Background

Springhouse is a tech startup that aims to reduce food waste through an innovative smart refrigerator ecosystem. One of the refrigerator’s core features are drawers that can detect when produce ripens and spoils by measuring the release of specific gases. For this R&D-focused project, the team was tasked with creating a fixture of drawers equipped with this technology that could be deployed remotely to collect gas data at an offsite lab. I worked with an electrical engineer and a director-level systems engineer. I was responsible for the full mechanical design and assembly of the rig, as well as optimizing the layout and assembly of all sensors, electrical components, and other hardware.

Desktop Scale Prototypes

As an initial proof of concept, I created a simplified representation of a single drawer. This included a sealed container to store produce, a fan to mix the gases of various densities in the container, sensors connected in series via PVC tubing, and a pump to circulate air in and out of the container over the sensor.

Iteration

As we developed more confidence in the desktop test fixture, we increased the fidelity of the prototype and testing by introducing calibration gases and a dehumidifier. This helped maintain the dew point of the air that passed over the sensors and ensured our data was as accurate as possible.

Initial Machined Prototype

I designed and outsourced a set of drawers to begin integrating our test setup to the final physical rig. We ordered an initial drawer to test sealing and ensure data consistency between our initial desktop setup and the new drawer format. After validating the design and making any necessary changes, we would order the final three sets of drawers.

I designed the drawers to be CNCed from ABS sheet stock thick enough to hold heat set threaded inserts along their sides. This made assembly simple and reduced cost by minimizing billet size.

The drawers sealed via a closed-cell foam gasket that lined the perimeter of the drawer face. A series of magnets attracted the face of the drawer to the body of the drawer, compressing the gasket.

CAD Development

For this project, it was important to maintain an accurate CAD model, detailing exactly how all of the mechanical and electrical hardware would be laid out. This included all sensors, pumps, filters, cameras, LEDs, MCUs, power supplies, and additional modules specified by the electrical engineer.

The top shelf of the rig had an electrical plate that acted as the “brains” of the rig and housed all components needed for wireless communication.

Each of the three drawers had a corresponding sensor plate behind them that housed all components needed for measuring gas data pulled from the main drawer.

Final Machined Prototype

After testing the single drawer and finalizing the CAD, I outsourced the full set of three drawers to be CNCed. I built the frame of the rig from 80/20 and assembled all drawers and electronics onto the rig.

The final prototype was deployed remotely at a food science lab, and we were able to successfully measure gases released from various different fruits and vegetables to detect ripening and spoilage.

Gas Sensing Rig