Introduction

Currently I am working on programming a PIC16F84 microcontroller to serve as a keyer and a frequency counter with Audio Frequency Annunciator (AFA). In other words, a keyer and Morse code frequency readout.

I really enjoy operating with homebrew single band transceivers. These little radios have limited tuning range, low power consumption, and a small form factor. They generally use a 10 turn pot for tuning so I sometimes use a turn counting knob and calibration chart to determine frequency. This arrangement is awkward but a full frequency counter with LED or LCD display doesn't make sense for these rigs. Neither does any kind of dial arrangement that I can think of. The idea of a counter that outputs its frequency measurement in Morse code however, seemed ideal. These devices are commercially available but I thought it would be fun to homebrew one. Ideally this approach will also yield a device with the features I most desire.

Here is a list of the features I hope to have in the keyer/counter when it is finished:

The Approach

While I enjoy writing code, sometimes you find things in the public domain that make it difficult to justify writing the code yourself. A while back I discovered some code for a great little keyer on the K1EL web site. I promptly downloaded the code (K8) and programmed a 12C509 PIC processor with it. I built this keyer into a single band rig and later built a stand alone PIC Keyer around it. The K1EL PIC code is well written, rock solid code that yields a great keyer.

Keyer Code and Processor Choice

Frequency Counter Code

There are plenty of good PIC frequency counter examples to follow. Several were found on the web and in the Microchip appnote library. The October 2000 QRP Quarterly had an article by WA1EDJ and AE4GX describing an AFA they built for the Georgia Sierra. It looked interesting so I e-mailed Sam, AE4GX and he sent me the source code. Their project was based on some 16F84 code that was written by Bernd Kernbaum DK3WX. I programmed a 16F84 with their code and experimented with it. It worked quite well and provided me with some good ideas. My approach will be to maintain as much of the keyer functionality as possible and keep the AFA features to a minimum. For example, the number of frequency digits sent and the frequency offset (IF frequency) will be configurable before assembly but probably not adjustable during operation. This should not be a problem since the intended application is single band transceivers where those parameters are pretty well fixed.

The Challenge of Putting it Together

With the keyer code in hand and several good examples of frequency counters, it seems like I am 90 percent of the way there. There are still a number of challenges though. First, I still have only 1K of memory and the K8 keyer uses almost all of that. Second, I have to make sure the two code segments are going to live together in the same program space without problems (assuming I can find room for them both).

The Development Process

My development tools consist of the following: 1.MPLAB, an assembler, debugger, integrated development package available for free from the Microchip web page. 2. PICSTART PLUS, a Development Programmer from Microchip used to burn the program into the PIC Flash memory. 3. A PIC16F84 prototype board that I built on perf board. The prototype board has a pin header that brings all the 16F84 I/O pins out where they are easily accessible. It also contains a 5 Volt regulator, pin header for external power in and out, and a reset switch. The prototype board also has enough extra space for future additions. Below are some pictures of the development tools.

Proto Board and AFA Test Circuit	PICKSTART PLUS programming a 16F84
MPLAB Development Environment	Keyer/AFA Schematic

Progress Report

As of the end of April, I had most everything I wanted form the K8 code successfully ported to the 16F84. I wrote some code to save the code speed and most preferences in EE_PROM so that they are restored on powerup. I also wrote some code to allow adjustment of code speed by holding down the pushbutton and pressing the dit or dah paddle. I started working on the frequency counter code and then got distracted by another project for a couple of weeks. Since the first weekend in May I have been back on this project and the code is nearly finished. There are still a few things I would like to do but I only have about 13 bytes of code space left in the 16F84.

Below is an updated timetable and progress report:

Future Development

There are still a number of things I need to do before this project can move over to the finished projects list. Below is the TODO list:

TODO List