Ham Radio
Ham Radio, Electronics, Software and more...

Home » Ham Radio Mods » Icom Mods » ICOM IC-735 RS232 Interface to meet RS232 Specs (ICOM IC-735 RS232 Interface to meet RS232 Specs)
ICOM IC-735 RS232 Interface to meet RS232 Specs [message #3074] Sat, 07 March 2015 22:49
root is currently offline  root
Messages: 207
Registered: December 2004
Senior Member
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 !
D. W. Bray, K2LMG -- Clarkson University

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.


Previous Topic: ICOM IC-735 Add Remote Control
Next Topic: ICOM IC-32AT Out of Band Mod
Goto Forum:
  


Current Time: Thu Nov 23 15:28:22 EST 2017

Total time taken to generate the page: 0.03619 seconds