August
2004, Issue 169
Ham
Radio Repeater Locator
CONSTRUCTION
The
circuit is straightforward (see Figure 3). I built the
system using a single-sided breadboard with holes on
0.1" centers. The solder side of the board has
horizontal traces connecting all the holes in a row.
I find that using this breadboard yields a much neater
layout than using one that just has holes with no traces.
Use a Dremel tool to cut the traces when necessary.
A magnifying glass or microscope makes the procedure
easy. You can purchase the blank board from Radio Shack
or other suppliers.
|
(Click
here to enlarge)
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Figure
3—There are two regulators, one for 5 V to run the
LCD and another for 3.3 V to run the microcomputer.
An optically isolated interface to the Icom CIV
programming bus is used to reduce receiver noise
caused by ground loops. The ubiquitous MAX232 is
used to interface to the PC serial ports. (The data
line currently isn’t used.) The microcomputer can
be programmed with Zilog software by connecting
the debug line to a serial port on your PC. |
Surface-mount
resistors, capacitors, and transistors can be mounted
on the circuit side of the board. Through-hole components
can be mounted on the other side. Components and jumpers
are aligned vertically.
An
option for construction would be to use the Zilog Z8F642
evaluation kit, which includes a full C compiler, a
simulator, program/debug interface hardware, and a board
containing most of the required circuitry. A breadboard
area could be used to add the few remaining parts. At
$40, this system represents a real bargain. The Zilog
board includes a Z8F6421 microcomputer part, which is
a pin-compatible replacement for the Z8F6401 used in
the HRRL. No software changes should be required to
use the latter part.
Note
the R2 resistor labeled near the optical isolator. You
may need to use a resistor here in order to speed up
the rise time of the isolator. By experimenting, I found
that a 100-kW resistor was needed with the particular
isolator I used.
