Network and Systems Laboratory nslab.ee.ntu.edu.tw

Network and Systems Laboratory nslab.ee.ntu.edu.tw Big Picture Physical world MSP430 Analog Interfacing Other Systems or ICs Digital Communication

Network and Systems Laboratory nslab.ee.ntu.edu.tw Sensors A device that converts a physical phenomenon into an electrical signal Physical phenomenon light, temperature, humidity, pressure, and etc. Electrical signal resistance, capacitance, current, voltage, and etc. Maps a physical phenomenon change to a electrical signal change

Network and Systems Laboratory nslab.ee.ntu.edu.tw Signal Path Sensors Signal Conditioning (if necessary) Convert to voltage Amplification Filtering Light Temperature Acceleration Humidity Pressure etc. Resistance Capacitance Current Voltage etc. Analog to Digital Conversion (ADC) Produce a proper output voltage level Converts voltage to digital number

Network and Systems Laboratory nslab.ee.ntu.edu.tw Sensors We Have Raw sensors Produce raw electrical signal Signal conditioned sensors Have some signal conditioning circuit Produce analog output Mostly Voltage Sometime Current

Network and Systems Laboratory nslab.ee.ntu.edu.tw Sensors We Have Digitalized sensors Have some signal conditioning circuit Convert analog to digital internally Provide digital output

Network and Systems Laboratory nslab.ee.ntu.edu.tw Our Focus Sensors Signal Conditioning (if necessary) Convert to voltage Amplification Filtering Light Temperature Acceleration Humidity Pressure etc. Resistance Capacitance Current Voltage etc. Analog to Digital Conversion Produce a proper output voltage level Converts voltage to digital number Sensors We are not going to talk about signal conditioning You can find many sensors that are signal conditioned and provide a proper analog output, or even digitalized We will focus on how to understand these signal conditioned sensors and get the output we want

Network and Systems Laboratory nslab.ee.ntu.edu.tw Some Raw Sensors Temperature Sensors Thermistors Temperature-sensitive resistor RTDs (resistive temperature devices) Temperature-sensitive resistor Thermocouples Temperature => voltage (mV) Pressure sensors Piezoresistive Resistance change with applied pressure

Network and Systems Laboratory nslab.ee.ntu.edu.tw Photodiodes Light => current Generate current proportional to light density

Network and Systems Laboratory nslab.ee.ntu.edu.tw Photodiodes Two on Taroko S1087: for visible range S : for visible to IR(infrared) range

Network and Systems Laboratory nslab.ee.ntu.edu.tw Signal Conditioned Analog Output Proximity sensor Sharp GP2D120XJ00F Analog voltage output Accelerometer ADXL330 3-axis accelerometer Analog voltage output Industry standard analog output Flow sensors, pressure sensors, gas sensors, etc. 4~20 mA, 0~5 V, 0~10 V

Network and Systems Laboratory nslab.ee.ntu.edu.tw Proximity Sensor Sharp GP2D120XJ00F Output voltage proportional to the reflection distance Measure range: 30 cm

Network and Systems Laboratory nslab.ee.ntu.edu.tw Accelerometer Analog Device Inc. ADXL330 Output voltage proportional to the acceleration Measurement range: +/- 3.6 g

Network and Systems Laboratory nslab.ee.ntu.edu.tw Gyro Invensense ISZ-500 Z axis gyro, ±500 °/sec 2.0 mV/°/sec Invensense IDG-500 X/Y axis gyro, ±500 °/sec 2.0 mV/°/sec Invensense IMU axis gyro, (±250, ±500, ±1000, ±2000) °/sec I2C interface

Network and Systems Laboratory nslab.ee.ntu.edu.tw Industry standard analog outputs Many industrial instruments provide analog outputs 4~20 mA current loop Most commonly used The instrument produce a current, range from 4 mA to 20 mA Physical measured quantity linearly maps to this current range Others 0 ~ 5 V 0 ~ 10 V

