Trailer Temperature Monitoring with Swappable Reefers

In refrigerated transport, the GPS tracker usually lives permanently in the tractor, while the cargo travels in trailers that get hitched and unhitched all the time. With firmware 1.09.28, Rinho devices recognize each trailer's temperature sensors on their own and put them in the right place, with no reconfiguration at every swap. It's one of the new capabilities of the iButton and 1-Wire bus, and this guide explains how to put it to work in your fleet.

🎯 Who this article is for: fleet managers in refrigerated transport working with tractors and rotating trailers or reefer boxes. At the end there's a section with the commands for your installer.

The problem: a fixed tractor, rotating trailers

The tractor carries a permanently installed GPS tracker, and each reefer trailer has its own wired probes. Today it leaves with trailer A, tomorrow with trailer B. What your tracking platform needs is for the "front" temperature to always arrive on the same channel, and the "rear" one too, no matter which trailer is hitched. That way alerts and reports keep making sense.

Every sensor ships with a unique factory code, and the classic approach is for the device to memorize each one. That's ideal for a fixed box, but when trailers rotate, every hitch-up means loading the sensors again.

The solution: each trailer carries its own numbered sensors

Firmware 1.09.28 adds another way of working: instead of the device remembering each sensor, the number is stored in the sensor itself, from 1 to 8. Sensor number 1 always goes to position 1 (the first temperature channel), number 2 to position 2, and so on up to 8.

• They're recognized on their own at hitch-up. With automatic mode on, in under a minute the tractor's device places each sensor of the hitched trailer in its position. Probe 1 of the new trailer lands on the same channel as probe 1 of the previous one.
• They're numbered from the device itself. No programmer or extra tools needed. The recommended practice is to mark each sensor with a color according to its number, so it can be identified at a glance.

What your operation gains

• No reconfiguring at every hitch-up. The tractor adapts to any trailer prepared with the same numbering scheme.
• No data mixed up between trailers. When a position switches to a different sensor, the device doesn't show the previous sensor's temperature: it waits for the first reading from the new one.
• Fewer installation mistakes. With the same scheme across the fleet (front probe is always 1, rear probe always 2) plus the colors, the installer knows where each probe goes.

Up to 8 sensors and the driver key on the same cable

A single cable can also carry:

• Up to 8 temperature sensors.
• The driver's iButton key can share the cable. On the Spider IoT, which has a single 1-Wire port, the key and the sensors now work together, and a quick touch of the key isn't missed. On the Smart IoT, with two 1-Wire ports, the key can go on either one.

With a single cable you know who is driving and at what temperature the cargo is traveling. Driver sessions are covered in detail on the iButton and 1-Wire driver identification page.

How to roll it out, in 4 steps

1. Number the sensors in the workshop. Each probe is connected to the device, given its number and marked with its color. Use the same scheme across all trailers.
2. Install the probes in each trailer, in the position that matches their number.
3. Turn on automatic mode on the tractor's device. The web configurator includes this mode from version 1.13.14.
4. Verify. With the trailer hitched, check that the device detects every sensor, that each one landed in its position and that the readings are updating.

If you're still choosing a sensor type, the temperature sensor installation tutorial compares wired and BLE options, and the temperature monitoring page summarizes the full solution.

For installers: commands

If you're also wiring the driver's iButton reader on the same cable, the guide on how to connect an iButton reader to a GPS tracker covers the wiring.

Sensors and positions

Supported sensors: DS18B20, DS18S20 and DS1822, including DS18B20-PAR (parasite-powered, no supply pin). Each one ships with a unique ROM code, for example 281F266A0A0000E4. Positions go from DT00 to DT07. For sensors that never change, classic loading by ROM still applies:

>SDT001,281F266A0A0000E4<

A sensor is "numbered" when it has the same number, from 1 to 8, written into its internal TH and TL registers. Factory-fresh, it has 75/70, meaning "not numbered".

