PIC-Encoder (PIC-E), is a general purpose encoder based on the PIC16F84 PICmicro® microcontroller The PIC-E is a design concept to provide generic interface between the digital world (in the form of serial data streams) and the packet radio world (in the form of AX.25 packets) and is fully programmable by the user. The user can program the PIC microcontroller to take serial data from a GPS receiver or weather station and transmit it as formatted packet frames. Virtually any data that can be provided to the device as a serial input stream can be reformatted and transmitted as 1200 baud packet radio. 

The PIC-E is relatively inexpensive idea because its based on only two chips: a Microchip, Inc. PIC16F84 microcontroller and a MX-COM, Inc. MX614P Bell 202 modem chip. The PIC16F84 is a general purpose "computer on a chip" that can be programmed and reprogrammed over and over by the end user. The PICmicro can be programmed to receive an incoming data stream and reformat it for transmission as AX.25 frames. It sends the resulting data to the MX614P that generates tones necessary to transmit 1200 baud packet over the radio's audio channel. The MX614P is a particularly interesting chip to use for this application because it also contains an "energy detect" circuit. If receive audio is routed to the MX614P, it can determine whether the channel is in use and send this information back to the microcontroller. As a result, no additional VOX or carrier detect circuit is required to prevent the PIC-E from colliding with other channel users. The MX614P can detect both digital signals and voice, so it is suitable for applications where digital and audio signals are mixed on the same frequency.

The PIC-E is an open system and it can be use as a platform for developing new and innovative applications. Almost any application that involves point to point or point to multi-point transmission of low-density data is a candidate for PIC-E development.

Most of what will be need to get started is readily available at little or no cost. The Proceedings of the 1998 ARRLTAPR Digital Communications Conference contains information on how to implement AX.25 UI frames in PIC microcontroller. While the PIC16F84 contains only 1K of program space, it turns out that this provides enough room not only to decode incoming serial data and construct outgoing packets, but to do a significant amount of processing and reformatting of the data as well.

To make it easier to program the PIC16F84 chip, the PIC-E has an on-board PIC programmer. As a result, to reprogram the chip, it is only necessary to connect a short serial cable between the PIC-E and a PC serial port and run the appropriate programming software.

Software for TAPR PIC-E

WX-PIC

PIC-et Radio: How to Send AX.25 UI Frames Using Inexpensive PIC Microprocessors

Introduction to PIC Development