Octolively load resistor calculations

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  • October 18, 2012 at 1:14 pm #20122
    Roms
    Participant

    Could you provide details as to how you came to 200ohm resistors for RED leds shown on the schematic. Maybe my calculation are incorrect but I come up with 180ohm. I want to make sure I do not exceed the 40ma max pin.

    • This topic was modified 6 years, 7 months ago by Windell Oskay.
    October 18, 2012 at 1:39 pm #20966
    Windell Oskay
    Keymaster

    As it says on the BOM, the kits with red LEDs actually have 220 ohm resistors; the “200 ohm” figure was a preliminary estimate.  

    The number that you need to be concerned about is normally the total current on the MCU, which needs to be 200 mA or less.  That gives you nearly 40 mA (for one IR LED) plus a little under 8*20 mA for the 8 visible LEDs, plus a few mA to run the MCU. With the standard component set, it runs pretty close to the limit.
    October 18, 2012 at 1:46 pm #20967
    Roms
    Participant

    Thank you. Hungry IR leds.

    October 18, 2012 at 1:49 pm #20968
    Windell Oskay
    Keymaster

    You can run them lower (and then, the other LEDs brighter), but you get better sensor range by running them higher.  

    October 18, 2012 at 2:01 pm #20969
    Roms
    Participant

    Going to have to play with one of the boards. Maybe I will use headers in R pins and see how this work out.

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