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TAPR PIC-Encoder (PIC-E)

The TAPR PIC-Encoder (PIC-E) is a general-purpose packet radio encoder based on the Microchip, Inc. PIC16F84 PIC microcontroller. The PIC-E was designed to provide a generic interface between the digital world (in the form of serial data streams) and the amateur packet radio world (in the form of AX.25 packets) and is fully programmable by the user. For example, 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 bps packet radio.

The PIC-E is based on two chips: a Microchip, Inc. PIC16F84 microcontroller and a MX-COM, Inc. MX614 Bell 202 modem chip. The PIC16F84 is a general purpose "computer on a chip" that can be programmed and reprogrammed by the end user. The PIC-E has an on-board PIC programmer. 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.

The PIC can be programmed to receive an incoming data stream and reformat it for transmission as AX.25 frames. The PIC sends the formatted data to the MX614 that generates tones necessary to transmit 1200 bps packet over the radio's audio channel. The MX614 contains an energy detect circuit. Receive audio can be routed to the MX614 and 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 circuitry is required to prevent the PIC-E from colliding with other users on the channel. The MX614 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 is hoped that many hams will use it 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. To write applications for the PIC-E you will need to learn how to develop PIC firmware. Don't worry, it is not all that difficult. Most of what you will need to get started is readily available at little or no cost. The software to get started in PIC development is available for free at http://www.microchip.com. A discussion of the basics of getting started in PIC programming can be found in an article by W2FS in the October 1998 issue of QST. The Proceedings of the 1998 TAPR/ARRL Digital Communications Conference contains information on how to implement AX.25 UI frames in PIC microcontroller. While the 16F84 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.


Ordering Information

Sorry, TAPR PIC-Encoder is no longer available


Although the complete kit is no longer available, we do have the bare PCB for sale.

Ordering Information

The price for the PIC-E Bare PCB is:

  • $ 13 US for members of TAPR

  • $ 15 US for non-members

    + shipping/handling if applicable.
(Place Web Order)

Shipping and Handling

Shipping and Handling within the US will be by USPS Priority Mail.

International shipping costs are calculated as closely as possible. If the actual cost exceeds the estimate by more than $5.00, TAPR will contact you to get approval for the additional funds. TAPR uses insured Priority Mail International, unless the purchaser requires something else.


Documentation


Acknowledgments

The PIC-E project team is:

  • Steve Bible, N7HPR, project manager
  • Steve Dimse, K4HG
  • Byon Garrabrant, N6BG
  • John Hansen, W2FS
  • John Koster, W9DDD
  • Dan Welch, W6DFW.

Presentations

PIC-E at the 1998 ARRL & TAPR Digital Communications Conference

Mystery Hardware 2 - TAPR PIC-E

Steve Bible, N7HPR

Software for TAPR PIC-E

John Hansen, W2FS, and Byon Garrabrant, N6BG

WX-PIC

Steve Dimse, K4HG

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

John Hansen, W2FS

Introduction to PIC Development

John Hansen, W2FS and Byon Garrabrant, N6BG


Several prototypes of the PIC-Encoder (PIC-E), a general purpose encoder based on the PIC16F84 PICmicroŽ microcontroller were shown and demonstrated at the 1998 ARRL/TAPR Digital Communications Conference in Chicago, IL. The PIC-E was designed to provide a generic interface between the digital world (in the form of serial data streams) and the amateur 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. At the DCC, the PIC-E was demonstrated as a minimal MIC-E (tm).

The PIC-E is relatively inexpensive because it is 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 is hoped that many hams will use it 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. To write applications for the PIC-E, however, you will need to learn how to develop PICmicro firmware. Don't worry, it is not all that difficult.

Most of what you will need to get started is readily available at little or no cost. The software to get started in PICmicro development is available for free at Microchip, Inc. A discussion of the basics of getting started in PICmicro programming can be found in an article by W2FS in the October 1998 issue of QST. 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.


TAPR kits can be complex depending on the kitting experience of each builder. We don't think you will have trouble with the PIC-E kit, but it does require some knowledge and experience to successfully go from a kit to a finished, usable unit, depending on the mode of operations.


MIC-E is a trademark of Bob Bruninga, WB4APR
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