MAX232 Level Converter
Yaesu VX5r programming interface
Two Transistor Level Converter
PLRI circuits
MAX232 Level converter
The MAX232 chip has a retail price under $5.00 US.
You can use this interface to computer control many radios and projects. This circuit is practically the same as
Icom's EXPENSIVE ($139.95 US as of March 2005) CT-17 level converter, both use the MAX232 chip.
You may want to power your MAX232 via your PC or even from a radio, as the typical current draw is just 5ma. The data sheet is available from the
Maxim/Dallas web site. If you rely on a PC for
power, you may find out that your level converter does not work with some PCs (especially laptops).
This is due to the PC's serial port not meeting the RS-232 specification. You should also be careful
not to short the supply line from the PC or radio, or overdraw it. You risk damage to the PC, radio, or both.
I decided to power my unit independent of the PC and radio. I included a 5 volt regulator on the PCB and installed a power connector on
my project box. This will allow operation with all PCs and radios. A 6 volt wall wart from a discarded cordless telephone
powers the unit. For mobile/portable use, a simple 9-volt battery would suffice, or I could use vehicle power instead.
I wanted this level converter to be capable of performing many tasks, such as Icom CI-v, so I used a three-terminal
(stereo) 1/8" (3.5mm) jack for the TTL/CMOS connections. To use this converter for a new task, I simply
build a new cable!
For Icom CI-v applications, combine TxD and RxD onto the tip of a 1/8" (3.5mm) mono phone plug. The ring is used for ground.
To control multiple Icom radios using one serial port, mount multiple 1/8" jacks on your project box wired in parallel (as Icom does), or
use audio-type 1/8" mono y-adapters.
For the EF Johnson radio programming cable, I used a standard CAT5 cable with RJ45 connector on one end, and a
1/8" (3.5mm) stereo connector on the other end. The RJ45 connector must be ground down to fit the socket on the
EF Johnson radios. I start with a bench grinder and finish with a file.
While this plan is specifically for programming EF Johnson mobile radios,
it can be adapted for just about any project requiring a level converter, such as Icom CI-v.
See below for a special schematic for programming the Yaesu VX5r radio.
Click on picture to enlarge image.
Completed MAX232 Level Converter in project box
Two Transistor Level Converter
Use any NPN transistor. See above for wiring details for Icom CI-v. I've heard some reports that
Icom radios may not communicate over 9600 baud with this interface. Try setting the baud speed on your
Icom to 9600 if it doesn't work at first. Believe me, 9600 is plenty fast for CI-v!
This one's even easier to construct! I built and used this level converter
first because the MAX232 is not readily available in my area.
Click on picture to enlarge image.
For radio control software, I use Ham Radio Deluxe (FREE!).
Click picture below to visit the HRD web site.
This site requires a frames-compatible browser for proper page viewing. If you're having
trouble viewing this page, or want to visit the non-frames page, click
here