Electrooculographics Systems
Ing. Jesus Talavera SuarezUNSA
Manuel Y. Carreño Vilca UNSA
[email protected] Jorge C. Ramirez Vilca
UNSA [email protected]
Carlos A. Durand Mendoza UNSA
[email protected] Roger Vilela Arias
UNSA [email protected]
Summary
This project involves the design and construction of an acquisition system biopotentials inexpensive to capture and display the electrooculographics signal (EOG) and can be used in biomedical applications. The project aims to have an amplification system hardware fully functional from which we can capture at EOG signal and display it in the form of data, which were appropriate in software created in Visual Basic 6.0
I. INTRODUCTION
EOG signal biopotentials is one of the weakest of the human body on a scale ranging from microvolts to a few milivolts and a bandwidth of very low frequency. The system hardware must perform signal amplification and filtering it to unmask the signal from the electromagnetic interference that accompany always considering safety in design of the experiment. Thus, the system hardware consists of an isolated stage differential pre-amplification, a stage of filtering and signal processing that defines the bandwidth required with minimal distortion, and a final amplification stage.
Electrooculographic signal obtained is transmitted via the PC USB port, the circuit having 2 different types of microcontrollers, a charge for the conversion of analog signals and the recognition of a pattern generating a code for each type of movement, and the other for intercommunication with the pc. The signal obtained has to propose to serve as the fundaments for a future deployment to biotechnology application, to help physically disabled people.
II. GENERAL CONSIDERATIONS
The electrooculographics system design is divided into two parts, the design of hardware (circuits) and software design (interface with PC)
A. Electrooculographic systems design HARWARE
The system comprises a signal acquisition phase, through the electrodes, the pre-amplification, a filtering stage, a amplification and offset, a phase encoding and conversion of the signal and finally a stage with intercom PC below been given a description of each circuit.
ELECTRODES DIFERENTIAL AMPLIFIER FILTER AMPLIFICATION OFFSET - CONTROL PATTERN RECOGNITION
Fig. 1. - Electrooculographic systems design HARWARE, Block Diagram.
(PIC 16F877)
USB INTERFACE
For acquisition the signal had to be applied to the input filter or directly to the electrodes, the circuitry of vertical motion of horizontal movement, which only vary in the horizontal motion has an electrode over the reference electrode which generates The emergence of a TL082 on the board of the horizontal movement, by this feedback is used, taking into account that it is not necessary to have two reference electrodes, below show circuit in stages.
For the vertical movement:
Fig. 2. - Vertical acquisition circuit. For the horizontal movement:
Fig. 3.-Horizontal acquisition circuit Descriptions of circuits
The signal is captured for the cables electrodes then passes through a RC filter to delete the Electromagnetic noise, signs
RF, and others signals that can be capture for the electrodes, then this signal enters a one stage of differential and pre - amplied by INA114,which is a cheap OPAM of biomedical instrumentation, it has a amplification of G=1+50Kohm/RG, RG=560*2ohm, generating a gain ( G= 45.64) , the next stage is a eighth-order filter with a cutoff frequency of 15HZ (fc=15Hz), below a stage of amplified formed by two amplifier, a fixed and an adjustable amplifier, where the fixed amplifier has a gain of 10, and the adjustable amplifier is regulated to what the output signal works with the saturation of OPAM, thus having an output signal of 5 and 5, the signal of -5 is regulated by the Zerner diode thus ensuring an output signal of 5.1 and 0V.
Fig. 4. - Gain trace. Signals from the circuits above are respectively:
Fig. 6. - Signal acquisition circuit horizontal. Signals have the following characteristics:
500ms/div 2v/div
For the noise filter:
Fig. 7. – Filter circuit.
Each circuit of the filter consists of 3 TL082. They give us a frequency of 15 HZ.
For Data Analysis and Interface USB:
Fig. 8. – Interface USB circuit.
B. Electrooculographic systems design SOFTWARE
For electrooculographics system design part SOFTWARE, describing the part of both microcontrollers and the design of the interface in Visual Basic 6.0.
