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Sunday, April 07, 2013

7 segment LED refresh memory blog posts

Now I am reading my old blog posts to refresh my memory of how I drove the 7 segment LEDs.
Seven Segment LED Display Experiments
2009年10月22日 下午7:42公開累計瀏覽次數 16

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Now I am testing the Birght LED (brightled.com, brtled.com)'s 0.36: SSD BS-C325RD, 3 dollars for 2 from Apliu Street, Shamshuipo.

The LED is as usual, operating at If = 10 mA, Vf = 2V.  Last time I was using ULN2003A (500 mA rating) to sink the common anode LEDs, so I need not bother about If limit.

This time I am using common cathode, and using the BCD to 7 Segment decoder 74HC4555 to source the LEDs, so I need to be careful.  HC4511 operate at about 8 mA mat 5V supply.  So I think it is safe to use 1K as limiting resistor. 

(5V - 2V) / 8 mA = 400 ohm.

(5V - 2V) / 1 k ohm =  3 mA.


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