Network and Systems Laboratory nslab.ee.ntu.edu.tw 4~20 mA current loop Examples Measure temperature: 0 ~ 100 o C Measure flow speed: 0 ~ 50 m 3 /h Measurements 0 o C 50 o C 100 o C Current Output 4 mA 12 mA 20 mA Measurements 0 m 3 /h 25 m 3 /h 50 m 3 /h Current Output 4 mA 12 mA 20 mA Usually this range is user configurable

Network and Systems Laboratory nslab.ee.ntu.edu.tw How to Convert to Voltage Add a resistor

Network and Systems Laboratory nslab.ee.ntu.edu.tw Digitalized Sensors Ultrasound sensors SRF10 Interface: I2C Temperature and Humidity Sensor SHT11 Interface : manufacturer defined

Network and Systems Laboratory nslab.ee.ntu.edu.tw Digitalized Sensors Magnetometer SFE MicroMag 3-Axis Interface : SPI Applications: detecting vehicles Digital compass Hitachi HM55B Interface : UART

Network and Systems Laboratory nslab.ee.ntu.edu.tw Digitalized Sensors GPS Garmin GPS18 Interface : UART Image sensor ST VS6451 Interface: I2C

Network and Systems Laboratory nslab.ee.ntu.edu.tw Understand The Analog Sensors Most important goal Obtain the relationship between voltage and the physical phenomenon quantity you want to measure Transfer function Understand the characteristics and limitation of the sensors

Network and Systems Laboratory nslab.ee.ntu.edu.tw Sensor Characteristics Definitions Transfer Function Relationship between physical quantity and output voltage Sensitivity Ratio of change between physical quantity and output voltage Accuracy Largest expected error Linearity How linear the transfer function is Noise In real world, signal are usually coupled with noise Resolution minimum detectable signal fluctuation Bandwidth response times to an instantaneous change in physical signal

Network and Systems Laboratory nslab.ee.ntu.edu.tw Transfer Function Ratiometric? Output voltage is a ratio of supply voltage Ratiometric? Output voltage is a ratio of supply voltage ADXL330 accelerometer From ADXL330 datasheet It means when supply voltage Vs is 3 V, if the acceleration is 0 g, the output voltage will be 1.5 V (typical) It means when supply voltage Vs is 3 V, if the acceleration increase by 1 g, the output voltage will increase 330 mV (typical) Transfer function: Voltage (V) = (0.3 * acceleration (g) )

Network and Systems Laboratory nslab.ee.ntu.edu.tw Transfer Function Proximity sensor: Sharp GP2D120XJ00F Transfer function Voltage (V) = f(Distance (cm)) Not a linear function Check datasheet if the manufacturer has provided Table mapping Approximations By a few straight lines Curve fitting

Network and Systems Laboratory nslab.ee.ntu.edu.tw Transfer Function Photodiode: S1087, S From Taroko Schematic Step 1: find the relationship between light level and current Step 2: find the relationship between current and the voltage at ADC4 (V = IR) Transfer function Voltage (V) = f(light level(lx)) Calculate by yourself

Network and Systems Laboratory nslab.ee.ntu.edu.tw Sensitivity ADXL330 accelerometer Sharp GP2D120XJ00F Not a constanst Photodiode: S1087, S (Current)/(light level)

Network and Systems Laboratory nslab.ee.ntu.edu.tw Linearity Photodiode: S1087, S ADXL330 accelerometer Sharp GP2D120XJ00F GOOD BAD

Network and Systems Laboratory nslab.ee.ntu.edu.tw Bandwidth How fast the next valid output ready Proximity sensor: Sharp GP2D120XJ00F ADXL330 accelerometer When power up, you have to wait for 52.9ms to get a first valid output. You have to wait another 47.9ms to get the second one. For the module we will use, the filter capacitor is 0.1 uF. It means the accelerometer module can have at most 50 different read-outs in one second

