Micro-Electro-Mechanical Systems (MEMS) based sensing system

Our Client

Our client is the Institute for Transportation at Iowa State University. They are looking for an inexpensive, reliable, and robust way to gather data on soil temperature and moisture throughout a period of time. Currently, our client is using commercial sensors and data acquisition modules that together cost anywhere from $400 to $1,000. Because of the costs being incurred, the Institution for Transportation at Iowa State has reached out to ECpE Senior Design to fabricate a data acquisition module to record soil characteristics.

Project Description

We have been tasked with creating a data acquisition module in order to observe soil moisture and soil temperature throughout the course of a month. Originally our team had been given MEMS sensors to interface with. However, our team found these sensors to be unreliable and ineffective. Because of this, we decided to go outside the scope of our project to create our own soil moisture/temperature sensors. One of our sensors is shown below.


The sensor is designed to measure soil moisture by measuring capacitance between the two plates on the PCB. The sensor will measure temperature by using a thermistor on the PCB. Both measurements will be read by the data acquisition unit as a voltage.

Our Solution

Our solution is to design a module that will allow us to accurately read and store data gathered from our new sensors. A block diagram of our proposed solution is shown in the following figure.


Using this block diagram we created a data acquisition system on a breadboard to prove it worked correctly before moving to a PCB. Once the PCB schematic was created we decided to utilize the PCB as the lid of the box which would house the battery and protect the components on the DAQ. In order for this to work, we created a custom box with a gasket to keep water from getting inside the box. We used a waterproof switch and connectors to make sure all components will be protected during precipitation. Our final assembly is shown in the images below.




As shown in the pictures above, the sensitive components of our data acquisition unit are completely shielded from moisture and precipitation. The user is also able to access the SD card and charging port easily by the use of thumb screws (no tools required).