Strain Meter
This strain meter shows whether a change in the shape of an object, like a crane strut, is compressive (shortening) or tensile (lengthening). A strain gauge is stuck to the thing being te…
Know the mission before touching a wire.
Understand what you are making, prepare the right tools, and make the workbench safe.
Project details
Strain Meter is a electronics project. This strain meter shows whether a change in the shape of an object, like a crane strut, is compressive (shortening) or tensile (lengthening). A strain gauge is stuck to the thing being te…
- Source pages
- 382-384
- Named parts
- 2
- 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
NETWORK
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 NETWORK; similar-looking parts are not always interchangeable.
- Confirm dimensions, ratings, connection method, polarity, and environmental limits.
What's this?Image, role, pros, cons, handling & specifications
PART LEARNING VIEWVR1, VR2 - preset potentiometers 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, VR2 - preset potentiometers 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.
Strain Meter: 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 1 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 noteThis strain meter shows whether a change in the shape of an object, like a crane strut, is compressive (shortening) or tensile (lengthening). A strain gauge is stuck to the thing being tested and measures the strain. The reading on the meter changes when the resistance of the strain gauge changes. For this, a voltmeter or other analog or digital meter with a full-scale deflection of 1V DC can be used. But it would be better to use a digital multimeter. The circuit shows how a single op-amp IC 741 (IC3) boosts the signal from a network of three resistors (R1–R3) and a strain gauge (SG1). Since the recommended strain gauge for this circuit has a nominal resistance of 120 ohms, each of resistors R1 through R3 should also be 120 ohms. The resistors should also have a tolerance of more than 0.1% so that changes in temperature don't cause the meter's reading to change in ways that aren't wanted. Circuit operation How the circuit works is easy to understand. When the strain gauge is not being pulled on, the variable resistors VR1 (coarse control) and VR2 (fine control) are set so that the multimeter reads zero. (These zero voltages could be any voltage that works for the circuit, like 1.5V. It doesn't have to be a zero-voltage supply.) If the meter reading goes up, it means that the
length of the strain gauge is getting longer (tensile strain). If the number on the meter goes down, the strain gauge is getting shorter (compressive strain). By changing the value of VR2, you can change how sensitive the op-amp is (IC3). It lets the circuit respond in different ways to different amounts of strain. The meter gives stable readings because voltage regulators IC1 and IC2 provide 5V and -5V power supplies. The output from the Wheatstone bridge is made stronger by the op-amp.
You built Strain Meter.
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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