Reverse Engineering Space Invaders Sound Chip

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.

7 thoughts on “Reverse Engineering Space Invaders Sound Chip

  1. 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!

    1. 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.

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