이산화탄소(CO2) 센서 SEN0159(MG-811) – 라즈베리파이

Posted on: 2020년 07월 12일 2020년 07월 12일
Categories: 강의자료, 라즈베리파이

아두이노 버전 보기
참조
1. 라즈베리파이에서 SPI통신을 통해 아날로그 센서 값 읽기
2. 센서 원리 : http://blog.naver.com/roboholic84/220570913403
3. SPI 설정 : https://m.blog.naver.com/roboholic84/220367321777
CO2 센서(모듈명 : SEN0159, 8만원) 동작 원리
1. 센서 내부에 히터와 금속판이 있고,
2. 공기를 가열(약 40도)하면 공기의 입자가 금속판에 달라붙음
3. 입자가 달라붙는 정도에 따라 저항값이 변함
CO2 센서(모듈명 : SEN0159, 8만원), 제조업체(DFRobot), 인터페이스(Analog)
1. 참조 : 엘레파츠
2. CO2 센서(MG-811) 연결 : Analog 0번의 SVG에 각각 연결하면 됨

소스 코드

import spidev
import time

MG_PIN = 0
#아날로그 값을 입력받을 핀 정의

DC_GAIN = 8.5
#define the DC gain of amplifier
#증폭회로의 전압이득 정의

#***********************Software Related Macros********************************
READ_SAMPLE_TIMES = 10
#define how many samples you are going to take in normal operation
#추출할 샘플의 개수

READ_SAMPLE_INTERVAL = 50
#define the time interval(in milisecond) between each samples in normal operation
#샘플 추출 간격(ms)

#**********************Application Related Macros****************************
ZERO_POINT_X = 2.602
#These values differ from sensor to sensor. User should derermine this value.
#lg400=2.602, the start point_on X_axis of the curve

ZERO_POINT_VOLTAGE = 0.324
#define the output of the sensor in volts when the concentration of CO2 is 400PPM
#CO2가 400ppm일 때의 전압(volt)

MAX_POINT_VOLTAGE = 0.265
#define the output of the sensor in volts when the concentration of CO2 is 10,000PPM
#CO2가 10,000ppm일 때의 전압(volt)

REACTION_VOLTGAE = 0.059
#define the voltage drop of the sensor when move the sensor from air into 1000ppm CO2
#공기에서 1000ppm CO2로 이동할 때 센서의 전압 강하(?)

CO2Curve = [ZERO_POINT_X, ZERO_POINT_VOLTAGE, (REACTION_VOLTGAE / (2.602 - 4))]

#Two points are taken from the curve. With these two points,
#a line is formed which is "approximately equivalent" to the original curve.
#You could use other methods to get more accurate slope
#CO2 Curve format:{ x, y, slope};
#point1: (lg400=2.602, 0.324),
#point2: (lg10000=4, 0.265)
#slope = (y1-y2)(i.e.reaction voltage)/ x1-x2 = (0.324-0.265)/(log400 - log10000)


spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1350000

def analog_read(channel):
    r = spi.xfer2([1, (8 + channel) << 4, 0])
    adc_out = ((r[1]&3) << 8) + r[2]
    return adc_out


def MGGetPercentage(volts):
    volts = volts / DC_GAIN                    # 8.5로 나눔
    if volts > ZERO_POINT_VOLTAGE or volts < MAX_POINT_VOLTAGE  :  # 측정범위를 벗어나면
        return -1
    else :
        return pow(10, (volts - CO2Curve[1]) / CO2Curve[2] + CO2Curve[0])  # volt -> ppm 변환
        volts = 0;

while True:
    reading = analog_read(0)
    voltage = reading * 5 / 1024    #사용전압이 5volt이기 때문에 5
    ppm = MGGetPercentage(voltage)

    print("Reading = %d\tVoltage=%f\t" % (reading, voltage), end="")
    if ppm == -1:
        print("Under heating/beyond range(400~10,000)");
    else:
        print("ppm=%5.2fppm" % ppm);

    time.sleep(3)

import spidev

import time

MG_PIN = 0

#아날로그 값을 입력받을 핀 정의

DC_GAIN = 8.5

#define the DC gain of amplifier

#증폭회로의 전압이득 정의

#***********************Software Related Macros********************************

READ_SAMPLE_TIMES = 10

#define how many samples you are going to take in normal operation

#추출할 샘플의 개수

READ_SAMPLE_INTERVAL = 50

#define the time interval(in milisecond) between each samples in normal operation

