From "66 programmi per ZX81 e ZX80 con nuova ROM + hardware" by Gaetano Marano in 1982.
https://archive.org/details/66programmi ... 5/mode/2up
2007 release (single side PCB):
http://zx81.ordi5.free.fr/brico/son/index.htm
2024 Release:
(8Bits outputs + 5 octave sequencer)
Release 0 (Kicad project r.8):
http://abandon.pcbs.free.fr/jackson/octavia
(temporary release, I had to place a Reset button to clean the buffer at the startup...)
Links (stefano):
https://www.sinclairzxworld.com/viewtop ... f=3&t=1791
3D rear case STL:
translate.google:
With an expense of less than 10,000 lire, you can connect to the ZX80 and ZX81 computers
(via the Interface circuit already described in the previous chapter) a
music card capable of producing 50 musical notes on 4 octaves through simple
BASIC instructions.
The main purpose is to allow the computer to produce music,
but this card lends itself to many other uses such as for example sounding games,
producing alarm signals, and, in any case, to insert acoustic notes into programs
wherever it can be useful.
The circuit (fig. 169) uses three common TTL-LS integrated circuits plus a 555 timer, a
2N2222 transistor and a few other passive components.
The configurations of the four integrated circuits and the transistor are in fig. 170.
The circuit
can be mounted on a piece of printed circuit board already drilled.
It is essential that the resistors are all at 5% (1/4 W), that the 4700 pF capacitor is of the 5 - 10 % maximum polyester type,
that the TTLs used are of the LS series and finally that the Trimmers are of good quality and possibly of the encapsulated type
(like the black and white Trimmers from PHIER) so that the calibration is not modified by accidental impacts.
The ten inputs (+5V, A ..... H, GND) of the music card thus created must be connected by ten pieces
of three-colored wire to the corresponding ten output terminals of the Interface circuit (fig. 171),
taking particular care not to reverse the connections that go to the + 5V and GND outputs.
The average current that the music card absorbs from the computer power supply ranges from 30 mA at
minimum volume to 65 mA at maximum volume.
The consumption can be reduced and the sound power can be increased by removing the transistor and
the speaker and connecting the output of the music card to a more powerful and externally powered audio
amplifier (fig. 172). The calibration of the 50 frequencies of the music card must be carried out by adjusting
only the six trimmers (tml...tm6) in order to obtain certain output frequencies, the seventh trimmer (tm7)
is used to adjust the volume, there is also a slide switch (SW1) which is used to mute the sound.
To carry out the calibration, it is necessary to connect a digital frequency meter to the "DFM" output of the music card
(see fig. 169) and run the following program on the computer:program needed to avoid writing the POKE 9999,n
instruction at each note.
After pressing RUN and NEWLINE, the six calibrations must be carried out according to the order indicated in Table 4, first introducing code 199 and adjusting the trimmer tm 1 so as to have an output frequency as close as possible to 523.25 Hz,
then continuing with the introduction of the other five codes and with the adjustment of the corresponding trimmers
so as to obtain the frequencies indicated in the table.
When carrying out the calibration, be careful to enter the six codes exactly and not to make a mistake in choosing
the trimmer to adjust each time, another important thing is to adjust the trimmers with a screwdriver without hitting the
other trimmers already calibrated and above all without touching the trimmers or other wires or exposed contacts
or pins of the integrated circuits with your hands, this is because the resistance of your fingers
could distort the reading on the frequency meter and consequently the precision of the entire
calibration. At the end of the calibration it is a good idea to re-check the six frequencies by re-entering the
six codes in Table 4, always using the CALIBRATION ROUTINE already exposed, a routine that is also useful later
to listen to the 50 notes that the card can produce.
The 50 notes together with their standard frequencies and the corresponding POKEs to perform to obtain them are
shown in Table 5, in the same Table the POKE (9999.15) to be performed to have a PAUSE is also indicated, that is,
no note or frequency emitted.
If the calibration has been carried out carefully, the precision of the 50 notes should be better than 0.5 - 1 % compared
to the standard values indicated in Table 5, the circuit used for the music card, in addition to precision, also has
excellent stability although it is not quartz but with resistance and capacitor.
Table 5 also shows the hexadecimal codes of all the notes and of the Rest, useful codes for making strings
containing long sound or musical sequences more compact within the programs.
Programs
The music card is certainly the most interesting circuit in this book, so 4 programs are dedicated to it
in this chapter on music and 14 sound effects programs in the next chapter.
In addition to music and to produce sound effects, the music card can be used in many other programs
wherever it may be necessary or useful to add sounds.
In this same book, there are some examples of such applications in the chapter before this one,
where the card is used as a sound monitor for the telegraphy key, and in the last chapter where
the card allows you to create games with sound too.
string A$ is different from 271 the program does not work, to check that you have inserted all
the codes and spaces, simply insert line 111 into the program (fig.174), then run the program
and stop it with the BREAK button; once