Network and Systems Laboratory nslab.ee.ntu.edu.tw Analog to Digital Conversion Periodically read the voltage of the signal Convert to a digital number Represent the voltage of the signal At the sampling time T

Network and Systems Laboratory nslab.ee.ntu.edu.tw Analog to Digital Conversion

Network and Systems Laboratory nslab.ee.ntu.edu.tw ADC takes two inputs Voltage reference (dynamic range) Range of voltage that it can measure It has a limited range Sensor signal Resolution How many bits the ADC can output Sample Rate How many sample it can takes in one second For MSP430F1611, it is about 200 ksps That’s why we need signal conditioning to produce a proper voltage output Analog to Digital Converter (ADC)

Network and Systems Laboratory nslab.ee.ntu.edu.tw Resolution You heard 10-bit ADC, 12-bit ADC, 16-bit ADC What are they? Number of bits the ADC can output This is a 4-bit ADC [0,0.1) V -> 0000 [0.1,0.2) V -> 0001 [0.2,0.3) V -> 0010 [1.5,1.6) V -> 1111 If it is a 6-bit ADC [0,0.025) V -> [0.025,0.05) V -> [0.05,0.075) V -> [1.575,1.6) V ->

Network and Systems Laboratory nslab.ee.ntu.edu.tw 1 bit  2 possible values 2 bits  4 possible values 8 bits  256 possible values 12 bits  4096 possible values 16 bits  possible values : : N bits  2 N possible values Discretization } Quantization error

Network and Systems Laboratory nslab.ee.ntu.edu.tw Dynamic Range Range of signal amplitudes which the ADC can resolve Max possible value Min possible value

Network and Systems Laboratory nslab.ee.ntu.edu.tw Voltage reference Input voltage compares to the voltage reference Ratio of (input voltage)/(voltage reference) determines the output number Two voltage references Positive voltage reference (Vref+) Negative voltage reference (Vref-) In this figure, Vref+ = 1.6V; Vref- = 0 V [0,0.1) V -> 0000 [0.8,0.9) V -> 1000 [1.5,1.6) V -> 1111 If we change the Vref+ = 3.2V; Vref- remains 0 V, then [0,0.2) V -> 0000 [1.6,1.8) V -> 1000 [3.0,3.2) V -> 1111

Network and Systems Laboratory nslab.ee.ntu.edu.tw About Voltage Reference Voltage reference can by internal or external Many ADCs have internal voltage reference integrated Unstable Voltage reference will affect the accuracy of the ADC Minimum, Maximum If input voltage > Vref+, always output 1111 If input voltage < Vref-, always output 0000 Voltage Reference cannot exceed power supply voltage

Network and Systems Laboratory nslab.ee.ntu.edu.tw Dynamic Range Too low Good resolution Saturation Too high Poor resolution No saturation

Network and Systems Laboratory nslab.ee.ntu.edu.tw Detectable Voltage Change Voltage reference + Resolution Define the detectable voltage change Detectable voltage change = ((Vref+) – (Vref-))/(2^resolution) Examples Vref = 1.6V, Resolution = 4-bit Vref = 3.2V, Resolution = 4-bit Vref = 1.6V, Resolution = 6-bit 1.6/(2^4) = 0.1 V 3.2/(2^4) = 0.2 V 1.6/(2^6) = V

Network and Systems Laboratory nslab.ee.ntu.edu.tw Sample And Hold There is a sample-and-hold circuit before A/D conversion Mostly integrated in the ADC chip When no conversion, switch S1 is open When a conversion start S1 closed Input signal charge C1 S1 open, C1 holds the value of input signal A/D conversion Sample-and-hold time Time between S1 close and re-open If it is too short C1 will not fully charged (error)

Network and Systems Laboratory nslab.ee.ntu.edu.tw ADC Clock ADC needs a clock For sample-and-hold and the A/D conversion

