Battery power with displays

[DenPit5]

I have built with Arduino a clock/calender which has a 16x20 LCD display, a 4 Digit LCD display for time display and a clock/timer chip which maintains its settings with a coin battery. I have tried powering the setup with 6 Eneloop AA batteries in series but it ran out of power in one day. I am looking for recommendations for a more suitable battery which would have a longer life before a recharge is required.

[andrew]

Before resorting to changing the battery there are one or two things you can do to extend the battery life. The Arduino board and your LCD's backlight will be the main two things draining your battery. First of all, if it is possible in your application, you may want to consider turning off the backlight if it doesn't need to be on all the time. Also if there are any other LED's turned on such as the 'L' LED on the Arduino make sure that is turned off as well. There is a section on the Arduino website about putting the boards into a sleep mode which may also save you a few mA's:

http://playground.arduino.cc/Learning/ArduinoSleepCode

If your using something like an Uno or a Mega, these boards are not ideal for battery powered applications. You may want to take a look at our 3.3V pro mini which can be powered from a battery without using a power hungry regulator.

To answer your original question I would take a look at Lithium Ion (Li-Io) or Lithium Polymer (Li-Po) batteries. These pack way more capacity for their size when compared to standard NiMH AA/AAA cell type batteries. There are a wealth of these available on places like eBay and Amazon and are used a lot in the radio control market. They generally come in 3 different voltages, 3.7V (1 cell), 7.2V (2 cell), and 11.1V (3 cell). The lower the voltage you can use the better as power is lost as heat stepping a higher voltage down to the required voltage. We don't sell these types of batteries ourselves but we sell little module that can charge a single cell 3.7V, and a module that will step-up a 3.7V battery to 5V.

[DenPit5]

Many thanks Andrew for advice and comments. I will look into Lithium batteries. About turning off the LCD's backlight - I am not sure how to do this. Can you please tell me how. ?

[andrew]

That would depend on what the display is I'm afraid. Is it one of ours? If not does it have separate pins to power the backlight?

[DenPit5]

Thanks again Andrew. The display is a 16 X 2 line with 16 pins like the one you sell ie:- the 1602 Model. There are no seperate pins for the backlight other than the 16 already mentioned.

[andrew]

Does it have two pins labeled 'A' and 'K' ? They will probably be the end two pins.

[DenPit5]

Thanks Andrew. The answer is Yes they do. At the moment they go to Gnd and VCC.

[andrew]

These will be the power pins to your backlight. If you disconnect one of them you should see the backlight turn off.

Unfortunately this does mean that there wont be an internal control of the backlight. You would have to control the power to it separately via a digital pin. If you do this I would consider a transistor to control the power via the digital pin as the backlights on LCD displays usually take 10's of mA of current and will probably overload your IO pin if you connect it directly.

[DenPit5]

Thanks Andrew. Not quite a simple job. I do not know which Pin I could use as the Display uses 6 and the RTC clock uses 3 so that only leaves 5,6 and 13. ??? Also I would not know how to put a transistor in circuit as I am fairly new to all this with the Arduino.

[andrew]

Well another simpler option would be to use a push button to connect the 5V supply to the backlight when it is pressed.