I'm using a dsPIC33 (16 bit Microchip proprietary CPU). Less memory, less CPU power, but most importantly a built-in 16-bit audio DAC. That really was the biggest problem before - I had to use a really powerful MCU (the PIC32MZ) coupled with an I2S CODEC chip. To keep size small I had to find a CODEC chip with a built-in amplifier. Otherwise the chip count would be just too high.
But now with the DAC built in to the MCU I am free to choose from a much wider range of amplifiers. So I did. The TPA3132, which in mono "Parallel Bridge Tied Load" mode, can pump out a massive 50W, and measures just 5mm square, is an ideal candidate, though possibly overkill (if there is such a thing...). However there is the little brother, the TPA3131 which is the same chip but less power if it proves to be too much.
I've also improved the on-board voltage regulator so that it should be easier to run from higher voltages (needed for the amplifier to work at its best), though heat may still be an issue if you have too high a voltage - that remains to be seen.
And the amazing thing? I didn't change the overall design at all. It looks (apart from there being more chips on it) the same as the old version. It did mean me using a 4-layer PCB though, which puts costs up. As does the extra chips.
I'm just about to order a batch of prototype boards to see if my design works (the proof of concept does, but lacks the amplifier), and if it's good then I will start selling them. I have to work out how much for yet though...
Update: The prototypes arrived, and I've built one up. There is only one error in the design, but that's very very easy for me to work around with a microscopic blob of solder, so no problem.
Apart from that they're perfect! And talk about loud (assuming you have a big speaker of course, but you won't get one into a pulse rifle alas...)
I also have the LEDs for testing, and they're really bright too. Just waiting for the LED driver boards to arrive, as well as the speakers I'm going to test. My next job I guess is to make a video of the board in action, and that means trying to find my workbench...