LED 3x3 matrix - Blinking LEDs cause non-blinking LEDs to dim

Discussion in 'The Projects Forum' started by masterspin11, Feb 15, 2015.

  1. masterspin11

    Thread Starter New Member

    Dec 2, 2014
    13
    1
    I am creating an LED matrix using shift registers, transistors and resistors with a MSP430.

    The LED matrix is strobed by row using one shift register with transistors. The cathode of each LED row is connected to a 100 ohm resistor and then to the transistor.

    If I keep that 100 ohm resistor there, the blinking LEDs cause my other LEDS in the same row to dim. If I take out the 100 ohm resistor, and just connect it straight to the collector of the NPN transistor, it does not dim anymore and it looks beautiful. The LEDs are as bright as possible I imagine...

    So my question... This sounds like a very bad thing to do... But so far it is the only solution I can come up with to prevent the dimming when other lights come on or blink in the same row. Add a static resistor number limits the current of a single row regardless of how many LEDs are on. What is the answer here??? Is there a variable resistor or a way to control the NPN transistor to adjust how much current is let through?
     
  2. masterspin11

    Thread Starter New Member

    Dec 2, 2014
    13
    1
    Ah... Maybe it is my shift register? I have a HC164PW112. I'm wondering if I get something like a HEF4794BT then the current of each output pin is independent of what else is turned on... Does anyone know if this is true. The HEF4794BT says it's for LED driving. The HC164PW112 just says its just a general purpose shift register.

    Any ideas?
     
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