TLC5940 driver boards

So with all those LED drivers lying around it’s time to do something fun with them. Given the amount of chips a PCB certainly wouldn’t be overkill so I whipped one up. It’s the max size Eagle freeware allows, but everything fits nicely. Of course using SMT would enable a smaller PCB, but since the drivers are already present, that’s not an option. The TLC5940 comes in 3 packages; SPDIP, SSOP with PowerPAD and QFN. ¬†Soldering PowerPAD packages is a pain because you need to put solder underneat and adapt the PCB to lead away heat. QFN packages have no leads, which is also a pain for a hobbyist. SPDIP is the only one easily used.

Each board has 3 TLC5040 chips and data is clocked in as 8x8x8 (aka RR…RGG…GBB…B). The board is designed to be Daisy chained, including a return path. The return path may offer possibilities to automatically detect the size of the array via the status information bits. It would be nice to have RGB…RGB, but 16 channels per chip isn’t really dividable by 3. Same problem arose when I thought up smaller PCBs, e.g. use 1 driver per PCB.

A potential problem with these big boards is that they’re harder to build into a system which has small dots. The jury is still out on what to use as a light source. Options are (large) regular LED’s, LED strips cut up into smaller pieces, etc. The TLC5940 can drive up to 120 mA, so that allows for a range of options. Using separate LEDs requires a huge amount of hole drilling, so for the time being I much prefer using LED strips. By cutting it into pieces holding 3 LEDs, oval shapes (in milk coloured acrylic) should be easy to accomplish.

One thing I greatly underestimated was the cost of connectors. Usually only a couple are needed, but in this case I’ve got enough drivers to make 15 boards. Each board has 16 RGB channels, which makes a grand total of 240 connectors. The initial idea was to use polarised connectors, but even low cost connectors from Thailand or China drove up the price too much for my taste. To give you an idea, the male part alone costs $140 at Mouser’s! So I settled on using standard angled pin headers and cheap Molex C-grid like connectors. Should work fine, just have to make sure that during hookup the connection is not reversed.

To be continued….

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