izua
Joined: 31 Oct 2006
Posts: 63
Helped: 2
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 13 Dec 2006 12:56 transistors and parallel port |
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i want to drive a few 8-seg displays, from my computer. i know it's evil to do it directly from the parallel port, since i can burn it up.
so, i was thinking of making each segment driveable by a transistor. i don't know what values i should put, for limiting the current through the base, and through the collector-emitter junction.
i'll need 8 transistors to control each segment, and another 4 to give each 8-seg display a ground. by switching which 8-seg is currently grounded quickly enough, i will achieve the effect of making all 4 of the 8-seg displays seem on.
but where do i need to limit the current through these resistors, to protect the parallel port? (the display is already made, each segment trace has a 2k resistor, just to be safe).
also, can this be done this way?
someone told me it can't, since i'll need a definite 1 and 0, (like adding a circuit), otherwise the transistors will be "in air" when not on. but i guess beeing "in air" is not grounding or connecting to v+.
thanks for ideas, suggestions.
izua
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