Programming the PIC 16F877
The PIC is responsible for the acquisition of analog signals, as well as conversion and identifier patterns as well as the generation of a code for each type of movement (horizontal, vertical, up and down).
It is necessary to use 2 channels of the module ADC. The detection of the movement is in 11000000b (~4.4 volts) and in 01000000b (~0.6 volts). To achieve this, a comparison was made bit by bit, and thus detects the movement and thus can send data to pic 18f2550 to display on the computer
CENTER: PB = 0 RIGHT: PB0 = 1 PB1 = 0 LEFT: PB0 = 0 PB1 = 1 UP: PB2 = 1 PB3 = 0 DOWN: PB2 = 0 PB3 = 1
Programming the PIC 18F2550
The PIC has the task of sending data from the PIC 16F877 circuit to the PC via the USB port, which is designed to operate with the program. For this we use the programming PICBasic PRO program, the power we used to have a good system performance data transfer.
Program in VISUAL BASIC 6.0
The interface is made in Visual Basic 6.0, which was performed with the help of software HIDE, which served a very useful when communicating with the USB port. The software is made so that circles show positions in ways that represent the 4 basic movements of the eye: Right, Left, Up and Down.
Using IF ... THEN instructions in Visual Basic, the bits generated by the pic16f877 are detected, changing the color of the circle which indicates that there is a movement in that direction. In the block text. In the text block shows the movement detected, which may be right, left, up and down
Fig. 9. – Interface. C. Materials
Microcontrolador (PIC16F877A, Microchip) Microcontrolador (PIC18f2550, Microchip) Instrumentation amplifier (INA114) Operational amplifier (UA741, TL082). Electrodes
D. Electrode Position
Fig. 10. – Without movement.
Fig. 11. – LEFT – RIGHT movements.
Fig. 12. – DOWN – UP movements.
The position of the electrodes is crucial for a correct signal.
E. Conclusions
• The acquisition of the signal was made by means of electrodes that are connected by cables, which for lack of resources had to be manufactured by ourselves, it was initially built with type coaxial cables, then turn to tow, and finally produce electrodes with our type of twisted pair cables, it is worth noting that an important factor was taken into account in the fabrication of the electrodes was the same weight which is a source of error because they produce a bad connection between the electrode and the face of the person you are testing.
• To correct the data acquisition by means of the electrodes was necessary placement in the circuit filter at the entrance of each electrode which contributes to the noise generated by the movement of the wires of
the electrodes (RF) that initially be despised, but the course of the project is concluded that it was vitally important to remove such interference.
• As the signal sequence of microvolts the position of the electrodes is another factor that can go wrong to take the data, that is why the measure was taken to capture the movement "Right" and " Left "must be put to the electrodes 2 cm from the eye (to the respective sides), to capture the movement of" Top "equal to 2 cm (top), unlike the movement of" Down "which has its electrode connected to only 1 centimeter of the eye (near the lid). For the reference electrode may change its position only requirement being that a bone in his face, in our case, place it in the forehead almost to the center of the face.
F. References
• Thijssen JM, Pinckers A (1974) Contralateral effects in the electrooculogram. Acta Ophthalmol (Copenh) 52:441-454
• PROJECTE FI DE CARRERA- Desarrollo de un sistema de adquisición y procesado de señales electrooculográficas para el diagnóstico de la ataxia. • Juan Ramos Castro ( [email protected] ), Tesis de
Doctorado “Detección de micro potenciales Auriculares de alta frecuencia”, Capítulo2.
https://www-eel.upc.es/~wwwdib/tesis/Jramos/cap2.pdf
• Jhon G.Webster, “Médical Instrumentation Applications and Design”, Capítulo 3, Amplificadores biopotenciales, Interferencia de equipos Eléctricos, Pág. 249.
• Jhon G.Webster, libro: “Médical Instrumentation Applications and Design”, Capítulo 3, Amplificadores biopotenciales, Tabla 6.1: “Sumary of Performance Requirements for Electrocardiographs (Anonimous, 1991)”
