The 2.5:1 ratio of the F3003/4 YL105 provides a tighter final fit around irregular shapes.

Arduino and NRF24L01 : 6 Steps (with Pictures) - Instructables

The standard module includes a comparator (LM393) for digital output. Throw that away. The potentiometer drifts with temperature.

Unlike sensors offering only analog output, the YL-105 provides both RS485 digital communication and 4–20mA analog signals. This dual-output design means you can integrate it with legacy PLC systems using analog inputs or modern SCADA systems using MODBUS-RTU protocol.

A standard Arduino Uno onboard 3.3V regulator is meant for low-power sensors and often drops below stable margins during RF transmission bursts. This power sag causes the radio to reset mid-packet, showing up as persistent 0x00 or 0xFF SPI register read errors in debugging consoles. The YL-105 completely offloads this burden by drawing from the much stronger 5V power rail and stepping it down locally. 2. Lack of High-Frequency Decoupling Another NRF24 problem - works on one Uno but not others

The most common mistake beginners make is assuming the datasheet’s logic table is absolute. Most YL-105 datasheets state: "IN = High → Relay OFF; IN = Low → Relay ON." This implies active-low operation. However, the better interpretation involves understanding the onboard NPN transistor (often a S8050) driving the relay coil.

The datasheet specifies ±0.2°C temperature accuracy and 0.1°C resolution, which is essential because chlorine readings vary significantly with temperature.

| If you need... | Choose YL105 | Choose DHT22/BME280 | | :--- | :--- | :--- | | Lowest cost for multi-node networks | ✅ | ❌ No | | 3.3V native operation (ESP32) | ✅ Yes | ⚠️ Needs level shifter | | Sub-1-second read intervals | ✅ Yes | ❌ No (2 sec limit) | | Laboratory-grade accuracy (2% RH) | ❌ No | ✅ Yes | | Outdoor weatherproofing | ❌ No | ✅ Yes (with housing) |