Development of an automatic measurement system for medical pills based on a PDMS capacitive sensor

Regular medication intake is extremely important to get the desired therapeutic effect. However, this is quite difficult for patients, especially for the elderly and patients with Alzheimer's and other neurodegenerative diseases. In this paper, we present a sensor system for the patients to monitor the number of pills in a pharmacy bottle so that missing or repeated medicine-intake can be avoided. Polydimethylsiloxane (PDMS) with a special pattern is used to make pillars as springs between metal plates to form a capacitive sensor. Stress analysis and computer simulation are conducted to prove the feasibility of the new design. A circuit for small capacitance measurement is also designed to convert the capacitance to the voltage signal. Moreover, a sandwich of five capacitive sensing layers is fabricated into a weighing system to detect the weight of a medicine bottle with pills. In the detection system, the output voltage corresponds to the weight of pills with an average sensitivity is 20.06 mV/g. We conducted experiments examining the unused pills in the pharmacy bottles. Our results indicate the number of the pills from 0 to 100 can be measured accurately. Therefore, our detection system by using the flexible PDMS capacitive sensor can detect and record the number of pills, facilitating the monitoring of medicine intake for the elderly and patients suffering from dementia.