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Mini serial console with three different serial ports

This is my “poor man’s HID” that I want in my projects to enter data and display messages.

It is a simple serial console that can be used for data display and data input. It can handle three (different) serial interfaces at the same time: 3.3V TTL for single-board computers and microcontrollers, via traditional RS-232 and serial over USB.

I. Hardware

1. Technical data
- Supply voltage: 5 V DC
- Supply current: approx. 30 mA
- Mechanical size: 100 x 60 x 50 mm
- Insulation class: Class 0
- IP protection: IP 00
- Mass of cover: termoplastic (PC), only top cover
- Display size: 20x4 characters
- Displayed character set: ASCII 32-127
- Connection: 3.3V TTL, RS-232 and via USB serial ports
- Serial port receive buffer size: 255 byte

2. General description
This is a Raspberry Pi Pico-based device. The display is 20x4 character-sized liquid crystal display, which displays 20x4 size area of the larger size virtual screen. This area is a can be moved with buttons. The default size of the virtual screen is 80x25 characters, this value can be set in the program.

The circuit has three serial ports, depending on the setting, all three can be used for data and system message transmission, or both at the same time. The #0 serial port is via USB port, #1 is a 3.3V TTL port, #2 is a conventional RS-232 serial port. Serial #1 can be connected to a 5V TTL serial port with an external level shifter circuit.”

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