Raspberry pi tutorial #2

Raspberry pi tutorial #2

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  1 Raspberry Pi Tutorial#2 - Measuring the light - Dong Ho Son POSTECH Pohang, Korea donghoson@postech.ac.kr
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  2 Measuring the light- Overview  Let’s use the sensor • Sensor : Analog  Digital − Analog : continuous − Digital : discrete • Photoresistor 3 pin (or light-dependent resistor, LDR) − A light-controlled variable resistor − The resistance increases/decreases according to the brightness of light • Let’s configure the circuit − The brightness of the LED is changed according to the brightness of the environment − If dark, the LED is turned on − If bright, the LED is turned off
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  3 Measuring the light- Overview  Measure the brightness of light and turn on/off the LED  Necessary Components • 1 x Raspberry Pi • 1 x Breadboard • 1 x red LED • 1 x Resistor • 1 x Photoresistor 3 pin • Jumper cables Anode Cathode GND OUT VCC
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  4 Measuring the light– Circuit configuration  Ground pin  the cathode of the LED  The anode of the LED  a ballast resistor  The ballast resistor  the pin GPIO 18  VCC of photoresistor  3.3V  OUT of photoresistor  the pin GPIO 17  GND of photoresistor  Ground pin Cathode Anode
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  5 Measuring the light- Python  Import RPi.GPIO as GPIO • Import Python GPIO module  GPIO.setmode(GPIO.BCM) • Use Broadcom chip number  GPIO.setup(17, GPIO.IN) • Select GPIO #17 as input pin • Measure the brightness using sensor  GPIO.setup(18, GPIO.OUT) • Select GPIO #18 as output pin • Turn on/off the LED
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  6 Measuring the light- Python  GPIO.input(17) • Return 0(bright) or 1(dark)  GPIO.output(18, GPIO.LOW) • Turn off the LED  GPIO.output(18, GPIO.HIGH) • Turn on the LED  time.sleep(1) • Delay for 1 second
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  7 Measuring the light- Result  If bright, the LED is turned off  If dark, the LED is turned on Cathode Anode