Transistors, Relays, and Controlling High-Current Loads

Most devices want to control need more current than that to operate. Need a component in between microcontroller and the device that can be controlled with this small voltage and amperage. Relays  and transistors are most often used for this purpose.

• Relays - is a switch that’s controlled by a small electric current
• Induction - Pass an electric current through a wire, a magnetic field is generated surrounding the wire as well.
• Transistor - is an electronic device that can work as a switch. It allows control of a large current by a smaller current as does a relay.
  • Two Major Classes:
    • Bipolar Transistors
    • Field-effect Transistors
      • All transistors have some similar properties though. They all have three connections, referred to as the base the collector and the emitter  (on FET transistors, the three connections are the gate the drain and the source)
  • Darlington transistor - two transistors in one, combined with a diode that protects the transistors from damage in case the load’s current runs in reverse.
• There are three differences between this transistor circuit and the relay circuit above.
  1. Because motors are inductive loads  (they work because of induction; for more, see the DC motor notes), they can create a reverse voltage when spinning down after you turn them off.
  2. protection diode in parallel with the transistor. The protection diode routes any reverse voltage around the transistor, thereby protecting it. Most transistors designed for controlling motors have a protection diode built-in.
  3. the microcontroller attached to the base (or gate) and the transistor’s emitter (or source) must have a common ground. If not, then the circuit will not work.

DC Motors: The Basics

Motors convert electrical energy into mechanical energy so that you can move things in the physical world.  They are based on the electrical principle of induction.

Torque is the measure of a motor’s turning force. It’s the force a motor can pull when the opposing force is attached to a shaft attached to its center rod.

LED

Voltage

Lumen

Mid-Term Project:

1. Visual Impairment: Can’t understand how many people are surrounding us unless they make noise or effort to touch. Using an IR sensor to give tactile feedback to how many people are around?Inspiration: Watch for the deaf that gives haptic feedback to the level of sound around.Interactions: Mostly implicit unless the user decides to go towards or away from the vibrations (people). Could be annoying with the constant buzzing. Is there a way to zone out of distractions? Do we pay attention to everyone who passes by? Should there be a threshold to the number of people around or the time they are around for to start buzzing?
2. Persona