Lab 3 - Introduction to Transistors

1. Force-sensitive resistor and LED with Arduino

1. FSR's could be used in mobility devices (walkers, wheelchairs, and the like) to detect signs of distress in their users - while it would work best when combined with a temperature sensor, a very sensitive FSR could be used to detect heart rates, which, when elevated, could prompt, say, a message to be sent to their phone, informing them that their heart rate is dangerously elevated, and perhaps giving them an option to call paramedics or family, if they need to. Additionally, an FSR could be used in automated lifts, detecting when someone has stepped onto the lift and moving up or down accordingly.

2. Temperature Sensor and LED Circuit with Arduino

1. The temperature sensor is not a variable resistor, and as such does not require the voltage divider circuit.
2. Interactive designs based on this sensor would need to generate effects that are slow and gradual as well, instead of quick and immediate responses.
3. Temperature sensors work well in Air Conditioning systems, reading the ambient temperature of a room, being fed in a desired temperature by the user, and heating or cooling the room depending on how the temperatures differ. This could also be used in a freezer (in a home, commercial, or laboratory setting) and alerting a specified user (or set of user) if temperatures fall above or below a specified range of values (this would be particularly useful for wine cellars, but could be useful in storing any temperature-sensitive objects).

3. Transistor as Amplifier

1. Current always flows through the past of least resistance, and the path through the 560 Ohm resistor provides a lot less resistance than the path running through both the switch and the 10 k-Ohm resistor, so the LED turned on by the transistor will be brighter than the one turned on by the switch.
2.  Give the approximate current flowing through each leg of the circuit (ignore any affect the transistor might have on the current flow or voltage drop).
1. I = V/R ; I = (5V)/(560 Ohms) = 8.9 mA.
2. I = V/R ; I = (5V)/(10 kOhms) = 0.5 mA.

4. Transistor as Switch

1. When the potentiometer is offering its maximum resistance, there is very little current that can flow to the photoresistor, so its sensitivity will be dulled, whereas when the potentiometer is offering its minimum resistance, there is a lot of current flowing to the photoresistor, and as such its sensitivity will be much greater.

5. Transistor Controlled by Arduino