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Starter Track (~$25) Science Fair (~$60) Full Send (~$120) Accessories The Real Numbers

Starter Track

~$25

The bare minimum to get a working speed trap. One ESP32, two IR sensors, a breadboard, and a Hot Wheels track. You'll have a full web dashboard with speed, time, and CSV data export.

Required

Optional / You May Have

Component	Specs	Est. Price
ESP32-S3-WROOM-1 N16R8 16MB Flash / 8MB PSRAM • Dual-core 240MHz • WiFi + BLE	Must be S3 variant with 16MB flash for OTA dual-partition. The N16R8 is the exact module used. Ryan paid $5.61/ea on AliExpress (Aug 2023). Amazon is ~$7 but ships faster.	~$7	Amazon
IR Break-Beam Sensors (pair) 5mm IR emitter + receiver • 3.3V compatible • Digital output	Need 2 pairs: one for start line, one for finish. Look for "IR obstacle avoidance sensor" or "photo interrupter".	~$4	Amazon
Breadboard + Jumper Wires 830-point breadboard • M/M + M/F jumper wire kit	No soldering required for basic build. Breadboard mounts right next to the track.	~$5	Amazon
USB-C Cable + Power USB-C data cable • 5V 1A minimum	Any phone charger works. Need data cable for first flash (not charge-only). After first flash, updates go over WiFi.	~$3	Amazon
Hot Wheels Track + Car Any straight track section • Any 1:64 scale car	You probably already have these. Any brand works. Longer track = more measurable speed difference between conditions.	~$6	Amazon

Estimated Total (Starter)

~$25

Ryan Says

The ESP32-S3 N16R8 is the sweet spot. The 16MB flash gives you dual OTA partitions (update without bricking) and 9.9MB for LittleFS storage. The 8MB PSRAM is overkill for this project but means you'll never run out of memory. Don't buy the S2 or the basic ESP32 — the S3 dual-core is what makes microsecond timing work.

Science Fair Ready

~$60 • RECOMMENDED

This is what Ben used for his 5th grade science fair project. Everything you need for a proper physics experiment with evidence chain of custody, guided testing, and auto-generated reports.

Required

Optional Upgrade

Component	Specs / Notes	Est. Price
Everything in Starter Tier ESP32-S3 + IR sensors + breadboard + wires + track	See Starter tier above for details.	~$25
Digital Milligram Scale ±0.001g precision • Range: 0-100g • Calibration weight included	Essential for measuring car mass accurately. We found two "identical" Hot Wheels trucks differ by 6.5g (20%!). Science fair judges love milligram precision.	~$12	Amazon
Tungsten Weight Set Assorted cubes/cylinders • ~3.5g, ~7g, ~14g pieces	Tungsten is 19.3 g/cm³ — almost as dense as gold. Tiny cubes add significant mass. Perfect for "does mass affect speed?" experiments.	~$10	Amazon
NTAG213 NFC Stickers (20 pack) 13.56MHz • 144 bytes • 0.025g each • iPhone/Android compatible	Apply to car underside. Phone scan auto-selects car in dashboard + arms track. Each sticker weighs 0.025g — we weighed them on the milligram scale because that's how we roll.	~$5	Amazon
MAX98357A I2S Amplifier 3W Class D • I2S digital input • No DAC needed	Gives the track a voice. Announces race results, calls out car names, alerts on condition changes. Kids love it.	~$4	Amazon
Small Speaker (3W, 4 ohm) 40mm or 50mm driver • Wired to MAX98357A output	Any small speaker works. Hot glue it to the track housing. Pair with the MAX98357A above.	~$3	Amazon

Estimated Total (Science Fair)

~$59

Did You Know?

Two "identical" Hot Wheels Ford F-150 trucks from the same package weighed 38.000g and 31.521g on the milligram scale. That's a 6.479g difference (20.5%) between "the same" car. This is why you weigh everything. Manufacturing variance is a real variable — and discovering it is a science fair goldmine.

Full Send

~$120

The "it's 3am and I'm still adding features" build. Three ESP32 devices on a mesh network. LiDAR auto-arming. Mid-track speed measurement. 1000 LED strip synchronized to race state. This is the build Ryan runs.

Component	Specs / Notes	Est. Price
Everything in Science Fair Tier Finish gate ESP32 + sensors + scale + NFC + weights + audio	See Science Fair tier above.	~$59
2nd ESP32-S3 (Start Gate) Same N16R8 module • Dedicated start detection + LiDAR	Auto-discovers the finish gate via ESP-NOW. Clock syncs to microsecond accuracy. Place at the top of the track.	~$7	Amazon
TF-Luna LiDAR Sensor 0.2-8m range • UART interface • 100Hz sample rate	Detects car at start position, auto-arms the track. No button pressing needed — just place the car and release. Game changer for science fair demo mode.	~$12	Amazon
3rd ESP32-S3 (Speed Trap) Same N16R8 module • Dual IR sensors at mid-track	Measures velocity at a specific track position using two IR sensors at known distance. Sends data to finish gate wirelessly.	~$7	Amazon
BTF-LIGHTING COB LED Strip (WS2811) 864 LEDs/m COB • 24V individually addressable • IP66	Mount along the track. WLED firmware drives race state animations. Armed = breathing blue. Racing = chase. Finish = celebration. Pure theater.	~$25	Amazon
BTF-LIGHTING WLED Controller (SP803E) ESP32-based • Pre-loaded WLED firmware • Controls LED strip	Dedicated WLED controller. Plug and play — already has WLED installed. M.A.S.S. Trap sends race state commands via HTTP API.	~$12	Amazon
24V 5A Power Supply (LED strip) 24V 5A 120W • ETL Listed • Barrel jack	USB can't power 800+ LEDs. Need a dedicated supply. The BTF-LIGHTING 24V supply matches their strips perfectly.	~$10	Amazon

Estimated Total (Full Send)

~$120

Ryan Says

The LiDAR is the single best upgrade after the basic build. It turns the track from "press a button to arm" into "put the car down and let go." For science fair presentations, this means hands-free operation — the track runs itself while you explain the science. Judges lose their minds.

