They provide an 8-bit parallel interface to the outside world which is used to both issue configuration commands and program the display registers, and there appears to be pretty good drivers for Arduino out there. However there is much less information available on how to program these displays with Raspberry Pi, and although Adafruit provides an HD driver for Raspberry Pi , it is not thoroughly documented. The datasheet is also a bit opaque, and there are a couple of subtleties that are not clearly documented anywhere; as a result, I struggled a bit in figuring out exactly how to make this display work. I did ultimately sort through all the issues, and what follows are some of the notes I took while getting there.
|Published (Last):||3 March 2017|
|PDF File Size:||15.17 Mb|
|ePub File Size:||1.98 Mb|
|Price:||Free* [*Free Regsitration Required]|
Initialize the LCD and specify the size. Since this is the first thing printed the cursor is at the default 0,0 position. This is the first place on the second line x,y. Parallel interface back light When using a LCD with a parallel interface you have full control over the back light. This not only includes turning it on and off but also dimming it.
Turning on and off is simply a case of connecting to power or not. To make back light appear dimmer we can use another potentiometer or PWM. A potentiometer offers manual control. PWM offers automated control. The back light of the JHDA is a LED matrix, this means we can make them dimmer by increasing the resistance, either by using different resistor values or by using a potentiometer. Here is the bread board example with an added potentiometer connected to LCD pin Turning the potentiometer increases or decreases the back light brightness.
To allow the Arduino to control the back light we use a PWM signal. It is tempting to connect the back light power connector directly to an Arduino pin and this may work. Although Arduino pins can supply a maximum of 40mA, 40mA is the maximum for very short periods of time.
Arduino pins cannot provide the full 40mA for any length of time. A better way is to use a transistor as a switch. Connect the back light plus pin to 5V via a ohm resistor or similar. Connect the back light minus pin to the collector C pin of the 2N Connect transistors emitter pin E to GND. Connect the transistors base pin B to a 1K ohm resistor and then the resistor to Arduino pin 6. I chose pin 6 because it can be used for PWM.
The following sketch increases the PWM value by 10 every loop. This increases the back light brightness 0 is off, is full on. You may notice that the value of brightness never gets to ! After you have added the 2N transistor to the circuit upload the sketch. The spaces clear the old value.
Required when we go from to 0. Automatic dimmer control using PWM. If you have read through the commands in the above table you may have noticed that the NewLiquidCrystal library has this function built in. The setBacklight command does exactly the same thing in the same way.
First let the library know what pin you are using with setBacklightPin then set the brightness using setBacklight.
Arduino with HD44780 based Character LCDs
Programming the HD44780 LCD Display with Raspberry Pi