Contrast vs. Temperature?

hooziewhatsit

New member
I was wondering if CF had any specs on how contrast will change with temperature, for a constant Vo voltage?

I'm developing a product that will be used in vehicle cabs, so the temp range could range anywhere from 0*F to ~150*F.

I'll be using the CFAH2004K-TMI, running at 3.3v (I've read here that will work?). Vo will be connected between +3.3v and -3.3v.

I'm curious to know if a constant Vo will keep the LCD visible over this range? If not, I plan on using a digital pot to automatically change the Vo voltage to keep the LCD readable over this range (probably user defined values of 'readable')

The datasheet for that LCD says it's operating temperature range is -20 to 70*C (-4*F to 158*F). How much of that is because under normal single supply operation, the voltage range available at Vo is insufficient to provide a readable display?

-Dave
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CF Tech

I do not have any direct Vo vs Temperature data.

Googling around came up with this app note: http://www.monolitic.com/esp/Notas/tempcomp.pdf

I think to really pin it down, you would have to take some data in a temp chamber, recording the optimal Vo for an actual display at each of several temperatures in a sweep.

hooziewhatsit

New member

I hadn't thought about using a thermistor to automatically adjust the voltage. I'll have to research that more.

Thanks for the ideas!
-Dave

cosmicvoid

Master
I used to do automotive programming for Visteon, instrument cluster firmware. Some of the clusters had lcd message windows, and those had epson controller chips with the variable contrast feature. One of the cpu tasks was to periodically read the thermistor on the cluster board, do some math to convert the A/D value to a temperature, and command the lcd controller with a contrast value from a look-up table. You'd have to develop the values in the table by doing the temp chamber tests.

It would be pretty tricky to do it 'analog', with the thermistor and op-amps, etc, since the contrast vs temperature is probably not very linear.