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Hi-temp LCD

I've only once spec'd an LCD display in a product. I recall lots of different issues, criteria (transflexive, transmissive, high temperature, etc.). But, have largely forgotten most of those issues (IIRC, transmissive/transflexive/reflexive have to do with the treatment of the back of the display)

I recall response time was sensitive to excitation voltage and temperature. I don't recall frequency being particularly critical. And, I know that duty cycle isn't, either (there are hacks you can exploit by using different duty cycles on different segments)

Today, I had to troubleshoot an electrical problem on a friend's vehicle so took an el-cheapo DMM along with me to probe voltages, continuity, etc. Leaving it in the back of her car was an oversight as when I went to retrieve it, the display was uniformly "black" (not just the segment areas).

I've experienced this before and know that it "recovers" once cooled. But, it got me wondering what is actually happening (physically) inside the glass when this condition manifests?

Reply to
Don Y
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ISTR it is bad for their ultimate longevity to have a waveform duty cycle that isn't roughly 50:50 duty cycle in the long term.

The liquid crystals have gone into the homogeneous state where they no longer change the polarisation of the light passing through them.

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Isn't a bad explanation. All bets are off if it gets so warm that the seal on the display fails due to differential expansion. The LCD will recover when it cools down and realigns.

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Regards, 
Martin Brown
Reply to
Martin Brown

A liquid crystal is something in between a fluid and a paste. Heat it , and it turns into a fluid entirley, and stops working. cooling restores the long chain molecules to the proper state(more or less). Those molecules stand like a cats hair normally on the glass surface. But not, if they get heated to much.

Reply to
Sjouke Burry

I used to leave a small LCD thermometer in my car before such things were always included in the dash display. On returning to the car one blisteringly hot day in summer 2003 I found the display completely black. It returned when the device had cooled down. Out of interest I pressed the min/max button to recall the highest temp that day. I was amazed to find it was 61.3 deg C! Of course, it could have been higher but the thermometer might not have stored it once it reached that temp.

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Jeff
Reply to
Jeff Layman

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