Chapter 17: Sensors

1
Chapter 17 Sensors

• CEG2400 - Microcomputer Systems

2
Contents

• Sensors for our robot
• Touch sensors
• Range IR proximity sensors Light sensors
• IR Path following sensors
• Sound sensors
• Ultra-sonic sensors
• Temperature Sensor
• Electromagnetic sensors electronic compass
• Accelerometers
• Analog-to-digital Conversion

3
1) Sensors for robot
4
Robot with sensors
5
2) touch sensorsKey switch interfacing

6
Key switch array
GPIO output port

GPIO input port
7
exercise

• Exercise 1 Exercise
• I. Determine which key has been depressed by
  using x and y?
• II. How to handle multiple key presses.

8
Key scan algorithm

• Key_scan_simple( )
• unsigned char i,x,y
• //handle denounce problem here, such as,
• // check if the previous key press has been
  released or not
• //scanning for a key press
• for(i0ilt4i) //4 times
• y1110(B) //Y(3),Y(2),Y(1),Y(0)1110
• output y to GPIO output port
• X read in GPIO input port
• If (X not equal to 1111(B))
• //a key has been depressed
• break
• rotate y 1 bit to left, i.e. 1110 will
  become 1101 etc.
• Find which key has been depressed by current X
  and Y values.

GPIO 4-bit Output port
GPIO 4-bit Input port
9
Tentacles

10
3) IR proximity range sensor

• Exercise 2 What is Schmitt trigger logic? Why do
  we need a Schmitt trigger inverter here?

11
Schmitt triggered inverter (7414)http//www.datas
heetcatalog.net/de/datasheets_pdf/7/4/1/4/7414.sht
ml

12
Frequency modulated range sensor(less sensitive
to surrounding light)

13
Infrared (IR) reflective proximity range sensorA
reliable practical solution from Mondotronics..

From http//datasheet.octopart.com/3-337-Mondotro
nics-datasheet-7285303.pdf
14
Using analog-to-digital (ADC)converter

• Using analog-to-digital converter to measure the
  distance between the lightsensor and the
  obstacle.
• ADCAnalog to digital converter
• DACDigital to Analog converter

15
N channels range measurement using IR,
multiplexer and ADC.

16
Algorithm for channel selection (one of N
channels) and conversion

• Main()
• Init. System (GPIO , ADC).
• Select channel
• Read sensor reading by ADC.

17
4) IR path following setup

18
5) Sound sensors

• Types of microphones
• Moving coil microphone
• Condenser microphone---
• Use ADC to convert to digital code
• Input to Speech Recognition system
• Clipping for simple sound detection

19
Moving coil microphone (battery not required)

20
Condenser microphone (more sensitive, battery
required)

21
Microphone with amplifier

22
A digital sound recorder using ADC and DAC

• Microphone uses a uA741 op-amp to amplifier the
  signal
• ADC circuit An ADC (ADC0820 or ARM ADC) circuit
  is used to convert speech signal input into
  digital form.
• Output Digital-to-Analog converter DAC that
  converts digital code into analog voltage
• Output is fed to an audio power amplifier (LM386)
  to drive a speaker.

23
Output power amplifier

5V power supply
Analog output from DAC
1uF
C250uF
To speaker
C150.05uF R10KOhms

24
Algorithm to drive the digital recorder

• xdata unsigned char ram_storeN, i
• record //sampling record and playback at one go
• for(i0 I lt N i)
• ram_storei read_in_sound_code_from_GPIO
• output_to_dac ram_storei
• delay() //this determines the sampling rate
• playback() // playback what has been rcordered
• for(i0 I lt N i)
• output_to_dac ram_storei
• delay() //this determines the sampling rate

25
Exercises

• Write the program for the interrupt method.
• (II) Write the algorithm to detect the sound of a
  handclap or a whistle sound.
• (III) What are the elements we need to implement
  a speech recognition system?

