Sunday, March 7, 2010
I setup the 1-Wire iButton Datalogger programmer on a 9V battery for testing. Unfortunately, the power consumption was significantly higher then the Newhaven serial LCD NHD-0216K3Z-FL-GBW data sheet indicated with peak total load at 236 mA! This caused an immediate 1.1V drop and exceeded the max recommended current of the 9V lithium battery.
Fortunately, Newhaven has a new side lit RGB 20 mA backlight display NHD-0216K3Z-FS(RGB)-FBW that was a drop in replacement on the software side. There are two additional wires needed for supply and ground to indepentantly drive the backlight. This display is considerably more efficient and Pulse Width Modulation (PWM) from the Arduino significantly reduces power further with no flicker. Without PWM, total current with the Arduino Pro Mini was down to 41.5 mA. Using PWM at a reduced brightness level (but very readable in light and dark conditions), peak current drops down to 25.4 mA with average of 23.4 mA! This is a 90% drop compared to the old display at start up!
Based on the Ultralife 9V Lithium battery data sheet, I should now get ~40+ hours of run time. A simple voltage divider is monitoring battery status through an analog-in pin. For a battery powered application, the serial (in I2C mode) NHD-0216K3Z-FS(RGB)-FBW with PWM is an excellent choice!
The circuit design is finalized with the Arduino Pro Mini on the breadboard. I haven't decided yet if I will go with the protoboard shown in the renders or create a PCB in Eagle CAD...