Microcontrollers Lab
LAB #4: LCD + Keypad
<Student 1 Name> <Student 1 ID>
<Student 2 Name> <Student 2 ID>
Start Date: September 10, 2013
Due date: September 17, 2013
(R): Section to be submitted in report
(P): Section to be showed in LAB
I. Pre-LAB.
1. (R) Given the following programs, compile them in your favorite C IDE like Dev-C
(http://www.bloodshed.net/download.html.) Add a screenshot of the console output. Explain the reason of
that result.
Code
LAB #4 – LCD + Keypad
Output
Explanation
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LAB #4 – LCD + Keypad
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2. (R) Explain the behavior of the circuit shown in Figure 1.
Figure 1. Keypad Circuit
A:
3. (R) Regular keypad scanning algorithms set all MCU pins connected to columns as outputs simultaneously.
There is a high risk of a short circuit if two keys are pressed at the same time. Explain why this is possible.
A:
4. (R) The keypad scanning algorithm presented in the project avoids this problem. How?
A:
5. (R) Explain the function get4NumericKeys() found in the keypad.c file. What is the role of the variable ptr?
A:
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Microcontrollers Lab
II. In-LAB
1. (P) Wire the circuit in figure 2. Note: the keypad pins are numbered assuming a bottom view, and counting
them from right to left.
Figure 2a. LAB4 Circuit
LAB #4 – LCD + Keypad
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Figure 2b. LAB4 Hardware Connections (photo)
2. (P) Implement a security box based on the state-machine in figure 3 using the following specifications:
 Two combinations for opening the box:
o Manager key (secret: 9876)
o User key (seed: 1111)

When in open state:
o Write “State: Open” in the LCD.
o If a new combination is entered, then the new combination becomes the user key.
o If the door is closed (emulated by pressing the user button) then new state = closed state.

When in closed state
o Write “State: Closed” in the LCD.
o If a combination is introduced, it is compared with the user combination. If the combination
introduced is equal to the user combination, then the door is open and new state = open state.

Use a switch-case control structure for the implementation.
Figure 3. State-machine for security box
3. (R) Incorporate here the c file that solves this exercise. Your code must be fully commented.
4. (P) Extension
o
When in open state and a new combination is entered, ask for confirmation (the new confirmation is
entered twice). If both are equal, then the new combination is accepted.
o
When state = closed, if three times a wrong user combination is introduced, then the system gets
blocked and only the manager combination will be accepted (unknown by the user).
o
(R) Incorporate here the c file that solves this exercise. Your code must be fully commented.
LAB #4 – LCD + Keypad
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II. Post-LAB.
1. Please, answer the following questions (this section is not optional).
a) Explain why state machines are useful for modeling embedded systems. Document your answer.
A:
b) Present two possible applications for the knowledge you have acquired doing this lab. Elaborate your
answer.
A:
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