How to keep your LCD warm or Choosing the best display for reallllllly cold temperatures

Design Engineering Series: LCD’s Designs® made simple through coffee

It seems strange for someone living in Phoenix to offer solution to keep LCD’s operating in cold temperatures. I mean we don’t have too many snow days. In fact, the temperature today is down to a mild, almost jacket weather, 108 in the shade. Brrrrrr.

I can empathize since I’ve seen photos of snow and cold, but we have much experience keeping LCD’s operating in ultra-cold ambient temperatures. Many of our customer’s product operate in the cold. In fact, we just finished a pump design for wells located all over the world in ugly-cold environments.

Choosing the correct LCD technology from the start simplifies the design and ensures the displays success when temperatures drop below zero.

Choosing the correct type of display for cold weather operation.

All display technology can be broken down into two categories: Multi-Color vs. Single Color (Monochrome)

Multi-color displays: TFT’s and OLED’s, display up to 64 million unique colors vs. Monochrome, which is limited to one-color background and a different color segment. As a general rule when selecting a display technology for a battery powered product: Color displays draw more power than monochrome displays, since monochrome is still readable when the backlight is off.

Below is a breakdown of each technology and how the perform in cold weather.

OLED

When you get to heaven, most displays will be OLEDs (Organic Light Emitting Diodes). They are:

Sharp

Low-power

Thin

Ability to operate down to -40C.

Of all the display technologies, OLEDs are the best for cold temperature.

The challenge is their popularity. Demand is outstripping the current supply which means:

1. Less popular displays are prone to the dreaded End-Of-Life (EOL) curse.

2. Lead-Times increase when large OEMs such as: E –cigs, Fit-Bits and Cell Phone manufacturers, demand more resources knocking smaller OEMs to lower priority.

TFT:

Thin Film Transistor Displays have been in use for many years and don’t look to go away anytime soon. Examples include: Laptops, Tablets, Medical equipment and most Consumer products. As a general rule most multi-color displays larger than six inches are TFT’s.

They operate down to -20C an -30C with the key advantage over OLEDs being their low probability to go EOL. They do suck (suck = engineering term meaning current draw) more power than an OLED or monochrome and may not be the best choice for battery powered products.

Monochrome:

Monochrome (single color) displays come in three varieties: Segment (photo), Character (photo and link) and Dot-Matrix(photo).

Monochrome displays consist of a nematic fluid between two layers of glass. There are several types of fluids and many will operate to -30C.

Keeping your LCD warm

We have a few suggestions to keep your display operating on those nights when the temps drop below -40C

Coffee:

This is my personal favorite. Nothing warms up an engineer on a cold, brisk morning better than a nice hot cup of dark roast coffee (unless you are in the UK and then hot tea will work). Well, the same is true for LCDs. I’m not suggesting pouring coffee on the LCD. But placing the shivering, cold display next to a hot steaming cup of coffee may be enough to push it over the threshold to start operating.

Why coffee to heat up the LCD?

If a display is operating as the temperature decreases, it will continue to operate when it reaches its lower limit. However, if the display is turned on at the coldest temperature, it may not operate right away. Warming up the display a bit may be enough.

If, for some strange reason, your customer does not have a hot cup of coffee nearby to heat up the poor frozen display, it might be wise to add something to the LCD to generate heat. Below are a few strategies that have worked.

Heater Film:

This is a clear film attached to the front polarizer (glass) to heat up the fluid. We have seen this used mainly in military and aviation products. It’s a bit more expensive, but requires the least amount of power if battery life is a concern.

Resistors:

This is a redneck solution, but it works, Y’All. Place several ¼ watt resistors around the base of the LCD. These babies are low-cost and generate heat. The downside is they are not the most power efficient solution for battery products.

We are able to add the resistors to the LCD with a separate power for independent operation of the resistors.

LED Backlights

The LED backlight may add enough heat to keep the display running during cold spells. The LED draws 10X the power (current) of a monochrome display. One option to conserve power is to pulse the LEDs.

Insulation:

Enclose the LCD within a case blocking the wind and holding in the heat, allowing the user to turn off the heater/resistor/LED for short periods of time to save battery life.