1. Analog And Digital Interfacing

2. Digital Communication
Big Picture
Physical world
Other Systems or ICs
Digital Communication
Analog Interfacing
MSP430

3. 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

4. Signal Path Produce a proper output voltage level Signal Conditioning
(if necessary)
Sensors
Amplification
Filtering
Analog to Digital Conversion
(ADC)
Light
Temperature
Acceleration
Humidity
Pressure
etc.
Resistance
Capacitance
Current
Voltage
etc.
Convert to voltage
Converts voltage to digital number

5. Sensors We Have Raw sensors Signal conditioned sensors
Produce raw electrical signal
Signal conditioned sensors
Have some signal conditioning circuit
Produce analog output
Mostly Voltage
Sometime Current

6. Sensors We Have Digitalized sensors
Have some signal conditioning circuit
Convert analog to digital internally
Provide digital output

7. Our Focus Sensors Produce a proper output voltage level
Signal Conditioning
(if necessary)
Sensors
Amplification
Filtering
Light
Temperature
Acceleration
Humidity
Pressure
etc.
Analog to Digital Conversion
Resistance
Capacitance
Current
Voltage
etc.
Convert to voltage
Converts voltage to digital number
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

8. Some Raw Sensors Temperature Sensors Pressure sensors Thermistors
Temperature-sensitive resistor
RTDs (resistive temperature devices)
Thermocouples
Temperature => voltage (mV)
Pressure sensors
Piezoresistive
Resistance change with applied pressure

9. Photodiodes Light => current
Generate current proportional to light density

10. Photodiodes Two on Taroko S1087: for visible range
S : for visible to IR(infrared) range

11. Signal Conditioned Analog Output
Proximity sensor
Sharp GP2D120XJ00F
Analog voltage output
Accelerometer
ADXL330 3-axis accelerometer
Industry standard analog output
Flow sensors, pressure sensors, gas sensors, etc.
4~20 mA, 0~5 V, 0~10 V

12. Proximity Sensor Sharp GP2D120XJ00F
Output voltage proportional to the reflection distance
Measure range: 30 cm

13. Accelerometer Analog Device Inc. ADXL330
Output voltage proportional to the acceleration
Measurement range: +/- 3.6 g

14. 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

15. Usually this range is user configurable
4~20 mA current loop
Examples
Measure temperature: 0 ~ 100 oC
Measure flow speed: 0 ~ 50 m3/h
Measurements
0 oC
50 oC
100 oC
Current Output
4 mA
12 mA
20 mA
Usually this range is user configurable
Measurements
0 m3/h
25 m3/h
50 m3/h
Current Output
4 mA
12 mA
20 mA

16. How to Convert to Voltage
Add a resistor

17. Others Analog Output Sensors
Ultrasound sensors
Gyroscopes

18. Digitalized Sensors Ultrasound sensors Temperature and Humidity Sensor
SRF10
Interface: I2C
Temperature and Humidity Sensor
SHT11
Interface : manufacturer defined

19. Digitalized Sensors Magnetometer Digital compass SFE MicroMag 3-Axis
Interface : SPI
Applications: detecting vehicles
Digital compass
Hitachi HM55B
Interface : UART

20. Digitalized Sensors GPS Image sensor Garmin GPS18 Interface : UART
ST VS6451
Interface: I2C

21. 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

22. 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

23. Transfer Function ADXL330 accelerometer 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 increase by 1 g, the output voltage will increase 330 mV (typical)
It means when supply voltage Vs is 3 V, if the acceleration is 0 g, the output voltage will be 1.5 V (typical)
Transfer function: Voltage (V) = (0.3 * acceleration (g) )

24. Transfer Function Proximity sensor: Sharp GP2D120XJ00F
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

25. Transfer Function Photodiode: S1087, S1087-01 Transfer function
Voltage (V) = f(light level(lx))
Calculate by yourself
From Taroko Schematic
Step 2: find the relationship between current and the voltage at ADC4
(V = IR)
Step 1: find the relationship between light level and current

26. Sensitivity ADXL330 accelerometer Sharp GP2D120XJ00F
Not a constanst
Photodiode: S1087, S
(Current)/(light level)

27. Linearity Sharp GP2D120XJ00F Photodiode: S1087, S1087-01 BAD GOOD GOOD
ADXL330 accelerometer

28. Bandwidth How fast the next valid output ready
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.
Proximity sensor: Sharp GP2D120XJ00F
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
ADXL330 accelerometer

29. Analog to Digital Conversion

30. Analog to Digital Converter (ADC)
ADC takes two inputs
Voltage reference
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

31. 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

32. 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

33. 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 ->

34. 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

35. 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)

36. ADC Clock
ADC needs a clock
For sample-and-hold and the A/D conversion

37. 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

38. An Example: ADXL330 ADXL330 3-axis accelerometer
Transfer function: V = (0.3 * g)

39. An Example: ADXL330 Taroko ADC setting Resolution: 12-bit
Voltage reference
Vref+ = 2.5 V
Vref- = 0 V
Conversion formula
NADC is the output number
For our setting

40. An Example: ADXL330 Conversion formula When the acceleration is 0 g
Transfer function: V = (0.3 * g)
Conversion formula
When the acceleration is 0 g
V = 1.5
NADC = 2457
When the acceleration is 1.5 g
V = 1.95
NADC = 3194
When NADC = 1784, what is the acceleration?
When NADC = 2635, what is the acceleration?

