Frequency to Voltage Converter Circuit using IC 555

Input signal with some frequency goes into FVC (frequency to voltage converter).

Output is DC voltage which matches that frequency.

We can make Frequency to Voltage Converter Circuit using IC 555 in monostable mode.

FVC useful for many things where we need check frequency like:

• Check speed RPM of spinning machine with motor, etc.
• Check liquid flow by watching how turbine spins
• Use light sensor like photodetector that give pulses to measure light
• Watch vibrations to see if machine have problem

Circuit Working:

Parts List:

555 IC in monostable mode is main part of this circuit.

In monostable mode 555 give one output pulse when it get trigger signal.

How long pulse stays depends on input signals frequency.

Making Input Signal Ready:

Input signal which is square or sine wave goes through diode D1 and capacitor C5.

This makes sharp spike and this sharp spike ensures 555 trigger every time.

Best spike voltage is around 2/3 to 1/3 of VCC.

Choosing Pulse Length:

Pulse time controlled is by resistor R3 and capacitor C4.

These are called timing parts.

We can change R3 and C4 to set pulse time for our use.

Cleaning Output Signal:

555 output may have noise.

Add resistor R1 and capacitor C1 to filter it and this gives clean output voltage.

Transistors Job:

Transistor Q1 helps the circuit.

It connects to timing capacitor C4.

When sharp spike comes transistor turns ON and discharges C4.

Then it turns OFF and C4 charges again.

This happens in sync with input signal.

Modification of the Circuit:

We can change R3, C4, R1 or C1 to adjust the circuit for our needs like different frequency or output voltage.

Summary:

This circuit smartly uses 555 IC to change input frequency into matching DC voltage output.

Formulas:

This circuit changes frequency into voltage using 555 IC in monostable mode.

Output voltage goes up when input frequency goes up.

How Monostable Mode Works:

When signal comes to pin 2 Trigger, pin 3 Output goes high for short time.

Time of this high pulse depends on R1 and C1.

Timing Formula:

T = 1.1 × R1 × C1

where:

• T is pulse time in seconds
• R1 is resistor in ohms Ω
• C1 is capacitor in farads F

Convert Frequency to Voltage:

Output voltage is like:

Vout = 1 / T = 1 / (1.1 × R1 × C1)

So:

High frequency with short T means high voltage

Low frequency with long T means low voltage

Final Tip:

Change R1 and C1 values to fit our signal and what we need from the circuit.

How to Build:

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

• Connect pin 1 of 555 IC to ground.
• Connect pin 2 to pin 6 of 555 IC.
• Connect pin 3 to voltage output through resistor R1.
• Put capacitor C1 between R1 and ground.
• Connect pin 4 to +12V DC supply.
• Connect pin 5 to ground through capacitor C2.
• Connect capacitor C4 to pin 6 and then to ground.
• Connect pin 7 to +12V through resistor R2.
• Connect pin 8 to pin 4 and both to +12V DC.

Transistor Q1 Wiring:

• Collector of Q1 connects +12V through resistor R3
• Base of Q1 connects input signal through resistor R4, diode D1 and capacitor C5
• Emitter of Q1 connects to ground
• Put resistor R5 between ground and point between R4 and D1
• Put resistor R6 between ground and point between D1 and C5

Safety Tips:

Follow safety rules to avoid shock or damage.

Be careful with power supply and always double check the connections.

Conclusion:

This Frequency to Voltage Converter Circuit using IC 555 in monostable mode to convert signal frequency into matching DC voltage.

It is with low cost and is useful.

Always build the circuit with safely.

References:

Capacitance to voltage converter circuit diagram.  

555 timer IC