This 20-character, 4-line parallel liquid crystal display provides a large viewing area. It features white text on a blue background OR black text on yellow green background with an LED backlight and uses the common HD44780 parallel interface.
|ground (0 V)
|5 V logic supply voltage
|H/L register select signal
|H/L read/write signal
|H/L enable signal
|DB0 – DB7
|H/L data bus for 4- or 8-bit mode
This LCD has an LED backlight. The voltage drop across the LEDs is typically about 3.2 V and the recommended current through the LEDs is 72 mA. This LCD includes a 25.5 Ω resistance (two 51 Ω resistors in parallel) in series with the backlight, so an external current-limiting resistor is not required for backlight supply voltages up to 5 V. For higher voltages, you should add a current-limiting resistor RLIMIT as shown above where:
RLIMIT = (VBACKLIGHT – 3.2V) / 0.072A – 25.5Ω
Any voltage above the diode-drop voltage will work (as long as you choose the appropriate value for your external current-limiting resistor for voltages over 5 V). You can also use a PWM-controlled MOSFET to achieve variable dimming of the backlight if so desired.