Network and Systems Laboratory nslab.ee.ntu.edu.tw ADC on Taroko 12-bit on-chip ADC in MSP430 Voltage reference Internal Vref: 1.5V, 2.5V No external Vref on Taroko User configurable combination for Vref+ and Vref- Sample rate Approximate 200 ksps User configurable sample-and-hold time User configurable clock sources

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: ADXL330 ADXL330 3-axis accelerometer Transfer function: V = (0.3 * g)

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: ADXL330 Taroko ADC setting Resolution: 12-bit Voltage reference Vref+ = 2.5 V Vref- = 0 V Conversion formula N ADC is the output number For our setting

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: ADXL330 Transfer function: V = (0.3 * g) Conversion formula When the acceleration is 0 g V = 1.5 N ADC = 2457 When the acceleration is 1.5 g V = 1.95 N ADC = 3194 When N ADC = 1784, what is the acceleration? When N ADC = 2635, what is the acceleration?

Network and Systems Laboratory nslab.ee.ntu.edu.tw Real World Design In practical design, there are always errors Noises Power supply noise Digital circuit noise RF noise Devices noise Devices Tolerances 5% resistor, 1% resistor 10% capacitor etc. Temperature drift Devices characteristics change when temperature change Two very simple methods to deal with two very common errors

Network and Systems Laboratory nslab.ee.ntu.edu.tw First Type of Errors Noise Dynamic ADXL330 at 0 g (1.5V) Sample at S1 -> ok Sample at S2 -> it is g Sample at S3 -> it is g Solution Average (S1 + S2 + S3)/3 = ( )/3 = V 1.4V 1.6V S1S2 S3

Network and Systems Laboratory nslab.ee.ntu.edu.tw How Many Samples How many samples needed to average Depends on your requirement Suggestion: factor of 2 (2 N ) Take 10 samples and average Take 16 samples and average Total += Si; //(i=1,…,10) Result = Total/10; Total += Si; //(i=1,…,16) Result = (Total>>4); Division => slow Bit shift => fast

Network and Systems Laboratory nslab.ee.ntu.edu.tw Cautions! Is the Total large enough to hold the summation Max possible Total = 4096*16 = Total should be at least 16-bit unsigned int IMPORTANT!! int in IAR for MSP430 is 16-bit long Total += Si; //(i=1,…,16) Result = (Total>>4);

Network and Systems Laboratory nslab.ee.ntu.edu.tw Second Type of Errors Offset Static For example: ADXL330 For A accelerometer, 0 g output maybe 1.5V For B accelerometer, 0 g output maybe 1.54V From ADXL330 datasheet 30% of ADXL330, 0 g output is 1.53V 4% of ADXL330, 0 g output is 1.5V

Network and Systems Laboratory nslab.ee.ntu.edu.tw Calibration Maintain a calibration constant, adjust the offset error ADXL330 with calibration Transfer function: V = (1.5 + C cal ) + (0.3 * g) C cal is calibration constant For A accelerometer, 0 g output is 1.5V C cal = 0 If N ADC = 2879, acceleration should be g For B accelerometer, 0 g output is 1.54V C cal = 0.04 If N ADC = 2879, acceleration should be ?? G

Network and Systems Laboratory nslab.ee.ntu.edu.tw Calibration Reference Calibration needs a reference Precision of the reference decide the precision of the calibration How do you calibrate the accelerometer ADXL330?? How do you calibrate a temperature sensor? Acceleration => voltage To calibrate, you want to know the voltage output at 0 g. But how to make 0 g? You must produce a precise 0 g (or 1 g) acceleration Temperature => voltage To calibrate, you want to know the voltage output at certain temperature (25 o C). You must produce a precise temperature

Network and Systems Laboratory nslab.ee.ntu.edu.tw Digital Communications Sending bits between each other Serial communication Sending bits one by one UART, SPI, I2C, USB, etc. Parallel communication Sending multiple bits at one time Ethernet AB AB AB Our focus