Sensor number	Device position	Example use
1	DT00	Front probe
2	DT01	Rear probe
…	…	…
8	DT07	Eighth probe

Numbering sensors (PAINT)

The number you give is the target DT:

>SDT PAINT0<      numbers the sensor for DT00
>SDT PAINT1<      numbers the sensor for DT01
...
>SDT PAINT7<      numbers the sensor for DT07

With a single sensor connected, the command is enough; with several, add the ROM:

>SDT PAINT0,<ROM><
>SDT PAINT OFF<         returns the sensor to its factory state
>SDT PAINT OFF ALL<     clears every connected sensor

The device only writes to a sensor when you ask it to with PAINT.

Automatic mode

>SCXOW1,2<

In SCXOW, the first 1 turns on 1-Wire and the second number picks the mode: 0 temperature only, 1 the sensor itself used as a key (previous mode, single sensor), and 2 automatic assignment. In mode 2, at startup and then every 30 seconds, the device looks for the numbered sensors on the cable and places each one in its DT.

Queries and manual assignment

>QDT AUTO<          lists sensors on the cable (ROM, number and DT) without changing anything
>SDT AUTO<          one-off assignment of numbered sensors, without copying ROM codes
>SDT AUTO RESET<    frees all 8 DTs at once
>QDT<               temperature readings

With >SDT AUTO<, a single unnumbered, unknown sensor goes to the lowest free DT, which lets you install sensors one at a time. Duplicate numbers or several unnumbered sensors are not assigned and are reported, so it's worth checking with >QDT AUTO< after numbering. In >QDT<, the age of each reading is normally between 00 and 06 seconds.

Bus timing

The device measures and powers the sensors one at a time, about 1 second per sensor (with 4 sensors, the cycle takes around 4 seconds). The iButton key is checked between one measurement and the next, roughly every second.

⚠️ Important: no wire on the 1-Wire bus should go to +12/24 V; the input can't handle it. And if the iButton reader's wires are swapped and its outer ring touches the chassis, the temperature sensor on the same bus stops working.

Which mode to use for each installation

Installation	Recommended setup
Van or fixed box, sensors never change	>SCXOW1,0< with manual loading (>SDTxx1,<ROM><) or a one-off >SDT AUTO<
A single sensor, nothing else configured	>SCXOW1,0<: with DT00 disabled, the sensor shows up in DT00 on its own
Sensors added one at a time	>SDT AUTO< after connecting each sensor
Trailers or reefer boxes that rotate between tractors	Numbered sensors + >SCXOW1,2<
Temperature + driver identification on the Spider IoT	Key and sensors on the same cable, firmware 1.09.28

Frequently asked questions

Which Rinho devices support this feature?

The Spider IoT and the Smart IoT running firmware 1.09.28. The Zero IoT has no 1-Wire port.

Does automatic mode modify my sensors?

No. Automatic mode only reads and places. The device writes a number into a sensor only when you ask it to while numbering it.

What happens if two sensors have the same number?

Duplicate numbers are not assigned and the device reports them. That's why it's worth checking the list of detected sensors after numbering and using the same color scheme across the whole fleet.

Does the device generate the temperature alerts?

The device measures and transmits the temperatures from its 8 positions, which can also be used in its rules and expressions. Thresholds, alerts and reports are set up in your tracking platform (Wialon, Traccar or whichever you use). For the bigger picture, read our guide to IoT in the cold chain.

Conclusion

With numbered sensors and automatic mode, the tractor adapts to any trailer prepared with the same scheme, with no reconfiguration at each hitch-up. With 8 sensors and the driver key on one cable, firmware 1.09.28 makes 1-Wire a solid option for refrigerated fleets with rotating trailers.

---

Running reefer trailers and want to set this up? Contact us and we'll help you plan the installation.

---

Related articles

• Driver identification with iButton keys
• How to connect an iButton reader to a GPS tracker
• iButton vs RFID vs BLE: choosing a driver ID system