Sensors III.... Awaiting... Jens Dalsgaard Nielsen - 1/25

Transcription

1 Sensors III... Awaiting... Jens Dalsgaard Nielsen - 1/25

2 NTC resume which end of curve? Accuracy Selection of R, R ntc Jens Dalsgaard Nielsen - 2/25

3 NTC II - simple version #define NTC_A E-03 #define NTC_B E-04 #define NTC_C E-06 #define NTC_D E-08 #define NTC_R #define ADC_Q 1024 #define FIXED_R #define V_SUP 5.0 float NTC_temp() { int i; float t, v, r, l; i = analogread(a0); v = V_SUP*i/ADC_Q; // 10 bit so [0-1023] == [0 - V_SUP] = [0-5.0V] r = v * (FIXED_R) / (V_SUP - v); l = log(r / NTC_R); } // steinhart & hart formula (2) on page two in datasheet // see circuit above in figure t = 1.0/ (NTC_A1 + NTC_B1 * l + NTC_C1 * l * l + NTC_D1 * l * l * l); return t; // in Kelvin! Jens Dalsgaard Nielsen - 3/25

4 Accuracy Fixed resisor in series (10kOhm) ~ 1 o/o tolerance NTC quality datasheet [ ] o/o ADC 10 bit ~= 1 o/oo 5 Volt supply 1 o/o?? to sum up o/o accuracy Varies over the range May need calibration (Dependent on your needs) not trivial!!! Jens Dalsgaard Nielsen - 4/25

5 3 axis analog accelerometer MMA > 466 mv/g : > 10 % NEEDS CALIBRATION Jens Dalsgaard Nielsen - 5/25

6 Analog sensors - resume Easy to interface Accuracy is your problem EOF Jens Dalsgaard Nielsen - 6/25

7 Primitive network aka Digital interfaced sensors Fieldbusses Instrument busses Jens Dalsgaard Nielsen - 7/25

8 Field busses not today at later semesters Jens Dalsgaard Nielsen - 8/25

9 1 asynchron, 2 synchron busses Jens Dalsgaard Nielsen - 9/25

10 CANBUS, ARCNET, 485, 422, I2C/TWI, SPI,ZIGBEE, ZWAVE and a few more.... Jens Dalsgaard Nielsen - 10/25

11 CANBUS, ARCNET, 485, 422, I2C/TWI, SPI,ZIGBEE, ZWAVE and a few more. We are interested in Master-slave solutions intelligent master (arduino, TMS,...) non intelligent slaves: accelerometer, gyro, temperature,... Cheap Rudimentary error control Cable length is not an important issue due to previous point Jens Dalsgaard Nielsen - 11/25

12 Synchronious communication SPI & I2C ( or IIC) SPI peer to peer -> not selected I2C multi slave pullup resistors SDA - data SCL- clock Jens Dalsgaard Nielsen - 12/25

13 Communication 1) Master can send data to slave 2) Master can request data from slave Slave is register based register 0 : parameter 1 (gain for ADC) register 1: writing a 1 will initiate ADC (just an example) You can write to one or more registers You can read one or more registers Up to you (as chip designer) to use this for communication Jens Dalsgaard Nielsen - 13/25

14 master transmit master start 7 address bits 8 databits Jens Dalsgaard Nielsen - 14/25

15 SIMPLE I2C SLAVE model (hex) ;-) You can only read 2 bytes Reading 2 byte will 1) start ADC in 2) send back 2 bytes result Jens Dalsgaard Nielsen - 15/25

16 Slave can slow master Jens Dalsgaard Nielsen - 16/25

17 Arduino - exercise has an I2C interface normally as master but can act as slave... Jens Dalsgaard Nielsen - 17/25

18 hook 'em up Jens Dalsgaard Nielsen - 18/25

19 Arduino I2C master and slave // MASTER #include <Wire.h> void setup() { Wire.begin(); // join i2c bus (address optional for master) } // SLAVE #include <Wire.h> void setup() { Wire.begin(8); // join i2c bus with address #8 Wire.onReceive(receiveEvent); // register event Serial.begin(9600); // start serial for output } void receiveevent(int howmany) Jens Dalsgaard Nielsen - 19/25

20 master write to slave byte x = 0; void loop() { Wire.beginTransmission(8); // transmit to device #8 Wire.write("x is "); // sends five bytes Wire.write(x); // sends one byte Wire.endTransmission(); // stop transmitting } x++; delay(500); Jens Dalsgaard Nielsen - 20/25

21 ... and slave reads #include <Wire.h> void setup() { Wire.begin(8); // join i2c bus with address #8 Wire.onReceive(receiveEvent); // register event } void loop() { delay(100); } // function that executes whenever data is received from master // this function is registered as an event, see setup() void receiveevent(int howmany) { while (1 < Wire.available()) { // loop through all but the last bq char c = Wire.read(); // receive byte as a character Serial.print(c); // print the character } int x = Wire.read(); // receive byte as an integer Serial.println(x); // print the integer } Jens Dalsgaard Nielsen - 21/25

22 Jens Dalsgaard Nielsen - 22/25

23 Arduino I2C master reads void loop() { Wire.requestFrom(8, 6); // request 6 bytes from slave device #8 while (Wire.available()) { // slave may send less than requested char c = Wire.read(); // receive a byte as character Serial.print(c); // print the character } delay(500); } Jens Dalsgaard Nielsen - 23/25

24 Arduino Slave writes void setup() { Wire.begin(8); // join i2c bus with address #8 Wire.onRequest(requestEvent); // register event } void loop() { delay(100); } // function that executes whenever data is requested by master // this function is registered as an event, see setup() void requestevent() { Wire.write("hello "); // respond with message of 6 bytes // as expected by master } Jens Dalsgaard Nielsen - 24/25

25 exercise Design a slave which can receive 1 byte and will save this in an variable will transmit this byte back +1 when requested If byte received by slave is turn on LED turn off LED 13 Master shall send 2 request data and print it send 3 request data and send 13 delay 1 second send 14 Jens Dalsgaard Nielsen - 25/25