ALFRED MAZHINDU

Transcription

1 SENSORS AND ACTUATORS LAB_2 ALFRED MAZHINDU DATA ACQUISITION FROM AN OPTICAL SENSOR LABORATORY STAGE 2_10/11

2 Contents Table of Figures... 2 Lab: Data acquisition from an optical sensor... 3 Introduction... 3 Data acquisition... 3 Test Program... 4 EXERCISE 1: CREATING A SUCCESSIVE-APPROXIMATION ADC... 5 Test program... 5 EXERCISE 2: TIMING THE SUCCESSIVE-APPROXIMATION ADC... 6 Test program... 6 EXERCISE 3: ASSESSING AN OPTICAL SENSOR... 8 Test program... 8 Observations... 9 EXERCISE 4: THOUGHTS ON MODIFYING AN OPTICAL SENSOR REFERENCE Table of Figures Figure 1: Diagram showing the components used to make an ADC and how they are connected together Figure 2: Diagram showing the connections to the source and detector in the optical sensor... 8 Figure 3: Circuit diagram for the optical sensor... 8 Figure 4: Test Results of 255 the maximum voltage displayed and Figure 5: Test Results of 9 the minimum voltage displayed Figure 5: The source and detector in the optical sensor connected to Flash card... 10

3 Lab: Data acquisition from an optical sensor Introduction The session involves creating a data acquisition system that displays the digitised output from a sensor on the development board s seven segment LED display, evaluating the sensor and making some suggestions for a modified sensor design Data acquisition Flight applications card has a terminal block with 5 V and 0 V connectors and a volt-in connector to which a voltage from an external sensor can be applied. A switch on the board can be set to compare this external voltage with the output from a DAC in order to digitise the voltage. The digital input signal for the DAC is provided by port B of the PIC16F84, whose eight lines must be configured as outputs. The output of the comparator is connected to bit 0 of port A of the PIC16F84 and this line must be configured as an input. The arrangement is shown in the figure below. Port A (Input and Output) 4 0 Comparator Analogue voltage to be digitised 7 Port B (Output) DAC Analogue Output 0 Figure 1: Diagram showing the components used to make an ADC and how they are connected together.

4 Test Program The comparator outputs logic 1 when the external voltage is greater than the DAC voltage and outputs logic 0 when the external voltage is less than the DAC voltage. Sensors and Actuators lab2 Data acquisition from an optical sensor Please type your name and your partner's name below Alfred Mazhindu BEng EEE Stage 2 const char pattern[] = /* */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, /* 8 9 A b C d E F */ 0x80, 0x98, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e ; unsigned char segments[4] ; /* storage for values to display in led segments */ void delay(unsigned int) ; void DecNumber(unsigned char) ; void refresh_segments (unsigned char) ; unsigned char adc(void) ; void main( void) unsigned char i ; set_bit (STATUS, RP0) ; TRISB = 0x00 ; /* all o/p */ TRISA = 00001b ; clear_bit (STATUS, RP0) ; while(1) endless loop i = adc() ; DecNumber (i) ; refresh_segments (i) ; end of main void delay(unsigned int n) unsigned int i ; for (i = 0 ; i < n ; i++) ; void DecNumber(unsigned char value) unsigned int temp ; put values to display in array segment segments[2] = value / 100 ; temp = value % 100 ; segments[1] = temp / 10 ; segments[0] = temp % 10 ; void refresh_segments (unsigned char i) if (i < 100) goto miss1 ; PORTB = pattern[segments[2]] ; PORTA = 2 ; miss1: if (i < 10) goto miss2 ; PORTB = pattern[segments[1]] ; PORTA = 4 ; miss2: PORTB = pattern[segments[0]] ; PORTA = 8 ; end of refresh_segments unsigned char adc(void) unsigned char i,bitn0,bitn1,value = 0; /* local variables */

