Electronic telegraph key on the PIC controller. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Electronic telegraph key on the PIC controller. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Civil radio communications

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The author proposes a simple electronic telegraph key using a modern element base - a PIC controller. This made it possible to minimize the size of the device and build it directly into the transceiver.

The telegraph key was designed to be built into the transceiver, but can also be used as a separate unit. The scheme of the device is shown in fig. 1.

Electronic telegraph key on the PIC controller

The key is designed to form characters of the telegraph alphabet. The principle of operation is very simple. In the initial state, the SB3 manipulator is in the middle position. There is a high level at pins 17 (RA0) and 18 (RA1) of the microcontroller DD1. When the manipulator is moved to the lower position according to the scheme, a series of pulses occurs at pin 6 (RB0), corresponding to the "points". "Points" will be generated while the manipulator is pressed. The duration of each "point" is determined by the set speed. Similarly, when the manipulator is moved to the upper position according to the scheme, "dashes" are formed.

Buttons SB1 and SB2 are designed to change the signal transmission rate. The set speed is written to the first cell of the EEPROM. The next time the device is turned on, the program reads the value of this cell and sets the speed. This solution, as well as the use of a quartz resonator, allows you to always and with high accuracy set the transmission rate, which depends little on temperature and supply voltage. The manipulation is carried out by an active low signal from the collector of the transistor VT1.

When developing the device, the main goal was simplicity and a minimum of details. The ability to write to memory was not developed due to the fact that computers are now mainly used at an amateur radio station. And in computer programs, work with the so-called "macros" is implemented at such a level that it is almost impossible to implement it in hardware. Therefore, the key is used, as a rule, in everyday radio communications or in the field. The key has a memory for one character - the so-called "iambic" mode. That is, if at the time of playback, for example, a dash, a dot is pressed, then at the end of the dash, this dot will also sound. And vice versa. The speed can be adjusted from the lowest to about 120 hours per minute.

Due to the fact that the key is designed to be built into the transceiver, it does not provide a tone output. The control is carried out via the QSK chain of the transceiver. When using the key as a separate device, you can add a sound generator for self-control and control it from pin 6 of the DD1 microcontroller. Another option is to use the so-called "buzzer" from the computer. This is a small capsule that, when voltage is applied to it, emits a tone signal in the range of 0,8 ... 2 kHz.

On fig. 2 shows a printed circuit board for a device assembled from ordinary parts, and in fig. 3 - for surface mount parts (size 0805). The arrangement of parts is shown on a scale of 2:1.

Electronic telegraph key on the PIC controller

When programming the microcontroller, the FOSC0 and WDTE flags must be set. Data for programming are given in the table. When first turned on, the microcontroller reads the speed value from the first EEPROM cell. If the microcontroller has not been programmed before, then the hexadecimal number FF will most likely be written in this cell. This corresponds to the smallest speed. If desired, at the programming stage, another hexadecimal number can be entered in this cell, for example, 2A, which will correspond to the average speed.

(click to enlarge)

The electronic stabilizer 78L05 can be replaced by the KR142EN5A in the usual version, while it may be necessary to increase the size of the printed circuit board. If it is supposed to work from a battery of galvanic cells, you can not install a stabilizer at all. Of course, the battery voltage should not exceed 5,5 V. The supply voltage for the PIC16F84 microcontroller, supplied by the manufacturer, can be in the range of 4,5 ... 5,5 V when using a high frequency crystal (HS) as a master oscillator.

The frequency of the quartz resonator ZQ1 may differ from that indicated in the diagram. The upper and lower speed values depend on the nominal frequency. As a transistor VT1, any silicon npn conductivity is suitable, for example, from the KT3102, KT645 series, etc. You only need to make sure that the maximum current and collector voltage are not less than required for switching the load.

If the SB3 manipulator is located at some distance from the device, you need to install blocking ceramic capacitors with a capacity of 1000 pF, connected to terminals 17 and 18 of DD1, and also use resistors R5 and R6 of lower resistance (1 ... 2 kOhm). Similar recommendations apply to the speed control buttons.

PIC controller firmware

Author: D. Sobol (EU1CC), Minsk, Belarus

See other articles Section Civil radio communications.

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