Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service Direct Sensor to Microcontroller Interfacing Presented by: Zivko Kokolanski, M. Sc. Research director: Prof. Dr. Cvetan Gavrovski Nis, November 2010

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service OUTLINE Comparison of programmable signal conditioning techniques Introduction to direct sensor- C interface Single point calibration technique Sources of measurement uncertainty Experimental results and discussion Effective number of resolution bits Conclusions

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service Sensor Programmable signal condit.circuit C A/D SensorOSCILLATOR C A/D converter based programmable measurement system Oscillator based programmable measurement system Conversion of the measurement quantity in to proportional electrical signal and use of an A/D converter Techniques based on measurement of frequency, period or duty cycle C Sensor C ref,R ref Relaxation oscillator Direct sensor-microcontroller interface

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service t p1 t p2 V TL Microcontroller PoPo PiPi RxRx C RpRp HZ 1 0 In NT 0 t p2 f0f0 DIRECT SENSOR- C INTERFACE BASED ON MEAS. OF DISCHARGING TIME OF RC CIRCUIT

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service CONSTANTS BUT: The constant k is not very stabile The output resistances and leakage currents of the microcontroller ports cause gain, offset and nonlinearity errors Therefore direct sensor-microcontroller interface in practice is realized by using some calibration method DIRECT SENSOR- C INTERFACE BASED ON MEAS. OF DISCHARGING TIME OF RC CIRCUIT

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service Microcontroller Po1Po1 PiPi RxRx C Po2Po2 RcRc RpRp VcVc t V th V0V0 tptp txtx tptp tctc SINGLE POINT CALIBRATION

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service Reference freq. uncertainty, Quantization uncertainty, Uncertainty in the triggering point, Program related errors, Uncertainty of the reference element They are small for short meas. intervals. Every digital system makes ±1 sample error. Errors are smaller for higher f 0. Better reference element. Dynamic element matching technique. Noise from the mC during the execution of the program cycle. SOURCES OF MEASURMENT UNCERTAINTY

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service Microcontroller PoPo PiPi C PxPx RxRx PcPc RcRc R0R0 PoPo PiPi C PxPx RxRx PcPc RcRc R0R0 VrVr + - K Schmitt trigger circuit Comparator circuit Without external circuit Schmitt triggerComparator with divider Comparator with TL431 (t x )[ s] 0,360,160,191,34 u(t x )/ t x x ,320,140,171,18 IMPROUVING THE MEASUREMENT UNCERTAINTY BY USING ADITIONAL ELECTRICAL CIRCUITS

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service Relative standard measurement uncertainty Effective number of bits PIC16F877 MSP430F2274 ATmegaAVR128 EFFECTIVE NUMBER OF RESOLUTION BITS

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service CONCLUSIONS Direct sensor- C interface is alternative approach for conditioning the resistive and capacitive sensors without use of A/D converter, Single point calibration is the simplest calibration technique that cancels the contribution of the unstable parameters, The output resistances and leakage currents of the microcontroller ports cause gain, offset and nonlinearity errors, One of the uncertainty sources is the microcontroller program noise while execution the program cycle, This uncertainty can be improved by using Schmitt Trigger or comparator circuit (one extra resolution bit), The ENOB when using Schmitt Trigger circuit at time constant of 4ms was approximately 11.5/12.3 bits Although this approach achieves relatively low measurement resolution (arround 13 bits max) and low sampling speed (arround 30 sps),its performances are remarkable considering the simplicity and the cost

Projekt ISSNBS DAAD Deutscher Akademischer Austausch Dienst German Academic Exchange Service THANK YOU FOR YOUR ATTENTION! Practical demonstration…