C O D I N G
(C) Ivan Roshchin
Tell vampires "No!"
The fan needs to suck
mosquitoes through the drive.
Folk wisdom.
Yes, yes, it will be exactly how
use a computer to deal with these
bloodsucking creatures - though not so
cruel way, as in the epigraph. :)
I read recently an interesting note [1]
about how one music radio station
adds to its broadcast audio
signal mosquito deterrent. There
mentioned that the frequency of this signal
12.3 kHz. And I decided to try
generate such a signal by
his ZX Spectrum.
Here is the first version of the procedure: the signal
played through the loudspeaker.
; When the CPU clock 3.5 MHz
, One period is, 3.5 * 10 ^ 6 / 12, 3 * 10 ^ 3
, ~ = 285 cycles (a precise, the value 284.55).
; Let the duration of one
; Halftime to 142 cycles,: and others -
, 143.
DI
M1 LD B, 8, 7
DJNZ $; 7 * 13 +8 = 99
INC HL; 6 130 +12 = 142
LD A, 16; 7
OUT (254), A; 11
LD B, 9, 7
DJNZ $; 8 * 13 +8 = 112
INC HL; 6143
LD A, 0, 7
OUT (254), A; 11
JR M1; 12
But the second option: to generate
signal is used musical
coprocessor.
CHAN EQU 0; Using. Channel :0-A, 1-B, 2-C.
VOL EQU 15; Volume (0-15).
LD HL, # FFBF
LD C, # FD
; When clocked at 1.75 Coprocessor
; MHz frequency divider value must tone
; Be equal to 1.75 * 10 ^ 6 / (12.3 * 10 ^ 3 * 16) ~ = 9
, (The exact value of 8.89). Taking it in
; Registers tone frequency:
LD B, H
LD A, CHAN * 2
OUT (C), A
LD B, L
LD A, 9
OUT (C), A
LD B, H
LD A, CHAN * 2 +1
OUT (C), A
LD B, L
XOR A
OUT (C), A
And includes the output tone frequency:
LD B, H
LD A, 7
OUT (C), A
LD B, L
LD A, # FF
RES CHAN, A
OUT (C), A
; Setting the volume:
LD B, H
LD A, 8 + CHAN
OUT (C), A
LD B, L
LD A, VOL
OUT (C), A
RET
Since music coprocessor
operates independently of the main
processor, by executing this procedure,
You can continue to work with programs
do not address the coprocessor, and no sound
will be interrupted.
Both procedures form the signal
simple rectangular shape. But the form
the original signal is much more complex: how
mentioned in [1], it takes 1 Mb
format Real Audio. Therefore, useful
the effect of using these procedures
may be lower than expected. Interesting
it would be if someone would share his
results: it helps or not?
Fido: 2:5020 / 689.53
ZXNet: 500:95 / 462.53
E-mail: asder_ffc@softhome.net
WWW: http://www.ivr.da.ru
