# 2.2.5.P KMappingUniversalGates_Fireplace INFOGRAPHIC (1).docx

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A B C D Fireplace Control Circuit Gas Line Emergency Cut-Off Valve Thermal Sensors (4) Project 2.2.5 Universal Gates and K-Mapping: Fireplace Control Circuit Introduction The Acme Fireplace Company has hired you to redesign the fireplace control circuit for their latest residential gas fireplace. The fireplace burner is equipped with four thermal sensors that output a logic (1) whenever a flame is present. These sensors are connected to the fireplace control circuit which outputs a (1) to the emergency cut-off valve to keep the gas flowing (i.e., a zero will turn the gas off). The original design of the fireplace control circuit was quite simple. For the gas valve to remain on, all four sensors needed to output a logic (1). During field testing it was discovered that variations in gas pressure and humidity cause the thermal sensors to occasionally output a logic (0) even when a flame was present. This caused frequent unnecessary shut downs and constant customer dissatisfaction. For the redesign, it has been determined that the emergency cut-off value should remain open as long as three of the four sensors indicate that a flame is present. Additionally, the designers have asked you to add a second output indicator to the control circuit. This indicator will output a logic (1) when the four sensors do not all agree (i.e., not all on or not all off). This indicator will be used by the service technician to diagnose whether a faulty sensor exists. Equipment Circuit Design Software (CDS) Breadboard (DLB or DMS) #22 Gauge solid wire Integrated Circuits (74LS00 & 74LS02) Procedure © 2014 Project Lead The Way, Inc. Digital Electronics Project 2.2.5 Fireplace Control Circuit – Page 1

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Design Design a combinational logic circuit that meets the above detailed design specifications. Additionally: The Karnaugh mapping technique must be used to obtain the simplified logic expression for both outputs. The circuit that controls the emergency cut-off valve must be implemented using only 74LS00 two-input NAND gates. The circuit for the possible faulty sensor indicator must be implemented using only 74LS02 two-input NOR gates. Simulation Using the Circuit Design Software (CDS), enter and test your Fireplace Control Circuit design. Use switches for the inputs A, B, C, and D and a probe or LED circuit for the two outputs. Verify that the circuit is working as designed. If it is not, review your design work and circuit implementation to identify your mistake. Make any necessary corrections and retest.
• Fall '19
• Logic gate, Acme Fireplace Company

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