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Dual Alphanumeric Display hard coded without backpack?
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Dual Alphanumeric Display hard coded without backpack?

by timothym on Sun May 02, 2021 12:57 pm

Hello!

I am building a ‘Back to the Future’ themed guitar, and purchased Dual Alphanumeric Display LEDs to create the ‘to’ and ‘from’ time travel dates. Since these dates are fixed, it was my thinking that I could simply hardcode the dates without the need for the Alphanumeric Display Backpack modules. The problem I’m having is that I can’t seem to figure out how to wire to set two individual read outs on each of the characters per board, as the common pins handle the segment illumination for both the 1st (left) and 2nd (right) characters thus mirroring the display in each character. E.g. pin 5 controls the same LED segment in each character. I’m sure I’m being incredibly dense and not seeing the simple solution, but any help would be appreciated. Thank you!

Tim
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Re: Dual Alphanumeric Display hard coded without backpack?

by adafruit_support_bill on Sun May 02, 2021 1:20 pm

These displays are designed to be multiplexed. There is just one set of segment pins and a common pin for each character. You rapidly cycle through each character by setting all the segment pins and pulling the common pin for just one character at a time. The backpack takes care of that. Or you can do it yourself with a microcontroller. But you can't just statically hard-wire them.

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Re: Dual Alphanumeric Display hard coded without backpack?

by blnkjns on Sun May 02, 2021 1:26 pm

Do you need all the segments? For numbers only 7 segments are needed. In that case you need 7pins per segment and 1 pin for each digit on a microcontroller.
With an ItsyBitsy 32U4 you could run 3 x 4 digits straight from the pins with 7 resistors, without needing backpacks.
With the 3V version it might even work without resistors, as 3V in combination with the current limiting on the output pins of roughly 20mA will be good to drive LED's:
https://www.adafruit.com/product/3675

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Re: Dual Alphanumeric Display hard coded without backpack?

by timothym on Sun May 02, 2021 4:53 pm

Thanks all! Looks like, the backpack will be the route I take (as was my suspicion). I will need to go this route as I need to utilize almost all of the segments for alphanumeric output as this is a month name abbreviated / numeric date display. I really appreciate the VERY quick help!
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