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This 20 x 4 LCD packs 80 characters into an outline smaller than that of most four-line displays. An LED backlight enables optimal viewing in all lighting conditions. This unit uses the HD44780 interface found on most parallel character displays.
This 20-character, 4-line parallel liquid crystal display achieves a large viewing area in a compact package. It features a yellow-green LED backlight and uses the common HD44780 interface, so sample interface code is widely available for a variety of microcontrollers. This is the same LCD that is included as part of some of our Orangutan X2 robot controller packages.
You can find sample HD44780 LCD interface code written for a variety of AVR microcontrollers as part of the Pololu AVR library.
Using Contrast and the Backlight
As shown in the diagram above, a potentiometer whose output is connected to Vo will allow you to set the contrast for optimal viewing of your display.
The backlight in this LCD is composed of LEDs in series. The total voltage drop across these LEDs is typically 4.2 V and the recommended current through the LEDs is 180 mA. You should use a current limiting resistor RLIMIT as shown above where:
RLIMIT = (VBACKLIGHT – 4.2V) / 0.18A
In the diagram above, VBACKLIGHT is shown as 5 V, but you are not restricted to 5 V; any voltage above the diode-drop voltage will work as long as you choose the appropriate value for your current-limiting resistor. You can also use a PWM-controlled MOSFET to achieve variable dimming of the backlight if so desired.
Note: no cables or connectors are included with this product, but a 2×8 shrouded box header and 20", 16-conductor ribbon cable can be purchased separately. The box header can be soldered into the through-holes on the left or right side of the LCD PCB and the cable is designed to plug into the header.
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