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ENT-DIGI-210 Lab 2 Notes ©Paul Godin Lab 2 page Updated September 2007 1 Basic Switch Configuration Lab 2 page 2 Introduction ◊ Switches and Keypads are a a critical component of digital circuits. These devices allow digital circuits to interface with the outside world. ◊ Switches are produced in a variety of formats. This presentation only addresses basic switches. Lab 2 page 3 Definitions ◊ Pole: the arm or lever that moves when the switch is thrown. ◊ Throw: the number of contacts a pole can connect to. Pole Throw Lab 2 page 4 Definitions SPST (Single Pole Single Throw) Pole Throw SPDT (Single Pole Double Throw) Throw #1 Pole Throw #2 Lab 2 page 5 Definitions DPST (Double Pole Single Throw) DPDT ( Double Pole Double Throw) Lab 2 page 6 Definitions ◊ SPST, SPDT, DPST and DPDT switches are commonly: ◊ Toggle or Rocker switches: The switch lever is pushed to the point where the pole snaps into place by spring action. Commonly used where high current or high voltages are present (reduces arcing). Used in digital electronics applications. ◊ Slide switches: The pole is slid into a contact. Cheaper to produce but more difficult to use. Lab 2 page 7 Common ◊ ◊ The common of a switch is the hinge point of the pole. It is typically identified with a “C”. It is called the common because it is the only point that makes an electrical connection with the other points. Throw #1 Common Pole Throw #2 SPDT (Single Pole Double Throw) Lab 2 page 8 Switch ◊ DIP switch ◊ SPDT (Single Pole Double Throw) ◊ Commons are labelled ◊ Internal wiring of the DIP switch Lab 2 page 9 LED Basics ◊ ◊ ◊ Light Emitting Diodes are a semiconductor that will produce light if the anode (+) is more positive than the cathode (-). It will block current in the other direction. LEDs need current limiting (resistor) in series otherwise the device will burn out. They have minimum and maximum voltage ratings. + Anode Cathode Logic symbol for an LED + Anode Cathode Physical LED Cathode is on flat side Lab 2 page 10 Layout of the Breadboard for Procedure 2 Flat Side of LED C1 C3 C2 C4 Resistor 330Ω Red wire for direct connections to Vcc; black for GND connections. Lab 2 page 11 Switch Preferred wiring for a digital switch This configuration ensures there is always a logic level present on the input to the digital device. Lab 2 page 12 Wiring diagram for a Digital Switch Always connect the common to ground. The common is labelled with a “C”. Lab 2 page 13 Layout of the Breadboard for Procedure 3 Resistor 1 kΩ C1 C3 C2 C4 To logic probe Always connect the common to ground. Black wire for direct connections to Ground. End Lab 2 page 14