Network and Systems Laboratory nslab.ee.ntu.edu.tw Agreements In order to communicate, two parties must at least agree on: Logic level MSP430 RS232 (COM port) Output data Start, stop Output data valid time (clock) 0V -> logic low (0) 3.3V -> logic high (1) -12V -> logic high (1) 12V -> logic low (0) What number it represent? Read x Read AB For digital, wired communication

Network and Systems Laboratory nslab.ee.ntu.edu.tw Protocols Chips to Chips SPI: Serial Peripheral Interface I2C: Inter Integrated Circuit Manufacturer defined UART: Universal Asynchronous Receiver Transmitter Systems to systems (usually) Define logic level RS-232: old traditional RS-485: popular in industrial control system Define output data UART: Universal Asynchronous Receiver Transmitter Define both USB AB UART RS232 or RS485

Network and Systems Laboratory nslab.ee.ntu.edu.tw SPI Master–Slave mode Synchronous protocol All transmissions are referenced to a common clock Clock generated by the master (MCU) Four main signals Master Out Slave In (MOSI): data from master to slave Master In Slave Out (MISO): data from slave to master Serial CLocK (SCLK or SCK): clock Chip Select (CS): select particular peripheral when multiple peripherals are connected to master

Network and Systems Laboratory nslab.ee.ntu.edu.tw Read data at clock edge Data Register Exchange Master transfer a byte to slave, push slave to transfer a byte back to master Master Read and Write Simultaneously Master write only Ignore the byte it receive Master read only Master must transfer a dummy byte in order to initiate a slave transmission SPI Transmission MOSI CLK Slave read MISO CLK Master read CS

Network and Systems Laboratory nslab.ee.ntu.edu.tw I2CI2C Two wires, multiple devices SDA (serial data) SCL (serial clock) I 2 C transmission START: SDA is pulled low while SCL stays high Transfer: SDA sets the transferred bit while SCL is low (blue) data is read when SCL rises (green) STOP: SDA is pulled high while SCL stays high Pull-up resistor

Network and Systems Laboratory nslab.ee.ntu.edu.tw I2CI2C Acknowledge (ACK) and Not Acknowledge (NACK) Upon the transmission of the eighth data bit Transmitter releases the SDA Master then generates an additional clock pulse on SCL Triggers the receiver to acknowledge the byte by pulling SDA low

Network and Systems Laboratory nslab.ee.ntu.edu.tw I2CI2C Addressing 7-bit address Direction bit If 0: master write to slave If 1: master read from slave 10-bit address Clock stretching A slave may hold the clock line (SCL) low after receiving (or sending) a bit, indicating that it is not yet ready to process more data 10-bit address 7-bit address

Network and Systems Laboratory nslab.ee.ntu.edu.tw Comparison SPII2C Four wiresTwo wires Full duplexHalf duplex Higher throughput (then I2C)Lower throughput Synchronous protocol No slave acknowledgmentAcknowledgment SimpleComplicated

Network and Systems Laboratory nslab.ee.ntu.edu.tw Manufacturer Defined Protocols The ideals are similar Feed a clock Start, stop Read/write the data Read datasheet Many times Get use to those timing diagrams We will use the temperature/humidity sensor SHT11 on Taroko as an example

Network and Systems Laboratory nslab.ee.ntu.edu.tw Implementations How to implement these protocols? Hardware There are SPI, I2C peripherals on MSP430F1611 You need to properly configure (setting registers) the modules Software Use GPIO Generate clock Read data: set the pin to input Write data: set the pin to output Things to consider Timing: some devices cannot operate too fast Check devices datasheet // use P1.0 as clock pin P1SEL &= ~(0x01); // GPIO P1DIR |= 0x01; // output // clock P1OUT |= 0x01; // high P1OUT &= ~(0x01); // low // add some delay between clock P1OUT |= 0x01; // high (delay some time) P1OUT &= ~(0x01); // low

