Jumbo calculator as source of big LCD?

Crossed my mind whilst out shopping the other day - you can pick up jumbo calculators for very little - seen them in the £1 shop I think, and I had looked briefly at using a big LCD for my meter project but discovered it's hard to find big LCD's with enough digits.

So anyway, it occurred to me, for future reference, jumbo calculators should be a cheap source of big LCD's with lots of digits, if you don't mind buying one to cannibalise it

No longer useful for me, but might be a good tip for someone else

The difficulty may be connecting to the LCD since they often use some type of conductive rubber between the circuit board contacts and the display edge contacts where the calculator case provides the pressure to keep them together and make contact. So you would need to determine the contact connection diagram for the LCD and then build a PCB with the matching connections to properly drive the LCD. Not a trivial project.

Yes, come across that before, I gutted an LCD watch aeons ago and built a transmitter in the case. It had clear rubber strips with black conductors running through them - looked like zebra stripes. I'm pretty sure that in the same era (80's) I came across strips of metal pins which clip onto the edge of that type of LCD - I think possibly Maplin sold them. All quite hard to align though - I'd forgotten about that.

But I was actually thinking it should be possible to saw across the pcb and connect to the traces, hack out the bezel where it fits the board. OK I know it's an ugly hack

Oh well, bedtime - g'night.

throbscottle said:

It had clear rubber strips with black conductors running through them - looked like zebra stripes.

Click to expand...

Interesting that you say that. That connector is called an elastomeric connector, also known as a zebra connector or zebra strip.
Wikipedia link

The problem I see with using those kind of LCD's is that they are probably the multiplexed type in order to reduce the pin count. They're a bit more difficult to drive than multiplexed LED's in that they require a more complex waveform. But, if you have a driver chip that will drive that type of LCD, you're all set.

Here's a link to a company that makes both multiplexed and non-multiplexed numeric displays.

Absolutely fascinating. Makes me want to get one and have a play - unfortunately can't because of lack of any kind of workshop (shed is still filled with a heap of boxes).

I agree, a chip specifically for driving LC display glass would make life so much easier and they are quite common, with many designed for 7-segment/numeric displays. You would of course have to drive that with a microcontroller, but it should be as, if not more straightforward than the character HD44780 drivers.

As for the connector, they are made to be independent of 'pitch', so as long as you get the pitch of the PCB trace connectors right, the alignment of that connector is non-critical, it simply provides a soft surface so pressure can be used to ensure a good connection for signals. For prototyping using an LCD from a old nokia phone (5510, I think...) I cut lines in blank single sided PCB material, and just soldered wires to that, with the LCD and rubber connector clamped on top - works a treat for developing software!

Vindicated!