Transistor Labs

Force-sensitive resistor and LED with Arduino

1. Give ideas of 2 applications of this sensor in the field of improving accessibility for handicapped people.
• As a way to help wheelchair access, a pressure sensor on the ground that when activated by a person size weight could open automatic doors would be a good application. 
• Also, since a pressure sensor can handle such variable input it would be very useful for someone who has very little movement. For example a quadriplegic or someone who relies on a motorized wheelchair could control acceleration with just the pressure of a single finger. 

Temperature sensor and LED circuit with Arduino

1. We use a voltage divider circuit for potentiometers, force-sensitive resistors, and many other sensors. Why do we not need to use a voltage divider circuit with this temperature sensor?
• The temp sensor has it's own variable voltage output, it controls it internally, therefore we don't have to control it. 

1. Unlike pressure sensed by force-sensitive resistors, or rotation sensed by potentiometers, ambient temperature sensed by temperature sensors almost always changes very gradually and slowly. How does this affect the design of interactions based on this sensor?
• Interactions with direct immediate input with the expectation of direct immediate output would not work. As the sensor is more calibrated to the ambient environment and inputs, processes, and outputs very slowly over time the interactions it can facilitate must also be in tune to the ambient environment. For example a thermostat that turns on at a certain temp and turns off when the environment has reached another temp.
2. Given the range of temperatures at which this sensor works, please give 2 ideas for applications of this sensor. Applications may involve anything from scientific research to artistic endeavors, but they should necessitate the use of this sensor, as opposed to other sensors.
• As I said above, this sensor would be ideal for a thermostat to regulate the temp of a room by turning the heat on or off depending on a previously input range.
• As an art project I think it would be really interesting to set up a room with the full color spectrum of lighting and use this sensor to change the 'coolness' and 'warmth' of the color of the lighting, but based on the ambient temperature of the room. So blue lights = cold, red lights = hot, and as the temp changes the color of light slowly changes. 

Transistor as switch

(Sorry about the narration, was talking politics with my roommate)

1. Why is the LED turned on by the switch dimmer than the LED turned on by the transistor?

• The transistor and the 560 ohm resistor must offer less resistance than the 10k resistor and the switch, therefore the first LED is receiving more current.

1. 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).

• i_switch = V/R = 5V / 10k ohms = 0.5mA
• i_transistor = V/R = 5V / 560 ohms = 8.9mA

Transistor as amplifier

1. How does turning the potentiometer to maximum resistance affect the sensitivity of the circuit to the photo-resistor's signal, as compared to turning the potentiometer all the way to minimum resistance?

• The potentiometer is used to tune the sensitivity of the photoresistor. With the potentiometer at max resistance the photoresistor controls most of the current to the LED making the circuit more sensitive, at min potentiometer resistance the LED is getting current directly therefore is less sensitive to the photoresistor.

Transistor controlled by Arduino

As Switch:

As Amplifier: