LUMEX 3" 7-Segment Displays
Apr 02, 2016 Filed in: Electronics | Arduino | Clocks
I picked up these sweet LUMEX S101D22TR 7-Segment LCDs the other day. They were only $3.50 a piece.
Maybe they don’t look that big in the above image. Here’s one next to a quarter to give you a sense of scale. They are 3” tall.
Just to give you a better idea of how big a clock would be using these displays, check them out next to my keyboard. Pretty big!
The trick with LCDs is that you can’t just drive them the same way as you do as LED displays. In the sense that usually common is tied to Vcc or ground, and then the segment you want to light up is either set high or low. This all depends on if you’re using common-cathode or common-anode displays. They are both the same, it just depends on what goes HIGH and what goes LOW.
LCDs are a different story. You have to feed an AC signal between common and the segment you want to light up. So, common can’t just be negative and the segment positive. You have to switch them back and forth really fast to keep the segment lit.
I connected one to my breadboard and started to play around with it. It’s really tricky trying to get an Arduino to drive them right. I tried everything I could, and I just couldn’t get them to look good. The segments look partially faded when viewed head on, and some weird blotches appear here and there. I suppose I could have broken out my scope to see if my signals were out-of-phase, but I didn’t bother.
If you switch the segments fast enough, they look pretty good.
However, that isn’t going to be the case with a clock. For one thing, the hours will be displayed for an hour. Leaving a digit displayed statically for more than a few seconds results in some weird artifacts and fading. Forget multiplexing, that’s out of the question. It looks like crap.
I’m going to have to get my hands on some LCD driver chips.See this project from start to finish:
LUMEX 3" 7-Segment Displays 3" LCD Clock - Part I 3" LCD Clock - Part II 3" LCD Clock - Part III 3" LCD Clock - Part IV 3" LCD Clock - Part V 3" LCD Clock - Part VI