Bingo on the annunciators and the button inputs.
But I did intercept the TTL output of the speaker flipflop. That is a much cleaner signal than what comes out of the AC-coupled speaker amplifier, and it is readily available on a solder pad intended for an integrated audio amplifier chip that was never populated on the Apple//e boards.
This TTL level is actually full of digital noise, as you would expect, so it is used to drive an inverter powered by a "quiet" +5v level created from the +12v supply to the audio processor board. The output of this inverter is clean, and is mixed with other similar outputs prior to being filtered by a three-pole Sallen-Key lowpass filter to eliminate the 22.05kHz PWM pulse frequency.
-michael
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Experience indicates that copyright law will always be adjusted so that Mickey Mouse never enters the public domain.
-michael
"The wastebasket is our most important design tool--and it's seriously underused."
Bingo on the annunciators and the button inputs. But I did intercept the TTL output of the speaker flipflop. That is a much cleaner signal than what comes out of the AC-coupled speaker amplifier, and it is readily available on a solder pad intended for an integrated audio amplifier chip that was never populated on the Apple //e boards.
This TTL level is actually full of digital noise, as you would expect, so it is used to drive an inverter powered by a "quiet" +5v level created from the +12v supply to the audio processor board. The output of this inverter is clean, and is mixed with other similar outputs prior to being filtered by a three-pole Sallen-Key lowpass filter to eliminate the 22.05kHz PWM pulse frequency.
-michael