# MAX7219 Binary Clock question

**URL:** <https://community.sparkfun.com/t/max7219-binary-clock-question/5757>\
**Category:** SparkFun Site Questions/Comments\
**Created:** [November 16, 2007, 4:53pm UTC](https://community.sparkfun.com/t/max7219-binary-clock-question/5757 "2007-11-16T16:53:52Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![treymeyer](https://avatars.discourse-cdn.com/v4/letter/t/47e85d/32.png) [@treymeyer](https://community.sparkfun.com/u/treymeyer)\
**Post date:** [November 16, 2007, 4:53pm UTC](https://community.sparkfun.com/t/max7219-binary-clock-question/5757/1 "2007-11-16T16:53:52Z")

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Hi,

I designed a binary clock project that uses a max7219 8 digit led driver. I use 3 of the digits to display the time in binary, and the other 5 to drive 7-segment displays for translation (for those that cannot read binary). It looks kind of like below picture

\_B\_\_B\_\_B

\_B\_BB\_BB

\_B\_BB\_BB

BB\_BB\_BB

HH:MM:SS

(ignore the “\_” uderscores, they are there for spacing only)

where "B"s are LEDs translating in BCD what is in the “H ours”, “M inutes”, or “S econds” 7-segment digit display at the bottom of the column. A toggle switch turns the 7-segment displays on and off. The high order Hour 7 segment display is either a 0 or 1 (using 12 hour clock) so I control it directly by the microcontroller.

The project works great with red LEDs, but when I try to use other colors the LEDs burn out. I have tried changing rset up to 50k and I still burn them out.

The datasheet for the colored LEDs I am using can be found at:

[http://www.well-ton.com/datasheet/HH-10PGD-50.pdf](http://www.well-ton.com/datasheet/HH-10PGD-50.pdf)

Surely I am overdriving the LEDs with current. There are no current limiting resistors because I didn’t think I needed them with the max7219. I don’t know how to measure the actual current of the circuit since the each LED is only on a portion of a second.

Can anyone please help me figure out what is wrong? I went through the trouble to burn boards and give a few of these away as gifts, then the LEDs (other than red) started burning out.

I know the voltage drop of the colored LEDs (other than Red) is around 3v, where the red is 1.8v. I have no trouble with the 7-segment displays, only the LEDs. Also, I never mix colors of the LEDs.

Thanks,

Trey