MASLab Sensors

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MASLab Sensors
January 2003 Alana Lafferty (and Christopher
Batten)
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Agenda

• Soldering
• Sensors, in general
• The specific kinds of sensors in 6.186
• Cable Making
• Sensor Characterization

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6.186 - Soldering

• What is soldering?
• Creating electrically conductive connections
  between electronic components
• Melting a lead-based metal called solder

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6.186 - Soldering

• Safety
• Temperature
• Stripping and Tinning
• Useful Soldering Tips

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Safety

• Do not leave a soldering iron plugged in when you
  are not using it
• Always place soldering iron back in its holder
  after use
• Never place the iron near other objects to avoid
  burning
• Do not pick up the iron by the tip, it?s hot
• Do not touch newly soldered joints, they are also
  hot

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Temperature

• The iron needs to be hot enough to heat the
  contacts so they melt the solder
• Do not use the iron to directly melt the solder
• Use the iron to heat both contacts, and apply the
  solder to the joint
• Do not heat the joint for too long, heat can
  damage components

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Temperature

• One of the biggest problems with soldering is
  cold solder joints
• This occurs when an air bubble or impurity enters
  the joint during cooling
• The solder does not flow properly into the joint
• And it does not make a good electrical connection

Bad
Good
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Stripping and Tinning

• Always use stranded wire for making sensor leads
• Strip the wire about ¼ inch from the end without
  cutting any of the strands
• Touch the tip of the iron to the wire and hold
  the solder touching the wire in order to tin the
  wire

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Soldering Tips

• Make sure the tip of your iron is shiny
• Do not paint
• Do not use large globs of solder
• Use a damp sponge to clean off the tip

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6.186 - Sensors

• What is a sensor?
• Common types
• Infra-Red (IR)
• Ultrasound
• Physical contact
• Other types
• Magnetic field detectors (Reed switches)
• Be creative!

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IR Sensors

• 750 nm to 1,000,000 nm
• Transmitters (LEDs or thermal)
• Detectors (photo diodes, photo transistors)

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IR Three common strategies
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IR Rangefinders

• What sorts of techniques can we use?
• Time of Flight (TOF)
• Signal Strength
• Triangulation

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Ultrasound

• 40Khz
• Time of Flight
• Depending on sensor,
• return analog waveform
• Return time until first peak
• Hard to resolve small detail
• Multipath

Small detail hard to resolve
Multipath can fool you!
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Sensors

• Primary
• Infrared range detectors
• Short Range
• Long Range
• Ultrasonic range detectors
• Secondary
• Photoreflectors
• Momentary contact sensors
• Reed switches
• Mercury switches
• Others ?

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Infrared Range Detectors

• Sharp GP2D12 IR range detectors
• Sensor includes
• Infrared light emitting diode (IR LED)
• Position sensing device (PSD)
• To detect an object
• IR pulse is emitted by the IR LED
• Pulse hopefully reflects off object and returns
  to the PSD
• PSD measures the angle at which the pulse returns
• Position Sensing Device
• Uses small lens to focus reflected pulse onto a
  linear CCD array

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Infrared Range Detectors
Theoretical Range 4in (10cm) to 31in
(80cm) Actual Range 4in (10cm) to 18in (45cm)
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Infrared Range Detectors

• Detecting Targets
• Placed target in various positions in front of a
  standard MASLab wall
• Relatively narrow field-of-view"
• Noise
• Output voltage follows normal-like distribution
  with constant std dev
• User-level averaging may be useful
• Sampling
• Sensor refreshes approx. every 32ms
• Can reasonably acquire 20 samples per second

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Infrared Range Detectors

• Uses
• Short range obstacle mapping - Mount sensor on
  servo and collect range data for various angles
• Bump sensors - Threshold output voltage, Use
  multiple sensors at appropriate angles to cover
  more area
• Target detection - Arrange multiple sensors to
  detect shape of waypoints and targets
• Final practical concerns
• Position IR sensors to avoid dealing with lt 4in
  readings

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Long-Range Infrared Range Detectors

• GP2Y0A02YK

Theoretical Range 20 cm (8 in) to 150 cm (60 in)
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Ultrasonic Range Detectors

• Devantech SRF04 Ultrasonic Rangers
• To detect and object
• Modulated (40kHz) ultrasound energy is emitted
  from one of the transducers
• The bursts reflect off an object and return
  to the second transducer
• The sensor outputs the time of flight

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Ultrasonic Range Detectors
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Ultrasonic Range Detectors
9.0
4.4
0.9
7.4
7.1
5.2
3.8
1.8
0.2
7.1
5.2
3.8
0.9
7.5
6.0
9.0
1 ft
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Ultrasonic Range Detectors

• Noise
• Relatively stable readings especially between 1ft
  to 6ft
• Readings for larger distances are less consistent
  but averaging or median filtering can help
• Beam spread is significant
• Sampling
• Can reasonably acquire 20-30 samples per second
• Uses
• Long range obstacle mapping
• Distance to target measurements

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Photo Reflectors

• Used for line following

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Other Sensors

• Other sensors we have
• Momentary contact sensors - Bump sensors
• Other possibly useful sensors
• Mercury switches - Tilt of see-saw robot
• Optical Encoders - Odometry
• IR Beam - Detect presence of target
• Solenoids ? electromagnet that opens and closes
• Whiskers, bumpers ?

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Pinouts
GP2Y0A02YK
GP2D12
Sig 5V CCP Gnd
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Cable Making
? First make the header side of an ultrasound
cable to practice soldering ? Each team
should make a battery cable ? 3 teams make long
range IR cables ? 4 teams make short range IR
cables ? 3 teams make ultrasound cables
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Sensor Characterization
Using the diagnostics on the orc or by writing a
C program, produce a voltage vs. distance plot
of the following ? long range IR sensor ? short
range IR sensor ? ultrasound sensor ? servo -
make it seek somewhere