LOG08-II, a stand-alone recorder for 1-Wire sensor readings

Most 1-Wire interfaces of the period were bridges: they read sensors on request and passed the numbers to a computer that had to stay switched on. LOG08-II was designed to be left alone. Once its options were set, it polled the bus on its own schedule, stamped each sample with the time from its on-board clock and wrote it to EEPROM. The stored history, covering more than three years of environmental samples, could later be dumped to a PC over the serial port for graphing or analysis.

The design builds directly on the TEMP08 1-Wire serial interface, and it keeps most of what made that board useful. It still presents a standard RS232 interface between the Dallas/Maxim 1-Wire bus and a host computer. It still takes the precision timing of the bus off the host's hands, which matters because 1-Wire communication depends on pulses measured in microseconds that a general purpose PC operating system cannot guarantee. And it still reads up to 60 sensors on one bus.

What changed is the logging layer. Of the sensors it can see, LOG08-II records up to 24. The real-time clock is backed up by a battery, so the time stamps survive a power cut, and the same clock is used to label live poll results when the board is connected to a PC. The first logger in the line, the original LOG08, drew on the older TEMP05 instead.

Configuration happens over the serial link with discrete commands, one for each important parameter, rather than with jumpers. That approach suited a logger that might be installed in an attic, a shed or a pump house: the options could be set at the bench, the board carried to its location and left running. Because the settings are held by the board, it keeps logging with the same configuration after being disconnected from the PC.

Retrieval is the reverse trip. The board is connected to a PC serial port and the stored readings are dumped as time-stamped samples, ready to import into a spreadsheet or plotting tool. Between dumps the LOG08-II can also act like its TEMP08 ancestor, reporting live poll results with the time of day attached.

Wiring the sensors follows the same rules as any 1-Wire network built around a Midon interface. Twisted pair cable such as CAT-5 carries the data line and ground, with the spare pairs available for the +5 V or +12 V supply where sensors are locally powered. With good CAT-5, runs of up to 300 ft are practical. Daisy-chained runs, where each sensor taps into one cable, behave better than sprawling star layouts, and every splice outdoors needs to be sealed against moisture, since a leaking joint can upset readings from every sensor on the same run. The 1-Wire network wiring guide goes through layouts in more detail.

LOG08-II is discontinued, and Midon Design stopped selling at the end of 2023. Anyone continuing a similar project today would typically use a USB 1-Wire adapter on a small computer with OWFS, the Linux w1 kernel driver or the Home Assistant 1-Wire integration, which read the same DS18B20, DS2438, DS2423 and DS2450 chips and leave storage to the host.