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DigiTemp v3.3.0 Frequently Asked Questions
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Copyright 2004 by Brian C. Lane <bcl@brianlane.com> www.brianlane.com
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Q. Where Do I buy Parts?
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From www.ibuttonlink.com
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I have discontinued my hardware products so that I can spend more time on
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software. ibuttonLink makes a great serial adapter, and they have picked
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up production of my DT1A sensors.
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www.aagelectronica.com produces a full line of 1-wire products at a
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very reasonable proce, including temperature sensors, humidity and pressure,
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weather stations, hubs, etc.
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Places to avoid are www.buffalorun.com, all I see are numerous complaints
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on the mailing lists about how he doesn't deliver and doesn't communicate.
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If you want to build them yourself you can get parts from either
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www.maximic.com or www.digikey.com for sensors. For serial port adapters
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I now recommend using iButtonLink instead of DS9097U's -- Maxim raised
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the proce so much that the little extra you spend for the Link is well
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I order my temperature sensors directly from Dallas Semiconductor
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at 1-800-336-6933 (http://www.dalsemi.com/sales/credit_card.html)
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DigiKey (http://www.digikey.com) now has DS18S20 sensors in stock as
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Q. How do I connect it to the RJ-11 of the DS9097U
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Take a look at the DS9097U data sheet at
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http://pdfserv.maxim-ic.com/arpdf/DS9097U-009-DS9097U-S09.pdf
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Ground is the pin on the right and data is the pin on the left (using
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the two center pins of the RJ-11).
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Even with this information you will probably get it backwards the first
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time so make a temporary connection the first time and confirm that
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you have the correct polarity.
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Holding the RJ-11 plug so that it is facing you (as if you were going to
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plug it into your mouth), with the clip on the top.
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The same applies for the RJ-45 connectors.
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Q. How many can I connect?
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Read the Dallas Semiconductor Tech. Brief on the One Wire Network.
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http://www.maxim-ic.com/appnotes.cfm/appnote_number/570
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It covers everything you want to know and more. The limit comes down to
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wiring, how much you have and how good it is. Other than that you can
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connect as many as you need.
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www.pointsix.com also has some very good app notes on network length
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Having a 1-wire hub for complicated netowrks and supplying +5v instead
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of using the sensors in parasite mode will also help you create larger
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and more reliable networks.
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Q. How long can the wire be?
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Again, read the Tech. Brief above. This depends on the cable. Using
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better cable will allow you to extend the cable longer distances. CAT5
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is the recommended cable for networks of almost any length. You can get
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away with other cable but be prepared to rip it all up and replace it
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with CAT5 if it doesn't work.
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Having a hub and supplying +5v to the sensors will increase the liklihood
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of your long network operating properly. I have had reports of people using
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CAT5 and a passive network up to 200m long.
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Q. I get a result of 85C when reading temperatures
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85C is the error state of the DS18S20 sensor, and it usually indicates that
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one of 2 things are wrong:
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1. If you are using parasite powered sensors you forgot to ground the +5v
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pin to put the sensor into parasite mode.
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2. You are trying to read the sensor too quickly. The DS18S20 needs about
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750mS of delay in order to properly convert the temperature.
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Q. I have glitches in my data, what do I do?
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The first solution is to check all of your connections to make sure
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they are soldered or well connected.
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Next, is your cable decent quality? Cat-5 is the best, with twisted
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telephone cable coming in second.
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If you are still having problems you should try Using a Schottky
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diode across the cable's end. Connect the diode reverse-biased with
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the cathode (the stripe) on the data line and anode on the return.
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I used a 1N5818 across my attic sensor -- before adding this I was
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getting multiple glitches per hour. Now I have seen 1 glitch in
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You can also buy pre-assembled sensors that include a 1N5817 diode from
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my DigiTemp Hardware page at http://www.brianlane.com/dthardware.php
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Q. What is the difference between the DS9097-U and the App. Note 74 type
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The DS9097-U adapter uses a serial port to 1-wire conversion chip that
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makes talking to the 1-wire network easier. DigiTemp v2.x uses this
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type of adapter (the DS9097U-009 and -S09 both work fine).
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The old style of adapter (sometimes called passive or App. Note #74)
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used only diodes and resistors to convert the serial port voltages to
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the one-wire voltages. Dallas still sells adapters of this type, part
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number DS9097 and DS9097E that is built on this design. DigiTemp v1.x
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supports this type of adapter, and include a HOWTO document with
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instructions for building your own.
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As of DigiTemp v3.0.0 support for both style adapters has been integrated
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into the same code tree. You no longer need to use v1.x for the DS9097 passive
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adapter and v2.x for the DS9097U adapter.
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Q. When will digitemp support the one-wire hub?
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It does! As of v2.3 it scand for the DS2409 couplers used in the hubs
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and keeps track of which branch it finds the sensors on. It doesn't
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support cascaded hubs (hubs connected behind a hub), only multiple hubs
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on the main 1-wire lan.
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Q. When will Digitemp support the one-wire Weather Station?
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Probably never. DigiTemp has 1 purpose - to read temperatures. Weather
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station support is more complicated and requires a dedicated program to
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be watching the station and recording events like weather vane movement
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and wind-speed calculations. I may add support for humidity and
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barometric pressure, especially if someone were to donate a unit for me
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I have found a possible source for Humidity, Barometer and Lightning
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sensors at http://www.jjware.com/index2.htm
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I do have plans to write my own weather station software though. No release
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date as of yet, but it is being worked on.
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Q. When will it support 1-wire device X?
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The quick answer is "When someone sends me one". DigiTemp v3.3.0 now has
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support for the DS2438 battery monitor which is used in many of the more
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complicated sensors, like humidity and pressure. It also has native
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support for humidity using the AAD TI-8540 humidity sensor.
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