Part of a control system has three
switches (A, B, and C) and one motor. The motor should come on (+5 V.
output from the logic circuit) when the switches are as follows:
Switches B and C are closed
or
Switches A and B are closed
or
Switches A, B, and C are closed
- Make a truth table.
- Make a Karnaugh map or a Vietch diagram, and use it to create a simplified equation.
- Draw a schematic to match the equation, using AND gates, OR gates, and inverters.
- As with almost all digital circuits using switches,
you'll need to have a pull-up resistor for each switch, and each switch
will switch between open and ground.
- In other words, when a switch is closed, a digital 0 will be produced, and when the switch is open a digital 1 will be produced.
- You'll probably need to use an inverter for each switch.
- Re-draw the schematic using only 2-input NOR gates.
- For inverters, use NOR gates with both inputs tied together.
- Wherever you used an AND gate in the previous schematic, use the DeMorgan's equivalent of a NOR gate.
- Wherever you used an OR gate in the previous schematic, use the regular symbol for the NOR gate.
- Be aware of the inverting circles. In some cases
they will eliminate the need for inverters you used in the previous
schematic. In other cases they will require inverters to cancel them
out.
- Simulate the NOR-gate circuit, using a lamp or probe to represent the motor.
- On the schematic you drew in step 4, write chip numbers (U1, U2, etc.) and pin numbers.
- Build the NOR-gate circuit using real components, with an LED indicator being used to represent the motor.
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