Network and Systems Laboratory nslab.ee.ntu.edu.tw In General You want to interface some digital ICs to MSP430 CC2420 radio chip (SPI) 8 Mbit flash memory (SPI) SHT11 sensor (manufacturer defined, similar to I2C) Typical process 1. How to interface? Connections: two wires, three wires, four wires, etc. 2. How to communicate? Available commands Timing diagram: start, transfer, (ack), stop 3. How to configure the IC Setting the registers on the IC 4. Start reading/writing data from/to the IC

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: SHT11 The temperature/humidity sensor on Taroko How to Interface two wires bi-direction SHT11 datasheet 1.Use a GPIO pin as clock (SCK), it is always output direction 2.Use another GPIO as DATA, dynamic setting it to input(read) or output(write) direction

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: SHT11 How to start What are the commands available

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: SHT11 Timing diagram Pull-up Data pin in output direction Set data pin to input direction, then SHT11 controls the DATA line

Network and Systems Laboratory nslab.ee.ntu.edu.tw An Example: SHT11 Configure device If you don’t understand what is the meaning, check datasheet

Network and Systems Laboratory nslab.ee.ntu.edu.tw Timing Check the timing requirement carefully The device won’t work at all if you exceed the limit

Network and Systems Laboratory nslab.ee.ntu.edu.tw UART UART: Universal Asynchronous Receiver Transmitter Two wires: Rx, Tx Full duplex Asynchronous No common clock required Without common clock How do they communicate?? A Rx Tx B Tx Rx

Network and Systems Laboratory nslab.ee.ntu.edu.tw Universal data rates Two devices agree on same data rate Baudrate: 1200, 2400, 4800, 9600, …, (bits per second) A (1 MHz system clock) B (8 MHz system clock) UART Baudrate generator 9600 Baudrate: 9600 bps Length of a bit = 1/9600 (seconds)

Network and Systems Laboratory nslab.ee.ntu.edu.tw UART Data Send one byte at a time Data One start bit Pull-down the line 7 or 8 bits data One or two stop bit Pull-up the line for one or two slots Simple error checking: parity (optional) Even parity: If the data has odd number of 1, parity bit = 1 (make it even); else parity bit = 0 Odd parity: If the data has even number of 1, parity bit = 1 (make it odd); else parity bit = 0 Four parameters for UART communication Baudrate, data-bit, parity, stop-bit We wrote: N1, Means: baudrate=9600, 8-bit data, no parity, 1 stop bit This bit became parity bit when parity checking is enabled

Network and Systems Laboratory nslab.ee.ntu.edu.tw RS232 Since the 1960s Cable lengths of up to 25 meters Signal level logic high -> -5 to -15V (typically -12V) logic low -> +15 and +1V (typically +12V) Interface SignalFunction25-pin9-pinDirection TxTransmitted data23From DTE to DCE RxReceived data32To DTE from DCE RTSRequest to send47From DTE to DCE CTSClear to send58To DTE from DCE DTRData terminal ready204From DTE to DCE DSRData set ready66To DTE from DCE DCDData carrier detect81To DTE from DCE RIRing indicator229To DTE from DCE FGFrame ground (chassis)1-Common SGSignal ground75Common

Network and Systems Laboratory nslab.ee.ntu.edu.tw RS485 Two-wire, half-duplex Multipoint serial connection Signal level Difference between the wires’ voltages A – B > 0.2V => logic high (0) A – B logic low (1) Why it is popular in industrial applications Only two wire 35 Mbit/s up to 10 m and 100 kbit/s at 1200 m

Network and Systems Laboratory nslab.ee.ntu.edu.tw USB Serial IC That’s what we have on Taroko FT232BL ( To communicate with PC It simulate a serial communication on PC through USB interface Virtual com port

Network and Systems Laboratory nslab.ee.ntu.edu.tw Applications MSP430 UART USB serial IC (FT232) PC or other systems RS232 IC RS485 IC Other systems COM PORT USB All you need to do is properly configure UART for both sides (baudrate, data- bit, parity, stop-bit), and start sending/receiving data