Simple 1 Hz Pulse Frequency Generator Circuit

A 1Hz pulse frequency generator circuit is a circuit that generates a series of pulses with a frequency of 1Hz, which means one pulse per second.

This type of circuit is commonly used in various applications such as clocks, timers and signal generators.

Circuit Working:

Parts List:

Here is a circuit diagram for a 1Hz pulse/frequency generator using the popular timer IC 555 configured as an astable multivibrator.

The output pulses are indicated visually by an LED.

An astable multivibrator, also known as a free running multivibrator generates rectangular waves.

Unlike the monostable multivibrator this circuit does not require an external trigger to change the output state, hence the name ‘free running.’

This circuit is useful in applications requiring clock pulses.

The timing of the high and low states of the output is determined by two resistors and a capacitor connected externally to the basic timer IC 555.

A clock is a square wave alternating between high and low states.

Each high low cycle forms a clock cycle with a specific frequency and duty cycle.

Frequency is the number of cycles completed in one second and duty cycle is the ratio of the time period of the high state to the time period of the low state.

The 555 IC can be configured to operate at the desired frequency by selecting the right combination of resistances and capacitance formula mentioned below.

The IC 555 can also produce waves with duty cycles other than 50%.

Duty cycle is the ratio of the time period when the output is high to the time period when the output is low is explained through below mentioned formula.

Capacitor C1 charges toward VCC through resistances R1 and R2 VR.

Eventually, the threshold voltage exceeds +2/3 VCC, causing comparator 1 to have a high output and triggering the flip flop so that its Q is high and the timer output is low.

With Q high, the discharge transistor saturates and pin 7 grounds allowing capacitor C1 to discharge through resistance R2 VR with a discharging time constant of R2 C.

As the capacitor discharges the trigger voltage at the inverting input of comparator 2 decreases.

When it drops below 1/3 VCC, the output of comparator 2 goes high resetting the flip flop so that the timer output is high.

This completes the auto transition in the output from low to high and then to low.

Thus the cycle repeats.

Formula:

1. The frequency of an oscillator circuit centered around a 555 IC set up in astable mode is found in 1 Hz Pulse Frequency Generator circuit using the formula frequency :

Frequency = 1.44 / ((R1 + 2R2) * C1)

where,

• Frequency: Measured in hertz Hz, is the circuits output .
• It shows how many cycles the output signal goes through in a second.
• There are more cycles per second at a greater frequency.
• R1 and R2: utilized in the timing circuit are represented by these values.
• Typically, they are attached to particular pins on the IC 555.
• C1: This is a representation of the capacitance of the timing circuits capacitor C1.
• It is also attached to particular pins on the 555 integrated circuit.
• 1.44: This constant is unique to the internal architecture of the IC 555 .

How the formula works:

The 555 IC regulates the timing of its internal charging and discharging cycles using a combination of resistors R1 and R2 and capacitor C1.

The output signals frequency is established by these cycles.

The connection between the resistors, capacitor and the final frequency is effectively represented by the formula.

2) The duty cycle of an astable oscillator circuit constructed around a 555 IC may be found using the formula below.

Duty Cycle = (R1 + R2) * 100 / (R1 + 2R2)

where,

• Duty Cycle: The percentage of a cycle that the circuits output signal spends in the high state relative to the entire cycle period is represented by this number, which ranges from 0% to 100%.
• A 50% duty cycle, for instance, indicates that the output is high for half of the cycle duration and low for the remaining half.
• The output spends more time in the high state than the low state when the duty cycle is more than 50%.
• A duty cycle of less than 50%, on the other hand, indicates that the output is high for a shorter period of time than the low condition.
• R1 and R2: These stand for the resistances of the two resistors R1 and R2 that are utilized in the IC 555 integrated circuits timing circuit.
• Usually, they are linked between particular timer pins.

How the formula works:

The resistors R1 and R2 are used by the 555 IC to regulate the internal charging and discharging cycles timing.

These cycles eventually impact the duty cycle by determining how long the output signal stays in its high and low states.

The duty cycle is effectively expressed as a percentage by the formula, which takes the ratio of R1 to R2.

Crucial Information:

Specifically, astable mode 555 IC circuits are covered by above formula.

For the majority of real world applications, the formula assumes that the capacitor C1 has less of an effect on time than the resistors.

More sophisticated analytical techniques can be required for circuits with particular design constraints or for extremely accurate duty cycle estimations.

3) Formula for Charging Time Constant in a 555 IC:

Resistor R1 inserted between particular pins of the timer IC and the capacitor C affects the charging time constant in a 555 IC astable circuit:

τ = R1 * C

Here:

• τ (tau): Charging time constant in seconds (s).
• R1: Resistance of the timing resistor in ohms Ω, this resistor controls the charging process.
• C: Capacitance of the timing capacitor in farads F.

How to Build:

To build a Simple 1 Hz Pulse Frequency Generator Circuit you can follow the below steps:

Connect the 555 IC:

• Place the 555 IC on the breadboard.
• Connect pin 1 to the ground of the breadboard.
• Connect pin 8 to the positive rail of the breadboard.

Connect the Resistors:

• Connect one end of R1 10k to pin 7 of the IC 555 .
• Connect the other end of R2 to ground of IC 555.
• Connect one end of R2 220Ω to LED.

Connect the Capacitor:

• Connect the positive terminal of C1 10μF to pin 6 of the IC 555.
• Connect the negative terminal of C1 to ground.
• Connect capacitor C2 between pin 5 and ground.

Connect the LED:

• Connect the anode longer leg of the LED to pin 3 of the IC 555.
• Connect the cathode shorter leg of the LED to a current limiting resistor 220Ω, and connect the other end of the resistor to the ground rail of the breadboard.

Power Supply:

• Connect the positive terminal of the power supply to the positive supply of the breadboard.
• Connect the negative terminal of the power supply to the ground of the breadboard.

Testing:

• Apply power to the circuit.
• The LED should start blinking at a frequency of approximately 1Hz indicating the output pulses generated by the 555 IC.

Note:

• Please note that actual component values and configurations may vary based on specific requirements and component tolerances.
• Adjustments may be necessary to achieve the desired frequency and duty cycle.

Conclusion:

To conclude, a 1Hz pulse frequency generator circuit is a simple yet versatile circuit that can generate a series of pulses with a frequency of 1Hz.

It is commonly used in electronic projects requiring precise timing or clock signals.

By using a timer IC like the 555 configured as an astable multivibrator this circuit can be easily built and adjusted to generate different frequencies as needed.

References:

How do I produce a 1Hz clock output using a 555 timer IC? Are there better ways other than a 555 timer IC?

How to make a 1 Hz clock circuit?