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The goal of LCD2USB is to connect HD44780 based text LCD displays to various PCs via USB. LCD2USB was meant to be cheap and to be made of easily available parts. It is therefore based on the Atmel AVR Mega8 CPU and does not require any difficult to obtain parts like separate USB controllers and the like. The total cost (without display and pcb) are about 5 to 10 Euros. LCD2USB currently comes with a simple demo application that works under Linux, MacOS X and Windows.
The hardware of the LCD2USB interface consists of the Atmel AVR Mega8 CPU, a cheap and easy to obtain microcontroller with 8 KBytes flash (of which ~3k are used in this application) and 2 KBytes RAM. The processor is surrounded by few parts, mainly connectors to interface to the PC and the LCD. The USB interface of the LCD2USB interface is based on a pure software implementation and uses three pins of the AVR (PC0, PC1 and PD2). This software implementation supports low speed USB only which is signalled to the PC by resistor R1. The current version 1.1 of the LCD2USB operates the USB data lines at 3.6V which complies to the USB spec and increases compatibility over version 1.0.
The LCD2USB interface supports several different HD44780 based text displays. It supports single controller displays (tested with 16*2, 20*2 and 20*4) and dual controller displays (tested with 27*4 and 40*4). The LCD2USB interface uses the 4 bit interface provided by the HD44780.