WS281x, SK6812 driver for the Omega2? [Solved]



  • Thanks Luz for this explanation.
    I forgot that HSL values could be transformed into the RGB values.

    I used python to control the 8 LED ring (WS2812b) using code like

    with open('/dev/ledchain0','w') as export:
    			export.write(col_string)
    

    where 'col_string' is a a text string containing all the RGB values for the hole ring.
    However sometimes (especially when I have to calculate the RGB values and then compose the string), I get an error 'ValueError: invalid \x escape'

    Maybe this isn't the best way to control the LED with python and you can advise a better one.

    Regards



  • @LaurentN Although I'm not fluent at all in Python, I'd say there's no reason why Python should not work fine controlling LED chains with p44-ledchain.

    @LaurentN said in WS281x, SK6812 driver for the Omega2? [Solved]:

    However sometimes (especially when I have to calculate the RGB values and then compose the string), I get an error 'ValueError: invalid \x escape'

    That sounds like you are trying to use the literal string syntax (the backslash escapes in \xhh form, with hh being a two-digit hex number) to construct your string, but maybe in a way that sometimes outputs only one digit instead of two, which could be the cause of the ValueError?

    Probably there's a more direct way to get numeric byte values into a string or byte array in Python.



  • Re: [WS281x](SK6812 driver for the Omega2? [Solved])

    Hi.
    In the last days I played a bit with Python to get the WS281x working wirth Luz' module.
    As I want to use HLS color schema (it allows to change the luminosity of the color by only one number), I programmed a function HLS to RGB color string:

    def hls2rgb(h,l,s):
    	r, g, b = colorsys.hls_to_rgb(h,l,s)
    	shr = str(hex(int(r * 255.0)))
    	shg = str(hex(int(g * 255.0)))
    	shb = str(hex(int(b * 255.0)))
    	# print ([int(255.0*r), int(255.0*g), int(255.0*b)])
    	if len(shr) == 3:
    		shr = shr[0:2] + str(0) + shr[2]
    	if len(shg) == 3:
    		shg = shg[0:2] + str(0) + shg[2]
    	if len(shb) == 3:
    		shb = shb[0:2] + str(0) + shb[2]
    	col_led_string = shr[2:4].decode('hex') +shg[2:4].decode('hex') + shb[2:4].decode('hex')
    

    By using the following additional function, it allows using a 2 dimensional color matrix which is converted in the corresponding hex color string needed for the module. (It might be useful and easier to use a matrix to handle LED chains instead of a string of hexadigitals)

    def hls2rgb_hexstring(hls_matrix):
    	dim1 = len(hls_matrix)
    	try:
    		dim2t = len(hls_matrix[0])
    	except:
    		dim2t = 0
    	if dim2t == 0:
    		dim2 = dim1
    		dim1 = 1
    	else: 
    		dim2 = dim2t
    	
    	if dim1 == 1:
    		h = hls_matrix[0]/360.0
    		l = hls_matrix[1]/100.0
    		s = hls_matrix[2]/100.0
    		col_led_string = hls2rgb(h,l,s)
    		return col_led_string
    	else:
    		col_led_string=""
    		for i in range(0,dim1):
    			h = hls_matrix[i][0]/360.0
    			l = hls_matrix[i][1]/100.0
    			s = hls_matrix[i][2]/100.0
    			col_led_string = col_led_string + hls2rgb(h,l,s)
    		return col_led_string
    

    To display a color gradient among several LED's (here 40) one has to run this code, which is using both function above:

    color_start = 0
    color_end = 359
    nr_led = 40
    lum = 2
    sat = 100
    colorMatrix = []
    for i in range(color_start,color_end, abs(color_end-color_start)/nr_led):
    	colorMatrix.append([i,lum,sat])
    	#print [i,lum, sat]
    print colorMatrix
    with open('/dev/ledchain0','w') as export:
    	export.write(hls2rgb_hexstring(colorMatrix))
    


  • @luz does it work for the omega 2+ version with kernel 4.4.6?



