Digital circuits generally use 5 volt supplies .
Digital voltages that are from 5v -2.7 volts in the TTL series(a type of digital integrated chip) are considered high and have a value of 1.
Digital voltages form 0-0.5 are considered low and have a value of zero .
In this circuit, I will use a simple inexpensive push button circuit to illustrate these states (high or low ).
If the voltage is high or 1 ,the LED will light .
If the voltage is low or 0 the LED will not light .
Step 1: The Pushbutton Switch
The push button switch is a small mechanism that completes a circuit when the pressed .In this circuit when the push button is pressed and a positive voltage is applied the LED will light .
If the push button is pressed and the voltage is low or close to zero the LED will not light
Step 2: NAND Gate
The 74HC00 is a quad NAND gate .It has 2 inputs for each gate and 1 output for each gate .
Step 3: Materials Used
The material used in this project are ;
1 pushbutton switch
1 74HC00 ,quad NAND
3 1000 ohm(brown ,black ,red) resistors
Step 4: Operation and Construction of the Circuit .
First lt's put the circuit together .
Place the NAND 74HC chip on the board .
Then on another board put a push button there .
Connect a 1000 ohm resistor to ground and the push button .
Place the other 2 resistor(1000 ohms) and LED as show in the image .
Connect a wire to ground and the cathode lead to the LED .
Connect the ground to each board with a wire .
Connect the 5 volt of the Arduino to the board as shown in the image and the ground as shown in the image .
What will happen ;
First look at the logic gate table .
It shows the NAND gate inputs and outputs .
If the inputs are zero as in the case of this circuit .
You will not there are no wire going to pins 1 and 2 .
The expected output will be 1 or high .Then the LED will light up when the
push button is pushed .
If the purple wire form the push button was put at pin 1 .When the push button is pressed the LED will not light
because the voltage is zero.
In this way, by using the logic gates truth table we can predict what the outputs would be with certain inputs .
Step 5: NAND Gate With Input ;pin1 Connected to the Push Button
In this image, you can see that the purple wire from the push button was put on pin 1 (input) to the NAND gate .
It has zero voltage at the input .When the push button is pressed the LED will not light because the voltage is zero.
Step 6: Other Types of Gates
This simple circuit could be used to analyze other gates (AND ,OR etc) .
If you look at the table for a gate . You can predict the outputs .
For example,if an AND gate was used and the inputs were zero volts(0),low and 5volts(1 ) high
the output would be zero .
A series of gates connected together also could be analyzed by using the truth tables .
Step 7: Conclusion
This simple push button circuit can be used to measure and analyze digital gates and circuits .
It is necessary to know the truth tables of the gate to predict the outputs ,high (5 volts or close to it) or
low ( 0 with zeros volts ).
This circuit was tested on Arduino and it works .
I have also used it on other circuits with Arduino .
It is recommended to use only with 5 volt circuits and not values higher than this .
I hope this Instructable helps you to understand digital gates, how to analyze them and measure the
voltages expected by a push button circuit,