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Experiments 5.2: Arduino - Serial to Parallel Conversion (74HC164 & 74HC595)

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Uploaded by on Apr 1, 2011

This video looks at serial to parallel conversion in digital electronic circuits. In particular it shows how we can drive a sequence of LEDs using a single pin of the Arduino. Also, it discusses the difference between latched and unlatched serial to parallel converters. The particular ICs that are examined are the 74HC164 and the 74HC595 (latched), where the video demonstrates how to drive 8 LEDs using a single pin and 16 LEDs using two pins of serial data. This video is part of an introductory module on digital electronics. The associated content can be found at http://www.eeng.dcu.ie/~molloyd/EE223/

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Uploader Comments (DerekMolloyDCU)

  • Nice vid.

    But I guess you forgot the current limiter resistors on the LEDs.

    BTW, I'm planing on making a big LED matrix using my arduino, I'll use 9 8x8 matrices, it'll be a 24x24 LED matrix and I'll use 6 74HC595 to drive the matrix, I'll use a bunch of BC547 to source the current to the LEDs, but I'm not sure if the 74HC595 will be able to sink all that current from 24 LEDs since a whole column might be lit at the same time, any ideas on how I can address this issue?

  • @sanosukke Thanks. There is a resistor R1 on the cathode side of the diodes that limits the current. In this case I have lit only one LED at a time, but if I was to light more than one LED they would be be less bright.

    On your second question - have a look at my video on 8x8 arrays as it deals with this issue exactly. You will need a ULN2803 to sink the current or you could overload your 74HC595. Good luck!

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  • Very good tutorial! Thanks! :D

  • Sorry for being finicky but in your code you wrote that "The 8 LEDs light for one second *exactly* on each pass", but isn't there some extra time used by the microcontroller to run the "for" instructions between a Timer Interrupt (or wathever the delay is) and an another one? I'm not really sure of this, infact I'm asking..! ;)

  • Great video. I was looking for the difference between the two and your explanation was right on!

  • @DerekMolloyDCU I'll use a bunch of BC547 instead of ULN2803, since it'll be cheaper, I have one ULN2803 that I used with one matrix, worked fine, but there was only one matrix, hence only 8 LEDs per row/column, with three matrices there'll be 24(48) per row/column (bicolor matrices), I'll use transistors as drivers on the anodes, but as for the cathodes, the LEDs will bedriven by the 74HC595 itself, I would like another driver here just to be on the safe side.

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