#샘플 추출 간격(ms)

#**********************Application Related Macros****************************

ZERO_POINT_X = 2.602

#These values differ from sensor to sensor. User should derermine this value.

#lg400=2.602, the start point_on X_axis of the curve

ZERO_POINT_VOLTAGE = 0.324

#define the output of the sensor in volts when the concentration of CO2 is 400PPM

#CO2가 400ppm일 때의 전압(volt)

MAX_POINT_VOLTAGE = 0.265

#define the output of the sensor in volts when the concentration of CO2 is 10,000PPM

#CO2가 10,000ppm일 때의 전압(volt)

REACTION_VOLTGAE = 0.059

#define the voltage drop of the sensor when move the sensor from air into 1000ppm CO2

#공기에서 1000ppm CO2로 이동할 때 센서의 전압 강하(?)

CO2Curve = [ZERO_POINT_X, ZERO_POINT_VOLTAGE, (REACTION_VOLTGAE / (2.602 - 4))]

#Two points are taken from the curve. With these two points,

#a line is formed which is "approximately equivalent" to the original curve.

#You could use other methods to get more accurate slope

#CO2 Curve format:{ x, y, slope};

#point1: (lg400=2.602, 0.324),

#point2: (lg10000=4, 0.265)

#slope = (y1-y2)(i.e.reaction voltage)/ x1-x2 = (0.324-0.265)/(log400 - log10000)

spi = spidev.SpiDev()

spi.open(0, 0)

spi.max_speed_hz = 1350000

def analog_read(channel):

r = spi.xfer2([1, (8 + channel) << 4, 0])

adc_out = ((r[1]&3) << 8) + r[2]

return adc_out

def MGGetPercentage(volts):

volts = volts / DC_GAIN # 8.5로 나눔

if volts > ZERO_POINT_VOLTAGE or volts < MAX_POINT_VOLTAGE : # 측정범위를 벗어나면

return -1

else :

return pow(10, (volts - CO2Curve[1]) / CO2Curve[2] + CO2Curve[0]) # volt -> ppm 변환

volts = 0;

while True:

reading = analog_read(0)

voltage = reading * 5 / 1024 #사용전압이 5volt이기 때문에 5

ppm = MGGetPercentage(voltage)

print("Reading = %d\tVoltage=%f\t" % (reading, voltage), end="")

if ppm == -1:

print("Under heating/beyond range(400~10,000)");

else:

print("ppm=%5.2fppm" % ppm);

time.sleep(3)

계산과정 풀이 : 엑셀 계산
1. ZERO_POINT_X = 2.602 <– x : 400ppm~10,000ppm (log(400)=2.602, log(10,000)=4)
2. ZERO_POINT_VOLTAGE = 0.324 <– 400ppm일때 측정되는 전압(volt)
3. MAX_POINT_VOLTAGE = 0.265 <– 10,00ppm일때 측정되는 전압(volt)
4. REACTION_VOLTAGE = 0.059 <– ???
5. 계산 : 측정된 전압이 0.309라면
  1. 0.309 * 5 / 1024 –> 0.00150879
  2. (0.00150879 – 0.324) / (0.059 / (2.602 – 4)) + 2.602 –> 2.9574
  3. math.pow(10, 2.9574) –> 907 ppm
ppm과 volt 관계 차트

whan0623

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