[HELP WANTED] Driving a calculator LCD

A place to hang out and chat with other like minded tinkerers

Moderators: phalanx, TS-Tim

[HELP WANTED] Driving a calculator LCD

Postby Atoss » Tue Apr 11, 2017 1:04 pm

So I have gutted this Citizen SDC-810N pocket calculator out of both interest and the false assumption it was dead. What interested me the most was whether I could re-use it's little 7-segment LCD. As you'd expect from such a calc, it's very primitive - you know the type, reflective, 10x 7-segment digits plus 10 decimal points, 3 thousand separators (apostrophes, I guess), M, E and a negative number indicator. Passive matrix, I guess. No controller on board for sure. 34-pin connection to the PCB. No markings whatsoever on the display - no model number, manufacturer or serial number, and googling for phrases like "generic calculator LCD" or "Citizen calculator LCD" reveal nothing.
Probing with a multimeter around the pins indicates that it runs on 1.5V - again, not surprising, given that this calc runs on either a single coin cell or a small photovoltaic panel. Applying that voltage to random pins of the LCD briefly lights up (or should I say darkens down??) random segments, and they fade out a second or two later. The polarity seems to be irrelevant - either way, I can't seem to get more than a couple of seconds out of the segments.

So, in the end, ladies and gentlemen, how do I control this little display? Seems to me that it's a bit more involved than just applying Vcc to the right pins.
Posts: 1
Joined: Tue Apr 11, 2017 12:28 pm

Re: [HELP WANTED] Driving a calculator LCD

Postby Valen » Sun Apr 16, 2017 5:26 am

Essentially those segments are like capacitors. They need an alternating voltage (low frequency) applied to keep the segments dark. DC voltage degrades them.
These two application notes explain a bit how they work.

http://ww1.microchip.com/downloads/en/A ... 00563c.pdf

In addition there is this Arduino based article. http://www.arduinoos.com/2014/08/lcd-direct-driving/
Support Volunteer
Posts: 1512
Joined: Wed Dec 22, 2010 2:05 am

Return to General Chit Chat

Who is online

Users browsing this forum: No registered users and 1 guest