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Topic: Seems like I need to toggle two grounds to control LED matrix... how?? (Read 976 times) previous topic - next topic


Jan 28, 2015, 07:27 pm Last Edit: Jan 28, 2015, 07:30 pm by Squirt_5432 Reason: wrong picture
    So, I got a few components from jameco electronics; they are double-character 17-segment LED displays; AKA two 17-segment displays combined into one unit (as shown in the picture). It has 20 pins: one of them is a common ground for the first character, one is a common ground for the second, and the rest control the pins when voltage is applied (except one mysterious pin that seems to do nothing...)
  So... when you connect 5V to a pin and GND to one of the grounds, it will light up a pin. If you connect 5V to the same pin but GND to the other ground, it lights up the same pin on the other character. My question ultimately is, how do I light up different characters on both at the same time? Is it possible? Or do I need to create an optical illusion by toggling between them really fast? If so, in that case, how do I do that? (the best way I could come up with was using a relay to toggle the grounds, but there has to be a better way...)
  Sorry for being a total n00b at this but any help is appreciated! :)


Drive anodes (thru current limit resistors) for 1 digit, connect its common cathode to Gnd via a transistor, hold for 5mS, turn off transistor.
Drive anodes for the other digit,  connect its common cathode to Gnd via a transistor, hold for 5mS, turn off transistor.
Persistence of vision will trick your eye into seeing both on.

While the outputs are sitting there for 5mS, your sketch can be doing other things - perfect time to implement "blink without delay" style coding.

Aren't those 15 segment (with DP)?
May have 2 CCs for each on.
And 1 unexplained pin.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


    Thanks for the replies! CrossRoads, yes now that you mention it that is a 14-segment; I just grabbed what I could find off of google images and didn't look very closely at it. What I have is a 16-segment with DP (although the DP isn't connected or being used) Thanks for the advice though; super helpful!
    Also thank you Paul__B; I haven't read the whole article yet, but what I have read looks very promising and helpful.
    Thanks again; I shall let you know how it turns out!


Thanks again! Update: I used two transistors (one for each ground) and then generated the characters using multiplexing. Works fantastically!`

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