May 14, 2007Slide 1ITSI Workshop Do-it-Yourself Electronics: Probeware on a Budget Robert Tinker The...

May 14, 2007 Slide 1ITSI Workshop

Do-it-Yourself Electronics: Probeware on a Budget

Robert TinkerThe Concord Consortium

http://concord.orgQuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.


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


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


Probe Interface Overview

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

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.Sensor Amplifier InterfaceProperty

• 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


The Kit: GoLink

• GoLinkShown here

connected to a computer through a standard USB port

Can be used with many probes


The Kit: Header

• The “Header” (at right)

• The header connected to the GoLink (left)


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




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


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


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


Light–Phototransistor

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.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.


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






On LED’s as detectors



http://www.pages.drexel.edu/~brooksdr/DRB_web_page/papers/UsingTheSun/using.htm


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


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


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



Sound

• An electret microphone in a plastic housing– Plugs directly into most

computers– No circuit needed!




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


Voltage

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




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 MΩ



The TLC272 Opamp. There are actually two “operational

amplifiers” in this tiny package.




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


Good Stuff!!!

Assorted Capacitors. Each kit should kit should have two. The values and

shapes do not matter.




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.

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.

Shrink Tubing. You can slip this over wires to insulate them. Heat with a blow dryer and it will shrink tight.

A Digital Multimeter or DMM for short

Wire cutters. These can be used to cut wire and strip off

its insulation.

Wire: solid core.

Magnet and a paperclip used to keep it from getting lost.

Phillips screwdriver


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 Always disconnect from the computer

before working on the Experiment board.


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

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.


The GoLink

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

V+5 V …0100100011010110100…

USB

GND

5V

SIG1GoLink Equivalent Circuit

– 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


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


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


A Motor as Motion Detector

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


A Second CircuitAn Amplifier

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




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


More to Come

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