nanoFramework.Iot.Device.Pcd8544 1.0.555

PCD8544 - 48 × 84 pixels matrix LCD, famous Nokia 5110 screen

This is the famous screen that Nokia 5110 used. It's a SPI based device. This Nokia 5110 was very popular and many of us used to have it in their hands and that young generation have seen it in pictures. This LCD is quite cheap and easy to use.

Documentation

• Nokia5110 datasheet

Circuit

It uses SPI and you can add PWM to control the 4 leds brightness which are around the screen. The pin have various names like BL or LED.

It requires as well a GPIO controller on top of the SPI device with a pin called Data Control, most often presented as DC.

In this schema, the Chip Select (active low) is most of the time called CE. The SPI Clock has to be connected to CLK or SCLK. And the MOSI pin to DIN or MOSI. Names for the pins varies a bit.

Reset pin is sometimes called RST.

Supply voltage can vary, 3.3 or 5V, up to 7V is acceptable. Make sure that there is a current limiting resistor between the brightness led and the controller you'll plug. Most of the kits you buy have it. If you don't add one, you will damage the external brightness leds.

The following example shows how to setup the screen with a PWM to control the brightness:

var resetPin = 32;
var dataCommandPin = 33;
var backlightPin = 21;

var gpioController = new GpioController();
var spiConnectionSettings = new SpiConnectionSettings(1, 5)
{
    ClockFrequency = 5_000_000,
    Mode = SpiMode.Mode0,
    DataFlow = DataFlow.MsbFirst,
    ChipSelectLineActiveState = PinValue.Low
};
var spiDevice = new SpiDevice(spiConnectionSettings);
var pwmChannel = PwmChannel.CreateFromPin(backlightPin);

var lcd = new Iot.Device.Pcd8544(dataCommandPin, spiDevice, resetPin, pwmChannel, gpioController, false);

If you don't want neither a PWM neither a reset pin, you can then pass a negative pin number for reset and null for the PWM:

lcd = new(27, spi, -1, null);

var lcd = new Iot.Device.Pcd8544(dataCommandPin, spiDevice, -1, null);

Note that there is as well the possibility to pass a normal pin number for the backlight. In this case, the light will be on once the BacklightBrightness property if more then 0.5, otherwise off.

Displaying text

Like for other screen bindings in this repository you have Write and SetCursorPosition to write text and set the cursor position.

A specific font is available and optimized for the screen. The font only contains a limited number of characters and will just ignore any characters that are unknown.

lcd.SetCursorPosition(0, 0);
lcd.WriteLine("First line");
lcd.Write("Second one");
lcd.SetCursorPosition(0, 5);
lcd.Write("last line");

The position of the cursor moves with the text you write. The screen has 6 lines in total. And a character is 5 pixels width and 8 pixels height.

You can as well provide your own character using the Write(ReadOnlySpan<byte> text) function.

Drawing lines, rectangles and points

Point, line and rectangle primitives are available:

lcd.DrawPoint(5, 5, true);
lcd.DrawLine(0, 0, 15, 35, true);
lcd.DrawRectangle(10, 30, 10, 20, true, true);
lcd.DrawRectangle(12, 32, 6, 16, false, true);
// You should not forget to draw what you have in memory
lcd.Draw();

Each can take Point, Size and Rectangle as well as input. You have to decide if you want to have the point on or off and if you fill or not the rectangle.

Also you should Refresh the screen once you'll finish your drawing. All drawing are in the memory and needs to be pushed to the screen.

Displaying raw images

The function SetByteMap allows you to draw anything, you'll just need to provide the raw buffer. Size is 504 bytes representing from the top left part columns of 8 pixels up to the right up to the next raw. A total of 6 raws are available with 84 columns each.

Here is an example on how you can convert an existing image to extract the raw data then convert it into a C# array you can copy into your code:

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;

var imageFilePath = args[0];
using var image = Image.Load<Rgba32>(imageFilePath);
image.Mutate(x => x.Resize(new Size(84, 48)));
image.Mutate(x => x.BlackWhite());

var colWhite = new Rgba32(255, 255, 255);
var width = 84;
var result = new byte[504];
for (var pos = 0; pos < result.Length; pos++)
{
    byte toStore = 0;
    for (int bit = 0; bit < 8; bit++)
    {
        var x = pos % width;
        var y = pos / width * 8 + bit;
        toStore = (byte)(toStore | ((image[x, y] == colWhite ? 0 : 1) << bit));
    }

    result[pos] = toStore;
}

var resultString = $"var bitmap = new byte[] {{{String.Join(",", result.Select(b => $"0x{b.ToString("X2")}"))}}}";
Console.WriteLine(resultString);
Console.ReadKey();

In case you want to convert existing images which have a different size than the 84x48 screen size, you have to resize the picture like this using ImageSharp and convert it to Black and White:

// Open an image and resize it
using var image = Image.Load<Rgba32>(imageFilePath);
bitmapLarge.Mutate(x => x.Resize(new Size(84, 48)));
bitmapLarge.Mutate(x => x.BlackWhite());
...

Note: you may want to reverse the colors first depending on what you want.

This code is also available as a simple C# Console Application in Img2Pcd8544 and you can execute it using this command:

Img2Pcd8544 <PATH_TO_IMAGE_FILE>

Advanced functions

You can adjust couple of factors like Bias, Temperature, Contrast and Brightness. The sample will run through all of them so you can understand the impact of each of them. The Bias will increase the voltage and darken the screen.

In general, it is recommended to leave Temperature to the 0 coefficient, if you are in normal conditions. The Bias can be left to 4 as well as a default value for normal conditions.

Then you can use the Contrast property to properly adjust the contrast. A value around 0x30 is usually a good one for normal conditions.

But you may have to adjust those depending on the conditions of lights, temperature you are in.

Brightness

The brightness is controlling the PWM. If you have not passed any PWM controller, this has no effect on the screen. Brightness goes from 0.0 to 0.1f.

lcd.BacklightBrightness = 0.2f;

InvertedColors

An invert mode is available, it just revert the screen colors. So white pixels become black and vice versa

lcd.InvertedColors = true;

Enabled

You can switch on or off the screen fully with the Enabled property:

lcd.Enabled = true;