How to Install the Sonoff TH Temp Sens WTS01 RJ9: A Step-by-Step South African Guide

Before You Cut, Crimp, or Climb a Ladder

The Sonoff TH WTS01 RJ9 is a 1-metre (approximately) temperature and humidity probe terminated in a 4P4C RJ9 plug. It is designed for Sonoff TH series switches - TH10, TH16, TH Elite, and similar - that expose an RJ9 sensor jack. In South Africa, this sensor turns up in everything from geyser blanket experiments and greenhouse monitoring to fermentation fridges and server-room alerts. This guide is a bench-to-installation walkthrough written for someone who has the hardware in hand and wants a reading today, not a theoretical overview.

A quick note on why the RJ9 connector matters: it is not Ethernet and it is not a telephone handset cable you can substitute. The WTS01 uses four conductors in a specific pinout. Mixing it with a random RJ9 cable can leave you with reversed power and data lines, which is a fast way to damage the sensor or the TH switch. Check the sensor and switch labelling before you plug anything in.

What You Need on the Bench

Gather the following before you start. Most of these items are stocked by local electronics distributors such as Communica, and if you are placing an order anyway, it is worth checking the all-products catalogue for the sensor and accessories in one shipment.

• Sonoff TH series switch (TH10, TH16, or TH Elite) with an RJ9 sensor port
• Sonoff TH WTS01 RJ9 temperature and humidity sensor
• Small flat-head screwdriver for terminal connections
• Wire strippers or a sharp craft knife
• Multimeter for continuity and voltage checks
• Your phone with the eWeLink app installed and a 2.4 GHz Wi-Fi network available
• If you are extending the cable: 4-core shielded cable, heat-shrink, and a soldering iron

The 2.4 GHz point is not trivia. Sonoff TH devices do not join 5 GHz networks, and in South African homes where the router broadcasts a single SSID on both bands, pairing can fail repeatedly. Split the SSID temporarily or enable a 2.4 GHz-only guest network for setup.

Step 1: Inspect the Sensor and Plan the Cable Route

Unpack the WTS01 and look at the RJ9 plug. You should see four gold-plated contacts. The cable is typically a flat 4-core ribbon. Hold the plug with the latch tab facing away from you and note the conductor colours if the cable is colour-coded. On many WTS01 units, the four wires are red, black, yellow, and green, but colours can vary between production batches. Do not assume red is always VCC - verify with a multimeter in continuity mode against the sensor body if you plan to cut and re-terminate.

Decide where the probe will physically sit before you mount the TH switch. The WTS01 measures the air around the probe tip, so placing it against a hot geyser shell or inside a sealed enclosure will not give you the reading you want. For a geyser application, aim for 50-100 mm clearance from the cylinder. For a greenhouse, mount the probe at plant canopy height, shaded from direct sun. For a fridge or fermentation chamber, route the cable through the door seal or a drilled grommet so the probe sits in the air, not against the evaporator plate.

Cable Length and Signal Integrity

The stock WTS01 cable is roughly 1 m. If you need more, you can extend it, but treat the extension as a proper wiring job rather than a twist-and-tape affair. The sensor communicates over a digital bus, and long unshielded runs near mains cabling can introduce noise. For runs up to about 5 m, 4-core shielded cable is a sensible choice. Beyond that, expect intermittent readings and consider a second TH switch closer to the measurement point instead of one very long cable run.

Step 2: Wire the RJ9 Plug Correctly

If you are using the stock cable, this step is simply plugging the RJ9 into the TH switch until it clicks. If you are extending or re-terminating, the pinout is the critical detail. The WTS01 uses four conductors: power, ground, and a two-wire data pair. The exact pin numbering depends on how you view the plug, so always refer to the datasheet or the labelling on the Sonoff TH device. The table below shows the typical function assignment you will encounter, but verify against your specific hardware revision.

When soldering an extension, stagger the joints so the heat-shrink sleeves do not bunch up into a fat lump that snags. Use flux, keep the iron around 320-350 °C, and tin both ends before joining. A common beginner mistake is to twist the wires together and flood the joint with solder; this creates a brittle connection that fails after a few thermal cycles. If you are working on a geyser installation, the cable will see temperature swings, so a mechanically sound joint matters more than a pretty one.

If you are uncertain about connector types or want to compare options, the collections page is a useful place to browse related cabling and connector categories before you commit to a build.

Step 3: Mount the TH Switch and Probe

With the RJ9 plug inserted, mount the TH switch in a position that keeps mains wiring away from the sensor cable. The TH10 and TH16 are designed for in-wall or surface boxes, while the TH Elite is often left on a bench or mounted with a bracket. In South African installations, the switch is frequently placed in a distribution board or a dedicated enclosure, with the sensor cable routed through a gland. Keep the sensor cable at least 50 mm away from live mains conductors where practical. If the cable must cross a mains line, cross at 90 degrees rather than running parallel.

