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RPi + OSMC Reason/solution WS2801 color problems

Discussion in 'Hardware Support' started by Squizzy, 5 July 2017.

  1. Squizzy

    Squizzy New Member

    Messages:
    16
    Hardware:
    RPi2
    So guys. My cheap Ws2801 annoys me because of my white level. i can get white with R255 G80 B50. That means. Red is to weak.
    On LED Strips like the WS2801 with the 5050 LED resistors are external. because of different RGB orders the chinese guys maybe overlook it and don't change their layout. OR they have some other resistors in their garbage collection and want to get rid of it.

    How can you check your resistors. Simple as that, look at your strip. Hope you have good eyes.
    Every LED Section has this setup:

    Connection --> WS2801 Chip --> 5050 LED --> 3 resistors (black) + 1 Capacitor --> Connection


    2 of the resistors needs to be the same. They are for green&blue LED. On my the are 100Ohm resistors.
    Their label is "101" it means "10 * 10^1 = 100" Ohms
    Thats fine. Your uC output is 5V. 3V over the blue/green LED and 2V over the resistor with a forward current of 20mA.

    For my red LED an "271" (27 * 10^1 = 270)Ohm resistor is installed. Thats too damn high. The voltage over the red LED needs to be around 2V. So you need 3V on your resistor. You get this with an 150Ohm resistor.


    I will test this next week and will tell you if this is the reason. SMD 805 resistors cost around 1€/100pcs..


    Please tell me your installed resistors if your white balance is almost fine with 255/255/255! THX!


    EDIT:

    150 Ohm is the way to go. tested it with one LED. much better! now the remaining 126 :(
     
    Last edited: 11 July 2017
    • Like Like x 1
  2. TPmodding

    TPmodding Administrator Staff Member Administrator

    Messages:
    712
    Hardware:
    RPi1/Zero, RPi2, RPi3, +Arduino
    Isnt it smarter to buy a led stripe with newer chipsets :)
     
  3. Squizzy

    Squizzy New Member

    Messages:
    16
    Hardware:
    RPi2
    wouldnt recommend to buy WS2801 except the seller can tell you the resistors with a picture.

    APA102 Chipset costs around 30 dollars. if you are a freelancer you can calculate your time in money but for me it is cheaper to change the resistors in my freetime for 3 dollars in total. have also a solder machine for smd parts available at my university. maybe it is 1-2 hours work :)