Accessories & Nice-to-Haves

Things that aren't required but make the build better, easier, or more impressive.

Item	Why You'd Want It	Est. Price
Label Printer (Brother P-Touch) PT-D210 or similar • For evidence tag labels	Print forensic evidence tags with case numbers. Not required — the system generates printable HTML tags — but a label printer looks more official.	~$30	Amazon
3D Printed Sensor Housing STL files on GitHub • Clips onto Hot Wheels track	Coming soon. Sensor mounts that snap onto standard Hot Wheels orange track. Designed in Fusion 360.	Free (STL)
Drag Tree Start Lights Amazon B0B58K7YZY • LED Christmas tree + servo controller	Full drag strip experience. Countdown lights + servo-controlled launch gate. Makes the science fair booth a showstopper. (Integration in progress.)	~$7	Amazon
Portable Battery Pack USB-C PD • 10000mAh+ • Powers ESP32 for hours	Run the whole setup without wall power. Essential for science fair booths, classroom demos, and backyard testing.	~$15	Amazon
Phone Tripod / Mount Flexible mini tripod • Phone holder clip	For photographing scale readings and test setup. The evidence system links photos to case numbers automatically.	~$8	Amazon

The Real Numbers

BRUTAL TRANSPARENCY

You deserve to know exactly what this project cost. No hand-waving. No rounding down. The receipts are real.

Category	What It Covers	Spent
Core Electronics	ESP32-S3 N16R8 boards (15× from AliExpress, Aug 2023, $5.61 each), IR sensors, TF-Luna LiDAR, breakout boards, power supplies, wiring, connectors, soldering supplies	~$250
Sensors & Instruments	MLX90614 IR temp (x2), BMP280 barometric (x5), ADXL345 accel (x4), BNO055 IMU, WT901 9-axis IMU, PN532 NFC reader, milligram scale, calibration weights	~$200
LED & WLED System	BTF-LIGHTING WLED controllers (x2), COB LED strip (864 LED/m), 24V power supply, RF remote	~$100
Track & Hardware	Hot Wheels tracks (40ft+), starting gates, clamps, mounting hardware, 3D printer filament, heat-set inserts, drill/tap set	~$150
Test Vehicles & Weights	Hot Wheels cars (F-150, VW, Street Wiener, etc.), tungsten weights, wheel weights, derby weight tape, Real Riders wheel sets	~$60
Displays & Future Prototypes	7" HDMI touch screens, ESP32-P4 dev board, Waveshare display board, XIAO ESP32-S3 Sense, HDMI cables	~$250
Tools & Consumables	Dupont crimper, solder flux, IPA, compressed air, forensic rulers, NFC stickers, microSD cards, antennas	~$90
Overkill / R&D / "Because I Could"	Laser line projector, traffic light modules, footbridge model, Edison bulb filaments, bearing balls... things that seemed essential at 3am	~$100

Total Project Spend (Hardware Only)

~$1,200

The Uncomfortable Truth

Yes, I spent roughly $1,200 on a Hot Wheels speedometer. In my defense: my 10-year-old is using it for his science fair, the system now has 21,500+ lines of code, and I've learned more about embedded systems in 3 weeks than in a year of tutorials.

You don't need to spend $1,200. The Starter build is ~$25. The Science Fair build is ~$60. I spent what I spent because I have a problem, and that problem involves buying sensors at 2am.

The origin story: The first purchase was 15× ESP32-S3 N16R8 boards from AliExpress on August 17, 2023 — $5.61 each, $93.07 total from the AITEXM ROBOT store. Those boards sat in a drawer for two and a half years waiting for me to figure out what to do with them. The brain of this entire system costs less than a combo meal.

Affiliate earnings so far: $0.00. This page went live today. If every link on this page earned me the maximum 4% commission, and 100 people built a Starter kit, that's roughly $100 — enough to cover one of my sensor shopping sprees. I'm not getting rich here. I'm a working forensic examiner who stays up too late soldering things.

Affiliate Disclosure: Links on this page use Amazon Associates affiliate tags (tag: ryanmassfelle-20). When you buy through these links, a small percentage supports the M.A.S.S. Trap project at no extra cost to you. We only link to products we've personally bought, tested, and used in our builds. No sponsorships. No paid placements. Just stuff that actually works.

Last updated: February 16, 2026 • Total affiliate earnings to date: $0.00 • Total project spend: ~$1,200

💬 Questions About Parts?

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Starter Track

Science Fair Ready

Full Send

Accessories & Nice-to-Haves

The Real Numbers

💬 Questions About Parts?