For the probe itself, consider the thermal mass of what you are measuring. A WTS01 dangling in a large room will respond slowly because the sensor element is small and the air around it is not well mixed. If you need a faster response for a fermentation fridge, place the probe in a small, ventilated enclosure near the product, or clip it to a metal surface that is in contact with the air you care about. For geyser monitoring, a probe strapped to the outflow pipe with insulation over it will track water temperature more closely than one floating in the roof void.

A Note on Enclosures and Condensation

The WTS01 sensor element is not designed to be immersed in water or sprayed directly. In a greenhouse or bathroom, condensation can form on the probe body. A simple solution is to mount the probe inside a small perforated plastic project box, which allows air exchange while shielding the element from drips. Communica stocks a range of enclosures and project boxes that work well for this. Avoid fully sealing the probe in resin or heat-shrink unless you have confirmed the sensor’s humidity measurement will still function - many humidity sensors need direct air contact.

Step 4: Power Up and Pair with eWeLink

Apply power to the TH switch. On first boot, the device enters pairing mode automatically for a few minutes - usually indicated by a blinking LED. Open the eWeLink app, create or log into your account, and tap the plus icon to add a device. Select the appropriate Sonoff TH model from the list and follow the prompts. You will need to enter your 2.4 GHz Wi-Fi credentials. If pairing times out, hold the pairing button on the TH switch for about 5 seconds to restart the process.

Once paired, the app should display a temperature and humidity reading. If it shows dashes or a fixed value like 99 °C, remove and reseat the RJ9 plug. If the reading persists, try the sensor on a different TH switch if you have one, to isolate whether the fault is in the sensor or the host. A known-good sensor on the same switch confirms the switch is fine; a still-bad reading points to the sensor or cable.

The eWeLink app allows you to set thresholds and automation. For a geyser, you might set a low-temperature alert at 40 °C and a high alert at 70 °C. For a greenhouse, a humidity alert above 85 %RH can trigger a vent fan via a separate Sonoff relay. These automations run in the app or on the device depending on your model and firmware. Test each threshold manually before relying on it.

Calibration and Verification

The WTS01 is not a laboratory instrument, and its accuracy is typically stated as a few degrees Celsius and a few percent RH in the datasheet. For most DIY and light industrial use, that is acceptable. If you need better accuracy, compare the reading against a calibrated reference thermometer and note the offset. Some eWeLink firmware versions allow a temperature offset to be applied. Do not expect a cheap sensor to match a calibrated thermocouple, and do not use it as the sole control for a critical process without independent verification.

A practical verification method: place the probe in a well-stirred ice bath (approximately 0 °C) and note the reading. Then place it in boiling water at your altitude - in Johannesburg, water boils around 95 °C, not 100 °C. This gives you two reference points and a rough idea of linearity. Remember that humidity measurement is harder to verify without a salt-chamber setup, so treat RH readings as indicative rather than precise.

Step 5: Final Checks and South African Context

Before you close the enclosure, do a final round of checks: confirm the RJ9 plug is fully clicked in, tug gently on any extension joints, verify the probe is positioned where you want it, and confirm the app is receiving updates. If the installation is in a location with load-shedding, remember that the TH switch will reboot when power returns. The eWeLink app should reconnect automatically, but automations that depend on the cloud may be delayed during network recovery. For critical alerts, consider a local hub or a UPS for your router and the TH switch.

Communica has been supplying South African makers, students, and technicians since 1977, and the WTS01 is one of many Sonoff accessories available through its shop-by-brand range. If you are building a monitoring system for a school project or a small business, buying locally means you can collect from a branch, get a VAT invoice, and avoid waiting weeks for an international parcel. The branches and trading hours page lists the Samrand, Pretoria, and Cape Town locations if you prefer to pick up in person.

One last piece of practical advice: label the cable. A small wrap of masking tape with “TH sensor - do not disconnect” prevents a future electrician or IT technician from unplugging it during maintenance. In shared workshops and school labs, this simple step saves hours of troubleshooting. Once the label is on and the reading is stable, you are done. The WTS01 is a straightforward sensor, but the details - pinout, cable routing, probe placement, and app pairing - are what separate a reliable installation from a flaky one.

Sources

• Communica - About Us
• Communica - All Products
• Sonoff - TH10/TH16 product page
• Espressif - ESP8266 Technical Reference (for general digital sensor interface context)
• South African Weather Service - regional climate data for environmental monitoring context