Download ITSI.wkshp - The Concord Consortium

Do-it-Yourself Electronics:
Probeware on a Budget
Robert Tinker
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May 14, 2007
The Concord Consortium
http://concord.org
ITSI Workshop
Slide 1
Why a Kit?
• Save $$
– This kit can be used to measure 14
different quantities!
– The parts cost $25 including a DMM,
tools, bags, and Experiment board
– (The header and GoLink are extra)
• Teach Electronics and IT
• Empower kids to innovate and
experiment
May 14, 2007
ITSI Workshop
Slide 2
KISS
• No soldering
• Some sensors connect directly
• Others require only very simple
circuits
• Only one input at a time
• No power supply needed
• Meter supplied for trouble-shooting
May 14, 2007
ITSI Workshop
Slide 3
Probe Interface Overview
• The flow of data from some physical
property into a computer:
Property
Sensor
Amplifier
Interface
Quic kTime™ and a
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• The ITSI kit provides the sensor and interface
• You will build a circuit inside the dotted lines
• Sometimes that is as easy as connecting three leads
May 14, 2007
ITSI Workshop
Slide 4
The Kit: GoLink
• GoLink
Shown here
connected to a
computer
through a
standard USB
port
Can be used
with many
probes
May 14, 2007
ITSI Workshop
Slide 5
The Kit: Header
• The “Header”
(at right)
• The header connected
to the GoLink (left)
May 14, 2007
ITSI Workshop
Slide 6
The Kit: Experiment Board
– Note the way the
holes are connected
– Attach the metal
backplane
– Plug chips across
the center gutter
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– Note how the
header attaches
May 14, 2007
ITSI Workshop
Slide 7
The 14 Sensors
–
–
–
–
–
–
–
–
–
–
–
–
–
Temperature–TMP36
Temperature difference–thermocouples
Light–phototransistor
Light (narrow band)–red and green LEDs
Magnetic field–Hall Effect probe
Motion–a small DC motor
Rotation–a 100 KΩ variable resistor
Sound–a microphone
Force–resistive foam
Humidity–dry bulb/wet bulb
Voltage–direct or through an amplifier
Current–using an op-amp
Conductivity–wires and a resistor
May 14, 2007
ITSI Workshop
Slide 8
Temperature Sensor
• The TMP36
– A sophisticated circuit
– Ground pin 3, put +5 V on pin
1, and the voltage on pin 2
that is proportional to
temperature
– The voltage is 0.75 V plus
0.01 volts per degree above
25C.
– STATIC DANGER
May 14, 2007
ITSI Workshop
Slide 9
Temperature Difference
• Iron and Constantan in
contact generate a voltage
– The voltage changes by 52
µV per degree
– An amplifier with a gain of
1000 is needed
– There is always a back-toback pair, so you measure
the temp difference
– You will have to twist the
leads together
– Very small and fast response
May 14, 2007
ITSI Workshop
Slide 10
Light–Phototransistor
Qu ic kTi me™ a nd a
TIFF (Unc om pres se d) de co mp re ss or
are n ee de d to s ee th is pi ctu re .
Note the flat part on the flange (that
ridge that runs around the bottom
part of the plastic.) The flat is
nearest the lead that must be
more negative.
May 14, 2007
ITSI Workshop
Slide 11
Two Light Detectors
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• Light emitting diodes (LEDs) can
also be used to detect light
– They are sensitive to light near their
emitted wavelength, but toward the
blue.
– The flat on the flange is near the
negative lead
– The longer lead
is positive
Quick Time™a nd a
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ar e nee ded to see this pictur e.
May 14, 2007
ITSI Workshop
Quic kTime™ and a
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Slide 12
On LED’s as detectors
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http://www.pages.drexel.edu/~brooksdr/DRB_web_page/papers/UsingTheSun/using.htm
May 14, 2007
ITSI Workshop
Slide 13
Magnetic Field Sensor
• The Hall Effect probe
– Measures magnetic field
perpendicular to its flat side
– Contains lots of sophisticated
electronics
– Ground pin 2, apply 5 V to pin
1, and the voltage on pin 3 is
proportional to the field!!
– STATIC DANGER
May 14, 2007
ITSI Workshop
Slide 14
Motion Detector
• Any DC motor
generates a
voltage
proportional to its
rotation speed.
– Software can
integrate this to
measure
displacement.
May 14, 2007
– It is noisy, so a
filter or integration
is needed
ITSI Workshop
Slide 15
Quic kT i me™ and a
T IFF (Unc ompres s ed) dec ompres s or
are needed t o s ee thi s pi c ture.
A Rotation Sensor
• This 100 KΩ variable
resistor can be used to
measure rotation.
– Attach the outer connectors
to ground and +5 V. The
center (wiper) will have a
voltage proportional to the
rotation of the shaft
May 14, 2007
ITSI Workshop
Slide 16
Sound
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• An electret microphone in a
plastic housing
– Plugs directly into most
computers
– No circuit needed!
