Last Updated June 26, 2015
Frequently Asked Questions - TEMP08
Need other information? Try the HomeSeer TEMP05/08 forum here.
ALSO, have a read through our 1-Wire Application Guide.
Parasitic Power is a term developed by Dallas Semiconductor to describe their method of powering their "1-Wire" devices. The DS18S20 sensor used by the TEMP08 is one of these 1-Wire devices. As the term implies, there is only one wire (well, 2 really. A ground is also required) used to communicate on a bus with all devices. The power is derived from the communication line. Whenever a logic "1" is sent on the 1-Wire bus, all devices on the bus use that logic "1" to charge up their internal circuitry. Providing that a logic "1" is sent often enough, that charge is sufficient to drive the individual devices. Fortunately, the idle state of the bus is a logic 1, so, statistically, a logic 1 is present very often.
If you must use parasitic power, please review the spec sheet for your specific device. Some of them, DS18S20 for example, require that VDD is shorted to VSS in order for the device to function properly when parasitic powering is used.
No. TEMP08 can be used with any combination of the following devices on the 1-Wire bus;
The sensors are connected via twisted pair wire, typically CAT-5 or better, to connector J3 or J5. The external wire can be "home run" (all sensors connected on their own wire and all end-points tied together), or daisy-chained (one, or more, wire runs are used and each sensor is "tapped" into the wire run where needed). The sensors themselves are then soldered on to the wire run wherever they are needed. If you don't like soldering these devices, some people have had success with crimping the sensors into RJ-11 plugs and running wires to RJ-11 sockets where the sensors are needed. Midon Design also provides small PCB mounts for attaching a DS18S20 sensor and either a RJ-11 connector or 2 terminal screw connector. They are shown here.
NOTE: if you are using parasitic power, you must connect the ground wire to both outer pins of the DS18S20 to ensure reliable readings.
Yes. They can be wired into anywhere along the wire run from TEMP08. A termination is not required at the end of the wire run when daisy-chaining, although care should be taken to avoid shorting out the end point.
Using good quality CAT-5 cable, you should be able to run sensors up to 300 feet (100 meters) away from the TEMP08.
The original manufacturer (Dallas Semiconductor) no longer makes this product. One manufacturer Tecnologia Aplicada (AAG) had replicated the original design (see also question 19), but no longer appears to be in business. Another source of similar product is Texas Weather Instruments Inc. . Midon Design has verified functionality of Technoligia Aplicada and Dallas Semiconductors products with the TEMP08.
A straight-through, not null modem, serial cable connects between the TEMP08 and your PC's serial port. The signal is 9600 bps, no parity, eight bits, with NO flow control. Hyperterminal can be used to monitor output from the TEMP08, or to configure it. See also #17. Here is an example of a serial cable that could be used to connect to your PC.
Yes, although care must be taken to ensure that the connections to the sensor, and the sensor leads, are properly water-proofed. Silicon RTV or epoxy could be used to accomplish this. Waterproofed DS18B20 sensors are available here.
The recommended method is to connect one sensor at a time, run the INI command on TEMP08 and then record the newest serial number found in the list displayed by the DIS command. That serial number will appear in the sensor output if the Show Serial Numbers option has been selected..
TEMP08 will notify you in real time as you connect and disconnect temperature sensors, providing that the sensor had initially been registered with TEMP08 via the INI command.
Just about any power adapter can be used with the TEMP08. Look through your discarded wall adapters from old electronic devices for something that is rated at least 9 Volts (AC or DC) and at least 100mA (milli-Amperes).
For example, to get temperature readings from 3 different areas you will
A sample HomeSeer script is available from the
TEMP08 web page.
No. Any PC application that reads the serial port can be used. HomeSeer provides some simple to use script and plug-in interfaces to the serial port, however. See a sample HomeSeer script and plug-ins here.
As an alternate, check out thermd for a stand-alone application.
Yes. TEMP08 has been successfully tested with a Belkin F5U103 USB Serial Adapter. Others should work fine.
Yes! TEMP08 will read humidity from multiple DS2438 Humidity sensors.
Yes. The PCB will fit into a standard PacTec CM5-125 enclosure. This enclosure is orderable from Midon Design or available from multiple other sources such as Allied Electronics, Mouser Electronics, Fry's, and SMC Electronics..
The document here describes this best. Basically, the DS18S20 has superior temperature accuracy and a wider power supply tolerance.
Correct settings in HyperTerminal are:
Follow the instructions here.
The Version 1 OWWS is the original unit developed and sold by Dallas Semiconductor. It is electrically equivalent to the Version 2 OWWS sold by AAG, a Mexican company. AAG improved the design to replace the DS2401-based wind direction sensors with a new DS2450-based design and were selling it as the Version 3 OWWS, but no longer appear to be in business. TEMP08 does support the Version 3 OWWS, but does not support the Version 1or Version 2 OWWS.
Dallas/Maxim have chosen not to label the DS18S20's with the "S". This may be due to the fact that they have discontinued the original DS1820 package and assumed that there would be no confusion. The DS1820 stopped production around May 2000. The only visible difference is the package style. The DS1820 was in a PR-35 package, whereas the DS18S20 is in a standard TO-92 package. See FAQ #16 for the electrical differences.
First, keep in mind that the DS18S20's are accurate only to within ± 0.5°C (± 0.9°F), so two sensors could be varying by as much as 1.8°F at worst case if one is at the low end of it's accuracy and the other at the high end. Secondly, Dallas/Maxim recently (2004) had a batch problem in production and as a result the manufacturing calibration was susceptible to fatal errors. This could significantly throw off the readings as well. This batch problem only affected lots with batch code B7. Lastly, if you are unfortunate enough to be using DS1820's instead of DS18S20's, then you need to keep in mind that the DS1820 had an inherent flaw that caused a 1 degree (C) reading error. This is one of the reasons that Dallas introduced the DS18S20.
You might have added a the sensor via a new wire leg in a star configuration. This might have created reflections on the One Wire bus. Try adding a 100 ohm resistor (Radio Shack part number 271-1311) in series with each leg of the star (only on the DQ lead). The figure below shows how the wiring should be done for this. The resistor needs to be physically located/connected to the TEMP08 terminal, not further down the line.
They were originally available from Dallas/Maxim, however, Dallas/Maxim announced the discontinuation of this product.
Exposure to direct sunlight can affect the sensors - they read too high. A solution for this is to put the sensors in a "pagoda". Pagoda construction articles are shown on the following links:
More discussion here: HomeSeer TEMP05/TEMP08 Messages
From a HyperTerminal session, issue an INI command. This will find the new sensor and add it's serial number to EEPROM memory. There is no need to do an ERA command, which will erase all the EEPROM memory, unless you want to delete some or all of the other sensors that were previously recognized. The new sensor(s) added by the INI command are automatically added to the next available (usually the last) memory position. If you want to delete some, but not all sensors, use the DEL command to do so.
No. We have looked into using the SHT (Sensirion) sensor series but decided that the 2 wire interface used to connect to it was not conducive to remote applications like the One Wire bus is used for.
Please see an excellent discussion about this on the HomeSeer message board here.
NOTE: TEMP08 no longer supports DS2405, DS2406 or DS2407 switch sensors.
The following schematic is good for any of the DS2405, DS2406 or DS2407 1-wire devices. As can be seen, the PIO port can be used for switch (or contact closure) inputs, or as an output to drive LED's, relays, or other devices.
Here is a table of all published connector schemes (that we could find) for various 1-wire devices:
The pin numbers are numbered per the diagram here.
Last Updated March 11, 2022
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