Click Here to View Video

1. OBJECTIVE

The objective of this lab exercise is to design and implement a 7-segment display.

 

2. EQUIPMENT

1. PAD-234
2. Selected SN7400 series integrated circuits
3. 7 red LEDs (light emitting diodes)

1. DISCUSSION

Digital displays are useful for displaying digital information in a format that’s easy to understand. Consider the following design:

 



 

Each segment should be activated according to the desired output. The number we would like to display, however, is in binary format. So we want one of the following patterns to be displayed, depending on whether the number being represented is 01, 10, 11, or 00:

 

                                                                                                       

 

FIGURE 1

2. EXERCISE

Using TTL logic, design a circuit using individual logic gates to implement the

digital display. Prepare a truth table, build the circuit, identify all IC pin connections (i.e., prepare a logic diagram with pin numbers and an IC diagram) and verify the circuit operation.

You will make use of the following IC’s:

The LEDs will need to be "buffered" in order for your circuit to function correctly. Since, by nature, the diode provides very little resistance, once it is turned on it is as if there is a "short circuit" from it’s positive side to ground. Therefore, immediately after each LED there should be a 2k-W resistor to both prevent burnout of the LED and to allow the circuit to function correctly.