Jessie Cho, jessiec
Daniel Terry, djterry
EECS 373

Project Description

This project involves the design of a programmable home thermostat using an LCD display, a matrix keypad, and a thermistor circuit. Functionality includes programming desired temperatures for time ranges throughout the week. The LCD is the user interface and displays the current temperature, the desired temperature, and the ac/off/heat status.

Components Details

• The LCD display requires 11 test points: 3 for control and 8 for data
  
• D7 to D0 connected to test points 24 through 31 respectively
• E, R/W, RS connected to test point 21 through 23 respectively
• The LCD display requires 3 Voltages: 5V, Gnd, and a voltage from a 10K potentiometer to determine character brightness
  
• The matrix keypad requires 8 test points: 4 for scanning rows and 4 for observing columns
  
• Scan 0 through 3 connected to test points 2 through 5 respectively
• Col 0 through 2 connected to test points 6 through 8, Col 3 ignored
• The thermistor is placed in series with a 10K resistor. This allows us to measure a voltage change across the thermistor in response to a temperature change. With this voltage we can determine the thermistor’s resistance and the corresponding temperature.

Most Difficult Issue

We thought that our most difficult issue with the project was getting our LCD and keypad working with all the different pins we were using. Many of the circuit boards in the lab did not function correctly when we used many of the pins. Some even had broken pins, which made our testing process very difficult. Only a few boards were working for us. Thus, most of our time spent trying to understand why our components were malfunctioning in the end led us to realize that it was the circuit board which wasn’t working appropriately.