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From: Gary Tait
Subject: Re: LCD Question
References: <firstname.lastname@example.org> <email@example.com>
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Date: Sat, 02 Nov 2002 10:29:11 -0500
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On Fri, 1 Nov 2002 19:08:17 -0500, "Jack B. Pollack"
>Thanks Wafer & Gary ,
>Both of your posts were helpful. From Wafer's post I envisioned the whole
>process as a data and address type of scenario for each digit, but was
>baffled when I masked out with tape one of the contacts to find what
>appeared to be random segments disabled.
>Gary's post was right on the money 'it is not even on a digit basis'.
>Now that I understand how this works let me try to ask a little more
>We have a really nice Jacob Jensen digital clock that only displays time in
>24 hour format, this drives my wife crazy. When I opened the clock I found
>a hardwired jumper to set the time format.
>The clock now displays time in 12 hour format, but the display lacks a PM
>indicator making the alarm function useless.
>I am sure that the 'blob' is outputting a signal for PM, but how do I find
>it (In a data/address scenario I would have looked for it on the 'digit'
>with the other indicators ('Alarm on', time set, etc)? But since segments
>are 'random' how do I find it?
Is there an AM indicator? If so, you could wire in a circiut (I think
an XOR gate), to figure if that segment is active, and use that signal
to drive your PM indicator, when it is "not" AM.
>Secondly, I was going to drive a small low current LED for the PM indicator.
>I dont think this will work based on the explanation of the 2 square waves.
>I guess I could NAND them and then use the NAND as a driver for the LED (I
>dont know if the square wave voltage is too low to drive TTL). Any
>suggestions on indicate PM would be appreciated.
I think an XOR gate is what you want. You can use other elements of
the chip as an invertor, if needed. I suggest a CD4070
>"Jack B. Pollack" wrote in message
>> I have several questions about a LCD display in a portable clock that I
>> There are 13 'pad' connections on the PC board that connect the LCD
>> to the PCB and 'blob chip'. If I look at these connections with a scope
>> there is a square wave on each of them.
>> The display has no electronics in it, how is the data transferred to the
>> display and decoded? How are the individual segments on the display
>> The second question is about the LCD backlight:
>> There is a thin film (looks like a piece of paper) with 2 contacts on it.
>> When 50V AC is applied the film glows blue and backlights the LCD. I would
>> like to find out more about this type of backlight technology and how to
>> build a similar driver circuit for the backlight.
>> Any insight would be appreciated.
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