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I am working on a project where I need to use around 50 LED's connected to an Arduino UNO board. To begin with i worked on the tutorial provided by Arduino (https://www.arduino.cc/en/Tutorial/ShiftOut) to connect two shift registers(74HC595). Everything works fine, but the shift registers get very hot in just a few minutes. Is this normal?

  • Check the specs to see how much amps they can drive. Increase the current limiting resistance or buffer the signal using transistors if needed. – ratchet freak Dec 14 '17 at 14:09
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    Calculate the total current driving your LEDs, and compare to the 74HC595 datasheet about the maximum driving current it can source. You may need to drive the LEDs with larger current-limiting resistors, or use the shift register to control transistors that do the actual switching. For example, the TI SN74HC595 (ti.com/lit/ds/symlink/sn74hc595.pdf) has an absolute maximum continuous current through Vcc or GND of 70mA. – jose can u c Dec 14 '17 at 14:10
  • @josecanuc Yeah I think I drawing too much current than it can provide. Thank you:) – shabeer ahamed Dec 14 '17 at 14:15
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    That tutorial has many errors. You should ignore it and find a better one. There is a post here somewhere about all the things wrong with it. – Majenko Dec 14 '17 at 14:47
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    Here's the post I mention: arduino.stackexchange.com/questions/39827/… – Majenko Dec 14 '17 at 14:47
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I can only think about two things:

  1. (least probably): the entrance (VCC) voltage is too high.
  2. (most probably): the resistors to the LEDs are (too) low .. Recalculate the values and check the max amperes which can be handled by the output pins of the shift registers.
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    Yeah the problem was with the LEDs having too low resistance. Thanks a lot:) – shabeer ahamed Dec 14 '17 at 14:19
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    You are welcome ... you can accept / upvote the answer to let others know the problem has been solved. – Michel Keijzers Dec 14 '17 at 14:34

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