5 bitn1 = b; set bit mask bitn0 = b; value = 0 ; for(i =1;i<=8;i++) value =(value bitn1); PORTB = value; nop () ; nop () ; 2.5 us delay if (PORTA & 1 == 0) value = (value & bitn0); output of the comparator bitn1 = (bitn1>>1); right shift bitn0 = ~bitn1; clear bit return value; end of adc EXERCISE 1: CREATING A SUCCESSIVE-APPROXIMATION ADC The first exercise was to create a new program from test4.c by replacing the ramp-and-compare ADC function with a successive approximation ADC function. The only way was to implement program and to proceed as instructed from lab script. The following program code was edited and displays the converted voltage for values from 0 to 255 using the adjustable voltage source provided on the Flight application card. Test program Sensors and Actuators lab2 Data acquisition from an optical sensor Please type your name and your partner's name below Alfred Mazhindu BEng EEE Stage 2 const char pattern[] = /* */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, /* 8 9 A b C d E F */ 0x80, 0x98, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e ; unsigned char segments[4] ; /* storage for values to display in led segments */ void delay(unsigned int) ; void DecNumber(unsigned char) ; void refresh_segments (unsigned char) ; unsigned char adc(void) ; void main( void) unsigned char i ; set_bit (STATUS, RP0) ; TRISB = 0x00 ; /* all o/p */ TRISA = 00001b ; clear_bit (STATUS, RP0) ; while(1) endless loop i = adc() ; DecNumber (i) ; refresh_segments (i) ; end of main void delay(unsigned int n) unsigned int i ; for (i = 0 ; i < n ; i++) ; void DecNumber(unsigned char value) unsigned int temp ; put values to display in array segment segments[2] = value / 100 ; temp = value % 100 ; segments[1] = temp / 10 ; segments[0] = temp % 10 ; void refresh_segments (unsigned char i) if (i < 100) goto miss1 ; PORTB = pattern[segments[2]] ;

6 PORTA = 2 ; miss1: if (i < 10) goto miss2 ; PORTB = pattern[segments[1]] ; PORTA = 4 ; miss2: PORTB = pattern[segments[0]] ; PORTA = 8 ; end of refresh_segments unsigned char adc(void) unsigned char i,bitn0,bitn1,value = 0; /* local variables */ bitn1 = b; set bit mask bitn0 = b; value = 0 ; for(i =1;i<=8;i++) value =(value bitn1); PORTB = value; nop () ; nop () ; 2.5 us delay if (PORTA & 1 == 0) value = (value & bitn0); output of the comparator bitn1 = (bitn1>>1); right shift bitn0 = ~bitn1; clear bit return value; end of adc EXERCISE 2: TIMING THE SUCCESSIVE-APPROXIMATION ADC Measuring the time it takes this ADC function to perform conversion times using a stopwatch. I have edited the program code from previous exercise 1. The time the ADC while converting input voltages around the low, middle and maximum settings of the voltage control. At low voltage = 10 sec At middle voltage = 9 sec At high voltage = 9 sec The program code below displays and controls the time output as illustrated on lab script. Test program Sensors and Actuators lab2 Data acquisition from an optical sensor Please type your name and your partner's name below Alfred Mazhindu BEng EEE Stage 2 const char pattern[] = /* */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, /* 8 9 A b C d E F */ 0x80, 0x98, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e ; unsigned char segments[4] ; /* storage for values to display in led segments */ void delay(unsigned int) ; void DecNumber(unsigned char) ; void refresh_segments (unsigned char) ; unsigned char adc(void) ; void main( void) unsigned char a; unsigned int i; set_bit (STATUS, RP0) ; TRISB = 0x00 ; /* all o/p */ TRISA = 00001b ; clear_bit (STATUS, RP0) ;

7 PORTA = 4; for (i = 0 ; i < ; i++) endless loop a = adc() ; DecNumber (i) ; refresh_segments (i) ; PORTA = 8; while (1); end of main void delay(unsigned int n) unsigned int i ; for (i = 0 ; i < n ; i++) ; void DecNumber(unsigned char value) unsigned int temp ; put values to display in array segment segments[2] = value / 100 ; temp = value % 100 ; segments[1] = temp / 10 ; segments[0] = temp % 10 ; void refresh_segments (unsigned char i) if (i < 100) goto miss1 ; PORTB = pattern[segments[2]] ; PORTA = 2 ; miss1: if (i < 10) goto miss2 ; PORTB = pattern[segments[1]] ; PORTA = 4 ; miss2: PORTB = pattern[segments[0]] ; PORTA = 8 ; end of refresh_segments unsigned char adc(void) unsigned char i,bitn0,bitn1,value = 0; /* local variables */ bitn1 = b; set bit mask bitn0 = ~bitn1; value = 0 ; for(i =1;i<=8;i++) value =(value bitn1); PORTB = value; nop () ; nop () ; 2.5 us delay if (PORTA & 1 == 0) value = (value & bitn0); output of the comparator bitn1 = (bitn1>>1); right shift bitn0 = ~bitn1; clear bit return value; end of adc

