Wiring multiple LCD displays to Arduino

Question

I have multiple LCD displays and one Arduino and I just want to show some text on each display separately.

Is it possible to Wiring multiple LCD Displays for the single Arduino board?

Or maximum how many display can I connect one single Arduino?

Answer 1

For HD44780 based displays all the data, register select and read/write pins can be shared. A display only exists at the moment the E pin is toggled. They are designed to share a microprocessor's data bus.

So if you have 50 displays then you can (theoretically, see "fan out" below) run them from 50 "E" pins plus 6 (or 10 depending on if you want to run in 4 or 8 bit mode) shared pins.

Here's an example with 2 displays in 4-bit mode - just replicate for more:

^{simulate this circuit – Schematic created using CircuitLab}

Note: power, ground and contrast connections omitted for brevity.

As you can see the LCDs share all their pins except the E pin. A third display will connect to the same pins, except its E pin would be unique.

Fan out

Fan out is an important concept in digital electronics. An IO pin can only deliver a certain amount of current and each device a pin connects to adds "load" to that pin. Too many devices and the IO pin will struggle to control the devices properly.

To combat this a "bus transceiver" (such as the 74HC245) is commonly used. If one IO pin is capable of driving, for the sake of argument, 5 devices, and one bus transceiver is also capable of driving 5 devices then the IO pin could drive 5 bus transceivers giving you control over a potential 25 devices.