Prototype Optical Bee Counter
This is a single gate optical bee counter using an integrated infrared LED and photo-diode optical detector.
Two sensors are mounted face to face in front of the hive to be able to detect and count incoming versus outgoing bees.
The sensors are available in lots of 10 for about $10.
The datasheet is available here. Experimental code to count bees is available from hivetool
Now what's needed is a 32 gate (16 slot) custom circuit board with a serial multiplexer and glue electronics.
Similar work has been done using discrete components sensing reflection instead of beam break.
Solid Scale Frame & Phidgets USB Bridge
March 13 2016 Update - The following was developmental work, I now use the Hivetool sensor interface board and Octonorm frame I have been working on a hive scale base utilizing the Phidgets #1046 4 cell USB bridge (cost $90). The 24 bit USB bridge is supplied with numerous software drivers and a basic PC interface. We constructed a rigid aluminum frame using 1.25" X .75" solid aluminum bar stock. The scale frame perimeter matches the Langstroth hive body and sits under a standard wooden hive base. Four 1/4" thick load compression pads (not shown) at each corner are used to equalize the load across the four Zemic L6D 30 kG load cells (Ebay $19.99 each). Maximum hive weight 265 pounds.
Although robust this approach proved too expensive at ~$250, utilized a custom PCB and required specialized tooling to get a precise fit.