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Do-it-Yourself Electronics: Probeware on a Budget Robert Tinker QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 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 TIFF (Unc ompres sed) decompress or are needed to see this picture. • 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. – 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 QuickTime™ and a TIF F (Uncompressed) decompressor are needed to see this picture. • 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 TIFF ( Unco mpre ssed ) dec ompr esso r ar e nee ded to see this pictur e. May 14, 2007 ITSI Workshop Quic kTime™ and a TIFF (Unc ompres sed) dec ompres sor are needed to see this pic ture. Slide 12 On LED’s as detectors QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. • 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 TIFF (Uncompressed) decompressor are needed to see this picture. 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 TIFF (Uncompressed) decompressor are needed to see this picture. The TLC272 Opamp. There are actually two “operational amplifiers” in this tiny package. QuickTime™ and a TIFF (Uncomp resse d) d eco mpres sor are nee ded to s ee this picture . 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!!! QuickTime™ and a TIF F (Uncompressed) decompressor are needed to see this picture. 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 TIFF (Unc ompres sed) dec ompres sor are needed to see this pic ture. 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 QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. • 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