May 14, 2007
ITSI Workshop
Slide 17
Force
• Resistive foam
– That black foam
conducts better
when
compressed
– The resistance is infinite with no force
and drops under pressure
– Not a great detector–it drifts
May 14, 2007
ITSI Workshop
Slide 18
QuickTime™ and a
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Voltage
• The AD623 instrumentation
amplifier (i-amp)
–
–
–
–
A precision device
The output is G(V+–V–)+(Ref)
The gain G, can be 1-1000
STATIC DANGER
May 14, 2007
ITSI Workshop
Slide 19
Current
• An op-amp can
measure nanoamps
– The TLC272 contains
two precision opamps
– With one resistor R,
you get an output
voltage V = –IR where
R can be 100 MΩ
May 14, 2007
ITSI Workshop
QuickTime™ and a
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The TLC272 Opamp. There
are actually two “operational
amplifiers” in this tiny
package.
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Slide 20
Conductivity
• With just a 100 kΩ
resistor, you can
measure Galvanic
Skin Response
(GSR)
– That’s aluminum foil
over leads held in
place with tape
May 14, 2007
ITSI Workshop
Slide 21
Good Stuff!!!
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Assorted Capacitors. Each kit should
kit should have two. The values and
shapes do not matter.
Wire cutters. These can be
used to cut wire and strip off
its insulation.
Magnet and a paperclip used to
keep it from getting lost.
Quic kTime™ and a
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A Digital Multimeter or
DMM for short
Clip leads. Each kit has four wires with “alligator”
clips on each end. Some may not work properly, so
always check them with your meter.
May 14, 2007
Wire:
solid
core.
Phillips screwdriver
Assorted Resistors. The values are coded
in color bands. For help reading the
codes, see
http://www.dannyg.com/examples/res2/re
sistor.htmYou need one each 100 Ω, 1
kΩ, 100 kΩ, and 1 MΩ and two 10 kΩ.
Shrink Tubing. You can slip this over
wires to insulate them. Heat with a
blow dryer and it will shrink tight.
ITSI Workshop
Slide 22
Safety for People
• Wear goggles
• Always disconnect from
the computer before
touching a circuit
• Never touch a circuit a
circuit while operating
• Do not touch other
grounded metal
May 14, 2007
ITSI Workshop
Always disconnect from the computer
before working on the Experiment board.
Slide 23
Safety for the Circuits
• Carefully pry up the chips,
or leave them in place
• Have buddy check your
circuit before connecting
• Use conductive foam and
plastic
• Make neat circuits
• Keep your work area neat
• Don’t attempt to measure
current with the DMM
May 14, 2007
ITSI Workshop
Do not use your fingers to remove chips—many have
ended up with the chip embedded in their fingers. Pry the
chips loose from underneath using the Phillips screwdriver.
A neat circuit. Everything is visible and clear. Note
the short wires--this required cutting the leads on
the resistors. The resistor on the right has been
insulated. There are no bare wires that can touch.
Slide 24
The GoLink
– The GoLink acts as a
battery to power your
circuits and a detector
to measure voltage.
SIG1
5V
GoLink Equivalent Circuit
+5 V
V
…0100100011010110100…
USB
GND
– It samples the voltage 100 times a second and
sends on the result as a binary number
– The input must be between 0 V and +5 V
– The output goes from 0000 0000 0000 to
1111 1111 1111. Each step is 12 mV
May 14, 2007
ITSI Workshop
Slide 25
A First Circuit
Direct Connection
• Temperature
– 1. Disconnect the header
from the GoLink
– 2. Place the header and the
TMP36 in the Experiment
board
– 3. Connect pin 3 on the
TMP36 to the GND of the
header
• Viewed from below with the flat
upward, pin 3 is on the right
• GND is the second from the
top of the header if the white
lettering is upright
May 14, 2007
ITSI Workshop
Slide 26
A First Circuit
Direct Connection
– 4. Connect pin 1 of the TMP36 to +5
V on the header
• Pin 1 is on the left of the TMP36
looking up from below with the
flat on the top
• +5 V is second from the bottom
of the header
– 5. Connect pin 2 of the TMP36 to the
SIG1 input on the header
• Pin 2 is the center lead of the
TMP36
• SIG1 is the bottom input on the
header
– 6. Check your work, connect to the
computer, and run it
May 14, 2007
ITSI Workshop
Slide 27
A Motor as Motion Detector
Hot glue
attaches the
cardboard
disk to the
motor shaft
and the motor
to the meter
stick
May 14, 2007
ITSI Workshop
Slide 28
A Second Circuit
An Amplifier
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• The DC motor needs
some amplifying This
circuit has a gain of 10
May 14, 2007
ITSI Workshop
Slide 29
A Second Circuit
• The previous circuit has
noise, so add a filter
– The resistor R and capacitor
C do the filtering
– They have a time constant of
2πRC, which should be
roughly 0.1 sec
May 14, 2007
ITSI Workshop
Slide 30
More to Come
May 14, 2007
ITSI Workshop
Slide 31