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Value-focused revision — October 3, 2026. SEN66 replaces the separate SCD41 and SEN54 ($101.90 combined) with one $62.03 sensor and adds NOx. Adapter/cable cost is extra, so savings are not a complete installed quote. BNO085 already combines motion sensors and orientation processing. INA228 already combines voltage/current/power monitoring, conditional on motor-current suitability. Three distance modules cover separate directions. Removed PIR: reuse the Watcher camera AI for visual activity detection once integrated, recognizing it needs light and a clear view. No new camera or microphone is needed. Additional sensor firmware/controller integration is required; stock Watcher software does not support SEN66.
| Environment option — choose one | Reference cost | Tradeoff |
|---|---|---|
| Previous SCD41 + SEN54 | $101.90 | Two modules; no NOx; SCD41 has stock Watcher support |
| Recommended SEN66 | $62.03 + adapter/cable | One combined sensor; adds NOx; separate controller/software needed |
| Simple climate-only SHT41 | $6.50 | Only temperature/humidity; choose instead if air quality is unnecessary |
Recommended core plus SEN66: $125.63 before adapter/controller/wiring. With optional light and water sensors: $132.03. Prices are manufacturer/distributor references, not verified Amazon seller quotes; tax/shipping/tariffs extra. Conditional support items are not fully priced. No account cart or wishlist was created.
SEN66 combines CO2, particulate, climate, VOC and NOx sensing. All parts shopping links use our Amazon affiliate ID. The SEN66 button opens the selected exact-part listing; other buttons search for the specified part. Check the model and included accessories before purchase.
3D-print files are not included. This project provides software and electronics guidance. Obtain the body, dome and other selected model files separately through Michael (Mr. Baddeley) on Patreon. Separate Patreon access is required for the chosen files; check his current membership options and model instructions. Membership, printer, filament and printed parts are not included.
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Recommended combined environment · Qty 1 · $62.03 each
Actual CO2; PM1/2.5/4/10; temperature; humidity; VOC and NOx indices
Replaces SCD41 plus SEN54 and adds NOx. Not supported by stock Watcher extension software. Keep air inlet/outlet clear; mounting affects climate readings. Adapter and cable are additional.
View selected SEN66 on Amazon ↗Required for SEN66 connection · Qty 1 · TBD each
Connect SEN66 to controller
Adapter is not the SEN66 sensor. Verify whether the purchased kit includes its cable; obtain the sensor separately. Price not verified.
Search exact part on Amazon ↗Droid expansion · Qty 3 · $7.90 each
Front/left/right obstacle distance
Three is a suggested layout. Identical default addresses require shutdown-pin sequencing or an I2C multiplexer; validate placement and surfaces.
Search exact part on Amazon ↗Droid expansion · Qty 1 · $24.95 each
Real body tilt, rotation and heading
Keep: combines accelerometer, gyroscope, magnetometer and onboard orientation processing, reducing integration work. Mount away from motor magnets; verify controller bus compatibility.
Search exact part on Amazon ↗Droid expansion · Qty 1 · $14.95 each
Droid battery voltage, current and power
Watcher battery is separate from the droid drive battery. Select shunt/current capacity for actual motors; do not route high motor current through an undersized breakout.
Search exact part on Amazon ↗Optional automatic lighting · Qty 1 · $3.20 each
Ambient brightness for automatic headlight behavior
Choose exact model before wiring; an RGB indicator is not a headlight.
Search exact part on Amazon ↗Optional low-cost protection · Qty 1 · $3.20 each
Water ingress detection in base
Detects damp/wet conditions; mount away from exposed power connections.
Search exact part on Amazon ↗Supporting hardware · Qty 1 · TBD each
Collect expansion-sensor readings and send to dashboard
Buy only if the existing droid controller lacks spare pins/capacity. Do not buy a duplicate controller unnecessarily.
Search exact part on Amazon ↗Supporting hardware · Qty 1 · TBD each
Connect selected modules
Quantity depends on selections. A passive hub does not solve duplicate I2C addresses or add stock Watcher support.
Search exact part on Amazon ↗Supporting hardware · Qty 1 · TBD each
Power and secure selected sensor modules
Confirm voltage/current budget and connector pinout before purchase; include airflow clearance for environmental sensors.
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