Low Power Character LCDs Explained
As the world becomes increasingly mobile, power cords are being replaced by batteries and solar. Low power consumption has now become the primary consideration regarding new product designs.
In electronic products, LCDs require the most power and although character LCDs are not the lowest power option for a display, they offer many benefits not available with bi-stable and seven segment LCDs.
Bistable displays are expensive and require a 18V step function to change.
Segment displays only display icons, numbers, and a few letters. The segments are burned into the glass and cannot change. They are either on or off.
Below are options and considerations when choosing the correct character LCD for your low-power needs.
Monochrome displays: Graphical, Segment, and Character can be operated on 3.3V or 5V Logic voltage. 3.3V is optimum for battery powered products since two AA batteries produce 3.3V. The cost and lead time are the same.
The downside to the 3.3V version is that display becomes sluggish in colder temperatures. It is possible to add a heater, but this ends up negating the power saving of the lower voltage.
If your product will operate in colder temperatures, choose a 5V option and add a charge pump to bring the 3.3V up to 5V.
Backlights drain batteries ten to fifteen times faster than the LCD itself. Character LCDs operate on as little as 3.3V at 1mA. In some cases, they will operate down to 2.7V, but not recommend due to a loss of contrast and response time.
Power consumption jumps off the charts when you turn on that bright LED backlight, drawing anywhere from 15mA all the way up to 60mA depending on the number of LEDs and their brightness, or if you are using pulse width modulation.
If your product needs to be readable in the dark, choose a transflective display that allows the display to be readable without or without the backlight being on.
Make sure to turn off the LEDs when not needed.
Backlights can add anywhere from .80 to $1.20 each to the cost of the display.
If you do need a heater, two options are: heater film and quarter watt resistors.
Heater film is more expensive, but provides a more even flow of heat. It is a thin film that takes very little room and draws less power than resistors.
If cost is king, using ¼ watt resistors is the lowest cost option and works great. Just add a few resistors in series around the LCD glass. Only turn on the resistors when the temperature falls too low.
This is a big power saver. If you keep your LCD enclosed and insulated, then in many cases, the LEDs alone will generate enough heat to keep the display operating.
If the LCD is operating while ambient temperature is below the display’s cold temperature rating, the display will continue to operate, albeit a bit slow.
If the display is off and below its rated temperature, the display will not turn on and will require heat.
There are several other ways to reduce your power consumption. Contact us with your design needs. Our character LCDs are in stock in Chandler, Arizona. If we don’t have what you need, we can custom build according to your requirements.