Arduino-based portable system for bioelectrical impedance measurement

Electrochemical Impedance Spectroscopy (EIS) has been recently proposed as a simple non-invasive technique to monitor the amount of fat and liquids contained inside the human body. While the technique capabilities are still questioned, a simple and low cost device capable of performing this kind of measurements would help testing it on many patients with minimal effort. This paper describes an extremely low cost implementation of an EIS system suitable for medical applications that is based on a simple commercial Arduino Board whose cost is below 50$. The circuit takes advantage of the ADC and DAC made available by the microcontroller of the Arduino boards and employs a logarithmic amplifier to extend the impedance measuring range to 6 decades without using complex programmable gain amplifiers. This way the device can use electrodes with sizes in the range of 1 cm² to 40 cm². The EIS can be measured in the frequency range of 1 Hz to 100 kHz and in the impedance range of 1 kΩ to 1 GΩ. The instrument automatically compensates the DC voltage due to the skin/electrode contact and runs on batteries. The EIS traces can be stored inside the device and transferred to the PC with a wireless link avoiding safety issues.