Do-it-Yourself Electronics: Probeware on a Budget

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Do-it-Yourself Electronics Probeware on a Budget

• Robert Tinker
• The Concord Consortium
• http//concord.org

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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

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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

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Probe Interface Overview

• The flow of data from some physical property into
  a computer

• 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

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The Kit GoLink

• GoLink
• Shown here connected to a computer through a
  standard USB port
• Can be used with many probes

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The Kit Header

• The Header (at right)

• The header connected to the GoLink (left)

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The Kit Experiment Board

• Note the way the holes are connected
• Attach the metal backplane
• Plug chips across the center gutter
• Note how the header attaches

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The 14 Sensors

• TemperatureTMP36
• Temperature differencethermocouples
• Lightphototransistor
• Light (narrow band)red and green LEDs
• Magnetic fieldHall Effect probe
• Motiona small DC motor
• Rotationa 100 K? variable resistor
• Sounda microphone
• Forceresistive foam
• Humiditydry bulb/wet bulb
• Voltagedirect or through an amplifier
• Currentusing an op-amp
• Conductivitywires and a resistor

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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

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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-to-back pair, so you
  measure the temp difference
• You will have to twist the leads together
• Very small and fast response

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LightPhototransistor

• 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.

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Two Light Detectors

• 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

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On LEDs as detectors
http//www.pages.drexel.edu/brooksdr/DRB_web_page
/papers/UsingTheSun/using.htm
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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

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Motion Detector

• Any DC motor generates a voltage proportional to
  its rotation speed.
• Software can integrate this to measure
  displacement.

• It is noisy, so a filter or integration is needed

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A Rotation Sensor

• This 100 K? 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

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Sound

• An electret microphone in a plastic housing
• Plugs directly into most computers
• No circuit needed!

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Force

• Resistive foam
• That black foam conducts better when compressed

• The resistance is infinite with no force and
  drops under pressure
• Not a great detectorit drifts

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Voltage

• The AD623 instrumentationamplifier (i-amp)
• A precision device
• The output is G(VV)(Ref)
• The gain G, can be 1-1000
• STATIC DANGER

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Current

• An op-amp can measure nanoamps
• The TLC272 contains two precision op-amps
• With one resistor R, you get an output voltage V
  IR where R can be 100 M?

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Conductivity

• With just a 100 k? resistor, you can measure
  Galvanic Skin Response (GSR)
• Thats aluminum foil over leads held in place
  with tape

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Good Stuff!!!
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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

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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
• Dont attempt to measure current with the DMM

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The GoLink

• The GoLink acts as a battery to power your
  circuits and a detector to measure voltage.

• 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

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A First CircuitDirect 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

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A First CircuitDirect 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

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A Motor as Motion Detector

• Hot glue attaches the cardboard disk to the motor
  shaft and the motor to the meter stick

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A Second CircuitAn Amplifier

• The DC motor needs some amplifying This circuit
  has a gain of 10

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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 2pRC, which should
  be roughly 0.1 sec

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More to Come