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A Simple PIC88 based APRS TNC:
In this project, special
attention is paid to get an economical APRS TNC with minimum
current consumption and simple task:
1. A stand alone TNC to replace
MX614 Modem chip
2. Route received data to COM
port suitable for aprs.
3. A Fix Station Position encoder
for APRS. (BTEXT)
Mini-TNC is a PIC88 based TNC which decode aprs
packets & route to COM port. Mini-TNC has two D9 connectors for outside communications. J1, a
D9F is
provided for your transceiver. J1, another D9F is for connection to your
PC using a simple serial cable to output your received data to your
PC for further processing.
Mini_TNC require a supply of +12V (+7-12V) at
DC connector J3 or same may be supplied at Transceiver connector J2 at
PIN 7. An internal regulator (78L05) provides +5V for digital
circuits. Current consumption is well below 20ma (Depending on LEDs)
which is good enough for most remote solar powered locations.
Mini-TNC uses a standard RS232 driver to interface
with your PC. A null modem is required for configuration of PIC88's
internal parameters, such as your callsign, Btext and if you want a
digi enabled.
Project
is
designed
on 10cm X 6cm Double
Sided PTH
board and
results
were very
encouraging. A free metal case is avail;ble with kits or
assembled.
PIC firmware is at 4800 baud. It should be
noted that since no input audio preset is onboard, audio level
supplied to this tnc may require careful adjustment of received
audio from radio.
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