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Author Topic: Max7219 24 Leds  (Read 608 times)
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Hi,

I have a Max7219 that I'm trying to use to individually control around 24 Leds. I'm a little unsure how I should group the Leds and determine the scan-limit and Rset values since it's not a standard 8x8 matrix. For 24 Leds would it be best to do 3 (SEG) rows of 8 (Digits)? Or something like 5 Rows of 5 Digits?

I may be reading the Datasheet wrong but the Scan-limit seems to allow you to block scanning columns of digits so in the 3x8 example would that mean I set the scan-limit to 0xX2? There seems to also be a warning in the Datasheet about using (0xX2) but I can't quite figure out what it means.

Thanks for any guidance.

« Last Edit: October 02, 2011, 10:03:10 pm by Existence » Logged

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Yes set the scan register for 3 digits only.

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There seems to also be a warning in the Datasheet about using (0xX2) but I can't quite figure out what it means.
It means when running only 3 digits then keep the current per segment below 30mA when calculating the Rset value.
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So when you say per Segment do you mean all the Digits on that segment together? So 10ma per Led (3x10)? or 30ma max for each led?

{edit}
After reading the Datasheet again I'm think it's per LED. I'm running 20ma 2V Leds so as per this Table I should go with a 28K resistor.

    Forward voltage
ISeg   1.5V           2.0V            2.5V            3.0V           3.5V
40mA   12.2kΩ   11.8kΩ   11.0kΩ   10.6kΩ   9.69kΩ
30mA   17.8kΩ   17.1kΩ   15.8kΩ   15.0kΩ   14.0kΩ
20mA   29.8kΩ   28.0kΩ   25.9kΩ   24.5kΩ   22.6kΩ
10mA   66.7kΩ   63.7kΩ   59.3kΩ   55.4kΩ   51.2kΩ
« Last Edit: October 03, 2011, 08:31:16 pm by Existence » Logged

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Yes that's right a segment is the same as an LED.
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