rm-hull/luma.led_matrix

7 Segment display writing backwards and needing leading spaces

matjspalding opened this issue · 6 comments

matjspalding commented

Hi

I've recently purchased a MAX7219 display and although it stated
raspberry Pi Python libraries were avail they aren.t On the off chance I tried yours. It is working after a fashion. The display is writing backward (from right to left) and requires 3 leading spaces.

I have attached my code and a pic of the display. I am using a Pi 4, Python 3.7.3.

As you can see the could should have displayed "HELLO" but I am getting "OLLE" on my display. Am I doing something really stupid?

Thanks

Mat

IMG_0438

import time

from luma.led_matrix.device import max7219
from luma.core.interface.serial import spi, noop
from luma.core.virtual import viewport, sevensegment

def show_message_vp(device, msg, delay=0.1):
    # Implemented with virtual viewport
    width = device.width
    padding = " " * width
    msg = padding + msg + padding
    n = len(msg)

    virtual = viewport(device, width=n, height=8)
    sevensegment(virtual).text = msg
    for i in reversed(list(range(n - width))):
        virtual.set_position((i, 0))
        time.sleep(delay)


def show_message_alt(seg, msg, delay=0.1):
    # Does same as above but does string slicing itself
    width = seg.device.width
    padding = " " * width
    msg = padding + msg + padding

    for i in range(len(msg)):
        seg.text = msg[i:i + width]
        time.sleep(delay)
        
def main():
    # create seven segment device
    serial = spi(port=0, device=0, gpio=noop())
    device = max7219(serial, cascaded=1)
    seg = sevensegment(device)
    
    #print('Simple text...')
    #for _ in range(8):
    #    seg.text = "HELLO"
    #    time.sleep(0.6)
        
    print('Simple text...')
    for _ in range(8):
        seg.text = "   HELLO"
        time.sleep(0.6)
        
    
    #print('Scrolling alphabet text...')
    #show_message_vp(device, "HELLO EVERYONE!")
    #show_message_vp(device, "PI is 3.14159 ... ")
    #show_message_vp(device, "IP is 127.0.0.1 ... ")
    #show_message_alt(seg, "0123456789 abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ")

if __name__ == '__main__':
    main()
rm-hull commented

I guess the “OLLE” is the last 4 characters of “ HELLO” backwards. It is probably like this because of the way your device is wired up. You could try setting the block orientation flag on initilialization, see here for example: https://luma-led-matrix.readthedocs.io/en/latest/python-usage.html#trouble-shooting-common-problems .. try setting it to 180 (or -180)

as to why you need the leading spaces ... max7219 IC’s control 8 seven segment devices serially, and I suppose the circuit you bought is wired up to the last 4 rather than the first four.

I would be curious to know where you got it from (I assume some sketchy eBay / Ali express seller or similar)

matjspalding commented
pjaselin commented

Hi @rm-hull I'm experiencing this as well using a 4 digit/7 segment display as well: https://www.mouser.com/ProductDetail/SparkFun/COM-11405?qs=sGAEpiMZZMvShe%252BZiYheisUaClgE6%2FvpGjlN%252BRV4q58%3D&countrycode=US&currencycode=USD

I'm having the additional issue that I can only show "."'s, 1's, and 7's. Any other digit causes the display to die, any idea what might be causing that?

pjaselin commented

Needed 4x the resistance! Still having the reversed text issue though

pjaselin commented

And I just figured it out @matjspalding, if you reverse the digits, ie. switch D0 -> D7, D1 -> D6, etc, it'll fix this!

zanzeoo commented

Same probleme here plus i don't know where to modify thoses lines thx!