Frequency to Voltage Converter Circuit using IC 555

An input signal with a specific frequency is fed into a frequency to voltage converter circuit FVC, which outputs a proportionate DC voltage.

An FVC like circuit may be constructed by configuring the 555 integrated circuit in monostable mode.

These come in handy for a variety of tasks where frequency based measurement or monitoring is required, such as:

• Measurement of speed RPM in spinning machinery such as motors
• liquid flow rate by keeping an eye on a turbines spin
• Using a photodetector that produces pulses in response to light level to measure light intensity
• Monitoring vibrations to find any problems with the machine

Circuit Working:

Parts List:

The 555 in Monostable Mode is the circuits central component.

This design uses the monostable multivibrator mode a particular 555 IC chip arrangement.

In this mode, whenever an incoming signal triggers the IC 555 it produces a single output pulse.

The crucial point is that the input signals frequency determines how long the output pulse lasts.

Modifying the Input Signal to Ensure Reliable Triggering

The incoming signal a square wave or sine wave passes through a preparation phase before it reaches the IC 555.

Together, a diode D1 and capacitor C5 transform the incoming wave into a brief sharp spike.

This guarantees that every incoming signal causes the IC 555 to fire consistently.

About two thirds to one third of the power voltage applied to the IC 555 VCC is the optimal voltage for this spike.

Choosing the Pulse Duration: A Tightrope Walk

Two parts govern the length of the output pulse that the 555 IC produces: a capacitor C4 and a resistor R3.

These resistor and capacitor are commonly known as the ‘timing’ resistors.

You may regulate the duration of the output pulse and customize it for your particular application by carefully choosing the values of these components.

Streamlining the Output Signal

The 555 IC raw output signal may include some undesired noise spikes.

A resistor R1 and capacitor C1 are added to the output circuit to remedy this.

By filtering the output voltage and producing a cleaner signal for later use this combination works as a filter.

The Transistors Function:

A Helping Hand in the circuit, the transistor Q1 has a supporting function.

It is driven by the triggering spike produced previously and is linked across the timing capacitor C4.

The transistor activates and releases C4 at high voltages.

On the other hand, the transistor switches off as the voltage drops enabling C4 to refuel.

In time with the frequency of the incoming signal this cycle is repeated.

Adjusting the Circuit to Your Requirements:

This circuits customizable nature is what makes it so lovely.

You may calibrate the circuit to meet the precise frequency range and output voltage needs of your application by varying the values of the timing components R3 and C4 and perhaps the filtering components R1 and C1.

Overall, this circuit shows a brilliant technique to use the IC 555 to transform an incoming signals frequency into a proportionate DC voltage output.

Formulas:

The output voltage of a circuit that converts frequencies to voltages using a monostable IC 555 is precisely proportional to the frequency of the input signal.

The monostable mode configuration operates as follows, along with the crucial formula:

Triggering: The settings of R1 and C1 control how long a trigger input signal at pin 2 Trigger causes the output at pin 3 output to go high.

Calculating Timing: The following formula provides the output pulses pulse width T in monostable mode:

T = 1.1 * R1 * C1

where,

• The units of measurement are seconds (s) is T
• ohms Ω for resistance of R1, and
• farads F for capacitance of C1.

The conversion of frequency to voltage:

The output voltage Vout is directly proportional to the inverse of the pulse width T.

V_out​ = 1/ T​ = 1​ / 1.1 * R1 * C1

• This means that shorter pulse widths at higher frequencies translate into greater output voltages, and vice versa.

Using the IC 555 in monostable mode, this formula and configuration serve as a foundation for the construction of a frequency to voltage converter circuit.

It is recommended to modify R1 and C1 in accordance with the particular needs of the application and the properties of the input signal.

How to Build:

To build a Frequency to Voltage Converter Circuit using IC 555 follow the below mentioned steps for connections:

• Assemble all the circuit parts as shown in diagram above.
• Connect pin 1 of IC1 555 to ground.
• Connect pin 2 to pin 6 of IC1 555.
• Connect pin 3 of IC1 555 to volt output through resistor R1.
• Connect a capacitor C1 to ground between resistor R1 and volt output.
• Connect pin 4 of IC1 555 to positive supply of 12V DC.
• Connect pin 5 of IC1 555 to ground through capacitor C2.
• Connect capacitor C4 to ground through pin 6 of IC1 555.
• Connect pin 7 of IC1 555 to positive supply through resistor R2.
• Connect pin 8 to pin 4 of IC1 555 to positive supply of 12V DC.
• Connect transistor Q1 collector to positive supply through resistor R3, connect transistor Q1 base to input signal through resistor R4, D1 diode and capacitor C5 , connect emitter of transistor Q1 to ground.
• Connect resistor R5 to ground between resistor R4 and D1 diode.
• Connect resistor R6 to ground between D1 diode and capacitor C5.

Safety Measures:

If you adhere to the safety precautions, you may reduce the possibility of mishaps and guarantee a secure and pleasurable experience when constructing and playing with this frequency to voltage converter circuit.

Conclusion:

In conclusion, by shrewdly utilizing a 555 IC in monostable mode, this circuit provides an affordable means of converting the frequency of an incoming signal into a proportionate DC voltage output.

Prioritize safety above all else when creating and utilizing this circuit by taking the advised safety procedures.

References:

Capacitance to voltage converter circuit diagram.  

555 timer IC