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7 segment led display

Discussion in 'LEDs and Optoelectronics' started by wedowelaugh, Mar 28, 2013.

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  1. wedowelaugh


    Mar 18, 2013
    K..So we're trying to build this digital clock for our digital project.
    And as I've seen in many schematics, certain values of resistances have been added between the outputs of the CD4511 decoder (BCD to 7 segment display decoder) and the inputs of the led 7 segment display.
    These resistance values were different for the different levels of seconds, minutes and hours part of the clock.

    Does anyone here know how to calculate the resistance values from CD4511 to 7 segment display?

    The schematic of a clock is as shown here -

    We'd like to add milliseconds display to this for which we don't know know how to calculate resistance to the 7 seg display.

    Your help is highly appreciated.
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The resistances are calculated the same way you calculate the resistance values for any other LED.

    First determine the desired current through the display (it may not be 20mA), then using this, your supply voltage, and the Vf of the display's LEDs, do the normal calculation.

    These displays are not multiplexed, so I see no reasons why they should differ.

    Oh, an the LED marked as "current limiting LED" is really a "voltage limiting LED"
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    @James Biden : you realized that this is an old thread from 2013? Not likely anyone will answer. I'll close this thread.
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