Beehive Scale

Intro

My father is a beekeeper. During a short school break in the 2022 summer, he presented me with a problem:

“I want a device that can notify me when honey is in a hive”.

This device would save him the trouble of opening the beehive, which is a laborious, invasive task. Honey bees use their propolis, a kind of glue, to cover openings and secure the hive’s structure. To open the hive, the propolis must be broken, resetting the bee’s work and weakening security. Beekeepers must occasionally open their hives to check the health and production state, but it is best to minimize this disturbance.

So how can we be sure a hive has honey? Honey is much heavier than brood or bees, so I reckoned a pressure sensor can do the job. I looked for large pressure sensors online, but couldn’t find anything that wouldn’t punch a hole in my dad’s wallet. Perhaps for one hive it would be fine, but beekeepers tend to have multiple - my father included. So, we would need to make our own sensor tailored to our needs.

We thought about multiple different solutions. At first, my father was convinced to take a mechanical approach, such as using springs. This is plausible, but we would need to buy some powerful springs. Thinking of the cheapest solution, I realized I could apply some physics II theory.

Building a large pressure sensor

You don’t need to be a magician to create a capacitor; it’s likely you have the materials to build one right now. A capacitor is just two parallel metal plates with insulating material, called the dielectric, isolating them. Here’s a formula for capacitance:

C = ε A / D

C is the capacitance, ε is the dielectric constant, A is the area of the overlapping plates, and D is the distance between the plates.

Because the distance is inversely proportional to the capacitance, capacitors can be used as pressure sensors. We confirmed this theory by building a capacitor with aluminum foil (originally for baking) as the plates and a newspaper as the dielectric material. Jumper wires were soldered to each plate and connected to a multimeter for measuring capacitance. Our capacitor was large enough to act as a structural base for a beehive, so we placed one on top and started stacking weight while watching the multimeter reading rise.

Building the circuit

We can build a large, inexpensive capacitor, place it underneath a hive, measure its capacitance, and compare it to previous measures to evaluate a change in weight. However, we need an inexpensive circuit to replace our multimeter. To measure an unknown capacitor in a resistor-capacitor (RC) circuit, we need to measure the time constant τ, which is the time for the voltage across the plates to rise from 0 volts to 63% of the supply voltage.

Pause: This part is still in progress, as this project is relatively new. Apologies for the wait.