I've purchased a 'bag of bits' type of thing from a local electronics shop. In it are a number of 7 segment type LED displays which I am OK with, but there is also 4 bare LCD displays - which have me intrigued.
Only one of the displays has any markings (lower right in the pic) - 'LPH1538-8' and 'QJ K125' which hasn't turned up anything datasheet wise that I could find.
Two of the displays have metal legs, the other two appear to have conductive tracks etched into the glass - dunno how I'll ever connect to them.
So, any ideas how I might go about figuring out how to run these from an Arduino? I'm still an electronics newbie, so plain and simple guidance is what I'm after. ;D
Bare LCDs are usually not worth the bother of messing with. If you value your time, you'll chuck them out and splash out $12 for an HD44780 compatible module that will work out-of-the-box.
The ones with no pins in particular, will be a bear to deal with. These ones need a conductive rubber strip that bridges between the LCD and matching pads on a circuit board.
The all that aside, the electrical requirements for driving them will not be too hard to do with an Arduio directly and a few resistors. As I recall you have to have a push-pull driver for these, and maybe multiple voltage levels. I believe it should be possible to do up the electronics on the cheap as a demo, but perhaps not as a practical solution.
There was a thread recently about going the other way -- having an Arduino snoop the control lines of an LCD to see what was being displayed -- and that thread had some pointers to details about how these things are driven.
All I can find in Google is about LCDs with controllers and that is not what you have -- but if you rummage around you may find someone else has done a bare LCD.
I already have a 16x2 LCD with a built in controller, so no worries there. I was just looking at these as a learning project rather than anything else. Given that I have no idea what the layout of the actual displays is it's hard to know if I could ever use them. From my prodding and poking of the large one I know that there is a bit of LC that reads 'Stereo', so I reckon it's come from a car stereo or HiFi. Probably never have a use for it, but still fun to poke around.
@PaulS
43 pins. But I have shift registers. Lots and lots of shift registers. ;D
First, there are likely pins not used. And if you are looking to drive just a few segments as an experiment, you can definitely ignore the majority of the pins.
When you hold them up to the light, can you trace where the pins lead to? You might consider taking the smallest one and trying to map things out.
Right, I've tried applying a few volts across the pins, with limited success.
The LCD at bottom left is a nice big clear pair of digits, straight forward enough pin to segment mapping. But the refresh rate is dreadful, on the order of 3 to 4 seconds. There may be a pin combination that clears the display but I haven't found it yet.
The large display at top left is definitely from a car stereo. I can get groups of segments to light up at a time (actually go clear, needs a back light) but not individual ones. It's one of the alpha/numeric segment types, so could have a use if I ever figure it out. There is way more segments than pins, so obviously some logic is required beyond simply setting pins high/low. Only time will tell if I can be bothered to figure it out.
Note that most LCDs require AC, not DC. And maybe more than 5V as well.
I am pretty sure all bare LCDs use an AC driving voltage - not only that, driving the displays with DC can permanently damage them. Back in the day, there were chips you could buy to drive them (mostly for 7-seg types)...
Well, if I damage them by driving with bare DC, then I damage them. It's not like they were expensive, or critical to a project. Plus if I have to buy additional hardware then they'll likely never get used.
