TEMP08 Frequently Asked Questions
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Last Updated June 26, 2015


Introduction  Description Schematic Instructions  Software Vintages  Differences with TEMP08  FAQ  HomeSeer Setup References Ordering Information Download the Instruction Manual Here


Frequently Asked Questions - TEMP08

Need other information?  Try the HomeSeer TEMP05/08 forum here.

ALSO, have a read through our 1-Wire Application Guide.

1. What is Parasitic Power?

2. Do I need a Dallas Weather Station to use the TEMP08?

3. How do I connect the temperature sensors to the TEMP08?

4. Can I daisy-chain temperature sensors?

5. How far away can the temperature sensors be run?

6. Where do I get a Weather Station?

7. How does TEMP08 connect to my PC?

8. Can the sensors be used in water (pools, fish tanks, spas, etc.)?

9. How can I tell which sensor is in which area?

10. What do I use for power?

11. What do I need to read temperatures from a few different rooms?

12.  Do I have to use HomeSeer to read the temperatures?

13.  Will TEMP08 work with a serial to USB converter?

14.  Will TEMP08 work with a Humidity Sensor?

15.  Is there an enclosure for the TEMP08?

16. What are the differences between a DS1820 and a DS18S20?

17. How do I set up HyperTerm to talk to TEMP08?

18. How do I set-up HomeSeer to use the readings from TEMP08?

19.What is the difference between a Version 1 and a Version 3 One Wire Weather Station?

20. I ordered DS18S20's, but the items I received are labeled DS1820.  What gives?

21. Will TEMP08 work with DS18B20, DS1920 and DS1822 temperature sensors?

22.  I have several DS1820's near each other but they read different temperatures.  Why?

23. I added a sensor and now my readings are coming back as "???".  Why?

24.  Where can I buy a Humidity Sensor?

25.  My outdoor temperature sensor appears to be inaccurate.  What can I do?

26. I connected a sensor  to the board. How do I get it recognized?

27.  Does TEMP08 interface with the SHT11/71 humidity sensor?

28.  How do I connect sensors around the house?

29.  How do I connect a DS2405, DS2406 or DS2407 to other components?

30. What are the pins used for on the RJ11/12 connectors?


1. What is Parasitic Power?

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.

2. Do I need a Dallas Weather Station to use the TEMP08?

No.  TEMP08 can be used with any combination of the following devices on the 1-Wire bus;

  • Dallas or AAG 1-Wire Weather Station (one only)
  • DS18S20 temperature sensors
  • DS1820 temperature sensors
  • DS18B20 temperature sensors
  • DS1822 temperature sensors
  • DS1920 temperature sensors
  • DS2401 1-wire ID sensors
  • DS2423 based Rain Gauge
  • DS2423 based Lightning detector
  • DS2423 general purpose counter
  • DS2438 based Humidity Sensors
  • DS2438 based Barometer
  • DS2438 voltage monitors
  • DS2438 Solar radiation monitors
  • DS2450 voltage monitor

3. How do I connect the temperature sensors to the TEMP08?

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.

4. Can I daisy-chain temperature sensors?

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.

5. How far away can the temperature sensors be run?

Using good quality CAT-5 cable, you should be able to run sensors up to 300 feet (100 meters) away from the TEMP08.

6. Where do I get a Weather Station?

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.

7. How does TEMP08 connect to my PC?

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 #17Here is an example of a serial cable that could be used to connect to your PC.

8. Can the sensors be used in water (pools, fish tanks, spas, etc.)?

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.

9. How can I tell which sensor is in which area?

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.

10. What do I use for power?

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).

11. What do I need to read temperatures from a few different rooms?

For example, to get temperature readings from 3 different areas you will need;

1 TEMP08 (assembled and tested)
3 DS18S20 Sensors
1 12VAC or DC adapter (available from Radio Shack, Best Buy, etc. or from midon design)

All items are on the ordering page.

The TEMP08 connects to your PC via a spare serial port.  You will need a straight-through serial cable, not a null modem cable, to connect TEMP08 to your PC.  An example cable would be Radio Shack's 26-117.

A sample HomeSeer script is available from the TEMP08 web page.

Note: if one of the temperatures you want to sense is in the same area as where you will place the TEMP08, then you will only need one extra sensor since there is one already built onto the TEMP08 board.


12.  Do I have to use HomeSeer to read the temperatures?

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.

13.  Will TEMP08 work with a serial to USB converter?

Yes.  TEMP08 has been successfully tested with a Belkin F5U103 USB Serial Adapter. Others should work fine.

14.  Will TEMP08 work with a Humidity Sensor?

Yes! TEMP08 will read humidity from multiple DS2438 Humidity sensors.

15.  Is there an enclosure for the TEMP08?

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..

16. What are the differences between a DS1820 and a DS18S20?

The document here describes this best.  Basically, the DS18S20 has superior temperature accuracy and a wider power supply tolerance.

17. How do I set up HyperTerm to talk to TEMP08?

Correct settings in HyperTerminal are:

  • 9600 baud
  • 8 bits
  • no parity
  • 1 stop bit
  • NONE for flow control (Important!)

18. How do I set-up HomeSeer to use the readings from TEMP08?

Follow the instructions here.

19.  What is the difference between a Version 1 and a Version 3 One Wire Weather Station?

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.

20. I ordered DS18S20's, but the items I received are labeled DS1820.  What gives?

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.

21. Will TEMP08 work with DS18B20, DS1920 and DS1822 temperature sensors?

Absolutely!

22. I have several DS1820's near each other but they read different temperatures.  Why?

First, keep in mind that the DS18S20's are accurate only to within 0.5C ( 0.9F), so two sensors could be varying by as much as 1.8F 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.

23. I added a sensor and now my readings are coming back as "???".  Why?

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.

24.  Where can I buy a Humidity Sensor?

They were originally available from Dallas/Maxim, however, Dallas/Maxim announced the discontinuation of this product.  An alternate source is Hobby Boards.

25.  My outdoor temperature sensor appears to be inaccurate.  What can I do?

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:

http://www.dpug.org/weather/newpagoda.html

More discussion here: HomeSeer TEMP05/TEMP08 Messages

26. I connected a sensor  to the board. How do I get it recognized?

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.

27.  Does TEMP08 interface with the SHT11/71 humidity sensor?

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.

28.  How do I connect sensors around the house?

Please see an excellent discussion about this on the HomeSeer message board here.

29.  How do I connect a DS2405, DS2406 or DS2407 to other components?

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.

30. What are the pins used for on the RJ11/12 connectors?

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.

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