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I'm using a QC2004A 20 x 4 LCD (blue back ground/white text) with a PCF8574 I2C backpack in a GPS trip logger. I leave the trip logger in the car. When I start the car, the trip logger starts automatically. Everything works fine except on days when the car is hot inside. When first started up the LCD is all white (like if the contrast potentiometer is set incorrectly). As the A/C cools the inside of the car, the LCD returns to normal.

Is this heat slowly killing the LCD or will the LCD be OK?

The QC2004A data sheet I have shows:

  • Operating Temperature -20°C~70° (158°F)
  • Storage Temperature -30°C~80° (176°F)

While the car is warm, I doubt the temperature exceeds the specs.

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    \$\begingroup\$ Don't confuse the temperature of the LCD with the temperature of the air. \$\endgroup\$ – AndrejaKo Jun 24 '19 at 13:20
  • \$\begingroup\$ @AndrejaKo Where does OP mention the temperature of the LCD? \$\endgroup\$ – Huisman Jun 24 '19 at 13:38
  • \$\begingroup\$ What distant is ambient? The 'ambient' temperature very close to the LCD could be higher than the 'ambient' temperature elsewhere in the car due to other electronics heating the air there locally (not due to the LCD itself). But still, I wonder if it would hit the 70°C. I rather suspect the circuit (outside the LCD) controlling the background power (maybe the contrast potentiometer itself?) is affected by temperature. \$\endgroup\$ – Huisman Jun 24 '19 at 13:57
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    \$\begingroup\$ The optimal contrast setting for LCD displays varies with ambient temperature. hantronix.com/files/down/tempcomp.pdf \$\endgroup\$ – Dampmaskin Jun 24 '19 at 14:53
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    \$\begingroup\$ @Dampmaskin That sounds like an answer to me. \$\endgroup\$ – Hearth Jun 24 '19 at 17:02
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Heat has been known to kill all sorts of electronics, but damage to the LCD module is not required in order to explain your particular contrast issue.

The optimal contrast setting for LCD displays varies with ambient temperature.

You can adjust the contrast manually to compensate for this, or you can make a circuit with a thermistor to do it automatically.

Application note: Temperature Compensation for LCD displays

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  • \$\begingroup\$ Are LCD modules so cost sensitive that the thermistor is normally left off? \$\endgroup\$ – D Duck Jun 24 '19 at 20:36
  • \$\begingroup\$ You can buy modules with or without temperature compensation. It's up to the product designer to choose a module with TC, implement TC themselves, or leave it out altogether. Nobody wants to pay extra mony (or extra current draw) for a feature they don't need, and most LCD modules are used in a fairly narrow temperature range. Contrast also depends on other factors like viewing angle, whether the display is multiplexed or not, battery voltage if not regulated, etc. So if you're designing for commercial or important use, it's best to put some thought into it. \$\endgroup\$ – Dampmaskin Jun 24 '19 at 22:45

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