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Red-neck LCD heater solution

Posted by Eric Hawkins on

When I was very young and lived in Phoenix, I saw a car in the parking lot with Minnesota license plates. It had a power cord hanging down from the radiator. I had no clue why the car needed a power cord. Now, of course, it is obvious that this is where you plugged in the car’s in-dash coffee maker for cold mornings in the winter.

Being located in Phoenix where summer temperatures reach 120+ degrees in the shade, the need to add a heater to a LCD did not come up very often. You would think that after sixteen years of supplying LCDs, someone would have asked us to add an air conditioner to a LCD.

Adding some heating element to a LCD module has become very common for many of the custom LCDs we supply. There are three methods of LCD heating available: Heated ITO glass, Film heater or ¼ watt resistors.

This short article will be limited to the ‘red-neck’ method of adding ¼ watt through hole resistors to heat the LCD’s fluid.

As a general rule, LCD technology will operate down to between -20C to -30C, without the need of a heater. As the ambient temperature drops, the fluid will start to freeze causing a slowdown in the displays response time. At some point, the display will freeze up and no longer change.

Temperatures from -30C to -40C will not permanently damage the display and once they return to warmer temperatures, the Liquid Crystal Display will operate normally.

Adding ¼ Watt resistors is one of the easiest and lowest cost methods of keeping the displays temperature north of the -30C threshold.

Adding the resistors to the LCD module:

16x2 Character LCD Amber color

We can take any standard Chip on Board (COB means the LCD glass is attached to a PCB) LCD and add a series of ¼ watt resistors to generate the necessary heat. The resistors are on a separate circuit to allow the LCD to operate independently of the resistors. There is a low one-time NRE cost to modify the display, but the difference in cost between a standard LCD an one containing the resistors is very small.

Two concerns with this solution

Power draw:

Heaters require a good deal of power. In fact, heaters alone will draw more than ten times (10x) the power required then that of the LCD alone. Add this to the power required to drive both the LED backlight and a heater and your power drain could be up to twenty times (20x) more than just the LCD alone.

If your product is battery powered, only activate the heater for very short periods of time. Set a low duty cycle.

If you are really tight on power, have your customer place your product close to their skin or better yet, place it next to hot cup of coffee (we believe a nice dark roast is best, but Focus Displays technical staff lacks enough analytical data to prove it. Research on this continues every morning.)

Insulation:

¼ Watt resistors provide a great deal of heat, but without proper insulation, the heat will not reach the LCD fluid. As is the case with all types of heaters: the better your LCD is insulated, the less power needed to keep the display warm.

Do you have a unique design requiring a LCD...Or an option on the best coffee to use to heat up a display? Give us a call at 480-503-4295.