Circuit description
When I designed this beacon keyer I wanted a keyer that was easy to operate with the minimal component count. I was interested to come up with a design using no more than 8 components. The end result a keyer with only 5 components and if you really want you can get away with only 3 components. I was also looking for a keyer that could run of a 3 volt battery. A lithium 3V battery (CR2430) is ideal for the purpose and can supply the PIC with power for several weeks if not months. (Red and Black wires) Note how small the keyer really is. If you are really pressed for space you can trim the PCB even further to suite your needs.
The PIC12F675 micro controller was chosen for this project since it is a very versatile controller with the necessary amount of on-chip memory resources. This PIC is really a PICADILLY - "A dilly of a wee PIC". I have been using this PIC for the past three years and have learned a lot about this PIC and its functions.
As mentioned before it is very versatile. Some of the futures include:
1024 x 14 bit words of programming memory
64 x 8 bytes of data memory
128 x 8 bytes of EEPROM data memory
A built-in RC oscillator operating at 4 Mhz (No resonator or crystal required)
5 ports that can be either inputs or outputs
1 port that can be an input or the MCLR (master clear pin)
4 ports can be used as Analog to Digital Converters (ADC's)
ADC reference voltage can be set or the supply voltage used
Operates from 2.0 to 5.5 VDC with a low current - very low SLEEP current
Each port can sink/source 25mA up to a total of 125 mA
Individual programmable weak pull-up resistors for each port
When programmed with the Beacon Keyer
firmware, the PIC12F675 performs all of the "smarts" from
the internal EEPROM, then convert the stored message to Morse Code
and key it out. However I choose the "KISS" concept in this
version. I only use one output (Pin 7 ) of the PIC12F675
to drive the
buffer transistor (2N2222) via R1(10K) and
to indicate visual operation through D1(Red LED). R2 (1K) act as a
load resistor for D1. Remember that you must not overdrive the
port. The PIC is not capable of directly keying a transmitter
and therefor requires a transistor buffer between the keyer chip and
the transmitter. The 2N2222 transistor is used for positive keying to
the transmitter.. (Green and Black wires)
Chip
Programming
Programming the firmware into micro
controller flash memory is a one time procedure. The PIC12F675 micro
controller must be programmed by a suitable PIC-Programmer.
Beacon Keyer Features
Compact and KISS (Keep It Simple Stupid)design
Minimal component count
Dot Timing and Dot/Dash Spacing options
Dash Generator and Letter Spacing options
25 CW character beacon message (Including callsign)
Keyer speed range: 8 - 14 WPM
Tone 700 Hertz
Keying mode: CW
Power requirement: 3V - 5V Max!! (See SIMPLE 5V VOLTAGE REGULATOR PROJECT)
Message example: DE ZS1I BEACON KF15BT
If you connect power to the keyer (Red +5V, Black
-0V) and the TO TX (green) and -0V (black) wires to the keying lines
of your transmitter the beacon will begin keying out the message
in a continuous loop.
Finally: This was a great experimental project. I learned so much about PICS and writing of the beacon firmware. Today the PIC used in this project is obsolete but with the Arduino Nano you can open up a complete new world in Beacon- and other Keyers. Somewhere in my project box lies a Arduino Nano that I used to build an automatic morse code keyer. Maybe one day I will run into it and fire it up to see if it still works.
