This circuit has no expressed or implied warranty of any kind.
It works very well for my IC-735 and with three different computers.
It has not been used on any other Icom radio but should be compatible
with a number of other desktop models.
BUT
!! USE IT AT YOUR OWN RISK !
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This design uses a chip designed to produce both the + and - voltages required
by RS232 from a single +5 volts, and incorporates two receiving and
transmitting inverters which meet the RS232 specifications. The only other
chip needed is a buffer which allows its output to be driven from another
source.
A circuit drawing is presented below. In words, the implementation is:
ICL232 Chip
Pin 14 is output to RS232 Pin 3; Pin 13 is input from RS232 Pin
2; Pin 11 is tied to 7417 Pin 2 and to a 270 ohm resistor, the
other resistor connection is tied to +5V; Pin 12 is tied to 7417
Pin 3.
ICL232 Chip
Capacitors. C3 + lead is tied to Pin 2, C3 - lead is tied to
+5V; C1 + lead is tied to Pin 1, C1 - lead to Pin 3; C2 + lead is
tied to Pin 4, C2 - lead tied to Pin 5; C4 + lead tied to GND, and
C4 - lead tied to Pin 6.
ICL232 Chip
VCC is Pin 16 which is tied to +5V. GND Pin is 15 which is tied
to ground. All leads not mentioned should be open.
7417 Chip
Pins 2 and 3 are tied as discussed above. Pins 1 and 4 are
connected together and to the center pin of a 1/8" plug for
connection to an Icom radio.
7417 Chip
VCC is Pin 14 which is tied to +5V. GND is Pin 7 which is tied to
ground. All leads not mentioned should be open.
The ICL232 chip uses an internal oscillator to create the +- voltages by
voltage doublers (which require C1 and C2). Pin 2 is a +10V source, Pin 6 is a
-10V source (but are not connect to anything is this design). The Transmitters
(Tx) and Receivers (Rx) meet RS232 specifications. One source of the ICL232
is: DigiKey Corp., Thief River Falls, MN 56701-0677 -- 1-800-344-4539. Price
approximately $4.80.
The 7417 is an open collector buffer chip. This allows a buffer output to be
driven from another source, and is compatible with the Icom IC-735 internal
pull-up circuit. Designs which use 1488/1489 chips, where the Icom
input/output lead is tied to a buffer output (in a similar manner to this
circuit), violate chip specifications.
In this diagram "+" means "cross", that is, no connection; '*' means
connection.
.----------. ---------------
| .---+-| 1 16 |---- +5V
| +| | | |
+| C1 --- --| 2 +10V 15 |----- GND
C3 --- --- | |
--- | | Tx Out 14 |------> RS232 Pin 3 .---> RS232 Pin 7
| ------| 3 | |
+5V .-----| 4 Rx In 13 |------< RS232 Pin 2 GND
+| | |
C2 --- | Rx Out 12 |-----. +5V
--- | | | |
| | Tx In 11 |--. | R
------| 5 | | | |
.------------| 6 -10V 10 | ---+---* -----------
| | 7 | | | .----| 1 14 |--- +5V
C4 --- | 8 9 | | -----+----| 2 13 |
--- --------------- ---------+----| 3 12 |
+| ICL232 *----| 4 11 |
GND | | 5 10 |
| | 6 9 |
C1, C2, C3, C4 = 47 uF | .-| 7 8 |
R = 270 ohms | | -----------
| GND 7417
Optional Regulator |
----<> ICOM-Radio
-------------
| |
13.8V >-*--| IN OUT |----> +5V
| | |
C5 --- | | C5 = 0.1 uF
--- | |
*--| Common | In words: Tie 13.8V to the Input Pin and to a
| ------------- 0.1 uF capacitor connected to ground.
GND 7805 Tie the Common regulator pin to
ground.
The Output Pin is +5V.
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