Barometric Pressure Sensor (SPI)

Copy
1/*
2
3 SCP1000 Barometric Pressure Sensor Display
4
5 Shows the output of a Barometric Pressure Sensor on a
6
7 Uses the SPI library. For details on the sensor, see:
8
9 http://www.sparkfun.com/commerce/product_info.php?products_id=8161
10
11 http://www.vti.fi/en/support/obsolete_products/pressure_sensors/
12
13 This sketch adapted from Nathan Seidle's SCP1000 example for PIC:
14
15 http://www.sparkfun.com/datasheets/Sensors/SCP1000-Testing.zip
16
17 Circuit:
18
19 SCP1000 sensor attached to pins 6, 7, 10 - 13:
20
21 DRDY: pin 6
22
23 CSB: pin 7
24
25 MOSI: pin 11
26
27 MISO: pin 12
28
29 SCK: pin 13
30
31 created 31 July 2010
32
33 modified 14 August 2010
34
35 by Tom Igoe
36
37 */
38
39// the sensor communicates using SPI, so include the library:
40#include <SPI.h>
41
42//Sensor's memory register addresses:
43
44const int PRESSURE = 0x1F;      //3 most significant bits of pressure
45
46const int PRESSURE_LSB = 0x20;  //16 least significant bits of pressure
47
48const int TEMPERATURE = 0x21;   //16 bit temperature reading
49
50const byte READ = 0b11111100;     // SCP1000's read command
51
52const byte WRITE = 0b00000010;   // SCP1000's write command
53
54// pins used for the connection with the sensor
55// the other you need are controlled by the SPI library):
56
57const int dataReadyPin = 6;
58
59const int chipSelectPin = 7;
60
61void setup() {
62
63  Serial.begin(9600);
64
65  // start the SPI library:
66
67  SPI.begin();
68
69  // initialize the  data ready and chip select pins:
70
71  pinMode(dataReadyPin, INPUT);
72
73  pinMode(chipSelectPin, OUTPUT);
74
75  //Configure SCP1000 for low noise configuration:
76
77  writeRegister(0x02, 0x2D);
78
79  writeRegister(0x01, 0x03);
80
81  writeRegister(0x03, 0x02);
82
83  // give the sensor time to set up:
84
85  delay(100);
86}
87
88void loop() {
89
90  //Select High Resolution Mode
91
92  writeRegister(0x03, 0x0A);
93
94  // don't do anything until the data ready pin is high:
95
96  if (digitalRead(dataReadyPin) == HIGH) {
97
98    //Read the temperature data
99
100    int tempData = readRegister(0x21, 2);
101
102    // convert the temperature to celsius and display it:
103
104    float realTemp = (float)tempData / 20.0;
105
106    Serial.print("Temp[C]=");
107
108    Serial.print(realTemp);
109
110    //Read the pressure data highest 3 bits:
111
112    byte  pressure_data_high = readRegister(0x1F, 1);
113
114    pressure_data_high &= 0b00000111; //you only needs bits 2 to 0
115
116    //Read the pressure data lower 16 bits:
117
118    unsigned int pressure_data_low = readRegister(0x20, 2);
119
120    //combine the two parts into one 19-bit number:
121
122    long pressure = ((pressure_data_high << 16) | pressure_data_low) / 4;
123
124    // display the temperature:
125
126    Serial.println("\tPressure [Pa]=" + String(pressure));
127
128  }
129}
130
131//Read from or write to register from the SCP1000:
132unsigned int readRegister(byte thisRegister, int bytesToRead) {
133
134  byte inByte = 0;           // incoming byte from the SPI
135
136  unsigned int result = 0;   // result to return
137
138  Serial.print(thisRegister, BIN);
139
140  Serial.print("\t");
141
142  // SCP1000 expects the register name in the upper 6 bits
143
144  // of the byte. So shift the bits left by two bits:
145
146  thisRegister = thisRegister << 2;
147
148  // now combine the address and the command into one byte
149
150  byte dataToSend = thisRegister & READ;
151
152  Serial.println(thisRegister, BIN);
153
154  // take the chip select low to select the device:
155
156  digitalWrite(chipSelectPin, LOW);
157
158  // send the device the register you want to read:
159
160  SPI.transfer(dataToSend);
161
162  // send a value of 0 to read the first byte returned:
163
164  result = SPI.transfer(0x00);
165
166  // decrement the number of bytes left to read:
167
168  bytesToRead--;
169
170  // if you still have another byte to read:
171
172  if (bytesToRead > 0) {
173
174    // shift the first byte left, then get the second byte:
175
176    result = result << 8;
177
178    inByte = SPI.transfer(0x00);
179
180    // combine the byte you just got with the previous one:
181
182    result = result | inByte;
183
184    // decrement the number of bytes left to read:
185
186    bytesToRead--;
187
188  }
189
190  // take the chip select high to de-select:
191
192  digitalWrite(chipSelectPin, HIGH);
193
194  // return the result:
195
196  return (result);
197}
198
199//Sends a write command to SCP1000
200
201void writeRegister(byte thisRegister, byte thisValue) {
202
203  // SCP1000 expects the register address in the upper 6 bits
204
205  // of the byte. So shift the bits left by two bits:
206
207  thisRegister = thisRegister << 2;
208
209  // now combine the register address and the command into one byte:
210
211  byte dataToSend = thisRegister | WRITE;
212
213  // take the chip select low to select the device:
214
215  digitalWrite(chipSelectPin, LOW);
216
217  SPI.transfer(dataToSend); //Send register location
218
219  SPI.transfer(thisValue);  //Send value to record into register
220
221  // take the chip select high to de-select:
222
223  digitalWrite(chipSelectPin, HIGH);
224}