JSN-SR04T (waterproof ultrasonic)
Also known as: JSN-SR04T · AJ-SR04M · A02YYUW · Distance & level
The classic cistern/water-butt level sensor: a sealed transducer on a cable, pointed down the tank, reporting how full it is. A whole generation of rainwater dashboards runs on it.
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Declining pick: it still works, but better options exist at this price — see the "vs" note.
At a glance
⚑ flag an error| Measures | distance |
|---|---|
| Accuracy | 25 cm–4.5 m; 25 cm blind zone |
| Interface | GPIO (trig/echo; solder-pad modes add UART output) |
| Supply | 5 V |
| Battery-viable | Yes (deep-sleep friendly) |
| ESPHome | Native ESPHome component — ultrasonic |
| Typical price | $4-6 (street, varies) |
Compare all sensor modules in one table →
Which one do I buy?
vs VL53L1X: ToF has no blind zone and mounts flush; ultrasonic shrugs off dust and doesn't mind a grimy tank.
Clone check
Low clone risk. Buy from any reputable listing.
Good for
Gotchas to know
- The 25 cm blind zone means it can't see a nearly-full tank unless mounted proud of the lid.
- Mode-select solder pads change the output protocol — know which mode your config expects.
- Condensation degrades it over time; the A02YYUW (UART, better sealed) and ToF/radar options are eating this niche.
Wiring it up
Simple wiring: one data GPIO on any ESP32 dev board.