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Saturday, 5 July 2014

Simple Method to Control 7407, hex buffer/driver, using Switch

by realfinetime  |  in Pull Up Resistor at  10:45

                We have already seen the pinout diagram and description of  7407. Here comes the operation of 7407 IC using switches. Controlling 7407 using switch is simple. For the proper operation of 7407 IC, some extra components need to be included in the circuit. They are

1. Pull Down resistor of high value (10K) across any of the input terminal (A) and ground.
2. Pull Up resistor of comparably low value (5K) across the positive terminal of  output voltage source ( Connected to top of pull up resistor ) and output terminal (Y) corresponding to the input terminal.

                 IC is shown by a rectangle in the following circuit diagram. Supply Voltage 7V is applied at the Vcc pin ( Pin 14 ) of  7407 IC. Gnd is given at the pin 7 of the 7407 IC. Here 1A (Pin 1) is taken as the input pin. 1Y ( Pin 2 ) is taken as the output pin. 



Pinout Diagram of 7407. 
Pull down resistor.

                Pull down resistor helps to ground ( LOW ) the input pin of 7407 when switch is off. When the switch turns on, input voltage will appear across the pull down resistor and the voltage across the input pin will be 5.5V ( HIGH ). If the pull down resistor is not connected, input pin will remain at HIGH level even if the switch is kept open or closed. 

Pull up resistor.

               Current required for the load comes through the pull up resistor. This current is supplied by a 30V Voltage source. So if the pull up resistor is not connected, circuit will kept open and current will not flow through the load. If the input voltage is HIGH, impedance of the logic gate buffer will be high and voltage will appear across the output ( HIGH ). Similary, if the input voltage is LOW, impedance of the logic gate buffer will be low and output current will flow through the pull up resistor and logic gate buffer to ground. So voltage across the output will be LOW.

Truth Table.

Truth table of 7407 when controlled by a switch is given below.
Read more :


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