Several of you have successfully built and used this circuit. Here are the
latest modifications suggested and a few more words of explaination.
CIRCUIT FUNCTION:
The FT990 needs control signal levels of 0v to +12V, but the PC LPT port
provides 0 +5V levels. This interface does both the level conversion and
booleans needed to control the PTT, DVS0, & DVS1 as )mostly) intended by
the CVB software.
The ON-AIR switch allows you to record and test your messages without
transmitting. When you are satisfied with the sound, close the switch.
CHANGE REQUESTS:
Has anyone found a way to make the "transmit while recording ON-OFF"
provided by the CVB sortware and eliminate the ON-AIR switch?
Has anyone used it successfully on the FT1000?
Has LTA decided to make this cable available? (I'll accept a small royalty)
When the PC resets the LPT hardware at boot time, the FT990 goes into
permanent transmit with some I/O cards! Some have found that moving the
emitters of the two NPN transistors to the Strobe line avoids this. The
schematic below shows this change, but I have not tested it yet.
Another fix is to load the CVB software, then unload it with the /U switch.
This is what I do.
DESCRIPTION OF FUNCTION OF FT-990 DVS PORT:
PTT DVS0 DVS1 Function
"1" "0" "0" Receiver Audio at Voice Out Voice In muted
"0" "0" "0" Voice Out and In both muted
"1" "0" "1" Transmitter Mic. audio at Voice Out, Voice In muted
"0" "0" "1" Transmitter Mic. audio at Voice Out, Voice In muted
"1" "1" "0" Voice Out muted, Voice In signal at Receiver Audio output
"0" "1" "0" Voice Out and In both muted
"1" "1" "1" Voice Out and In both muted
"0" "1" "1" Voice Out muted, Voice In signal at Receiver Audio output
and Transmitter Audio
LEGEND:
"0" means pin at 0V, "1" means pin at +12V.
WIRING DVS PORT 8-BIT SOUND BLASTER FOR USE WITH LTAs "CONTEST VOICE BLASTER"
Pin# Name Description
1 VOICE IN Input from Sound Blaster Speaker output. ~Line level.
2 VOICE OUT Output to Sound Blaster Mic input. ~Line Level.
3 PTT Push To Talk line. Internally pulled up to +12V in rig.
4 +12V Power Supply. +12V.
5 DVS0 DVS control line. Internally pulled down to 0V in rig.
6 DVS1 DVS control line. Internally pulled down to 0V in rig.
7 GND Ground. 0V.
SCHEMATIC:
to Sound Blaster Mic input-+
from Sound Blaster Speaker output----+ |
(USE A 1:1 TRANSFORMER) | |
+12V +----^-----^-------+
| | | \>| 2N3906
| | | |----+-----+
| | O /-| \ \
+--------++---^--O4 2 5O----+ / /
2N3906 |</ | +-O1 3O-+ \ 330 \ 330
+--| | O6 7O | SW / /
\ |-\ | | ^ | | ON AIR \ \
/ | | | DVS | | ___| | |
\ 330 | | | | +-O O----+ |
/ | | | | | |
\ | 2N3906|</ | | | |
| +-------| | | | |
| \ |-\ | | | |
| / +-----+ | | |
| \ 330 | | |
| / | | |
| \ | | |
| | | | |
| +----------------------^-------+----+ |
| | | |
+----------------------------^-------^----------+
| | |
Printer Port pins 18-25, Ground---------------+ | |
| |
1000 |/ 2N3904 |
Printer Port pin 3, D1-----------/\/\/--------------| |
|\ |
1000 > |/ 2N3904
Printer Port pin 2, D0-----------/\/\/-----------------^-------|
| |\
| >
| |
Printer Port pin 1, Strobe ----------------------------+----------+
AE0M, Tony Becker - becker@shell.portal.com - Silicon Valley, U.S.A.
--
Submissions: na-user@eng.pko.dec.com
Administrative requests: na-user-request@eng.pko.dec.com
Problems: reisert@eng.pko.dec.com
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