Getting started using LCD displays from a Windows PC using the U421

Full function monitors are admittedly cheap these days (roughly $100 on the low end), so using an LCD display from a PC has little value. But you can build an LCD solution for $60 and the information on it will be visible even when your screensaver is active or the machine is locked. They also allow you to more immediately focus on the information you display on them (as opposed to the multiple windows on your monitors).

Assuming you have a need to use an LCD display from your Windows PC, here’s a solution that will work:

• an LCD display based on the very commonly used HD44780 interface. I get mine from Gravitech (http://store.gravitech.us/lcds.html)
• a USB interface. In this case I use the USBMicro U421 from CircuitGizmos (http://www.circuitgizmos.com/). It’s based on the Cypress CY7C63743C chip
• A breadboard and wiring

The strength of the U421 in this case is that it has LCD APIs, so you don’t have to worry about the subtleties of timing the data transfer and coordinating RS, R/W, and E.

The wiring is fairly simple:

• B data lines to the LCD data lines (i.e. B0 to DB0, B1 to DB1, etc.)
• A data lines to the RS/Rw/E lines (A0 to Rw, A1 to Rs, A2 to E)
• power lines as appropriate, except nothing to VDD (unless you want to set up a control for contrast)

Preparation for the coding is:

• copy the USBMicro USBm.dll into the bin\debug folder of the application
• add “using System.Runtime.InteropServices” to the ‘using’ part of your code
• add the public class USBm from the USBMicro sample code to your application

The key code is:

result = USBm.USBm_FindDevices();
Device = 0; // assuming there’s only one device
USBm.USBm_DirectionA(Device, 0xFF, 0xFF); // output only
USBm.USBm_DirectionB(Device, 0xFF, 0xFF);
result = USBm.USBm_InitLCD(Device, 0x01, 0x12); // A.0 is the RW line, A.1 is the RS line; data port B, A.2 is the E line
result = USBm.USBm_LCDCmd(Device, 0x30 + 8); // function set: 8 bit; 2 lines, font 0
result = USBm.USBm_LCDCmd(Device, 0x04); // entry mode – not incrementing, in either direction
result = USBm.USBm_LCDCmd(Device, 0x0C); // display on; no cursor, no blinking
result = USBm.USBm_LCDCmd(Device, 0x01); // clear display

output[0] = “initialized”;
for (int i = 0; i < output[0].Length; i++)
    result = USBm.USBm_LCDData(Device, Convert.ToByte(output[0][i]));

p.s. There’s a key difference between the LCD-20x4Y (black on green) and LCD-20x4BW (black on white) displays – the second line starts at a different DDRAM address. Use 64 rather than 40.