Speaker and audio
Contents |
The basic Sound section
The Spectrum 48 sound is very basic, and the computer will work without it. This provides only the 48K sound, the 128 Sound requires a AY-3-8910 chip, which will be done later.
Theory
The Speaker, and Tape in and out are all handled from the same pin on the ULA. This has the downside that when saving or loading, sound will come out of the speaker. They are all controlled by seperate pins on port $fe however, so if this gets too annoying, it can be re-implemented without using the ULA which we can seperate the ports. For the moment, we are using the original schematic version.
Schematic
The changes I made were as follows:
- I used a MPS2369 transistor instead of the original ZTX450 Mainly because no-one has made ZTX450's for years.
Finished product
The board i made contains all the circuitry. Note that the input terminals are 0v, Audio, +5V, and the output are to the speaker.
Testing
Full testing involves testing all three parts.
- The Beeper can be tested by entering "Beep 1,1"
- The "Ear" can be tested by saving a file and seeing if you can hear it using headphones plugged into "mic"
- The "Mic" output can be tested by trying to load a game.
