This is an adapted layout for two tlc5940 hooked up to an Arduino nano. The original project can be found here. I am a little unsure about the capacitors and resistors as that project had it hooked up to a 5v wall plug.

My Design will be running a pattern of PWM, blinking and chasing lights. The two red lights are off of the TLC5940s circuits because reds need a different resistance. If i am wrong, please let me know as that would simplify things. enter image description here

Also as is the way of the stack community, any other red flags you can point out would be greatly appreciated as i am new to this game.

  • TLC5940 is a constant current driver. May 15 '17 at 20:10
  • Also, its supply is given as 5.5V max. May 15 '17 at 20:11
  • No resisor in the red leds? As for the capacitor; it might not be needed, but doesn't hurt. I'd move the smaller capacitor as close to the TLC as possible.
    – Gerben
    May 15 '17 at 20:24
  • Hey @Gerben I have added the resistors to the reds, i always forget them! Should i use two smaller capacitors so i can get them even closer to each tlc5940? May 15 '17 at 20:49
  • That would be ideal. Adding some decoupling capacitors near the chip can prevent (electrical) noise, and thus prevent weird behavior of the chip.
    – Gerben
    May 15 '17 at 20:54

As Ignacio has mentioned the TLC5940 is a constant current driver. The 2kΩ resistor sets the current for the LEDs regardless of the forward voltage (or colour) or the supply voltage.

Also as Gerben says, move the 0.1µF (100nF) capacitor close to the TLC5940 as you can. There should be one for each TLC5940 since they are decoupling capacitors.

You might like to increase the capacitance of the electrolytic too. The purpose of that capacitor is to provide a low impedance energy source to supply the circuit (batteries are actually quite high impedance by comparison). Since you have lots of LEDs being controlled by PWM the current draw will be fluctuating wildly all the time, and lots of energy over brief periods will be wanted.

Another thing to watch, mentioned again by Ignacio, is the supply voltage for the TLC5940 is 5.5V absolute maximum. I wouldn't go much above 5V. Depending on what your batteries actually are you may be better running from 3 of them (4.5V alkaline AA - Ni-MH would be ~3.6V, so 4 of them, giving 4.8V, would be better in that situation).

I would also question your use of the TLC5940. They are not the easiest chips to drive requiring quite a strange protocol. Personally I prefer the TLC59116 which is the I2C variant of the same chip. Much easier to control from an Arduino, and requiring just 2 pins. Not so easy for bread-boarding though as they're SMD only.

  • Hi @majenko Thank you for the great explanation! What size electrolytic capacitor would you suggest i use? May 16 '17 at 21:22
  • Whatever you have handy. 10µF minimum.
    – Majenko
    May 16 '17 at 21:22

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