I recently took up electronics as a hobby and I'm attempting to create a 5x6 matrix of RGB LED's. I'm using an arduino uno R3 and 6 of the TLC5940 chips daisy chained. I downloaded the TLC library from https://code.google.com/p/tlc5940arduino/ and I'm using their knight rider sketch called BasicUse. I wired the chips up according to this website http://tronixstuff.com/2013/10/21/tutorial-arduino-tlc5940-led-driver-ic/. I looked at the example sketch BasicUse and the wiring diagrams from it and the tutorial I used are the same. I also changed the number of TLC's in the library file to 6. Each column of my matrix is controlled by one chip so there are 5 RGB LED's or 15 inputs out of the max 16 per chip. Each chip does have its own iref 2k resistor (for ~20mA) and i gave each chip the two capacitors shown from the tutorial. The RGB LEDs are common anode with recommended current of 15mA.
My issue is that when i try to run the sketch, the board will randomly blink lights from all over the matrix and after really close inspection i can see that it is doing the sketch but their are so many other lights blinking on and off that its hard to see. I figured out that if i disconnect the gsclck (pin 18 on TLC/pin 3 on arduino). that the sketch works as its supposed to but the lights flash rapidly and the brightness changes and sometimes blanks out. What is causing all the random lights flashing? Is there a clock sync issue? capacitance issue? floating ground? I don't really know how to debug these issues being new to electronics and I do not have access to an oscilloscope to see what the signals are doing. I'm using an old computer power supply for a regulated 5 volts to power the LED's and the chips. and I'm using the regulated 12 volts from the same power supply to power the arduino through the "Vin" port.
If i input the simple code of "Tlc.clear(); Tcl.update" all the lights would go off and stay off. But anything that involves them being on would make them all flash randomly. I took out all the TLC chips except one and tried the sketch and it worked perfectly. no strange flashing or flickering. When i tried two chips, it would still work great except I would see a very brief, dim flash from all the LED's connected to one chip. and both chips would do this flash at random intervals. I couldn't see a pattern to the flashes. When i plugged in 3 chips it would do the random bright flashing. I even tried bypassing to another column of lights to see if it my soldering for those set of lights was bad but it still did the same thing and i tried different chips. On my breadboard I only had space for 2 chips so i hooked them up to see if i had hardware or software issues and the chips and lights worked perfectly. No flashes or any erratic behavior. Today i unhooked the gsclck and the pattern wouldn't work like it originally did but if i grabbed the insulation of the gsclck wire then it would work. Any ideas on my problem(s)?