41. 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

42. First Type of Errors Noise Solution 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 = 1.5
1.6V
1.5V
1.4V S1 S2 S3

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

44. Cautions! Is the Total large enough to hold the summation IMPORTANT!!
Max possible Total = 4096*16 = 65536
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);

45. 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
30% of ADXL330, 0 g output is 1.53V
4% of ADXL330, 0 g output is 1.5V
From ADXL330 datasheet

46. Calibration Maintain a calibration constant, adjust the offset error
ADXL330 with calibration
Transfer function: V = (1.5 + Ccal) + (0.3 * g)
Ccal is calibration constant
For A accelerometer, 0 g output is 1.5V
Ccal = 0
If NADC = 2879, acceleration should be g
For B accelerometer, 0 g output is 1.54V
Ccal = 0.04
If NADC = 2879, acceleration should be ?? G

47. 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?
You must produce a precise 0 g (or 1 g) acceleration
To calibrate, you want to know the voltage output at 0 g. But how to make 0 g?
Acceleration => voltage
You must produce a precise temperature
To calibrate, you want to know the voltage output at certain temperature (25 oC).
Temperature => voltage

48. 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 A B
Our focus A B A 1 B 1 1 1 1

49. Agreements
For digital, wired communication
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 (0)
12V -> logic low (1)
What number it represent?
Read
2x Read 1 1 1 1 1 1 1 1 A B

50. Protocols Chips to Chips Systems to systems (usually)
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
Define both
USB A B
UART
UART
RS232 or RS485
RS232 or RS485

51. SPI Master–Slave mode Synchronous protocol Four main signals
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

52. SPI Transmission 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
MOSI
MISO
CLK
CLK 1 CS CS
Slave read 1 1 1
Master read 1 1 1 1

53. I2C Two wires, multiple devices I2C transmission SDA (serial data)
Pull-up resistor
Two wires, multiple devices
SDA (serial data)
SCL (serial clock)
I2C 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

54. I2C 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

55. I2C Addressing Clock stretching 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

56. Comparison SPI I2C Four wires Two wires Full duplex Half duplex
Higher throughput (then I2C)
Lower throughput
Synchronous protocol
No slave acknowledgment
Acknowledgment
Simple
Complicated

57. 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

58. Implementations How to implement these protocols? Things to consider
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

59. 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
How to interface?
Connections: two wires, three wires, four wires, etc.
How to communicate?
Available commands
Timing diagram: start, transfer, (ack), stop
How to configure the IC
Setting the registers on the IC
Start reading/writing data from/to the IC

60. An Example: SHT11 The temperature/humidity sensor on Taroko
How to Interface
two wires bi-direction
Use a GPIO pin as clock (SCK), it is always output direction
Use another GPIO as DATA, dynamic setting it to input(read) or output(write) direction
SHT11 datasheet

61. An Example: SHT11
How to start
What are the commands available

62. An Example: SHT11 Timing diagram Pull-up Data pin in output direction
Set data pin to input direction, then SHT11 controls the DATA line
Timing diagram

63. An Example: SHT11 Configure device
If you don’t understand what is the meaning, check datasheet

64. Timing Check the timing requirement carefully
The device won’t work at all if you exceed the limit

65. UART Without common clock Two wires: Rx, Tx Full duplex Asynchronous
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

66. Length of a bit = 1/9600 (seconds)
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)
9600
9600
Baudrate generator
Baudrate generator
UART
UART
Baudrate: 9600 bps
Length of a bit = 1/9600 (seconds)

67. This bit became parity bit when parity checking is enabled
UART Data
This bit became parity bit when parity checking is enabled
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

68. 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
Signal
Function
25-pin
9-pin
Direction Tx
Transmitted data 2 3
From DTE to DCE Rx
Received data
To DTE from DCE
RTS
Request to send 4 7
CTS
Clear to send 5 8
DTR
Data terminal ready 20
DSR
Data set ready 6
DCD
Data carrier detect 1 RI
Ring indicator 22 9 FG
Frame ground (chassis) -
Common SG
Signal ground

69. RS485 Two-wire, half-duplex Multipoint serial connection Signal level
Difference between the wires’ voltages
A – B > 0.2V => logic high (0)
A – B < -0.2V => 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

70. USB Serial IC That’s what we have on Taroko FT232BL (www.ftdichip.com)
To communicate with PC
It simulate a serial communication on PC through USB interface
Virtual com port

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