Ohm my!

I have to take a break from the circuits and layouts and go back and verify a couple of calculations. I am referring to the Rset for the MAX7221. I need to be sure that this is going to be correct in relation to the 7-Segment units chosen – and also the discrete LEDs for the indicators.

  • 7-Segment: NKR161B
    • Vf = 1.7V per segment
    • Maximum forward current = 30mA
  • LED:
    • Vf = 2.0
    • 20mA Test current

For Rset,

image

image

In theory, the MAX7221 should be able to drive the 7-Segment displays directly using a 50KΩ resistor. It also looks like the discrete LEDs for the indicators can be accommodated. What the impact will be in real terms of brightness and evenness of illumination, I will wait to see it for my self.

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