Early on in my love of electronics I ran across the Texas Instrument SN76477N Complex Sound Generator IC, and it was love at first project. Up to that point my sound effect projects mainly consisted of a simple transistor oscillator with a monostable vibrator ( such as a 555 or 4011 quad nand wired as a pulse generator) triggering a capacitor bleed from the transistor's base. Laugh if you will, but it could generate some cool sound effects.
But then the SN76477N came along. Suddenly I had access to a real sound processor, with an envelope and the works, at my disposal. Man, this was one fun chip to play with. With a few analog parts and some patience one could build a full on synthesizer. The super chip featured a super low-frequency oscillator, voltage-controlled oscillator, noise generator, and a mixer. Sweet!
[T]he SN76477 generates complex audio signal waveforms by combining the outputs of a low frequency oscillator, variable frequency (voltage controlled) oscillator, and noise source, modulating the resulting composite signal with a selected envelope and, finally, adjusting the signal's attack and decay periods. At each stage, the process can be controlled at the programming inputs of the signal modification and generation circuits, using control voltages, logic levels, or different resistor and capacitor values.
– Lou Garner, Solid State, Popular Electronics magazine, October 1978
Even today, with any number of micro controllers at your disposal, one would be hard pressed to duplicate the exact sound the chip provides. Now, you may ask, why am I taking this troll down memory lane? Well, it appears that BG Micro is again offering the chip for sale, and only for a modest $8.99. Given the ease of working with the package and simplicity of construction this would be a great project for anyone interested in electronics. But to show you how easy this chip is to use, below is a typical schematic to have the chip make explosions or gunshot sounds, taken from the application PDF.
So, there you have, a great simple low cost project that can both entertain and possibly bring back memories. What more can you ask for in a quick project? Not bad for a chip that dates back to 1978. We're talking the golden age of disco, baby!
