Micro Pressure Sensor Model and the Wheatstone Bridge (SCME)
This lab introduces students to the fundamental principles of microelectromechanical systems by building a macro-scale model of a micro pressure sensor. Participants construct a functional sensing device using a paint can as a reference chamber, a balloon as a flexible diaphragm, and a custom-made piezoresistive paste composed of graphite and rubber cement. By arranging the conductive paste into a Wheatstone bridge configuration, students observe how mechanical stress and deformation change the material's resistance and the circuit's output voltage. The activity covers critical electrical concepts including Ohms Law and Kirchhoffs Laws, while teaching students how to collect data, perform sensor calibration using known weights, and analyze the relationship between physical pressure and electronic signals.
Uploaded by demo on 2026-07-19 · ready · Electronics · Original source ↗
Readiness checks
Latest report — 2026-07-19 14:18
Readiness: Micro Pressure Sensor Model and the Wheatstone Bridge (SCME)
Verdict: Ready · 2026-07-19 · est. parts cost $50–$120
This is a cold check for the Micro Pressure Sensor Model lab; no previous readiness report exists. All required materials are currently available from major retail and electronics distributors. The primary cost driver is the specialty 3M conductive tape, though acceptable lower-cost substitutes have been identified. The lab remains implementable as long as the SCME Instructor Guide stencil is available to the instructor.
Action required
None — all checked parts are sourceable.
Parts
Sensed Materials and Active Components
| Part | Spec/Package | Status | Stock | Price | Source |
|---|---|---|---|---|---|
| Pencil Lead (Graphite) | 0.9 mm HB | Active | High | $5.99 | Walmart |
| Rubber Cement | Solvent-based | Active | High | $2.84 | Walmart |
| Copper Foil Tape | 3M 1181, 1/4 inch | Active | 1,016 | $33.32 | DigiKey |
| Batteries | 1.5 V AAA | Active | High | $7.99 | Harbor Freight |
| Battery Holder | 2xAAA with leads | Active | High | $1.85 | DigiKey |
Structural Components and Housing
| Part | Spec/Package | Status | Stock | Price | Source |
|---|---|---|---|---|---|
| Paint Cans | 1-quart metal | Active | High | $1.25 | Best Containers |
| Balloons | 12-inch latex | Active | High | $1.00 | Walmart |
| Plastic Syringes | 3 cc (3 mL) | Active | High | $0.26 | VitalityMedical |
Tools and Instrumentation
| Part | Spec/Package | Status | Stock | Price | Source |
|---|---|---|---|---|---|
| Multimeter | DMM (mV/Ω range) | Active | High | $19.96 | Walmart |
| Alligator Clip Leads | Standard pair | Active | High | $3.49 | Harbor Freight |
| Mortar and Pestle | Lab/Kitchen grade | Active | High | $4.50 | Home Science Tools |
| Calibration Weights | 50 gram | Active | High | $6.86 | Walmart |
Consumables and Shop Supplies
| Part | Spec/Package | Status | Stock | Price | Source |
|---|---|---|---|---|---|
| Painter's Tape | 1 inch wide | Active | High | $1.75 | DPCIwholesale |
| Cardstock | For stencils | not checked | — | — | — |
| Paperclips | Large | not checked | — | — | — |
| Ice Pick or Nail | For punching metal | not checked | — | — | — |
| Protective Gear | Gloves/Glasses | not checked | — | — | — |
Substitutes
| For part | Substitute | Differences | Judgment |
|---|---|---|---|
| 3M 1181 Tape | Micro Center Copper Tape | Generic; significantly lower cost ($7.99 vs $33.32). | Acceptable; dual-conductive requirement met. |
| 3M 1181 Tape | Lowe’s Double-Sided Tape | Generic; retail available ($10.99). | Acceptable; dual-conductive requirement met. |
| Calibration Weights | Large steel washers | Commodity hardware; weight is approximate. | Acceptable per snapshot guidelines. |
Verify any substitute against its datasheet before ordering.
Other dependencies
- SCME Instructor Guide (p. 27): Necessary for the bridge pattern stencil sized for 1-quart cans; not checked (assumed provided with lab).
- Graphite/Rubber Cement Mixture: Success depends on viscosity (aim for "toothpaste" consistency). Procedural dependency.
- Airtight Seal: Procedural requirement for the syringe-to-can interface; may require additional sealant if "snug fit" fails.
Watch list
- Balloon Fatigue: Latex loses elasticity over repeated pressure tests; ensure ample stock of 12-inch balloons is available for replacement.
- Copper Tape Pricing: 3M 1181 is a high-cost item; instructors should monitor the availability of generic dual-conductive substitutes to manage budget.
- Syringe-to-Can Interface: Monitor for air leaks at the reference port, as this will prevent successful calibration.
Snapshot What the lab depended on when it was uploaded — the baseline the readiness checks research against.
This snapshot describes the temporal dependencies for the "Modeling a Micro Pressure Sensor Activity," a lab module originally developed by the Southwest Center for Microsystems Education (SCME). This lab constructs a macro-scale analog of a MEMS pressure sensor using a paint can as a reference chamber, a balloon as a flexible diaphragm, and a hand-mixed graphite/rubber cement paste to form a piezoresistive Wheatstone bridge circuit.
Bill of Materials
The following items are required to build the sensor model. While originally available as a pre-packaged SCME kit, the lab is designed to be buildable using retail and commodity components.
