Seven Segment LED Display Experiments
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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