Do-it-Yourself Electronics: Probeware on a Budget

1. Do-it-Yourself Electronics: Probeware on a Budget Robert Tinker The Concord Consortium http://concord.org ITSI Workshop

2. 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 ITSI Workshop

3. 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 ITSI Workshop

4. Property Sensor Interface Amplifier 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 ITSI Workshop

5. The Kit: GoLink • GoLink Shown here connected to a computer through a standard USB port Can be used with many probes ITSI Workshop

6. The Kit: Header • The “Header” (at right) • The header connected to the GoLink (left) ITSI Workshop

7. 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 ITSI Workshop

8. 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 ITSI Workshop

9. 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 ITSI Workshop

10. 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 ITSI Workshop

11. 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. ITSI Workshop

12. 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 ITSI Workshop

13. On LED’s as detectors http://www.pages.drexel.edu/~brooksdr/DRB_web_page/papers/UsingTheSun/using.htm ITSI Workshop

14. 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 ITSI Workshop

15. 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 ITSI Workshop

16. 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 ITSI Workshop

17. Sound • An electret microphone in a plastic housing • Plugs directly into most computers • No circuit needed! ITSI Workshop

18. 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 ITSI Workshop

19. 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 ITSI Workshop

20. The TLC272 Opamp. There are actually two “operational amplifiers” in this tiny package. 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 ITSI Workshop

21. 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 ITSI Workshop

22. 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/resistor.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. Magnet and a paperclip used to keep it from getting lost. Wire cutters. These can be used to cut wire and strip off its insulation. Phillips screwdriver Wire: solid core. A Digital Multimeter or DMM for short Good Stuff!!! ITSI Workshop

23. Always disconnect from the computer before working on the Experiment board. 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 ITSI Workshop

24. 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. 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 ITSI Workshop

25. SIG1 5V +5 V V …0100100011010110100… USB GND GoLink Equivalent Circuit 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 ITSI Workshop

26. 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 ITSI Workshop

27. 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 ITSI Workshop

28. A Motor as Motion Detector Hot glue attaches the cardboard disk to the motor shaft and the motor to the meter stick ITSI Workshop

29. A Second CircuitAn Amplifier • The DC motor needs some amplifying This circuit has a gain of 10 ITSI Workshop

30. 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 ITSI Workshop

31. More to Come ITSI Workshop