8 EXERCISE 3: ASSESSING AN OPTICAL SENSOR This exercise I was observing the behaviour of the sensor in terms of its digital output from the ADC under different conditions such as nearby objects. The sensor can be used as a limit switch, paper sensor, rotation sensor, coin sensor, position sensor etc. Figure 2: Diagram showing the connections to the source and detector in the optical sensor 5 V 390 IR LED Phototransistor 220 k To ADC 0 V Figure 3: Circuit diagram for the optical sensor The program code below from Exercise 1 was used to operate the proximity sensor. Test program Sensors and Actuators lab2 Data acquisition from an optical sensor Please type your name and your partner's name below Alfred Mazhindu BEng EEE Stage 2 const char pattern[] = /* */ 0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, /* 8 9 A b C d E F */ 0x80, 0x98, 0x88, 0x83, 0xc6, 0xa1, 0x86, 0x8e ; unsigned char segments[4] ; /* storage for values to display in led segments */ void delay(unsigned int) ; void DecNumber(unsigned char) ; void refresh_segments (unsigned char) ; unsigned char adc(void) ; void main( void) unsigned char i ; set_bit (STATUS, RP0) ; TRISB = 0x00 ; /* all o/p */ TRISA = 00001b ; clear_bit (STATUS, RP0) ; while(1) endless loop i = adc() ;

9 end of main DecNumber (i) ; refresh_segments (i) ; void delay(unsigned int n) unsigned int i ; for (i = 0 ; i < n ; i++) ; void DecNumber(unsigned char value) unsigned int temp ; put values to display in array segment segments[2] = value / 100 ; temp = value % 100 ; segments[1] = temp / 10 ; segments[0] = temp % 10 ; void refresh_segments (unsigned char i) if (i < 100) goto miss1 ; PORTB = pattern[segments[2]] ; PORTA = 2 ; miss1: if (i < 10) goto miss2 ; PORTB = pattern[segments[1]] ; PORTA = 4 ; miss2: PORTB = pattern[segments[0]] ; PORTA = 8 ; end of refresh_segments unsigned char adc(void) unsigned char i,bitn0,bitn1,value = 0; /* local variables */ bitn1 = b; set bit mask bitn0 = b; value = 0 ; for(i =1;i<=8;i++) value =(value bitn1); PORTB = value; nop () ; nop () ; 2.5 us delay if (PORTA & 1 == 0) value = (value & bitn0); output of the comparator bitn1 = (bitn1>>1); right shift bitn0 = ~bitn1; clear bit return value; end of adc Observations a) The sensor is sensitive to ambient light, and the sensor output values when it is pointed in different directions towards distant objects is 255 V. High voltage towards an object. b) The minimum output I got is 9V when the sensor is stationary at one position. Low voltages output when not near an object. c) The sensor is useful to detect objects in front of it and the useful range is around 253 V of the device, so it means the sensor has to be closer to an object to detect (short range).

10 Figure 4: Test Results of 255 the maximum voltage displayed and Figure 5: Test Results of 9 the minimum voltage displayed Figure 5: The source and detector in the optical sensor connected to Flash card EXERCISE 4: THOUGHTS ON MODIFYING AN OPTICAL SENSOR Suggestions on how I might modify the sensor construction, in order to increase the effective range, the resistor value has to be reduced and the result in high current and provides enhanced intensity. Suggestions on how I might modify the operation of the sensor, in order to increase its effective range, by modifying the program code. Example a: You could put a tube in front of the detector to screen it from ambient will only see a small fraction of the, surrounding region and so the background illumination will be substantially reduced. A lens placed at the end of a tube of length equal to the focal length of the lens could also be used to increase the amount of light falling on a small detector and simultaneously reduce the background illumination. Example b: Modulate the light signal to make it more sensitive to the emitted light. REFERENCE SEM1 SENSORS AND ACTUATORS (CY-0205M_2010-1_SEM1_A) > DOCUMENTS > RESOURCES - PING JIANG > LABORATORY EXPERIMENTS > C CODE > SaA_C_Lab SEM1 SENSORS AND ACTUATORS (CY-0205M_2010-1_SEM1_A) > DOCUMENTS > RESOURCES - PING JIANG > LECTURES > OPTICAL SENSOR.