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Easy 4 channels * 8 bits Covox C/A for Atari 8bit
by: Gumi/Tight
mfranczak@ajax.umcs.lublin.pl
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List of needed items:
chips:
1 * 74LS138
4 * 74LS574
resistors:
36 * 1.2 kOhm
28 * 2.4 kOhm
capacitors:
4 * 100-220 nF
To pins of chip 74LS138 you must to attach this signals:
pin 1 - A0
pin 2 - A1
pin 3 - R/W
pin 4,5 - $D6 (page $d6 decoder)
pin 6 - o2 (fi2)
pin 8 - 0V - GND
pin 12 - to clock of #4 C/A
pin 13 - to clock of #3 C/A
pin 14 - to clock of #2 C/A
pin 15 - to clock of #1 C/A
pin 16 - +5V
other pins - not connect
You must to do 4 C/A, like this one:
---. .---
| | | |
GND>--|1 '-'20|----|2 19|-->----R1----* R1 is 1.2 kOhm resistor
| | R2 R2 is 2.4 kOhm resistor
D1>--|3 18|-->----R1----* C is 100-220 nF capacitor
| | R2
D2>--|4 17|-->----R1----*
| | R2
D3>--|5 16|-->----R1----*
| | R2
D4>--|6 15|-->----R1----*
| | R2
D5>--|7 14|-->----R1----*
| | R2
D6>--|8 13|-->----R1----*
| | R2
D7>--|9 12|-->----R1----*-----C--->out analog signal
| |
GND>--|10 11|-------*
|
out #4--->-----*---------- LEFT channel
out #2--->-----*---------- RIGHT channel
|
out #3--->-----*
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