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