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How to interface with kid's wrist watch glass LCD?

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nandiram

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Hi,

A couple of day back, my daughter destroyed her cute litttle bunny wrist watch. Well, only the plastic band got chewed. The clock was still working.

So I tore it off and got the PCB out. The PCB is hardly 20 mm in dia, has a crystal, a button battery, and a glass LCD. The glass LCD is 14mm wide and 6mm high. It can only show 4 digits with a colon (blinking second) in between. The glass LCD is connected to PCB via a flaxible rubberized black colored ribbon. The PCB has only 13 connections with the LCD.

I have used LCD modules before with my PIC development board, and that was not so hard. This is so, because the LCD modules have the controllers built in and all my PIC had to do is to send data through data pins and control few 'control' pins, that's it. Everything was done by the controller chips on the modules.

But now I have a bare glass LCD, with no controller. I do not even know which of these 13 pins do what. And frankly, I do not know how to interface with bare glass LCD.

I have read up farely good amount of articles to understand how LCD works (polarization and stuff), but did not find anything useful beyond that. Surprizingly, I could not find much DIY projects on this.

Can anybody help me by sharing their valuable knowledge? The following pointers will be of real healp.

1. If you have working knowledge with bare glass LCDs, I would love to listen to you.

2. If you know any online project which explains how to interface with bare glass LCD, please let me know the links.

3. If you know any controller chip which is meant for controlling these basic glass LCDs, please point me to that datasheet, or IC part number.

4. Do these glass LCDs need to be fed with any clock for them to work?

5. I have a small logic analyzer with which I can probe the 13 pins while the clock is working. What should I look for? I do not even know which pin in ground. There are few pins that are showing 0 volts. I have no idea which one is true ground pin.

Hoping to see lot of lights.

Regards,
Nandi
 

M!k

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There's a good application note by Microchip about passive LCDs: LCD Fundamentals Using PIC16C92X Microcontrollers
As you've read a lot about it you'll also know that there's no ground connection at the display glass, just connections for segments and backplanes.
But perhaps you can use the battery ground as ground for your logic analyzer. Better use a DSO to see the signals.
There's also no clock. All signals are altered by the display controller.

Everything's about segments, backplanes, Mux, Bias and different voltages. Try to determine these values.
They are needed if you want to connect the glass to another controller. e.g. PIC.
 

nandiram

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Hey M!K,

Thanks for the reply.

After posting the message to this board I found a company called pacific display devices. THey have lot of informetion in their website. From their I found some standalone LCD controllers, and pointer to 2 AtMega with integrated LCD drivers. So, I searched microchip and they also have quite a few. I am going to buy one of these and do some playing.

Yes, right now it is pretty much playing. But it may lead to some interesting project, for example, a weekly sprinkler timer with 16 on time and 16 off time settings. If I buy the PIC to drive the LCD, I may as well use the rest of the PIC resources to make something useful out of it :)

--Nandi
 

galgatenikhil

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Hi Nandi,

Did you get the wrist watch LCD working?

I am trying the same.

Please let me know as soon as possible.

Thanks,
Nikhil
 

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