Sensed Materials and Active Components
- Pencil Lead (Graphite)
- Quantity: 2 packs of 15 leads each.
- Specification: 0.9 mm thick, HB hardness. Must be ground into a fine powder.
- Substitution: Other thicknesses or hardness levels (e.g., 0.5 mm or 2H) will change the base resistance and sensitivity of the bridge; HB 0.9 mm is the established baseline for the lab's calculations.
- Sourcing plan: retail shopping search: "0.9mm HB mechanical pencil lead refills".
- Rubber Cement
- Quantity: 1 bottle (minimum 3 mL used per model).
- Specification: Standard solvent-based contact cement. Used as the binder for the graphite powder to create a flexible, conductive paste.
- Sourcing plan: retail shopping search: "rubber cement".
- Copper Foil Tape
- Quantity: 4 strips, 6 to 8 cm each (per model).
- Specification: 1/4 inch wide, conductive on both sides (e.g., 3M copper tape).
- Substitution: Must be conductive on both sides to ensure contact between the graphite paste (top) and the alligator clips (bottom/sides).
- Sourcing plan: distributor lookup: 3M 1181 or equivalent 1/4 inch dual-conductive copper tape.
- Batteries
- Quantity: 2.
- Specification: 1.5 V AAA or AA.
- Electrical Constraint: Provides a 3 V DC excitation voltage (Vin) for the bridge.
- Sourcing plan: retail shopping search: "AAA batteries".
- Battery Holder
- Quantity: 1.
- Specification: 2-cell AAA or AA holder with wire leads.
- Sourcing plan: retail shopping search: "2xAAA battery holder with leads".
Structural Components and Housing
- Paint Cans
- Quantity: 2 (one for the model, one spare).
- Specification: 1-quart size, metal, empty and unused.
- Constraint: The container must be rigid to act as a reference chamber and approximately the width of a standard 1-quart paint can (approx. 4.25 inches diameter) to match the provided stencil.
- Sourcing plan: retail shopping search: "empty 1 quart paint can with lid".
- Balloons
- Quantity: 6 (to allow for breakage/fatigue).
- Specification: 12-inch latex balloons.
- Constraint: Acts as the flexible diaphragm. Must maintain elasticity to return the bridge to a "reference" voltage after pressure is removed.
- Sourcing plan: retail shopping search: "12 inch latex balloons".
- Plastic Syringes
- Quantity: 4 per kit.
- Specification: 3 cc (3 mL) capacity with tip.
- Usage: One used for measuring rubber cement; one used as an applicator for the graphite paste; one used to inject/withdraw air from the paint can to simulate pressure changes.
- Sourcing plan: retail shopping search: "3ml plastic syringe with tip".
Tools and Instrumentation
- Multimeter
- Quantity: 1.
- Specification: Digital Multimeter (DMM) capable of measuring Resistance (Ω) and Voltage in the millivolt (mV) range.
- Sourcing plan: retail shopping search: "digital multimeter with alligator clip leads".
- Alligator Clip Leads
- Quantity: 2 pairs (minimum 4 leads total).
- Specification: Standard test leads with alligator clips at both ends.
- Sourcing plan: retail shopping search: "alligator clip test leads".
- Mortar and Pestle
- Quantity: 1 set.
- Specification: Small laboratory or kitchen grade. Used to grind pencil leads into powder.
- Sourcing plan: retail shopping search: "small mortar and pestle".
- Calibration Weights
- Quantity: 3.
- Specification: 50 gram weights or washers.
- Usage: Used to apply known, repeatable force to the diaphragm for creating calibration curves.
- Sourcing plan: retail shopping search: "50g calibration weights" or "large steel washers".
Consumables and Shop Supplies
- Painter's Tape: 1 inch wide blue tape or electrical tape (used to secure the balloon diaphragm to the can).
- Cardstock: For cutting out the bridge pattern stencil.
- Paperclips: Large size (used as stirring rods and to clear syringe clogs).
- Ice Pick or Large Nail: Used to punch a port hole in the side of the metal paint can for the pressure syringe.
- Protective Gear: Nitrile or latex gloves and safety glasses (required due to rubber cement fumes/flammability and graphite dust).
Geometric and Procedural Dependencies
Stencil Geometry The lab depends on a specific "bridge pattern" provided as a template in the documentation (Instructor Guide, page 27). This template is sized for a 1-quart paint can (approximately 3 and 3/8 inches or 8.57 cm in diameter). If a different container size is used, the stencil must be scaled proportionally, or the calculations for pressure (Force/Area) must be adjusted.
Paste Viscosity The success of the "sensing element" depends on the mixture ratio of 15 ground pencil leads to 3 mL of rubber cement. The resulting paste must have a viscosity similar to toothpaste to be applied via syringe without running or clogging.
Physical Fatigue The lab notes a significant temporal dependency regarding the balloon diaphragm: the latex loses elasticity as increased pressures are applied. Resistance readings may not return to the original reference value after multiple tests, necessitating the replacement of the balloon (hence the quantity of 6).
Reference Pressure Port The model requires an airtight seal between the syringe tip and the hole punched in the paint can. Inconsistent sealing will cause the pressure to bleed off, making calibration impossible. Users may need a small amount of adhesive or sealant if the "snug fit" described in the lab fails.