I have constructed the TTL to RS-232 interface for the Kenwood radios and now have it working. Until I get software I am using a terminal emulator to talk to the Kenwood. I thought others might be interested in the interface. Any comments would be welcome. Joe Wilkes att!hound!wa2sff ____________________________________________________ The following is a diagram for an RS-232 to TTL converter for use with the Kenwood series of radios. I built the interface and have transmitted and received data between the computer and the TS-140. Parts list: 1 1488 1 1489 1 7404 1 1K resistor 1 rs232 connector 1 six pin connector for kenwood (radio shack) 1 box 1 power supply with +5v, +12v and -12v. 3 IC sockets 1 perf board misc. wire, nuts, bolts, washers, bypass capacitors (0.1 ufd) Notes: 1) I had to invert all TTL signals to make the interface work. The data with the computer interface for my TS-140 would lead me to believe that I only had to invert the CTS and RTS leads. If you have trouble making the interface work correctly try removing the inverters. 2) An RS-232 break-out box is useful in debugging the interface. 3) Cn means computer interface lead n. 4) Rn means radio interface lead n. 5) Someone told me the Kenwood interface is optically isolated but I don't hear any more RFI from the computer with the interface connected than with the interface disconnected. 6) For best results use shielded cables between the computer and the converter box and between the converter box and the rig. 7) Bypass the +5v, -12v, and +12v to ground near each IC. Typical values are 0.1 ufd or higher capacitor. Deluxe approach--- 0.1 ufd and 10ufd in parallel. RADIO-TTL COMPUTER RS-232 1 GND--- GND---1 2 TXD--- TXD---2 3 RXD--- RXD---3 4 CTS--- RTS---4 5 RTS--- CTS---5 6 NC --- +5v--1K res------DSR---6 GND---7 1488 -TTL to RS-232 ___________ 3 |. 4 | | R2----| .------|2 3|-----C3 |. | | 7404 | | | 6|-----C5 9 |. 8 | | R5----| .---|--|4 | |. |--|5 7|-----GND 7404 | | |_1___14__| | | | | | | -12v +12v 1489 - RS-232 to TTL ___________ | | 1 |. 2 C2--------------|1 3|-----| .-----R3 | | |. 7404 | | | | 5 |. 6 | 6|-----| .-----R4 C4--------------|4 | |. 7404 | | | | |_14_____7| | | | | | | +5v GND six pin connector on radio (viewed from rear) 3 o 2 o o 4 o 1 o 6 o 5 ||| --- key Joe Wilkes att!hound!wa2sff