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TRIAL ONE ENTRY PAGE


TRIAL ONE: Revision of digital logic gates, use of a simple digital trainer for hardware experiments and a practical task to apply this knowledge.



The revision material was worked through with the student before moving on to the digital trainer. A CMOS 4071 Quad two input AND gate was used to introduce manufacturer data sheets as a source of gate connection information. The revision material used was part of this course which can be accessed HERE.
The digital trainer used a special connecting method for prototyping circuits without solder. The details of type of board are given HERE.


The trainer has two slide switches generating logic 1 or logic 0. Using these two switches as a two digit binary number gives four possible combinations. The task was to decode the switch values and display the decimal equivalent value on a seven segment display. The first stage of this task was to calculate the boolean expression for each of the seven segments in terms of the two logic switch values. The circuit using AND, OR and NOT for each of the segments was then designed. [Boolean Algebra was used to simplify the expression before designing the circuit]. The diagrams below shows the arrangement of the seven segments and the connections on the seven segment display.


A driver circuit is required to drive each segment as logic output from a gate is not able to supply enough current to drive the LED. The seven circuits required are usually supplied as one package for ease of use. The image below shows the package designed for this trial. It has a connector with 16 pins so that it can be used with the digital trainer.








Driver circuit connections
(Pin 1, segment a, is to the left of the "notch"
viewed from the top of the 16 pin connector)

Use of the Driver Circuit
The seven inputs, "a" to "g", are connected to the corresponding outputs on the logic circuits from the digital trainer. The seven outputs, "a out" to "g out" are connected to the corresponding inputs, "a" to "g", on the seven segment display.
0 Volt [pin 8] on the 16 pin driver circuits connector must be connected to 0 Volt on the Digital trainer. This links the 0 volt of all the seven driver circuits to the same 0 volt as the digital logic curcuits on the trainer.

Connecting a segment
[The connections for segment "a" are described here as an example.]
  • Segment "a" output from decoding cicuit on digital trainer
  • Input to "a" on the display driver circuit [pin 1]
  • Output from "a out" on display driver circuit [pin 13]
  • Input to "a" on seven segment display [pin 1]

NOTE: The connection marked "Common" on [pin 14] of seven segment display must be connected to the +V supply from the digital trainer.

It is called "Common" as it is connected to the anode of each of the LEDs in the seven segment display.

MONITOR OUTPUTS

This connection strip provides access to "a" to "g" segment signals and 0 Volts coming into the driver circuit.
NOTE: + V [pin 16] of the driver circuit connector needs a connection to +V on the digital trainer to make it available on the MONITOR OUTPUT strip.

The MONITOR OUTPUT strip will not be needed in trial1, but is there to allow extra circuits to be added for later trials, if required.