Issues for Consideration

The above schematic was used for the production of the prototype printed circuit boards.  Several hardware issues were not addressed since the prototypes were primarily developed to debug coding issues.

LCD

The LCD used for prototyping was the ASI-D-1223A-G-BS/W manufactured by All Shore Industries.  Any of the 122x32 LCDs with the SED 1520 or compatible driver could be used for final production.

R1

A potentiometer is currently being used for the prototypes to adjust the contrast of the LCD.  A resister may be suitable for this task depending on how quickly the power source voltage drop decreases over time due to battery drainage. 

R2

A 1K resister is used to control the current supplied to the Atmel chip.  Depending on the power supply solution this may vary.

D1-D5

The diodes are used to create an AND gate to trip the external interrupt when a button is pushed.  A silicone AND gate or surface mount diodes are possibilities if they would better design. 

Battery

Currently the prototype device is using two 3V CR2032 Lithium coin batteries.  These batteries are placed in series to create the 6V potential drop needed for the LCD and the 3V needed for the Atmel chip.  Ultimately the device should only use one battery if possible. 

Is it possible to use one 3V coin battery or better yet, one 1.5V battery and add circuitry to boost the voltage to the 5V needed by the LCD and 3V for the Atmel chip.

Power On-Off

When the device is powered off the Atmel chip consumes less then 1uA.  The LCD is currently consuming 0.5 mA.  Circuitry must also be added to allow the LCD to be connected to the power supply when on, and disconnected when the device is off.  A transistor could be connected to one of the free pins on PORTA to act as a switch for the LCD.