TLC 5940 behaves erratic


I'm dealing with a TLC5940 setup that behaves erratic. It should show the basic Knight Rider animation example, but there appear lots of other blinky action. Also, when I pick it up by the power cable, hold the protoboard between two fingers or whatever, the behaviour changes, for the better or worse, randomly. In the example video, the animation stops when I grab the power cable, but it's really unpredictable.

I already have an 8x8 matrix with four daisy-chained TLC5940 that works flawlessly. What I have built here was intended to be a prototype for testing heat and power when driving superflux LEDs at 60mA before scaling the 8x8 up to the end product.

I have already replaced the TLC, the Arduino and the power supply. Also, the same Arduino with the same sketch works perfectly on my 8x8 concept.

Have I messed up the signal cabling between the Arduino and the TLC5940? Maybe some issue because the cables are crossing each other (as can be seen in the last seconds of the video)? Are there any guidelines that I can follow to avoid this?

It looks like a loose connection. Maybe a poor solder joint?

Does that Arduino have a LED on Pin 13? You might consider adding a flashing heartbeat. It will help give you an idea if the Arduino itself is "locking up."

Thanks for your reply, James!

I was literally blind yesterday from staring at these superbright LEDs. In fact, the XLAT pin of the TLC was not connected to the Arduino at all. The wire was in place, but not bridged to the respective Arduino pin.

After all data is clocked in, a high-level pulse of XLAT signal latches the serial data to the internal registers.

So XLAT was unconnected and floating, which probably led to the behaviour I saw.

Now things work perfectly. :-)

Thanks & have a great sunday!