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Pico Keyer

PicoKeyer is shared in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Pico Keyer is a simple Morse code keyer project to demonstrate how to use a GPIO on the RPi Pico microcontroller to key a radio or code practice oscillator. GPIO voltage when turned ON is +3.3V. This GPIO voltage can be used to drive a transistor keying circuit. See ELECTRONICS.md for more information.

The "build" folder has been included with the binary .uf2 file for evaluation convenience and for use with the RPi Pico ONLY. The ".vscode" folder is also included for those who wish to build the project in VS Code themselves.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! To build for the Seeed XIAO RP2040 device #define XIAO2040 at the top of keyer.cpp. This uses pin 6 for UART TX, pin 7 for UART RX and pin 8 for GPIO KEYER !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

The Pico's onboard LED is keyed to demonstrate the keyed letter and punctuation and prosigns. See alphabet.h for the full list of implemented characters. In addition, the GPIO pin 6 (Pico physical pin 9) is also keyed for use with a keying circuit. The "R" sent at startup (Ready) and speed changes are only sent to the LED.

A keying circuit is highly recommended. A simple transistor switch, such as a 2N2222A with an appropriate bias resistor connected between the GPIO pin and the transistor's base is likely all that would be needed as a switch between ground and the radio's key line. If clicking is encountered in the RF output, the use of an opto-isolated transistor may be necessary. A device such as a 4N25 or VO610A may be appropriate.

The keying is treated as one would use a "straight key", meaning a simple on/off switch (a telegraph key). Thus the radio settings should be for using a straight key and key jack wiring as required by the radio manufacturer. Typically, the "tip" of the radio's key jack would be connected to the Collector of the transistor switch, and the Ground of the radio's key jack would be connected to the Emitter of the transistor. So when the GPIO pin turns the transistor switch to ON, the key line will be grounded and the radio will be keyed. The above demonstrates the most common radio keying implementation in radios or code practice oscillators. Please ensure that your radio works this way before designing your switching circuit.

To supply the ASCII characters for the Pico to key, UART0 is used as a serial input device. Characters are echo'd back on the port so the user may see what has been typed into the Serial terminal or UI application.

If an RPi is used as the input computer, one of it's UARTs may be directly wired into the Pico on pins 1 (TX) and 2 (RX). The code has commented lines which deal with the setup and use of the USB instead of the UART. Please also make the adjustments in the CMakeLists.txt file as indicated for use of a USB. Also note that the USB use only seems reliable when used with an RPi computer. Windows gives wildly varying results.

Use of a UART and an external serial cable will necessitate the use of an inexpensive UART to RS-232 conversion module. These are very inexpensive and turn the UART into an RS-232 serial port. That serial interface can then be used with a computer serial port or attached to a USB to RS-232 converter cable.

Speed of keying is specified by an input command to the USB. The format "@nn" is used to set the keying speed to "nn" words per minute based on the formula for WPM using the "PARIS " word methodology.

The formula is :

 T = 1200 / W

where T = time for a single "dot" in milliseconds and W = "PARIS " Words per minute.

When the users sends "@12" for example, the keyer will adjust it's "dot" time to 1200/12 = 100 ms.

Future designs may also include an "iambic" keyer for radios which have electronic keyers built into them. In effect, this is a keyer keying a keyer! But it provides the convenience of using a keyboard instead of an iambic key, which for movement impaired people may be welcome.