26
Sound DC level shifterfor sound level detector

27
6) Ultrasonic radar system- non invasion range
detection system - Batmans radar system

Ultrasonic Transmitter receiver
picture from http//szsaibao.taobao.com/?spm2013
.1.2-543493819.1.TCe5j8
28
The transmitter circuit

29
The receiver circuit

30
Method 1 Ultrasonic-radar control using MCU and
timer

Algortithm_radar1() //by polling Send out
pulses switch on timer Wait until echo is
received. Stop timer //wait-loop Read
timer, Convert time into length
Timer clock is 13824 KHz
31
Method 2 Ultrasonic- radar control using
interrupt and MCUs internal timer

Timer clock is 13824 KHz
Video http//www.youtube.com/watch?vqHuVhR6-Q1E
32
Algorithm_radar2 Ultrasonic- radar control
using MCU interrupt and its internal timer

• Algorithm_radar2 ( ) // by interrupt and timer
  method, tested with good result
• initialize internal_timer interrupt
• instruct the GPIO to send out pulses
• start timer //32-bit internal timer counting
  at 13.824MHz
• //loop
• wait a while // wait a while, the echo is
  expected to arrive
• read internal_timer value // result, convert
  into distance
• //ISR ////////////////////////////////////////////
  ///////////////////////////////////////////
• isr2_type2_for_timer1_for_radar2 //executes when
  echo arrives
• Stop internal_timer

33
Exercises

• I. Compare the two methods Algorithm_radar1(
  )polling and Algorithm_radar2( ) using
  internal timer interrupt shown above.
• II. For Algorithm_radar2( ), if the object is 3
  meters away and the speed of sound is
• 330m/s, what is the time-of-flight of the sound
  wave from the transmitter to the receiver?
• III. What is the result at the count?
• IV. What is the accuracy (-meters) of this
  design? What factors determine the accuracy of
  this system?

34
7) Temperature sensors

35
8) Electromagnetic sensorElectronic compass,
accuracy /- 1 degree

2 perpendicular coils
36
HMC1501 and HMC1512 Linear, Angular, and Rotary
Displacement Sensor

http//www.ssec.honeywell.com/magnetic/datasheets/
hmc1501-1512.pdf
37
9) Accelerometers

• An accelerometer measures acceleration,
  vibration, and shock.
• Example car airbag triggering sensor, 3D mouse
  -- tilt sensor.
• From National Instruments Corporation
  http//www.ni.com/products/

38
Example of using accelerometer Fromhttp//www.cs
l.sony.co.jp/person/rekimoto/tilt/
Youtube Link
39
Accelerometers in WII

• http//myskitch.com/keith/wii-20070724-011824.jpg/
  preview.jpg

• IMU camera control / stabilisation

Video link https//www.youtube.com/watch?v7GVXqNL
LH7Q
http//youtu.be/CQ_P5XWkYcI
40
Gyroscopes can be applied to building self
balancing robots

• 2-side wheels self balancing robot

• Motor cycle

• Our robot has one of the hottest self balancing
  robots in YouTube.
• 52759 clicks on 18 Dec 2012

• http//www.youtube.com/watch?v0312BNqIBFI

41
Summary

• A number of different sensors have been studies
• And examples of how they are used are also
  demonstrated

42
Apenxi Answer for Exercise for ultrasonic
radar

• I. Compare the two methods Algorithm_radar1(
  )polling and Algorithm_radar2( ) using
  internal timer interrupt shown above.
• II. For Algorithm_radar2( ), if the object is 3
  meters away and the speed of sound is 330m/s,
  what is the time-of-flight of the sound wave from
  the transmitter to the receiver?
• Answer sound traveled 3x26m.
• Time_delay (dt)6m/(330m/s)18.18ms
• If interrupt is 13.824MHz, each timer clock is
  1/13.824M72.33ns
• III. What is the result at the count?
• so counting result for dt18.18ms/(1/13.824M)18.1
  8ms/72.33ns251347.
• IV. What is the accuracy (-meters) of this
  design? What factors determine the accuracy of
  this system?
• Each clock pulse is (1/13.824M)s72.33ns, that
  represents dL330m/s(72.33ns)
  (330/13.824M)m0.239mm
• The real accuracy is half of it because it is an
  echo , so 0.239mm/20.119mm