The ASA16 integrated circuit by Interstate is a 16-channel audio spectrum analyzer for speech recognition systems. If you are lucky enough to pick one of these up they can be lots of fun for making a visual spectrum analyzer system.
To build an interface circuit for the ASA16 requires first building several other sub-circuits, such as a 1 MHz. clock source and a voltage inverter which were mini-projects in and of themselves. A block diagram showing all the sub-circuits for this project is shown to the right along with the completed circuit on a breadboard.
We built the circuit entirely out of CMOS chips for power and flexibility, and used a +9VDC power source (6 AA batteries).
Because it is designed for speech recognition the frequency response range is more limited than, say, the spectrum analyzers you'll find on a stereo system. Stereo spectrum analyzer displays typically range from 25 - 10KHz, while the ASA16's range is linmited to a typical speech range of 250 - 6KHz.
The ASA16 has 16 output channels and 1 MUX channel. Our circuit utilizes only the lower 8 channels as they were the most visually pleasing. We chose not to use the MUX channel because we were experimenting with the different channels directly. Utilizing the MUX channel would eliminate some of the circuitry. Regardless, we hope our experimental circuit helps out anyone who might come across one of these unique chips.