Around here, a new blog post from [Ken Shirriff] is almost as exciting as a new Star Trek movie. This time, [Ken] tears apart a 76477 sound effects chip. This chip was state-of-the-art in 1978 and used in Space Invaders, along with plenty of other pinball machines and games.
[Ken] started out with a die photo from [Sean Riddle] and mapped its functions. Unlike a modern sound chip, this one created sounds based on networks of attached resistors and capacitors. Even if you aren’t interested in the chip, per se, [Ken] explains how the die implements active and passive devices, along with some key analog design principles like current mirrors (although we are pretty sure he got his right and his left mixed up, or maybe it was a very subtle mirror joke).
Before electronics magazines were full of computer projects, they were full of music synthesis projects and the 76477 is like a crude synthesizer on a chip. It has voltage controlled oscillators (VCOs), and generates envelopes with specific attack and decay times to create the sounds of interest.
This reminded us a little of the sounds from the more advanced MOS6581. [Ken] has looked inside a lot of ICs, including at the 2016 Hackaday SuperConference.
Radio Shack (RIP) carried this chip in their blister pack IC series back in the early 80’s. I finally got one and wired up a primitive synthesizer. That was a lot of fun to play with!
The SN-Voice went and added a not-too-large pile of external support hardware to make it actually a musically usable analog synthesizer (e.g. with standard 1V/oct input).
Picking up a complete set of the component drawers next Saturday. RIP Radio Shack.
I hope you find some nice loot in your Radio Shack drawers.
Here’s a 76477 that came from Radio Shack back in the day. Chip is dated 1979.
http://www.wrljet.com/freecycle/SN76477.JPG
I bought one because I was interested in electronic music. Unfortunately, I knew almost nothing about electronics. But I’d unfold the data-sheet, read it, and after a while it started to make sense, so it actually became a portal for understanding electronics.
I built a few simple circuits with it, but the linear VCO pretty much killed any fantasies of making a musical device out of it.
Amazed that there are still some of these around, nearly 40 years later.
Hey, this is pretty cool stuff… I learned a thing today.
Al, you’re correct: I had left and right reversed. For some reason the spell checker didn’t catch that :-)