Tachometer
In a motor or other type of equipment, the rate of rotation of a shaft or disk can be determined using an instrument called a tachometer. Here is the basic tachometer with a digital displ…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Tachometer is a electronics project. In a motor or other type of equipment, the rate of rotation of a shaft or disk can be determined using an instrument called a tachometer. Here is the basic tachometer with a digital displ…
- Source pages
- 458-461
- Named parts
- 4
- Build goal
- Working, tested prototype
Tools you need
- Digital multimeter
- Wire stripper and side cutters
- Soldering iron with a fine tip
- Current-limited bench supply
Use eye protection, good lighting, and a clean insulated surface throughout the build.
Safety precautions
- Disconnect every power source before changing a connection.
- Check component polarity, pinout, and supply voltage twice.
- Use a current limit for the first power-up.
- Keep liquids, loose metal, and uninsulated wires away from the bench.
Gather, identify, and understand every part.
Use the standardized inventory, then open What's this? to learn each part's role, advantages, limitations, handling, and specifications.
What's this?Image, role, pros, cons, handling & specifications
CD4081
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for CD4081; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
CD4069
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for CD4069; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
CD4033
A semiconductor stage performs switching, amplification, regulation, rectification, or logic.
What it does hereIt controls current or signal flow at a defined point in the circuit.
Buy / compare this part ↗Advantages
- Fast and efficient
- Compact
- Can control larger loads from smaller signals
Limitations
- Pin order varies
- Sensitive to overvoltage and reverse polarity
- May need cooling or bias components
Handling
- Verify the datasheet pinout
- Avoid static and soldering heat
- Check notch, stripe, or flat-face orientation
Specifications to verify
- Use the exact model, value, package, and rating listed for CD4033; similar-looking parts are not always interchangeable.
- Confirm pinout, maximum voltage/current, dissipation, gain or forward voltage, and package.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWVR1 - preset potentiometer identified in the circuit
A named project component whose exact role is defined by the source circuit and build guide.
What it does hereIt performs a documented electrical, control, interface, or construction function in this project.
Buy / compare this part ↗Advantages
- Selected for this project
- Can be checked independently
- Supports modular troubleshooting
Limitations
- Substitutes may differ
- Generic names can hide variants
- Pinouts and ratings vary
Handling
- Compare the received part with the source
- Keep it labelled
- Do not force connectors or adjusters
Specifications to verify
- Use the exact model, value, package, and rating listed for VR1 - preset potentiometer identified in the circuit; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
Connect one verified path at a time.
Explore the named components and standardized signal flow, then use Source Check to verify exact physical pins, values, and topology before applying power.
Trace this circuit.
Tachometer: interactive parts, standardized terminals, responsive anchored wires, student explanations, and the original circuit reference in one shared system.
Trace before wiring
Follow power, ground, inputs, processing, and outputs in that order. Never guess a pin from package shape alone.
Connect with power off
Make short, labelled connections and share a common ground only where the schematic requires it.
Inspect every joint
Check continuity, polarity, adjacent shorts, and loose connections before the first power-up.
Open all source diagrams and build views 2 visuals
Confirm the hardware-only control path.
This project does not include firmware in the source. The circuit itself provides the required behaviour.
How to connect
- Match every controller label to the circuit view and source pin map.
- Join grounds before signal wires when separate low-voltage supplies are used.
- Keep motors, relays, pumps, and other loads on a suitable driver and external supply.
Common mistakes
Reversed VCC/GND, board-label versus GPIO-number confusion, missing common ground, and charge-only USB cables.
Troubleshoot
Disconnect loads, continuity-test one path at a time, then test with a current limit.
Software preparation
No IDE, board package, library, or firmware upload is required for this project.
If you add a programmable controller as an extension, document its pin map separately.
How to upload code
The original design is implemented entirely in hardware, so proceed after verifying the circuit and supply.
Assemble, deploy, test, and troubleshoot.
Use the complete source notes in build order, then pass the final checks before calling the project finished.
Build in functional stages
- Power and regulation
- Controller or processing stage
- Inputs and sensors
- Outputs and loads
- Enclosure and strain relief
Power up safely
- Inspect unpowered continuity first
- Apply the lowest safe current limit
- Measure supply rails before signals
- Add one load at a time
- Record expected and actual results
Work from simple to complex
- Confirm power, ground, polarity, and orientation
- Compare each pin with the source
- Test inputs separately from outputs
- Replace only one variable at a time
- Power off before every correction
Follow the documented instructions.
These notes come from this project's source and remain in their original order.
Project overview
Project build noteIn a motor or other type of equipment, the rate of rotation of a shaft or disk can be determined using an instrument called a tachometer. Here is the basic tachometer with a digital display that shows the number of turns per second (RPS).
Fig. 1: Block diagram of the tachometer Figure 1 shows the tachometer's block diagram. Figure 2 shows the tachometer's circuit, which is made up of a timer IC 555 (IC1), an IC 7811 (IC2), an IC CD4081 (IC3), an IC CD4069 (IC4), two ICs CD4033 (IC5 and IC6), two common-cathode displays (each LTS543), and some other discrete parts. When switch S2 turns on IC1 in monostable mode, it makes a one-second pulse. IC1's time period is set by the variable resistor VR1. When the shaft is moving, IC2 sends out pulses.
Fig. 2: Circuit of the tachometer IC5 (CD4033) is a decade counter that has a seven-segment decoded output. It is coupled to DIS1 so that the place of the unit can be displayed on the screen. Pins 2 and 14 of IC5 are connected to the ground. When the count goes too high, IC5's Pin 5 (CO) sends a pulse (count reaches from 0 to 9). Through NOT gate N3, this pulse is used as the clock input to IC6. That is, IC6 will go up by one pulse after IC5 has pulsed ten times. So, when the unit's count on DIS1 is done, the count continues on DIS2. On DIS1 and DIS2, you can count and show up to 99 digits. Tachometer circuit How the circuit works is easy to understand. Set up IC2 so that when the motor shaft turns, it cuts the IR signal and sends pulses to pin 3 of its output. In other words, when the motor turns, the shaft cuts the light beam inside the optocoupler (IC2). Pulses are made because of this. This series of pulses is sent to pin 1 of the AND gate N1. The output of IC1 is linked to pin 2 of the AND gate N1. To determine the RPS of the shaft, briefly engage the switch S2 to make gate N1 active through the monostable multivibrator for a period of duration equal to one second (IC1). The pulses
are used to tell IC5 what time it is. The counter adds one to itself and makes the code that tells the seven-segment displays what to do. The screens show how many counts are made in one second. So, you can easily figure out the number of turns per minute (RPM).
Construction & testing
Project build noteBuild the circuit on a general-purpose printed circuit board (PCB) and put it in a cabinet with room for the battery, switches, and motor. After you connect the 9V battery, the module is ready to show the motor's RPS.
You built Tachometer.
You followed the full workflow from understanding the mission to testing the finished project. That is a real engineering achievement - well done.
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