Controlling strings of leds with Arduino

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Every year I have the same discussion with my wife about how many strings of light we should have in our christmas tree. Every year, she wants me throw a string (100 lights) more than we already have in the tree. I think we had 5 string last year, while I think 4 strings is enough.

Anyway, I talked her into having a more dynamic light setup this year (if I manage to get everything ready before december). The tree (fake) has about 8 layers of 6-8 branches. If I remember correctly I counted 79 branches last year. I am thinking about giving each branch about 6 leds (close to 400 leds total) and make them dimmable. If you would number them, all 8 branches in a layer would have a led 1 in parallel, a led 2 in parallel, led 3 in parallel, etc… All leds (on the first layer) numbered with 1 are in parallel with the leds numbered 1 on layer 2 (and layer 3-8)

In short I have to power 6 strings with 64 leds each (8 layers with ~8 leds per layer) = 384 leds and I want to make them controllable through an Arduino.

I have been looking into a TLC5940 (16 channels, more than I need), but since my knowledge of electronics is not good enough to make the right calculations I am not sure if this IC is the way to go.

All hints, suggestions, caveats are welcome.

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You may want to read the datasheet for the 5940. The most you can drive off the whole chip is 120 mA. If you have an average LED that takes ~20 mA, you will go over that 120. So you will need to blink them.

That takes me to my next opinion. The TLC5940 library is complex. If you know C++, then go for it. I am a novice at programming and it took the last 2 days just to get 2 LEDs to fade together. If you don’t, I would look at using a shift register like the 74HC595 or TPIC6B595N which can take more current.

I have been looking into a TLC5940 (16 channels, more than I need)

16 channels = 16 LEDs. for 384 LEDs, you will need 24 5940s.

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Thank you very much for your reply. I think 25 is a little too much for this project. I will look into the suggested shift registers.