TEMP05, the serial box behind early 1-Wire weather logging

The TEMP05 began life as a serial logging interface. Its job was to take care of the 1-Wire bus so the host computer did not have to: the board polled the sensors, handled the tight timing the bus requires and sent finished readings out of an RS232 port. The first target was narrow. It read the Dallas Semiconductor 1-Wire Weather Station plus up to 20 additional DS18S20 thermometers, which was enough for an outdoor station and a thermometer in most rooms of a house.

Firmware updates widened that scope considerably. Later versions read several 1-Wire rain gauges, barometers and humidity sensors alongside the weather station and thermometers, with a ceiling of 60 devices in total. A single report interval, adjustable in one-minute steps from 1 to 99 minutes, controlled how often a full set of readings went out of the serial port. Temperatures could be reported in Celsius or Fahrenheit. Wind speed was only ever reported in miles per hour with the firmware of the time.

Midon Design stopped producing the TEMP05 on June 30, 2003. Its successor, the TEMP08 1-Wire serial interface, kept the same idea of a smart serial bridge and also handles up to 60 sensors over RS232. The TEMP05 documentation remained online for owners of existing boards, and the most common owner questions are collected on the TEMP05 frequently asked questions page.

The TEMP05 board was small enough to read at a glance. A Motorola 68HC705C8 microcontroller ran the firmware from a 4.0 MHz crystal, and a 93C66 serial EEPROM gave it non-volatile storage. An LM78L05 regulator produced the 5 V logic supply after a full-wave bridge rectifier, so the input could be AC or DC of either polarity. A single DS18S20 thermometer came with the kit.

The serial side used a MAX233 RS232 interface, the Maxim part with built-in charge pumps that needs no external capacitors. The parts list allowed a MAX232 instead, which does the same job with four extra 10 µF capacitors; that is why it counted five of them when a MAX232 was fitted. The port itself was a PC-mount DB-9 female connector, wired for a straight-through cable. The rest of the parts list was passives and connectors: a 1.5 kΩ resistor, a 10 MΩ resistor, a nine-way 10 kΩ SIP resistor network, a status LED and two PC-mount terminal strips.

Everything the TEMP05 reported arrived as human-readable lines, which made it easy to parse from a script. A polling cycle started with a short banner and was followed by one line per device. Each line carried a device label and number, the 64-bit address of the sensor in square brackets and the value: a percentage for humidity, inches of mercury for the barometer, a compass point such as WNW for wind direction, miles per hour and gust speed for wind, a running count for the lightning counter and degrees for each thermometer.

The address is useful for more than bookkeeping. Printed the way the TEMP05 showed it, the family code sits at the right-hand end: 10 for a DS18S20, 28 for a DS18B20, 26 for a DS2438 and 1D for a DS2423 counter. That makes it possible to tell from the output alone which kind of chip produced a reading.

The board also reported changes on the bus as they happened. A sensor that stopped answering produced a Missing line with its address, and a Restore line appeared when it came back. Switch devices produced On and Off lines when their state changed. A reading that could not be trusted was shown as three question marks rather than a number, which is the first clue when a sensor, a splice or a cable leg has failed.

An optional connector, J3, extended the board to a relay interface. The firmware could switch up to eight relays through that extension. Midon Design offered a matching kit, the RELAY05 relay board, and the interface was simple enough that builders could wire their own relay stage instead.

The best-known pairing was with HomeSeer, the home automation package from HomeSeer Technologies. Using HomeSeer's built-in scripting, logged temperatures, wind speed and wind direction were written to disk and pushed to a web page in real time. The same scripts could react to thresholds, for example raising an alarm or sending an e-mail when an attic got too hot. HomeSeer was never a requirement, though. Any program that reads a serial port could collect the data, and a sample logging script for HomeSeer was part of the kit documentation.

Today the same kind of setup is usually built with a USB 1-Wire adapter and software such as OWFS, the Linux w1 kernel driver or the Home Assistant 1-Wire integration, which read the same sensor chips directly.

Dallas Semiconductor eventually discontinued its 1-Wire Weather Station, but a station was never needed to use the rest of the TEMP05. Tecnologia Aplicada (AAG) made a compatible station, and Midon Design fully supported the AAG Version 3 model. Texas Weather Instruments shipped an equivalent product as well.

The station versions differ in how wind direction is sensed. The Version 1 unit from Dallas and the electrically equivalent Version 2 from AAG used DS2401-based direction sensing. AAG's Version 3 replaced that with a DS2450-based design. TEMP05 firmware V4 read all three versions, while V5.00 and later dropped support for Version 1. The 1-Wire weather station guide covers how these stations are built and read.