Voltage Dividers and Transistors

Sometimes technological developments take sudden leaps.  It was in the early 1950s that a small group of engineers developed one of the most important components of any electronic system.  The transistor was a device that allowed one part of a circuit to switch or control another circuit.  It is often regarded as one of the most important inventions of all times.  It is the fundamental component of every computer circuit.

Transistors come in all sorts of shapes and sizes.  In this class, we will investigate a transistor where the circuit is controlled by light.  It is a very important sensor in many STEM projects.  It is simple of way of controlling an "opening" event when light levels will change.

Please read this week's Tasks and Activities.

  • The picture shows a phototransistor
  • All transistors have 3 leads or terminals. 
  • The leads are named Collector, Base and Emitter.
  • In a phototransistor like this one, the Base is not connected. 
  • The voltage changes in the circuit are controlled by light.

 
  • Here is the diagram of the circuit tha was used to divide the voltage for the light sensors in many prototype projects.
  • The resistor is attached to the Emitter terminal to provide a continuous circuit
  • The other half of the divided terminal leg is then used in the Arduino program as an input to another program
  • Here is the code line from the work station: int sensorValue = analogRead(A0);
  • Click this image to see how this phototransistor might feed an input to a control program.

Tasks and Activities

  1. Go to one of the work stations set up around the room.  Run the Tools Serial Monitor menu.  What is the range of number values you see in that terminal as you wave your hand over the sensor?
  2. What are the names of the three legs of a transistor.
  3. How is the voltage "divided" in the example seen in class?
  4. Write a Pseudo Code example that might control the project you are building.
  5. How is the phototransistor used in the prototype toy coffee machine?

 

  

Don't forget to email your choices/answers to Mr. Widmer by the end of this week.  Keep a copy of that email in your Google Docs folder.