  • @Jakofff-Parker sorry for the 2 month delay, must have missed a notification here!

    The answer is yes.

    The p44-ledchain module does not depend on many kernel internals, the only subsystem it actually uses is hrtimer (high resolution timers), so it should run on any not really ancient kernel version.
    On the other hand, it strictly limited to the MT7688 SoC, as it directly uses the PWM hardware without any abstraction. So it's good for Omega2/2S, LinkItSmart and possibly HLK7688.



  • Hi, just a note regarding WS2811 I had a go with @luz's driver and I found out that even my led strip is branded as WS2811 (BTF-LIGHTING WS2811) it didn't work properly if I set the ledchain to type 0 (ledchain0=0,200,0), but it did work well using type 2 with both 3.3V and 5V signals.

    BTW, many thanks @luz for the driver!



  • @Marti-MG Thanks for this information!

    I made a separate mode for the WS2811 because the timing specs from the datasheet I had were definitely not compatible with those I knew working with the WS2812/13. But I had no WS2811 to test back then.

    I'm not too surprised that apparently the datasheet is not correct. I saw the same for WS2813 which had the T0L time specified 300nS, which is definitely not working with real WS2813 as I found out.

    The modes are actually just timing numbers in a table in the driver, see line 157 in p44-ledchain.c. So it would be simple to nudge the WS2811 entry towards the WS2813 timing until it works.

    For the time being, I just added a note to the p44-ledchain README.md to also try WS2813 mode in case WS2811 does not work.



  • @LaurentN
    export.write(hls2rgb_hexstring(colorMatrix))
    TypeError: expected a string or other character buffer object

    alt text



  • Mr @luz! Can you write full tutorial? It's very difficult for beginners like me.
    I want to control RGB LED strip WS2813.



  • @luz
    @Jakofff-Parker said in WS281x, SK6812 driver for the Omega2? [Solved]:

    @luz does it work for the omega 2+ version with kernel 4.4.6?

    When I did the opkg install, I got the error:

     * satisfy_dependencies_for: Cannot satisfy the following dependencies for kmod-p44-ledchain:
     * 	kernel (= 4.14.81-1-5c1ea8a282d7395b1a2c86bf6b1669fc) * 
    

    then, after:

     echo-en '\ xFF \ x00 \ x00 \ xFF \ x00 \ x00'> / dev / ledchain0
    

    Omega immediately hung, omega wifi dropping, yellow led turns off, and I did her a power reset.

    Is this problem happening because the module is for another kernel?
    I have Omega 2+ with 4.4.74 kernel

    root@Omega-1D19:~# ls -l
    -rw-r--r--    1 root     root           940 Jan 14  2019 greeting.py
    -rw-rw-r--    1 1000     1000          6936 May 16  2019 kmod-p44-ledchain_4.14.81+2.0-7_mipsel_24kc.ipk
    root@Omega-1D19:~# opkg install --force-depends kmod-p44-ledchain*
    Installing kmod-p44-ledchain (4.14.81+2.0-7) to root...
    Configuring kmod-p44-ledchain.
    Collected errors:
     * satisfy_dependencies_for: Cannot satisfy the following dependencies for kmod-p44-ledchain:
     * 	kernel (= 4.14.81-1-5c1ea8a282d7395b1a2c86bf6b1669fc) * 
    root@Omega-1D19:~# 
    root@Omega-1D19:~# insmod /lib/modules/4.14.81/p44-ledchain.ko ledchain0=0,5,1
    root@Omega-1D19:~# echo -en '\xFF\x00\x00\xFF\x00\x00' >/dev/ledchain0
    packet_write_wait: Connection to 192.168.3.1 port 22: Broken pipe
    
    
    


  • @Nikolay-Vetrov Yes, it is!


  • administrators

    @Nikolay-Vetrov Yes, upgrade to the very latest available firmware: oupgrade -l -f and the ledchain kernel module will work right away.

    That's actually what controls the notification LED on the Omega2 Pro


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