page_title: Texas Instruments SN76477
section_title: Overview
hierarchical_section_title: Texas Instruments SN76477 / Overview
caption_attribution_description: English: This is a re-draw of a demo circuit for the 76477 sound generator chip.
context_page_description: SN76477 "complex sound generator" is a sound chip produced by Texas Instruments. The chip came to market in 1978, and TI ceased production of the part. A 100% compatible version, identified as ICS76477, has been listed as 'in stock' by at least one US-based component stockist. The chip is typically used as a sound effects generator in arcade games and toys and for hobby projects. The use of the SN76477 in a musical context is limited by the fact that it was difficult to electronically control the pitch of the produced sound.
context_section_description: The following quotation summarizes its facilities:
  [T]he SN76477 generates complex audio signal waveforms by combining the outputs of a low frequency oscillator, variable frequency (voltage controlled) oscillator (VCO) 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.
  There were two different sizes of the SN76477 available. The SN76477N was in a standard 0.6 in (15.24 mm) width dual in-line package (DIP). The SN76477NF was in a less common 0.4 inch (10.16 mm) width DIP.
  The text below is intended to explain the use of the 76477 in the demo circuit shown at the right.
  SW1 is a five position rotary switch that selects which capacitor controls the one-shot circuit that sets the envelope timing.
  SW24 (toggle or momentary) is the one-shot trigger switch, closed position is active.
  R1 a one megohm linear potentiometer sets the actual one-shot timing (in series with fixed 27k resistor R2) within the range selected by SW1.
  SW2 is a five position rotary switch which selects which capacitor sets the range for the low frequency oscillator (SLF oscillator in future references).
  SW3 (toggle or momentary) is the switch used to turn the low frequency oscillator on or off.
  R3 a one meagohm linear potentiometer (in series with 27k fixed resistor R4) sets the actual frequency for the SLF oscillator.
  SW4 (toggle or momentary) is the switch that takes control of the voltage-controlled oscillator's (VCO) duty cycle (called pitch control). If the switch is off the VCO operates at 50% duty cycle by default.
  R6 a 50k ohm linear potentiometer is used (in series with a 50k ohm fixed resistor R5) form a voltage divider used to set the VCO duty cycle, the on time vs off time of the waveform (most variable inputs to this chip are looking for a resistance, this input looks for a voltage). The source voltage for this voltage divider (R5 & R6) is the five volt busbar.
  SW6 is a four position rotary switch which selects which one of three resistors (or no resistor) sets the range of frequency for the VCO.
  SW5 (toggle or momentary) is the switch that turns the VCO on or off.
  R8 is a one megohm linear potentiometer (in series with 27k fixed resistor R7) which sets the actual frequency of the VCO (within the range selected by SW6).
  SW7 is a six position rotary switch which selects which of six capacitors also sets the VCO frequency range.
  SW8 (toggle or momentary) is the switch that selects either an internal voltage control or an external voltage control for the VCO (if set to the external input with no input connected then there is no extra VCO control).
  R12 a 50k ohm linear potentiometer is used (in series with a 50k ohm fixed resistor R13) form a voltage divider to set an internal voltage to mimic the action of an external VCO input. The source for this voltage divider is the five volt busbar.
  SW9 is a five position rotary switch which selects which resistor to set the audio output level (called out as amplitude control resistor on the chip pinout).
  SW10 (toggle or momentary) is the switch that enables attack timing. If this switch is open, there is no attack slope (tone is instant on). If this switch is closed the attack slope is set by R24 (within the range selected by SW11).
  R24 is a one megohm linear potentiometer (in series with a 27k fixed resistor R23) which sets the actual attack timing (within the range selected by SW11).
  SW11 is a six position rotary switch which selects which of six capacitors also sets the limits of the timing of the attack and decay envelope generator.
  SW12 (toggle or momentary) is the switch that enables delay timing. If this switch is open, there is no decay delay slope (tone is instant off). If this switch is closed the decay slope is set by R24 (within 
caption: A redraw of a demonstration circuit used to try out most of the capabilities of the 76477 sound chip
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