June 2006, Issue 191

Measurement System for Weight and Dimensions
Renesas M16C Platform Design Contest 2005

MEASUREMENT FRAME

The measurement frame is made of wood. I drilled holes 1² apart along the measuring surfaces at an angle pointing up toward the light. I painted the surfaces matte black in order to minimize the amount of stray reflections into the photocells.

One lead of each photocell is connected to a bare wire to ground. The other lead is connected to a special ribbon cable that attaches to the Weasure motherboard. To wire the photocells, I started with ribbon cable. The leftmost strand was pulled apart from the rest, stripped, and tinned. I trimmed the remaining conductors back 1², stripped and tinned the next lead, and then repeated the process for each photocell connection on each axis.

The photocells fit snugly in the holes I drilled in the measuring frame. I stripped 1² or so of insulation off 24-gauge wire. I put the insulation on one lead of a photocell and used a toothpick to push the photocell into place from the outside (the bare wire facing down and the insulated one facing up). With the photocells in place, I soldered a bare wire along the bottom leads and connected it to ground. I connected the tinned ends of the ribbon cable to the top (insulated) photocell leads.

In retrospect, creating circuit boards for mounting the photocells would have been a major time-saver. Preparing the ribbon cables and manually wiring and soldering all of the connections took me the better part of a day!