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QRZ! Ham Radio 19
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QRZ Ham Radio Callsign Database - Volume 19.iso
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kpc3_1.txt
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2001-11-01
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Subject: KPC3 power and reset changes
From: Warren Stone <ar772@chebucto.ns.ca>
KPC-3 battery backup and reset
Along with upgrading my KPC-3 mailbox and node to 512k, I have added two
other features. One is a battery backup and the other is an external
microprocessor reset. Both of these are very useful for using the TNC
at a remote site.
Normally the TNC is powered via the DB25 connector from the same 12 volt
power supply as the VHF radio. Instead of simply putting jumpers at
J8 and J9 as described on page 96 of the manual, I have placed a single
1N914 diode from J8 pin 2 to J9 pin 1. The cathode connects to J8 pin 2.
The 9V battery is installed as well. It has another 1N914 diode in its
positive lead, sealed with heat shrink tubing. The cathode side connects
to the BATT+ terminal on the PC board. The DC power connector is NOT used.
In this configuration the 12V supply powers the TNC under normal use. If
power fails, the internal 9V battery will take over. The diodes prevent
current from the DB25 power input from charging the 9V battery as well as
preventing a heavy current drain from the 9V battery to the VHF rig when
power is lost. Of course the station will be off the air, but the 9V
battery will ensure the TNC clock continues to run and remains accurate.
The second mod is even easier. A single wire will allow an external
microprocessor reset to the KPC-3. Instead of using the hard reset line,
as described in the manual, I decided to use a microprocessor reset. A
hard reset will return all paramaters to default values, wipe all memory
contents, and you will have to go to the site to reprogram everything. The
microprocessor reset will act as if the power is shut off and back on. No
memory contents or parameter settings are destroyed or changed. However all
connections will be lost. By placing a ground at the junction of R35 and
R49 the microprocessor is reset. R35 and R49 are to the side of the power
switch near the front of the circuit board. Look at page 125 of the manual
for placement. R49 isn't actually installed in the board, and a
convenient hole is provided. Place a wire from the empty hole to pin 2 of
J9. You will then have a reset line on pin 7 of the DB7 connector.
The reset control is provided by a homemade DTMF controller board. The board
also has a control code to disable the PTT circuitry of the transceiver, and
another to enable it again. This is useful in the case of interference.
Finally a second watchdog circuit provides added security. I can provide
more information on this circuit to anyone interested.
Send a message to VO1KS @ VE1BBS.NS.CAN.NA if you have further questions or
comments.
73 de Warren VO1KS