Wavefront (formerly Alesis) have developed a very low-cost DSP chipset (the 1K) for the mass audio market, that has great possibilities for applying DSP to amateur radio. It's a 24-bit device, and thus has plenty of dynamic range. To go with it are a 24-bit DAC and ADC. The three chips sell in small quantities for about $15! The Wavefront 1K development software may be downloaded free from their web site.
I accordingly bought some chips from Profusion, the UK distributor, and, having perused the documentation, set about designing a simple development system that could also be used as a standalone DSP. I decided to use the little 16-lead AL3102 DSP, interfaced to an Atmel AT90S2313 micro-controller. The ADC and DAC are interfaced to the DSP, with their analogue I/O circuitry (two op amps). The 2313 handles comms to/from a host system such as a PC, running the development software, and also handles DSP program/data loading, and programming of an EEPROM, for standalone operation, with the 2313 reading code from the EEPROM and loading it into the DSP. An RS-232 interface (external drivers required) is provided, the same I/O lines may also be used for an LED and push-button.
To keep it simple, this system is intended only for mono applications. A stereo version will be available subsequently.
Here is the PCB design for the prototype:
The board is four layers, normally quite expensive, but not too bad in this case because it is so small. It also made the layout very easy and minimises unwanted emissions. I've had some prototypes made, here is one of them partly assembled and waiting for me to test the loading of the DSP from the microcontroller: