YAESU--VX-7-Computer-Interface.pdf

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For the West Somerset Amateur Radio Club
VX-7/5R Computer Interfacing
by Bas Helman G4TIC
Introduction
Having recently acquired a Yaesu VX-7R handheld with a heavyweight manual and a
complex and laborious data entry procedure I sought an easier option. By using the
rig’s Clone facility it is possible to download pre-prepared, but editable, lists of
memory data including repeaters, offsets, CTCSS tones, broadcast and other bands
from files posted on the Internet to the rig via a computer to PC linkage. In addition it
is possible to alter the rig’s frequency coverage for use when travelling abroad.
There is a commercial package available consisting of a customised lead and software
but this costs between £40-50 and doesn’t allow band adjustments. There are free
software packages available for download which do the same job and more so the
problem reduces to providing the interface cable. The software I chose to use is VX-7
Commander V 1.3.3 by Jim Mitchell KC8UNJ available from
http://mywpages.comcast.net/sllewd/vx7rmain.htm
then select the [PC Hardware]
link.
Whilst there are a number of interface circuits available on the internet these are
generally designed for the VX-5R. Fortunately the circuit required is the same for
both rigs but the plug required for the VX-7, a four section jack with a screw in fitting
to preserve the water tight feature of the rig, is unavailable as a separate commercial
product. I tried to cobble a jack together from a standard four section plug but as I
filed it down to the necessary diameter it fell apart. No one said amateur radio should
be easy! The solution was to buy Yaesu’s accessory breakout lead the CT-91. A
similar product can be had for the VX-5R ,the CT-44, but a standard four section jack
would probably work plugged directly into this rig as there is no need for the screwed
section.
The next problem was to choose a circuit to convert from the RS232 voltages to those
of the rig. So far I have tried three circuits one with no success another with partial
success (it communicated in one direction only) and the one documented here with
complete success. Testing continues on these problem circuits and any break-through
will be reported at a later date.
What follows is my attempt to collect together in a single document the essential
information for completing the project. I have provided a matrix board layout for the
chosen circuit and, hopefully, some encouragement and tips for the reluctant or novice
home constructor.
The Circuit
The circuit I have used is a six transistor design with a number of desirable features:
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The components are cheap and readily available
The circuit is powered from the computer’s RS232 interface so no
separate power supply is required
As it is constructed from discrete components it is both easy to test and
to maintain.
The Circuit Design
The Matrix board Layout
The layout was compressed to fit into an aluminium “u” box measuring
75x50x25mm.
The Solder side of the Board
Components list for VX-7R Interface
Q1
Q2
Q3
Q4
Q5
Q6
Q7
D1
D2
D3
D4
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
TO-18, 2N2222
TO-18, 2N2222
TO-18, 2N2222
TO-18, 2N2222
None!
TO-92, 2N3906
TO-92, 2N3906
Si-diode, 1N914
Zener-diode 500mW, 5.1V
SI-diode, IN914
Si-diode, 1N914R8
Resistor, 47K
Resistor, 47k
Resistor, 10K
Resistor, 12K
Resistor, 470K
Resistor, 47K
Resistor, 47K
Resistor, 47K
Resistor, 100K
Resistor, 100K
There are ten jumpers to be positioned according to the matrix board layout.
If you source your 2N3906 from Maplin the pin out is not the TO-92 indicated but the
TO-92b variant! Yes I had to revert to the transistor tester to find out!
Construction
A few tips for those of you unfamiliar with matrix board.
•
•
•
•
•
Mark out the size of board you require
Score both sides of the board with a craft knife
Snap to break to length
Remove the rough edges with the knife or a file
Before mounting any components clean the copper tracks with a BrilloPad and
dry
The usual order of construction is to start with the lowest profile components and
work systematically to those of the highest profile. I find it easier, when working
with matrix board, to start from the left-hand side and work towards the right ignoring
component size. This results in less hole counting. (Left-handers would reverse the
direction).
A soldering iron tip of 2.5mm is ideal for this work.
The only specialist requirement for constructing with matrix board is a device for
cutting the copper tracks. A spot face cutter is available from Maplin’s, at a price.
Fortunately there are many convenient alternatives. A drill bit set into a piece of
dowelling makes a very effective tool as do some reamers – check your Swiss army
knife. For a small project like this digging the track away with a craft knife is a
practical alternative.
Once the board is complete and working the project needs to be boxed. A cheap light
weight aluminium or plastic box is all that is required. In either case I find it easier to
drill the necessary holes undersize and then open them up with a reamer. This results
in a much neater hole for the grommet. If you have a set of chassis punches you have
no need to read this! Pass the leads through the grommets and secure them with a few
dabs of superglue. The board itself can be fixed by nuts and bolts, double sided
adhesive foam pads or hot melt glue - just avoid shorts
Paste a scaled down circuit diagram in the lid of your box for future reference.
The only test equipment you should require is a multimeter to check resistance,
voltages and continuity.
The Completed board

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