Introduction to Wiring Logic Gates Presentation Name Course Name Unit 7 – Lesson 7.# – Lesson Name Introduction to Wiring Logic Gates

What are Logic Gates A logic gate is an electronic device that performs a logic operation. One or more logic inputs are processed to produce a single logic output.

Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Wiring Logic Gates In solve logic problems, logic gates must be set up properly. Begin by setting up a “bus” A circuit that allows many connections This works best if two boards are used, side-by-side, in portrait orientation.

Wiring Logic Gates Add and power the logic chip + connects to the + bus - connects to the – (Ground) bus Three connections remain Input A Input B Output Y

Wiring Logic Gates Output Y is connected to the Ground bus Use a 100Ω resistor in series with the LED as the output The resistor is used to limit the amount of current to the LED When proper inputs are present, the output will be turned on.

Wiring Logic Gates Providing logic to inputs A and B LED will light when inputs A and B are tied directly to + bus LED will not light when inputs A and B are tied to the - bus

Wiring Logic Gates Connecting inputs directly to + bus can show you what voltages are needed to produce output but….. True importance of logic gate can only be seen when decisions being made are based on varying inputs

Wiring Logic Gates Logic gates cannot be allowed to “float,” a voltage must be present or the logic gate will make up it’s own mind. Voltage below a certain level are read as a 0 Voltage above a certain level are read as a 1

Wiring Logic Gates Since each chip is slightly different we can use pull up and pull down resistors. A pull up resistor is connected to the + bus A pull down resistor is connected to the - bus

Wiring Logic Gates Pull up and Pull down resistors Digital inputs require fixed resistors Analog inputs require variable resistors Variable resistors allow a certain amount of calibration

Wiring Diagram – No Inverter Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Wiring Diagram – No Inverter While there are many different solutions to the Logic Problems, all the problems may be solved by using Pull-down resistors on the inputs, as well as the AND, OR, XOR, and Inverter gates. This diagram shows how to set up the Snap Circuits® with two inputs, pull-down resistors, and one logic gate. Copy it into your Engineering Notes.

Wiring Diagram – with Inverter Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Wiring Diagram – with Inverter Notice that the Inverter Gate also has to be powered (connected to the bus). Again, the Logic Problems can be solved with Pull-Up resistors, simply by switching the location of the Input sensor with it’s pull down resistor. Copy this diagram into your Engineering Notes.