Early detection of plant diseases is crucial to minimize crop losses and reduce the usage of pesticides. Electronic Nose (E-Nose) detect volatile organic compounds (VOCs) emitted by stressed or diseased plants, and one such device is a pixelated capacitive sensor (PCS). We designed and built a setup to investigate the influence of light (wavelength and intensity) on the sensitivity of a functionalized PCS for VOCs detection. Our test results indicate that UV illumination, particularly at 375 nm, enhances the sensitivity of the PCS, with a 3-fold enhancement compared to dark conditions. The sensor showed fast saturation (<1 min) and recovery (<2 min) times, confirming the effectiveness of the chamber design for repeatable gas exposure. ... Read more

This report outlines the design and implementation of a subsystem within the automated e-nose prototype, which is based on a CMOS Pixelated Capacitive Sensor (PCS) array. The objective of the e-nose prototype is to detect the presence and identify the type of volatile organic compounds (VOCs). A potential use case is to accommodate greenhouses with these e-noses to detect infestations in plants.
The subsystem presented in this report is tasked with programming the FRDM-MCXN947 development board to enable and improve communication and control between the PCS array and the microcontroller unit (MCU). In addition, the development board is also explored to investigate the feasibility of replacing currently used external modules with on-board peripherals. To achieve this, the CTIMER and SCTIMER are analyzed and implemented with the MCUXpresso IDE. The results showed that both of these peripherals have difficulties in simultaneously generating clock signals of different frequencies required for the communication protocol between the sensor and the MCU. However, the SCTIMER is capable of generating a differential clock, currently produced by the AD9552 external clock, though with lower signal quality. ... Read more

This thesis presents the design and implementation of a socket, a chamber and an automated control system for an electronic nose (e-nose) based on CMOS Pixelated Capacitive Sensor (PCS) array chip in a Quad Flat No-Leads (QFN) 5 mm x 5 mm chip package. The objective of this project is to enable repeatable and reliable detection of volatile organic compounds (VOCs) by ensuring a gas-tight sensing environment and minimizing human intervention in experimental procedures, while ensuring good electrical connections by the socket.

A socket was developed to ensure good electrical contact using an anisotropic conductive sheet, allowing the QFN-packaged PCS chip to be inserted and removed without the need for soldering. The socket interfaces with a tightly sealed chamber to prevent gas leakage (< 0.1 ml/min) and maintain a stable gas flow across the sensor. Both components were prototyped in Polyethylene Terephthalate Glycol (PETG) and therefore do not fulfill the final requirement for heat and chemical resistance yet.

To automate gas delivery, the system integrates Bronkhorst mass flow controllers and RVM industrial microfluidic rotary valves. A Python-based graphical user interface (GUI) was developed to schedule gas flow profiles, control valve positions and compute VOC concentrations using the Antoine equation and Dalton's Law of Partial Pressures. This enables dynamic delivery of programmable VOC concentration. Although the automated control system meets most mandatory requirements and all trade-off requirements, some limitations remain. These include unreliable serial communication with the valve during automated operation, even though manual operation through the GUI is executed reliably. This inconsistency is likely caused by timing or firmware-related issues. ... Read more

This thesis addresses the development of a supporting electronics platform for a CMOS Pixelated Capacitive Sensor (PCS) array intended for high-sensitivity applications. The work focuses on enabling accurate extraction of capacitance changes at the sensor interface and translating them into signals suitable for digital processing. The design process emphasizes functional integration and signal integrity.

A custom analog front-end was developed, featuring a transimpedance amplifier (TIA) optimized for low input-referred noise and sufficient bandwidth to preserve pixel-level signal integrity. The complete analog signal path supports capacitive measurements with attofarad-level resolution and readout frequencies ranging from 1 to 100 MHz.

The main PCB integrates the readout circuitry with a central microcontroller (MCXN947), DAC-controlled programmable power supplies, and a variety of user interface connectors, all within a compact six-layer mixed-signal stackup. Particular attention was given to minimizing electromagnetic interference (EMI) and power supply noise through careful grounding, power segmentation, and layout strategies. Although the PCB theoretically satisfies most mandatory and trade-off requirements, including spatial and interface constraints, final verification of the noise performance remains pending due to fabrication lead times. ... Read more

The Epson ET-8500 inkjet printer was modified to deposit precise quantities of ink on CMOS chips, enabling the fabrication of capacitive sensors. This project explores the potential of using affordable, consumer-grade printing technology for advanced sensor development, typically requiring expensive equipment. The research focused on understanding the interaction between printed ink and environmental variables such as humidity, light, and temperature. Three measurement setups were developed to detect capacitance changes under varying conditions. The setups for light and humidity successfully generated usable data, while the temperature setup needs redesigning for consistency. Key findings include the exponential relationship between humidity and capacitance in water-based inks. Light exposure generally decreased capacitance, except for white, zinc oxide and tin oxide under UV light. A machine learning model, using a neural network with a cross-entropy loss function, effectively identified inked electrodes but requires more variance in the datasets. ... Read more

The manufacturing of sensors often requires the precise deposition of small volumes of liquid. In order to do this, expensive industrial equipment is often used, giving this form of manufacturing a high financial barrier to entry. As standard desktop inkjet printers operate by precisely depositing small volumes of paper onto a substrate, typically paper, the goal of the project was to modify a desktop inkjet printer, the Epson EcoTank ET-8500, to allow it to be used to deposit small droplets of fluid onto a CMOS sensor chip.

This report covers the design process of the hardware modifications that were necessary in order to allow the Epson EcoTank ET-8500 to print onto CMOS sensor chips packaged in a QFP- 44 package. These modifications include a custom chip tray to safely house the chips as they go into the printer, as well as an external fluid system to allow the user to easily use ink other than the stock ink provided by Epson or to put a cleaning fluid into the system in order to clear out any residue deposited by the inks used.

The results obtained indicated high levels of precision, and the system’s accuracy was sufficient for the sensor chips used. The external fluid system was also tested and successfully allowed the printer to work with fluids not placed into the built-in tanks. ... Read more