DECADE COUNTER USING NE555 AND CD4026

About: 18 y/o guy with huge ambitions

A decade counter is a device which is used to count up to 10. It is then reset. A seven segment display is used to display the value stored by the counter. The circuit operates on 9v, supplying a greater voltage may damage the circuit; and supplying lesser voltage may result in the counter not working as proper and efficiently. Counters are used in various places such as stopwatches, timers and calculators.

Step 1: Components Required, and Their Functions

The Components you'd require are:

  • IC NE555 Used to generate and supply pulses to the decade counter when the push button is pressed.
  • IC CD4026 Functions as both a counter and as a de-multiplexer .
  • Seven Segment Display Used to display the state of the counter in digital form.
  • 3 x 10K ohm Resistors Used to restrict the flow of current.
  • 100K Resistor Used with a capacitor contributing to the RC circuit, in order for only one pulse to flow at a time.
  • 22uf Capacitor Used with a resistor contributing to the RC circuit, in order for only one pulse to flow at a time.
  • 1uf Capacitor Used to operate the IC555N in monostable mode.
  • 2 x PushButtons Used to supply pulse and rest.
  • Connecting Wires Used to connect the circuit.
  • Battery(9v) Used to supply power to the circuit.

Step 2: Functions of Important Parts Explained in Detail:

To supply pulse to the decade counter we use IC NE555 in Monostable mode.

IC NE555:

It is an integrated chip used in a variety of timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays as an oscillator, and as a flip flop element. It was introduced by Signetics in the year 1972, and is still widely used due to its low price, ease of use and stability.

Monostable mode of IC NE555:

It is also known as Single Shot mode. In this state it remains in its stable state
until external triggering is applied. This trigger is very essential for the NE55N to enter the unstable state. After some time the IC re-enters stable state. This time in between is termed as quasi stable state. The time is determined by the RC network in the circuit. The external triggering is given by connecting the Trigger PIN 2 to the ground using a push button.

Here's how the pins of the IC NE555 are connected in order to operate it in the single shot mode:

Pin 1.Ground: This pin should be connected to ground.

Pin 2. TRIGGER: Trigger pin is dragged from the negative input of comparator two. The comparator two output is connected to SET pin of flip-flop. With the comparator two output high we get high voltage at the timer output. If this pin is connected to ground (or less than Vcc/3), the output will be always high.

Pin 3. OUTPUT: This pin also has no special function. This is output pin where Load is connected. Pin 4. Reset: There is a flip-flop in the timer chip. Reset pin is directly connected to MR (Master Reset) of the flip-flop. This pin is connected to VCC for the flip- flop to stop from hard resetting.

Pin 5. Control Pin: The control pin is connected from the negative input pin of comparator one. Normally this pin is pulled down with a capacitor (0.01uF), to avoid unwanted noise interference with the working.

Pin 6. THRESHOLD: Threshold pin voltage determines when to reset the flip- flop in the timer. The threshold pin is drawn from positive input of comparator1. If the control pin is open. Then a voltage equal to or greater than VCC*(2/3) (i.e.6V for a 9V supply) will reset the flip-flop. So the output goes low.

Pin 7. DISCHARGE: This pin is drawn from the open collector of transistor. Since the transistor (on which discharge pin got taken, Q1) got its base connected to Qbar. Whenever the output goes low or the flip-flop gets reset, the discharge pin is pulled to ground. Pin 8. Power or VCC: It is connected to positive voltage (+3.6v to +15v).

IC CD 4026:
The IC CD4026 counter is used for both counting and de-multiplexing, so as to get the counter state on the connected seven segment display. The pin-out pin functions of IC CD4026:

1 CLK Clock in Increments the counter with each Positive clock pulse (LOW to HIGH). 2 CI Clock inhibit - when low, clock pulses increment the seven-segment. Freezes the counter when HIGH, active HIGH.

3 DE Display enable- chip will be ON when this pin is HIGH, and OFF if it is LOW.

4 DEO Display enable out - for chaining 4026s

5 COThe CARRY-OUT (Cout) signal completes one cycle every ten CLOCK INPUT cycles and is used to clock the succeeding decade directly in a multi-decade counting chain

6 F Connected to ‘f’ of the 7 segment.

7 G Connected to ‘g’ of the 7 segment.

8 VSS Ground PIN

9 D Connected to ‘d’ of the 7 segment.

10 A Connected to ‘a’ of the 7 segment.

11 E Connected to ‘e’ of the 7 segment.

12 B Connected to ‘b’ of the 7 segment.

13 C Connected to ‘c’ of the 7 segment.

14 UCS Ungated C-segment - an output for the seven-segment's C input which is not affected by the DE input. This output is high unless the count is 2, when it goes low.

15 RST Reset PIN, active HIGH. Reset the counter to 0 when HIGH.

16 VDD Power supply PIN

Step 3: Circuit Diagram & Working

In this circuit, the IC NE555 is used to provide clock pulse on each button press, so whenever

the button is pressed counter is incremented by one. An RC circuit (22uf capacitor & 100K resistor) is connected at clock at pin 1 in the CD 4026 IC so that only one pulse is counted each time the pushbutton is pressed. The pushbutton connected with pin 2 of the IC NE555 is used for the purpose of incrementing the counter by one; and the pushbutton connected at pin 15 of the IC CD 4026 is used for resetting the counter to zero.

Step 4: You're All Done!

Connect the 9v battery and the display should light up.

I've attached 2 pictures of the PCB board i've soldered the components on.

I'm open to criticism, so please feel free to comment your views on this instructable. Do message me if you have any problems related to this project.


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