Pablo Andrés García

A capacitive electrode with fast recovery feature

Capacitive electrodes (CEs) allow for acquiring biopotentials without galvanic contact, avoiding skin preparation and the use of electrolytic gel. The signal quality provided by present CEs is similar to that of standard wet electrodes, but they are more sensitive to electrostatic charge interference and motion artifacts, mainly when biopotentials are picked up through clothing and coupling capacitances are reduced to tens of picofarads. When artifacts are large enough to saturate the preamplifier, several seconds (up to tens) are needed to recover a proper baseline level, and during this period biopotential signals are irremediably lost. To reduce this problem, a CE that includes a fast-recovery (FR) circuit is proposed. It works directly on the coupling capacitor, recovering the amplifier from saturation while preserving ultra-high input impedance, as a CE requires. A prototype was built and tested acquiring ECG signals. Several experimental data are presented, which show that the proposed circuit significantly reduces record segment losses due to amplifier saturation when working in real environments.

A Dual-Mode Conditioning Circuit for Differential Analog-to-Digital Converters

Several devices such as load cells and pressure sensors, among others, provide differential outputs. Given that present high-resolution analog-to-digital converters (ADCs) have differential inputs, fully differential (F-D) circuits are required to adapt the sensor output to the ADC input. This paper proposes an F-D conditioning circuit that allows adjusting both differential- and common-mode signals to the levels required by the ADC. A design example is presented, and a prototype was built and tested. It transforms a differential input signal of ±25 mV with a common-mode voltage of 5 V to a differential output signal of ±5 and 2.5 V, respectively. It shows an input-referenced peak-to-peak noise of 120 nV, which results in a 112-dB dynamic range (18.7-bit noise-free resolution) for a signal bandwidth of 10 Hz.

An embedded system for evoked biopotential acquisition and processing

This work presents an autonomous embedded system for evoked biopotential acquisition and processing. The system is versatile and can be used on different evoked potential scenarios like medical equipments or brain computer interfaces, fulfilling the strict real-time constraints that they impose. The embedded system is based on an ARM9 processor with capabilities to port a real-time operating system. Initially, a benchmark of the Windows CE operative system running on the embedded system is presented in order to find out its real-time capability as a set. Finally, a brain computer interface based on visual evoked potentials is implemented. Results of this application recovering visual evoked potential using two techniques: the fast Fourier transform and stimulus locked inter trace correlation, are also presented.

A versatile hardware platform for brain computer interfaces

This article presents the development of a versatile hardware platform for brain computer interfaces (BCI). The aim of this work is to produce a small, autonomous and configurable BCI platform adaptable to the users needs.

A simple and reproducible capacitive electrode

Capacitive Electrodes (CE) allow the acquisition of biopotentials through a dielectric layer, without the use of electrolytes, just by placing them on skin or clothing, but demands front-ends with ultra-high input impedances. This must be achieved while providing a path for bias currents, calling for ultra-high value resistors and special components and construction techniques. A simple CE that uses bootstrap techniques to avoid ultra-high value components and special materials is proposed. When electrodes are placed on the skin; that is, with coupling capacitances C(S) of around 100 pF, they present a noise level of 3.3 µV(RMS) in a 0.5-100 Hz bandwidth, which is appropriate for electrocardiography (ECG) measurements. Construction details of the CE and the complete circuit, including a fast recovery feature, are presented.

Capacitive driven–right–leg circuit design

Capacitive electrodes allow to pick–up biopotentials through a dielectric layer, without using electrolytes. However, this technique is vulnerable to electric–field interference, mainly to common mode voltages produced by the 50 Hz power–line. A fully Capacitive Driven Right Leg (CDRL) circuit is proposed to reduce the patient common mode voltage vCM. The design of this circuit takes into account several factors as electrode impedance, stray coupling capacitances and amplifier transfer function response. All these parameters are addressed to ensure the circuits stability in most biopotential acquisition scenarios. Monte Carlo analyses were performed to find the worst conditions, resulting in a maximum CDRL gain between 70 and 80 dB. The CDRL was implemented as an independent block that can be used for different applications such as ECG, EMG or EEG. Several experimental results are presented, showing good quality recordings even using SE amplifiers, an appropriate approach for multichannel acquisition systems.

An Embedded Hybrid BCI Speller

The present work proposes an embedded real time hardware-software platform for brain computer interfaces (BCI) based on steady state visual evoked potentials (SSVEP) and alpha rhythm. The complete implementation of the embedded system is described, including the electroencephalogram (EEG) amplifier, signal acquisition and processing stages, and practical implementation. The device is a 25 characters hybrid-BCI speller that uses 5 visual stimulus and visual alpha waves for control instructions. The system focuses on simplicity and portability, using only two electrodes, a simple EEG amplifier and an embedded computer. The speller does not require any training from the user and provides real time biofeedback to increase attention on stimuli. The platform is based on an embedded system with a real time operative system, Windows CE. Experimental results are presented in order to show the feasibility of the proposed system.

Barcode reader sensor based on optical navigation technology

The Waste Electrical and Electronic Equipment (WEEE) cause a major ecological problems. This paper shows how to reuse an optical mouse and CD reader into disuse in the implementation of a linear low-cost scanner to be used for educational purposes. The heart of the device, the ADNS2610 sensor of AVAGO, has ability to record images in grayscale. It is equipped with optical navigation technology for computer mouse applications among other possible uses. The mechanical part of a CD reader is also rescued to perform the linear movement of the scanner.