Following the previous electronics update, a few tradeoffs has to be made.
Battery Life
Taking measurements at high rates 100+sps requires the microcontroller (MCU) to be active most of the time. This has a large impact on the battery life of the device. For this reason, we will be using larger batteries which takes up more space. In addition, we will be using 18650 Li-Ion cells as they are more energy dense than the more common LiPo cells.
Size
The size of our datalogger will be relatively large, with the majority of the space taken up by the Li-Ion cells. As a result, we will not make an attempt to compact the PCB, and optimize for performance instead.
Instrumentation
Since we are moving towards research grade instrumentation, is more economical to have the sensor interface separate from the main MCU and data storage board. This allows us to design new interfaces for different sensors as needed without redesigning the costly MCU section.
Furthermore, this means that we can adapt the datalogger to accept any kind of sensors.
Proposal
Here we present the 3rd revision electronics.
As discussed, the PCB is broken into 2 parts – motherboard and daughterboard.
At the heart of the motherboard is the ESP32, a MCU with a built-in WiFi transceiver. Stores data into a SD card and sends data over WiFi to the UAV as it flies past.
The purpose of the daughterboard is to power the various sensors and amplify the signal before sending it over to the Analog to Digital Converter (ADC) on the motherboard.
Analog signals are differential and sent over twisted pairs. This ensures that the signal is not affected by any nearby electromagnetic interference (EMI).
Lastly, the option of external power supply allows the operator to attach a high capacity battery (eg lead acid battery) for long term operation.