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Electronics Raspberry Pi and SN74HC595N's

Discussion in 'Modding' started by nry, 3 Jan 2013.

  1. nry

    nry Member

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    Hi

    Playing around with my raspberry pi. I have a bunch of the above 8 bit shift registers

    Could anyone explain to me how to connect these to the raspberry pi gpio headers?

    Controlling them looks fairly straight forward with the following
    https://projects.drogon.net/raspberry-pi/wiringpi/shift-library/

    I don't really know how to design circuits just follow a diagram usually but can't find any for this particular chip!

    Cheers
     
  2. henros

    henros New Member

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    It is fairly simple, but you need to watch your voltage levels. If your whole system is running at 3.3V, then it's easy; if you want to run the external devices at 5V (or more), then you need buffers between the Pi headers and the 595's. Fortunately, you only need 3 lines buffered (for a minimum system) - data, clock and latch.

    The code in your reference takes care of shifting the data into the 595, but it does not deal with triggering the latch in the 595 to get the data into the output register - this needs another function to toggle the latch after shifting out 8 bits of data.

    Depending on what you are doing with the data, you may need to control the reset (MR) and the output enable (OE), otherwise tie MR high and OE low. You can also cascade the 595's, and then toggle the latch only after all blocks of data have been loaded. It is also possible to reload the data from the 595s back into the Pi, although this is not an efficient method of data storage.
     

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