Simple Tachometer Circuit

A basic tachometer circuit is a DIY electrical instrument for determining a shafts or disks rotating speed.

We need a tachometer to determine the rotation speed or revolutions per second RPS of a rotating shaft or wheel.

This basic tachometer circuit was created using two seven segment display units and a slotted opto isolation module MOC7811 two components that are readily available.

With the help of this circuit, we can measure the RPS of a spinning shaft or disc.

You may add another decade counter stage to this circuit to get more value, it can count RPS from 00 to 99.

What is a Sensor MOC7811?

The MOC7811, referred to as an opto slotted coupler or opto interrupter module is a reliable tool in the communications and electronics arsenal.

With the integration of a phototransistor and an infrared emitter IRED, this little gadget is incredibly potent.

Its ingenious configuration makes it possible to accurately identify objects or obstructions in the infrared light beam it emits.

Because of this the MOC7811 is quite adaptable and a well liked option for a range of applications like position sensing, object detection and rotational encoding.

Circuit Working:

Parts List:

The circuit utilizes several integrated circuits ICs to create a tachometer that measures rotations per second RPS.

Below are the circuit working details:

IC555:

This timer IC functions as a monostable multivibrator.

Pressing switch S2 triggers a timing pulse, and LED1 green visually indicates the sensing duration.

MOC7811 IC2:

This optocoupler combines an infrared IR emitter and a photodiode.

The photodiodes logic level changes depending on whether the IR beam is blocked or interrupted.

AND logic gate N1:

This gate controls the Johnson decade counter CD4033.

CD4033:

This decade counter drives the seven segment display LTS 543 to show the measured RPS.

This configuration allows displaying RPS values from 00 to 99.

Two decade counters and displays:

The provided information also includes instructions for building a rotating interrupter.

It emphasizes the importance of measuring the slot width and depth of the MOC7811, as well as the spinning shaft nose.

Each interruption of the IR beam by the nose counts as one rotation.

The total count of rotations within the sensing duration provides the RPS value.

By multiplying the RPS by 60, you can convert it to rotations per minute RPM.

Formulas:

Using the ICs and other components listed above, one can design a tachometer circuit that measures the frequency of a signal produced by a spinning item (such an engine or motor) and shows the RPM (Revolutions Per Minute) on a 7-segment display.

Here are some general formulas and points to think about:

Converting Frequency to RPM:

RPM = f × 60​ / PPR

where,

• If the number of pulses per revolution PPR from your sensor is known, you can use the following formula to convert frequency (f) to RPM:

Using the IC 555, one may create a monostable multivibrator, also called a one shot pulse generator.

In reaction to a trigger signal, this circuit generates a single pulse with a predetermined length.

Pulse Duration T:

The duration of the output pulse T in monostable mode is determined by the values of R1 and C1.

T = 1.1 × R1 × C1

where,

• T is the pulse duration in seconds,
• R1 is the resistance in ohms Ω
• C1 is the capacitance in farads F.

You may efficiently create a tachometer circuit utilizing the ICs and components specified by following these steps and taking into consideration the components indicated.

Depending on your particular applications needs and performance specifications, change the component values and settings as necessary.

Safety Measure

• Double check the connections before turning it on, make sure all the parts are connected correctly in accordance with the circuit schematic.
• To keep the rotating shaft and interrupter from breaking free and posing a risk, make sure they are firmly fixed.
• While the circuit is working, keep your hands and other items away from the moving elements.
• To avoid unintentional contact with moving parts, if the circuit will be used in a permanent arrangement, think about enclosing it in a safe box.

Conclusion:

With the help of simple tachometer circuit, you may construct a tachometer that measures spin speed using readily accessible electrical components.

It might be entertaining to build a basic tachometer circuit as an electronics hobby.

However, the required features and output format might affect the circuits complexity.

References:

Arduino digital tachometer circuit

Tachometer