P6h Even More Logical
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State and recognise the input and output signals in an electronic system with a combination of logic gates.
Describe that a latch in a car or burglar alarm causes it to remain on once it has been triggered.
Recognise that the output current from a logic gate is able to light a LED.
Recognise and recall the symbol for a relay.
State that a relay can be used as a switch.
Complete a truth table of a logic system with up to three inputs made from logic gates.Describe the use of an LED as an output for a logic gate.
Describe how a relay uses a small current in the relay coil to switch on a circuit in which a larger current flows.
Explain how to work out the truth table of a logic system with up to four inputs made from logic gates.
Describe how to connect NOR gates to make a bistable latch circuit.
Explain how, for a NOR gate latch:
- a brief high signal at one input results in a permanent high signal at the latch output;
- a brief high signal at the other input causes a low signal at the latch output;
- a low signal at both inputs leaves the latch output signal unchanged.
Explain how an LED and series resistor can be used to indicate the output of a logic gate.
Describe that a relay is needed for a logic gate to switch a current in a mains circuit because:
- a logic gate has a low power output;
- the relay isolates the low voltage from the high voltage mains.
Lesson ID:
ID_a
Starters:
Starters_a
Objectives:
Explain the meaning of digital levels 0 and 1 in terms of volatges 0V and 5V (TTL logic levels)
Learn the symbols and truth tables for the simplest logic gates NOT, AND and OR
Two gate combinations including NAND and NOR
Prior Learning:
Digital communications
Difficult Concepts:
Appreciation of logic gates as logical devices - black boxes - that follow very simple rules.
combinations as result of 2 to the power of number of inputs ie 2,4,8,16 for 1,2,3,4 inputs AND knowing what these combinations look like.
Outline:
Go over binary the digital language. Relate this to computers as very complicated logic gate circuits. Electronics as at its simplest a means of aloowing circuits to automatically solve problems. Introduce NOT, AND and OR gates formally with truth tables. Develop two gate circuits showing the NAND and NOR gates with their truth tables and symbols.
Suggested Practicals:
MFA decision modules with cards to solve basic problems. NOTE: Do NOT lose the leads we have very few of them!
Extension Activities:
Solve more complicated MFA board problems
Find a way of building an XOR gate from NOT, AND and OR gates
Homework:
Homework1
Lesson ID:
ID_b
Starters:
Starters_b
Objectives:
Be familiar with 3 gate combinations upto and including 3 input logic gate circuits
Recognize and understand the operation of the NOR gate bistable latch circuit
Prior Learning:
Digital communications and two input logic gates
Difficult Concepts:
Intermediate steps in complex logic gate problems. Sequential logic gate circuits depend on prior state of inputs. Explanation of NOR gate latch circuit.
Outline:
Demo the relay and LED as possible outputs froma logic gate circuit. Logic gates can not supply much current and hence power to drive power outputs. Hence relay to say turn on motors in a washing machine. Go over two 3 input 3 gate logic gate circuits. Demo the NOR gate bistable latch circuit. Go over the idea of sequential logic gate circuits using timing diagrams. Understand the action of the NOR gate latch circuit. Explain as the basis of computer memory - one bistable remembers one bit of information.
Suggested Practicals:
Bread board latch circuits - suggest pre-made with LEDs for outputs on the Q output. Alternaitveley use the MFA boards with the XXX modules
Extension Activities:
MFA board progammable board to demonstrate the workings of a computer processor and memory
Homework:
Homework2 again