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Driving a 8 segment LED array — Parallax Forums

Driving a 8 segment LED array

JavalinJavalin Posts: 892
edited 2010-11-04 05:53 in General Discussion
Hiya

Quick one. Doing a LED clock (just for fun) using the multiplexing / persistance of vision technique.

Turns out that the LED's need +5v power to get some brightness - 3.3v is very dim, is the best way to have a PNP to switch 5v to power each segment and a NPN to switch each digit on/off?

[edit - diagram attached]

Thanks,

James
leds.JPG
1064 x 1093 - 45K

Comments

  • kwinnkwinn Posts: 8,697
    edited 2010-11-04 05:52
    This is basically correct but you need current limiting resistors on the segment drive transistors (collector or emitter), and between the chip pins and the transistor bases. You also need to protect the chip pins from being damaged by the high voltage (~4.3V) on the base of the pnp transistors.

    By chip I mean the 3.3V microprocessor or clock chip driving the display.
  • JavalinJavalin Posts: 892
    edited 2010-11-04 05:53
    Hiya

    Yes, I hadn't included them in the diagram. Thanks for the once-over though!

    James
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