Gas station without pumps

2012 June 28

What sensors for circuits class?

Filed under: Circuits course — gasstationwithoutpumps @ 22:33
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What sensors are appropriate to use in a sensor-focused circuits class?  I listed a bunch that I’ve been thinking about in Why teach circuits to bioengineers?, but in this post I want to focus a bit more on what criteria we should use for deciding which sensors to include or exclude.

Some criteria:

  • Price. We want students to be able to buy a kit of parts for the course and take everything home with them when they are done.  All sensors should be under $5 (ideally under $1) each in quantities of 10.
  • Variety of things sensed.  I’d like for there to be at least 5 and preferably 8 or 9 different properties detected.
  • Variety of different electrical properties as sensor outputs (at least current, resistance, voltage, and capacitance, maybe also inductance or mutual inductance).
  • Some sensors should be rapidly varying (for oscilloscope output).
  • Some sensors should be slowly varying (for recording time course with Arduino).
  • Some sensors should require amplification.
  • Easy breadboarding.  Students won’t have time to do a lot of soldering, particularly of SMD parts.  We should do one or two labs where they do some soldering, but if we use SMD parts for other labs, we’ll need to design and assemble breakout boards for them.
Device Senses Output Catalog Price Notes
thermistor temperature resistance NTCLE413E2103F520L 35¢ non-linear, very sensitive, slowly time varying, no amplification needed
RTD temperature resistance 480-2017-ND $1.94 slowly time varying, only 0.4% change/degree, similar to high-precision  (which cost over $10 each)
temp sensor temperature voltage MCP9700-E/TO-ND 25¢ slowly time varying, not very accurate, linear, not much challenge for circuitry
electret mic sound current 102-1721-ND 75¢ rapidly time varying, can be amplified or not
potentiometer angle resistance 987-1277-ND 66¢ slowly time varying, hard to connect to mechanically?
potentiometer angle resistance 3382H-1-252 $2.23 slowly time varying, easier to incorporate into a goniometer?, lead in for servos
breathalyzer alcohol resistance 605-00011-ND $4.50  fun for students? needs humidity and temperature correction.
pH probe pH voltage SeroSystems pH probe $21 Too expensive and needs temperature correction.
humidity sensor humidity capacitance 480-2903-ND $3.61
pressure air pressure voltage MPXM2053GS-ND $6.51
gel electrodes EKG voltage SilveRest 22¢ (cheaper without snap), very low voltages and 60Hz noise requires good amplifier, time varying
gel electrodes GSR resistance SilveRest 22¢ (cheaper without snap), slowly time varying
CdS photoresistor visible light resistance PDV-P8104-ND 80¢
ambient light sensor visible light current 1080-1019-ND 46¢
phototransistor IR light current 754-1468-ND 19¢
reflectance sensor reflectance current QRE1113-ND 83¢ LED + phototransistor in same package, 5mm sensing distance
IR emitter 754-1600-ND 19¢ IR emitter and red LED needed for pulse oximeter
red LED 660nm 754-1218-ND ? IR emitter and red LED needed for pulse oximeter
green LED 754-1591-ND green LED needed for simple pulse sensor
conductance cell salinity bulk conductance ? ? May require student design and construction. Cheap with Al foil, expensive with Ag/AgCl electrodes.
touch sensor touch capacitance ? ? May require student design and construction.  Al foil and plastic wrap?

Richard Hughey had an interesting idea for an air-flow sensor. Use one of the siren whistles for kids that cost about 50¢ each in quantity. They have a plastic turbine in them, and we could use an LED and light sensor (perhaps one of the reflectance sensors) to get a pulse stream from the turning of the turbine, timing the pulses with an Arduino.

I just noticed that I don’t have any switches, accelerometers, magnetic sensors, … on that list. A breath switch might be a useful sensor for those thinking of the rehabilitation concentration.  A tilt switch is also a reasonable option. A lot of the sensors I have looked at are too expensive for their value in the course, though it might be worth spending a little lecture time going over how they work.

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1 Comment »

  1. [...] sensor ideas from What sensors for circuits class? that I have the parts for now include phototransistors, LEDs and IR emitters, and reflectance light [...]

    Pingback by Capacitive sensing « Gas station without pumps — 2012 July 8 @ 18:49 | Reply

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