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Adventures in making a type 76477 Complex Noise Generator synth
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README.md Added chip pinouts and howto Feb 3, 2020
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README.md

The SN76477

Is a complex sound generator in the form of a monolithic chip produced by Texas Instruments in 1978. If you played Space Invadors or Sheriff it was this chip that gave you the sound effects.

Being a kid of that time, and one interested in sounds and music, I felt building up a synthesisor around this chip was a good way to learn electronics. This repo is my own private Idaho and hopefully it's of some use to you.

Footprint

Layout

The chip is a 28-DIP and has the following measurements:

  • 1.78 Mm (0.07 In) Pitch
  • 10.16 Mm (0.40 In) Span
  • 25.15 X 8.89 X 5.08 Mm Body

Looking inside the chip via an X-ray is cool

Layout Layout

I've created an Eagle library of the above, so you can just import it into your project and use it straight away.

Breakout Board

To make this work better with modern bread boards, you need a breakout board in order to connect all the various components up to.

Layout

Eventually this will be turned into a fully-fledged PCB

Pin Functions

  1. Envelope Select (input)
  2. Ground
  3. External Noise Clock (input)
  4. Noise Clock Resistor
  5. Noise Filter Control Resistor
  6. Noise Filter Control Capacitor
  7. Decay Control Resistor
  8. Attack/Decay Timing Capacitor
  9. System Enable
  10. Attack Control Resistor
  11. Amplitude Control Resistor
  12. Feedback Resistor
  13. Audio Output
  14. VCC
  15. Envelope Select
  16. Mixer Select C
  17. Mixer Select A
  18. Mixer Select B
  19. One-Shot Control Resistor
  20. One-Shot Control Capacitor
  21. VCO Select
  22. Super Low Frequency OSC. Control Capacitor
  23. Super Low Frequency OSC. Control Resistor
  24. Pitch Control
  25. VCO Control Resistor
  26. VCO Control Capacitor
  27. External VCO Control
  28. VREG

How The Magic Happens

The SN76477 has the ability to create complex signal waveforms by combining a number of outputs. These outputs (low frequency oscillator and voltage-controlled VCO) added to a selected envelope and manipulating the signals attack, decay, sustain and release (ASDR) results in some beautiful noises.

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