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Author Topic: Dallas/Maxim One-wire over Xbee  (Read 3127 times)
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Oslo, Norway
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Have anyone tried to implement Dallas one wire sensors over an Xbee link.  Is it even possible with the tight timing required.
I know this might sound like a contradiction, but could I read from a DS 18B20 temp sensor over a Xbee link using pin status transmission?  Simple one sensor setup, without the need to poll for other sensors.

Appreciate any suggestions
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Don't think it's possible without an MCU.  I'm not aware that that XBees can talk the Dallas 1-wire protocol.  Now, with custom firmware in the XBee, I suppose anything might be possible but that'd be advanced XBee.

Still, a good question.  I like the DS18B20.  I wonder what a minimum XBee/DS18B20 configuration might look like, perhaps with one of the smaller/cheaper MCUs.  It'd be especially interesting to put both the XBee and MCU into low-power sleep modes, waking up just every few minutes to send the temperature, so it could run on a couple AA cells for some time.
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I know that Xbee is not supporting 1-wire protocol directly.  I was thinking I'd provide the DS18B20 with local 5v and Ground, and then use DIO pin Change Detect on the Xbee for a wireless bi-directional 1-wire  signal carrier.  The question is if I can manage the timing correctly.

If anyone have tried this, I would be grateful for any feedback..
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nr Bundaberg, Australia
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The question is if I can manage the timing correctly.
I think this would be a bridge too far.

What about putting an ATtiny85/84 at the remote end to read serial from Xbee and drive the 1-wire.

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Rob
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Rob Gray aka the GRAYnomad www.robgray.com

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I think this would be a bridge too far.
Thanks for the feedback, and I think you're right.  I have looked into the details, and I don't think the Xbee (or I) can cope with the complexity of the timing.

I will look into the ATtiny, but I also think I can solve this in a simpler manner.  All I really need from the temp sensor on the remote end, is a high pin when the temperature is over a specified trigger value.  Even though I'm not an electronics wiz, I should be able to do this with a simple circuit.  Then the Xbee can transmit the pin status...
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nr Bundaberg, Australia
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All I really need from the temp sensor on the remote end, is a high pin when the temperature is over a specified trigger value.
That's a whole different ball of wax then. The Xbee has digital IO doesn't it? So an analogue temp sensor, a comparator, and a trimpot should be all you need.

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Rob
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Rob Gray aka the GRAYnomad www.robgray.com

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Just mentioning that Xbee (1 and 2 series) also have analog in pins btw. (10-bit, 3.3V reference)

Jeroen

edit: No use for one-wire devices obviously.
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It gets simpler with every post. Before long you won't need anything at all to do the job. smiley

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LOL
Yes.  Since I am already using the DS18B20 in my project, and I kind of like it, I was initially thinking a bit to complicated.  Simplifying the project, I realized that I don't need to read the actual temperature from the remote sensor, but only need to detect if the temp has passed a fixed threshold.   Sometimes you just need a little help to peel of the unnecessary complexity.  Thanks....
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Maybe the DS1821 is a solution.

From http://www.maxim-ic.com/datasheet/index.mvp/id/2794:
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The DS1821 can function as a standalone thermostat with user-programmable trip-points or as 8-bit temperature sensor with a 1-Wire® digital interface. The thermostat trip-points are stored in nonvolatile memory, so DS1821 units can be programmed prior to system insertion for true standalone operation. The DS1821 has an operating temperature range of –55°C to +125°C and is accurate to ±1°C over a range of 0°C to +85°C. Communication with the DS1821 is accomplished through the open-drain DQ pin; this pin also serves as the thermostat output.
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