Max7219 Analog LED clock

Discussion in 'The Projects Forum' started by McZlik, Jun 27, 2012.

  1. McZlik

    Thread Starter New Member

    Jun 9, 2012
    Hey all,

    For me next project I'm going to build an analog clock with LEDs (I must be nuts :p). And my idea was to control all the LEDs with an MAX7219.

    The idea
    A short built-up of my LEDs.

    3 rings of LEDs, each containing 12 LEDs.
    The outer ring are the hours, middle ring are minutes, inner ring are seconds.

    To be able to show every minute, in the middle are 4 extra LEDs to show the extra minutes between each 5th number.

    Underneath that are 5 LEDs in a half circular shape, that's going to act as a pendulum, a light that goes from left to right every second.

    Which gives me a total of 45 LEDs to control.
    See the attachment for the drawing

    With my understanding I know that I can control 8 columns and 8 rows of LEDs with the MAX7219, a total of 64.
    My idea was to group the LEDs together in groups of 8, connecting the positives of each group LEDs together(Columns), and connecting the negatives with the same LED number of the other groups(Rows).
    Sow the outer ring has 2 groups, number 1 to 8 are group 1, 9 to 12 are group 2.
    Same for the 2 other circles. Giving me 6 groups for the rings.

    Group 7 are the 4 minute LEDs in the middle and group 8 are the pendulum LEDs.

    LED Count
    Group 1: 8 LEDs
    Group 2: 4 LEDs
    Group 3: 8 LEDs
    Group 4: 4 LEDs
    Group 5: 8 LEDs
    Group 6: 4 LEDs
    Group 7: 4 LEDs
    Group 8: 5 LEDs

    The MAX7219 is controlled by a arduino circuit built on a perf-board.

    Now my question to this all is, do I need resistors to connect this mother-load of individual LEDs? And if so, how strong ones? All I can find about the MAX7219 are how to connect them to an LED Matrix.

    I hope this story make my idea a bit more clear, else just ask away :p
    Last edited: Jun 27, 2012
  2. WBahn


    Mar 31, 2012
    Interesting project.

    You might want to look at the data sheet for the MAX7219 a bit closer. In the first paragraph of the General Description section at the top of the first page it states, "Only one external resistor is required to set the segment current for all LEDs."

    Also, on p8, "Intensity Control and Interdigit Blanking", it describes how to control the intensity digitally by writing to a register.

    Data sheets are wonderful things. Make them your friend (they can be intimidating, but forcing yourself to use them will tame them pretty quickly).

    Good luck and keep us posted on how the project progresses.
    McZlik likes this.
  3. McZlik

    Thread Starter New Member

    Jun 9, 2012
    Oh ups, sorry, should have looked into that before asking :p

    Thanks for the tip, I will take a look at it and try to figure it out!

    And of course, I will post again when I have some updates. :)
    I'm currently still in the designing process, and trying to figure out what stuff to get.

    Next up, the circuit diagram :)
  4. Wendy


    Mar 24, 2008
    I agree with WBahn, interesting idea. I like clocks.

    If you finish maybe you could formalize your plans and put it in the Completed Projects forum (read the rules on the sticky).