Circuit diagram

This circuit stores a single morse code message as bits in an EPROM chip, the message is sent to a relay which can key a CW transmitter. The keyer can output either a one-shot message such as "CQ DX DE CALLSIGN", or a continuous message. The continuous mode is useful for making low power (QRP) beacons. A One-shot message is controlled by the start/stop buttons, a continuous message is sent by turning on the free run switch. EPROMs other than the 2732 can be used if suitable changes are made to the circuit. For larger EPROMs, just ground the higher order address input lines on the EPROM chip, and wire the appropriate chip select pins for outputs enabled and chip selected.

It is also possible to store more than one message in different banks of a larger EPROM, for instance, if a 2764 part were used, the A12 address line could be used to select the upper or lower message.

Theory
CMOS Nor gates U1c and U1d form a gated astable clock oscillator, the frequency can be adjusted by potentiometer VR1. Gates U1a and U1b form the run/stop flip-flop. In one-shot mode, this is activated by pressing the start switch, and deactivated either by pressing the stop switch, or by the end of message signal that comes from the EPROM d1 line.

The clock oscilator causes U2, a binary counter, to step through some of an 11 bit binary count. This sequence is used to step through the addresses on EPROM U3. Morse code data is stored in the EPROM d0 bit, it is used to turn on and off Q1 and RL1, the keying relay. At the end of a one-shot message, a single 1 bit arrives on U3 pin d1, causing the run/stop flip-flop to turn off, and resetting the U2 counter to zero. D1, C2 and R4 cause U2 to reset when the power is applied. R5 is used to prevent the U3 d1 line from being shorted to +5v when the stop switch is pressed.

Programming the EPROM
I have written a C language program called cw2hex that is used to convert a sequence of ASCII characters into a hex data image that can used for programming the EPROM chip that is used in this circuit. The program takes text input and produces an Intel Hex format file as output. The hex file should be readable by most modern EPROM programmers.

The C source code and Unix Makefile are in the file cw2hex.tar.gz (tar.gzip). A DOS executable version of the code is available as cw2hex.exe. It should be possible to compile cw2hex.c on any machine with a C compiler. The C program source files are available if you want to look at the code from your web browser.

This circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Circuit draws about 30 mA from a 6-9 volt battery and can be received to about 100 yards. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less effect on the frequency.  

Fine frequency adjustment can be made by adjusting the 200 ohm resistor in series with the battery. Oscillator frequency is set by a 5 turn tapped inductor and 13 pF capacitor. The inductor was wound around a #8 X 32 bolt (about 3/16 diameter) and then removed by unscrewing the bolt. The inductor was then streached to about a 3/8 inch length and tapped near the center.

FM Beacon Broadcast Transmitter Circuit Diagram
The oscillator frequency should come out somewhere near the center of the band (98 MHz) and can be shifted higher or lower by slightly expanding or compressing the inductor. A small signal diode (1N914 or 1N4148) is used as a varactor diode so that the total capacity in parallel with the inductor varies slightly at the audio rate thus causing the oscillator frequency to change at the audio rate (600 Hz).

The ramping waveform at pins 2 and 6 of the timer is applied to the reversed biased diode through a large (1 Meg) resistor so that the capacitance of the diode changes as the ramping voltage changes thus altering the frequency of the tank circuit. Alternately, an audio signal could be applied to the 1 Meg resistor to modulate the oscillator but it may require an additional pullup resistor to reverse bias the diode. The N channel JFET transistors used should be high frequency VHF or UHF types (Radio Shack #276-2062 MPF102) or similar.