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 Mini-TNC: A 1200 Baud Radio Modem using PIC16F88

Mini-TNC: AN APRS/Packet  TNC. (Obsolete)

Now Revised to Mini-TNC-1217 (with Metal Case)


 Mini-TNC Rev0711 with Firmware V1.09

A Simple PIC88 based APRS TNC: Rev0711

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. Send & Received APRS data to COM port.

3. Supports "Converse Mode" and Packet/APRS with Version 1.09 firmware by Dennis/N5VRP

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 may be powered by either +5V from USB (J3) or from D9 Radio connector with +8 to 12V DC. In this case, 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. You will require a serial cable to configure internal parameters of the PIC88

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 for Mini-TNC is available at 4800 & 9600baud and its at V1.09 provided by Dennis/N5VRP.  Please refer N5VRP Document for more details on new firmware compatibility with your PC.

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. 

However, a modification to previous design is made keeping in mind varied audio levels. In this design (Rev0711) you may feed receiver audio direct to PIN17 of PIC88 or route thru MPC6023 active filter.

Mini-TNC Rev0711 Document

1200 baud modem using MX614

V1.09 Formware Details by Dennis/N5VRP

1200 baud modem using MX614

Mini-TNC Rev0711 KIT Parts List

1200 baud modem using MX614

Rev0711 Schematic & Parts List

1200 baud modem using MX614

Configuration Document

1200 baud modem using MX614

Using Hyper Terminal of Windows

1200 baud modem using MX614

Mini-TNC Rev0711 Schematic



1200 baud modem using MX614

N5VRP Firmware V1.09



With this modem, you can use many software available either as a freeware or shareware. Please go thru following links & find one suitable to your communication requirements.
Digital Communication Software Collection
Digital Communication Software links
Understanding Digital Communication



This project is now Revised to Mini-TNC-1217 (with Metal Case)
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