In preparation, use the "virtual ground" (happy opamp) method to analyze this circuit. Find Vout in terms of Vin and the adjustment-potentiometer setting, which we will call f, ranging from 0 to 1 as the slider of the potentiometer moves from the bottom to the top. Hint - use the fact that R3>>R2 to find Vadj in terms of f as a very simple expression.
Suppose U1 is a typical 741 opamp, its supply rails are +/-15 volts, and the drift of the circuit (when Vin=0) is nulled using R2. Then the ambient temperature changes 10 degrees celsius. How long will it take for the circuit's output to drift out of range (to "saturation")?
You are given a sensor element of one of the following types:
• Load cell (four strain gauges in a bridge configuration) How do you "excite" it? How can you tell which of the four colored wires are opposite ends of the bridge, rather than adjacent?
• Diodes which can be used as a temperature sensor - How do you use it? How do you get a constant "forward current" in the diode? Look for the "forward voltage vs. temperature" curves for particular diodes, e.g. BAV21 or any others, or find the "diode equation" and plot it.
• Photodiode. Photonic Detectors Inc PDB-V107 (large area photodiode) or just pick a photodiode (not a phtotransistor) from Digikey. How do you use it? Can you find a "photodiode amplifier" circuit somewhere? Why does it make any sense at all to "reverse bias" a diode? (Wouldn't it just refuse to conduct?) Are normal diodes in glass capsules photodiodes too? (i.e. do they respond to light) Are LEDs photodiodes?
• Analog output hall sensors (for measuring magnetic field) - see allegromicro.com - Allegro A3515EUA. See if you can soup up the sensitivity (and shift the output volatge bias (no field = 2.5 volts out) so that you can make it sensitive to Earth's magnetic field.
• Optical interruption detector. QVA11234. How do you use it? It's normally used only on/off. Can you use it as a sensitive position detector, as the edge of something opaque intercept the IR beam? Could it be a smoke detector? Visualize the IR with a a special card for that purpose. Have your circuit give output in the range 0-5 volts as light fraction goes 0-100%
In each case, be resourceful to find out how to use your device. (web, digikey.com, Horowitz & Hill "The Art of Electronics".)
Make a circuit using op amps or instrumentation amps to amplify the output of your device up to a convenient level. You can find datasheets for a lot of useful chips on the 433 website. If you can't find it there, try digikey.com or the printed catalog.
Show me your circuit so I can help you avoid problems. (the sooner the better)
Find an analog to digital converter chip. Again be resourceful. Read its datasheet so you have some idea how to use it and whether it is the kind you want. (There are lots of kinds.)
Use LEDs to display the digital output of your ADC. Or, if you want to, you can drive seven-segment LED digits.
Optionally, use a comparator (and a potentiometer) to set a threshold, beyond which an LED lights.
Make sure digikey.com has your parts in stock (budget ~$20) Email me a list of the parts you need by WEDNESDAY AFTERNOON so you can build your circuits in lab on THURSDAY.