Data Transmission Unit
During my first co-op at Lorcan I prototyped with a TI microcontroller to create a long-range mesh network that transmits environmental sensor data. I also tested with solar panels and rechargeable batteries to see if the microcontrollers could operate only on solar power in the wilderness. My last project was to design a housing for the electronics as a proof of concept product to show investors.
Design Considerations
- IP 65 Ingress Protection - Dust and Splash Proof
- Size - Requires a specific surface area to get sufficient power from solar panels
- UV Resistant and withstand large temperature fluctuations
- Electronics need to be securely mounted inside
- Withstand harsh outdoor environments
Housing Solutions
- The overall shape is a pyramid such that the solar panel faces all directions and any light snow will run off of the enclosure. Housing consists of a base and lid that gets fastened with three screws.
- The material of the housing was selected to be ASA plastic which is similar to ABS but is much more UV-resistant. Its mechanical properties do not change very much with temperature and can be easily injection moulded or 3D-printed.
- A silicone rubber gasket will go around the perimeter of the device and is compressed using the three screws that fasten the base to the lid. Silicone rubber has great mechanical properties at low temperatures and will keep it's elasticity. To seal wires entering the housing from the exterior, cable glands can be used.
- A polyurethane foam is inside the housing surrounding the electronics. This protects it from impacts but also provides thermal insulation.
- Inside the housing there are several ribs to improve the rigidity and strength of the part. Screw bosses can also be found in the base of the housing for fastening all of the hardware.
Electrical Design
The TI CC1312R is an MCU with a Sub 1-GHz antenna that is used for transmitting environmental data long distances. The intent is that this board can be placed in the wilderness and will always be supplied with enough power to transmit. I designed and tested a prototype circuit that uses a 12V DC solar panel to recharge 1.5V Li-ion batteries. Four of these batteries then power the MCU with 6V such that it is always on. The charging circuit consists of a voltage regulator, a diode and a capacitor to ensure that the batteries are always supplied with 1.5V for recharging.
Takeways
I learned a lot about product design by working through all of the steps in the design process. I did extensive modelling in SolidWorks. I learned how to do material selection based on constraints using CES Edupack. I got my first taste of circuit design, prototyping, and testing. Last, I was able to perform DFM and design a product that can be mass-produced via injection moulding. To improve the prototype, the solar panels need to be oriented more horizontally. This will allow each panel to absorb more solar power and the batteries will be able to recharge faster.