Problem/Statement
In this activity we were instructed to redesign the fireplace control circuit for a residential gas fireplace. The fireplace had four thermal sensors that when ever a flame was present would output a logic of (1). these sensors were connected to the fireplace control circuit which outputs a (1) to the emergency cut off valve to keep the gas flowing, a zero (0) will turn the gas off. The Problem was that when for the gas valve to stay on all sensors had to have a logic (1), they found that variations in gas pressure and humidity caused the sensors to output a (0) even when the flame was present. This caused shut downs that were unnecessary.
Our design had to keep the fireplace on when at least three of the sensors indicate a flame is present. Additionally a second output indicator is to be added to the. It will output a (1) when not all of the sensors agree.
Our design had to keep the fireplace on when at least three of the sensors indicate a flame is present. Additionally a second output indicator is to be added to the. It will output a (1) when not all of the sensors agree.
Brainstorming/Calculations
Emergency Shut Off ValveFurther instruction said that the circuit that controls the emergency cut off valve must only use NAND gates and the circuit for the faulty sensor must only use NOR gates.
FIRST I had to determine the logic equation, i did this by simply looking at the problem statement. It states that at least three sensors need to be on for the flame to be on meaning; GAS= ABCD'+ABC'D+AB'CD+ABCD would give you a flame. SECOND To create less work, i used K-Mapping to simplify the logic expression. Bellow is a picture of the K-Mapping that took place to simplify the circuit for the emergency cut off valve. Now that there is a simplified logic equation, a sketch of the Circuit for the Emergency Shut off valve can be draw. Shown below. In the sketch you discover that some of the NAND gates can be cancelled out because when two NAND's are next to each other they cancel out.
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Faulty Control CircuitFurther instruction said that the circuit that controls the emergency cut off valve must only use NAND gates and the circuit for the faulty sensor must only use NOR gates.
FIRST I had to determine the logic equation, i did this by simply looking at the problem statement. Fault Indicator= A'B+A'D+B'D+AC'+CD'SECOND To create less work, i used K-Mapping to simplify the logic expression. Bellow is a picture of the K-Mapping that took place to simplify the circuit for the faulty indicatior Now that there is a simplified logic equation, a sketch of the Circuit for the Faulty Sensor Indicator can be draw. Shown below. In the sketch you discover that some of the NOR gates can be cancelled out. The sketch below is the final simplified sketch.
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Simulation
To verify that the design works, i created a simulation on the computer using MultiSim a Circuit Design Software. I recreated the design i sketched and tested it using probes to test each minterm in the equation. Below is a picture of the circuit. These two circuits (The emergency cut off valve and the Faulty Sensor) were to be connected so that they may work at the same time.
Prototyping
The last step is to use a Digital Logic Board to build and test my Fireplace control Circuit design. Shown Below is the Emergency Shut off valve circuit. Four NAND gates were required after the simplification process. Each input was a switch which represented the sensors. When the switch was off the sensor recognized no flame present. To breadboard this circuit, simply wire each input to the other required input as shown in the sketches of the design.
Reflection
This was a very interesting project for me, NAND seems easier to me than NOR. Therefor making the Emergency Shut off valve easier for me to design and Simulate. It pleases me to know that i now know how an electric fireplace works, to an extent at least. If i were to go back i redo this project, again i would try to make things a little neater, but i would also have checked each minterm as i went along breadboarding becuase at the very end i had a problem and spend a chunk of time trouble shooting.