1. (Dec 23, 2012) After a successful burn of a preliminary sketch onto the standalone ATmega328P (see tutorial) the display cycles the range from 0.00 to 9.99. Note the 16 MHz resonator attached to pins 9 and 10. The resonator replaces the 16 MHz crystal and 2-22pf capacitors.

2. A Reset button with a pull-up resistor is added. When the Reset button pressed, the display resets back to -0.00 after a few seconds.

3. Currently, to demonstrate that an external interrupt can be detected, a button with a pull-down resistor is configured so INT 1 (ATmega328P pin 5) can trigger on RISING as, eventually, the photointerrupter will do as the ruler with its tick marks pass through.

4. To support a standalone version a PCB was required. EAGLE was used to develop the schematic and board layout (EAGLE files). M. Elia created both the calibrated ruler and terrific acrylic base. The Gravometer sketch is also included in the zip file.

5. Here is a video confirming the results of three trials.