Python usage¶
Pixel Drivers¶
The PCD8544 is driven with python using the implementation in the
luma.lcd.device.pcd8544
class. Likewise, to drive the ST7735,
UC1701X or LS013B4DN04, use the luma.lcd.device.st7735
,
luma.lcd.device.uc1701x
, luma.lcd.device.ls013b4dn04
or
class respectively. Usage is very simple if you have ever used Pillow or PIL.
First, import and initialise the device:
from luma.core.interface.serial import spi
from luma.core.render import canvas
from luma.lcd.device import pcd8544, st7735, uc1701x, ls013b4dn04
serial = spi(port=0, device=0, gpio_DC=23, gpio_RST=24)
device = pcd8544(serial)
The display device should now be configured for use. Note, all the example code snippets in this section are interchangeable between PCD8544 and ST7735 devices.
The pcd8544
, st7735
,
uc1701x
and
ls013b4dn04
classes all expose a
display()
method which takes an image with
attributes consistent with the capabilities of the device. However, for most
cases, for drawing text and graphics primitives, the canvas class should be
used as follows:
with canvas(device) as draw:
draw.rectangle(device.bounding_box, outline="white", fill="black")
draw.text((30, 40), "Hello World", fill="red")
The luma.core.render.canvas
class automatically creates an
PIL.ImageDraw
object of the correct dimensions and bit depth suitable
for the device, so you may then call the usual Pillow methods to draw onto the
canvas.
As soon as the with scope is ended, the resultant image is automatically
flushed to the device’s display memory and the PIL.ImageDraw
object is
garbage collected.
Color Model¶
Any of the standard PIL.ImageColor
color formats may be used, but
since the PCD8544 LCD is monochrome, only the HTML color names
"black"
and "white"
values should really be used; in
fact, by default, any value other than black is treated as white. The
luma.core.render.canvas
object does have a dither
flag
which if set to True, will convert color drawings to a dithered monochrome
effect (see the 3d_box.py example, below).
with canvas(device, dither=True) as draw:
draw.rectangle((10, 10, 30, 30), outline="white", fill="red")
Note that there is no such limitation for the ST7735 device which supports 262K colour RGB images, whereby 24-bit RGB images are downscaled to 18-bit RGB.
Landscape / Portrait Orientation¶
By default the PCD8544, ST7735 and UC1701X displays will all be oriented in
landscape mode (84x48, 160x128 and 128x64 pixels respectively). The LS013B4DN04
supports a native resolution of 96x96 pixels. Should you have an application
that requires the display to be mounted in a portrait aspect, then add a
rotate=N
parameter when creating the device:
from luma.core.interface.serial import spi
from luma.core.render import canvas
from luma.lcd.device import pcd8544
serial = spi(port=0, device=0, gpio_DC=23, gpio_RST=24)
device = pcd8544(serial, rotate=1)
# Box and text rendered in portrait mode
with canvas(device) as draw:
draw.rectangle(device.bounding_box, outline="white", fill="black")
draw.text((10, 40), "Hello World", fill="red")
N should be a value of 0, 1, 2 or 3 only, where 0 is no rotation, 1 is rotate 90° clockwise, 2 is 180° rotation and 3 represents 270° rotation.
The device.size
, device.width
and device.height
properties reflect the rotated dimensions rather than the physical dimensions.
Seven-Segment Drivers¶
The HT1621 is driven with the luma,lcd.device.ht1621
class, but is
not accessed directly: it should be wrapped with the
luma.core.virtual.sevensegment
wrapper, as follows:
from luma.core.virtual import sevensegment
from luma.lcd.device import ht1621
device = ht1621()
seg = sevensegment(device)
The seg instance now has a
text
property which may be
assigned, and when it does will update all digits according to the limited
alphabet the 7-segment displays support. For example, assuming there are 2
cascaded modules, we have 16 character available, and so can write:
seg.text = "HELLO"
Rather than updating the whole display buffer, it is possible to update ‘slices’, as per the below example:
seg.text[0:5] = "BYE"
This replaces HELLO
in the previous example, replacing it with BYE
.
The usual python idioms for slicing (inserting / replacing / deleteing) can be
used here, but note if inserted text exceeds the underlying buffer size, a
ValueError
is raised.
Floating point numbers (or text with ‘.’) are handled slightly differently - the decimal-place is fused in place on the character immediately preceding it. This means that it is technically possible to get more characters displayed than the buffer allows, but only because dots are folded into their host character.
Backlight Control¶
These displays typically require a backlight to illuminate the liquid crystal
display: the luma.lcd.aux.backlight
class allows a BCM pin to
be specified to control the backlight through software.
Examples¶
After installing the library, head over to the luma.examples repository. Details of how to run the examples is shown in the example repo’s README.