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  1. #1
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    Mastercard outputs

    Is it okay to put 2 leds on each output of the mastercard?

    Jerry

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    Re: Mastercard outputs

    Jerry,

    The outputs of the Master Card are rated at 25mA each. Current draw for leds will vary according to their type but the rule of thumbs is 20mA each. You can work around this limitation by using a transistor to drive the leds. See this link:

    http://www.ecs.umass.edu/ece/m5/tuto..._tutorial.html

    Pierre

  3. #3
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    Re: Mastercard outputs

    The leds I'm using are 5mm 2vf 35mA max. If I put 2 leds per output will they just be dimmer or do I risk burning the IC?

    One other thing. I'm using a 300W Power Supply to supply my 5v for master cards. Is it necessary for each master card to use a separate line from the ps or can I put all 4 master cards on one line?

    Jerry

  4. #4
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    Re: Mastercard outputs

    No problem with the current draw for these 2 leds. The 2N3904 maximum collector current is 200mA. The leds will not be dimmer. You can get the limiting resistor value on: http://ledcalc.com/

    As for the power supply, you can run one line from the power supply to where your cards are mounted and split it. You can make an octopus cable, use a distribution block or a terminal strip. I would also recommend fusing, just in case.

    Pierre