A tachometer is an important tool used to measure how fast a shaft or disk is spinning in motors and different machines.
The speed it measures is usually shown in revolutions per minute or RPM for short.
In this article we will explore how a simple tachometer circuit is designed, how it works and how it is built as shown in the diagram provided.
Tachometers are widely used in many fields like industry, car engineering and labs where they help keep track of the speed of rotating parts.
They provide important information that helps improve and control performance.
The tachometer circuit we are discussing uses basic parts to measure the RPM of a motor.
It can run on a 12V DC power supply and gives a clear reading on an analog meter.
Circuit Working:
Parts List:
| Component | Value/Type | Quantity |
|---|---|---|
| Resistors | 10k | 1 |
| 1k | 3 | |
| Potentiometers | 50k, 1k, 10k | 1 each |
| Capacitors | Ceramic 0.1μF | 1 |
| Electrolytic 1μF 25V | 1 | |
| Semiconductors | Transistor BC547 | 1 |
| Diodes 1N4007 | 2 | |
| Bridge Rectifier 1N4007 diodes | 4 | |
| Analog Meter | 1mA FSD meter | 1 |
The input signal we are talking about shows the pulses made by something that spins like an electric motor.
This signal can come from different places like a magnetic pickup or a Hall effect sensor which are both good at making pulses.
The diodes D1 and D2 are really important because they change the input signal so that only the positive pulses can move on to the next part of the process.
In this setup, capacitor C1 helps to smooth out those rectified pulses while resistor R1 is there to keep the current from getting too high in the circuit.
The stronger pulses then go to the base of the transistor Q1 and this transistor makes the signal stronger so it can power the next parts of the circuit.
Also, VR1 acts as potentiometer, which lets you change how much the transistor amplifies the signal.
After that the amplified pulses get filtered again by capacitor C2 and resistor R4 making sure that a steady direct current DC voltage is created which matches the motors revolutions per minute RPM.
The bridge rectifier D3 makes sure the signal is ready to drive the analog meter known as M1.
In the end the analog meter shows a reading of the DC voltage that corresponds to the RPM giving the user a simple and clear output.
Formulas with Calculations:
Formulas with calculations are mentioned below to Measure your own RPM with a Tachometer Circuit:
Frequency to Voltage Conversion:
Vout = Im * Rload
where,
- Im is the current through the meter
- Rload is the effective resistance of the circuit
Capacitor Sizing:
fc = 1 / (2 * pi * R * C)
where:
- fc is the cutoff frequency
- R is the resistance in ohms
- C is the capacitance in farads
This ensures that high frequency noise is filtered while maintaining the accuracy of the RPM measurement.
How to Build:
To measure the RPM with a Tachometer Circuit following steps are needed to follow:
- Gather all the components mentioned in the above circuit diagram.
- Connect the base of transistor Q1 to center leg of pot VR1, upper leg of VR1 pot to one end of resistor R2 and other end of R2 to +12V DC positive supply, and third leg of VR1 pot to upper leg of VR2 pot.
- Connect collector of transistor Q1 to center leg of VR3 pot, and the upper leg of VR1 pot to one end of resistor R3 and other end of R3 to +12V DC positive supply.
- Connect from base of transistor Q1 capacitor C1, diodes D1 an D2 and resistor R1 in series to Audio input and GND.
- Connect emitter of transistor Q1 to resistor R4 and capacitor C2 in parallel and GND.
- Connect one end of bridge rectifier D3 to collector of transistor Q1, other end to positive of M1 FSD meter, third end to negative of M1 and fourth end to GND.
Safety Measures:
Always be careful when using this circuit and make sure to follow safety rules when dealing with motors and machines that move.
The spark plug terminal gives off a high voltage, so it is important to keep the engine turned OFF while you are connecting things.
Be extra cautious to prevent any electric shocks.
Only try this circuit on your car if you really know what you are doing with car electrical systems.
I can not be held responsible for any accidents that might happen.
Conclusion:
This tachometer circuit is an easy and affordable way to measure how fast something is spinning like a motor.
It uses common parts that you can find easily and works really well.
You can use this circuit for different projects, but make sure to test and adjust it correctly before using it for real.
This design is perfect for hobbyists and anyone interested in electronics who wants to create and learn about tachometer systems.