clerew5 wrote:
> --- In nslu2-linux@
>
>> 1-wire sensors: http://en.wikipedia
>>
>
> Ah, but that actually requires 2-wires :-( .
>
Indeed. Apparently somebody thought that it might be possible to use
the ground in a building, for example, as the return conductor. I think
that's marketing talk, as the devices really work better with a proper
2-wire system.
> And it would seem that the idea is to put the A-D converter at the far end of some wire alongside the sensor.
>
Yes. The wire (or pair of conductors, if you prefer) is actually a
digital network connection. Many of the devices do A-D conversion, and
send the results digitally back to the host. However, some devices are
completely digital. And some do the reverse -- I have a relay board
that I intend to use to control the heating/cooling system once I finish
this project, although right now it just blinks LEDs and looks cool -
everyone likes blinking lights ;-).
> And how does one interface that to a Slug? Can it be done from an i2c bus, or is it necessary to bring out the UART connection from the Slug? And can somebody recommend a suitable sensor/converter for use with that system (I am looking for a temperature resolution of 0.1°C, and an absolute accuracy not too much worse than that).
>
I use a pre-packaged USB device:
http://www.hobby-
> I would also like some advice on the path I have been following so far:
>
> I intended to attach an i2c bus (that seems a well-established hack to the Slug). On that bus there will be assorted LEDs and pushbuttons, an LCD, an EEPROM, and a 4-channel 12-bit A-D converter. I had intended to use LM35DZ temperatures sensors (as manufactured by both MS and Texas). And I had identified an i2c A-D chip from the Farnell website (AD7991) that appeared to have all the required characteristics.
>
> But I did not check enough. It turned out to be a SOT23 style chip which was about the size of a baby's fingernail :-( . Not nice for building on a breadboard. I looked for a suitable breakout board, but the only available one for an 8-pin SOT23 was in California, and I am in the UK. The only breakout boards readily available in the UK are for 6-pin SOTs (well, there is a possible one from Microchip, but at a ridiculous price).
>
> So back to the Farnell website for a chip with a larger footprint. But they all seem of be surface mount and with TSSOP or MSOP format, where the pin spacing is still 0.025in (the same as SOT23).
>
> So can anyone suggest any better chip? I might get away with SOIC format (0.05in spacing). The only chips I can find with good ol' DIL fomat are from Microchip, and they use Yet Another Nonstandard Interface (Microport).
>
Check out the kits and parts at the supplier I listed above. That will
give you some idea about size and nature of the various one-wire chips
and devices, and from that you can decide if the one-wire parts are more
practical.
In terms of the temperature sensors, I needed a network of them, and
found that the pre-packaged or kitted parts were all too expensive -- I
was paying more for connectors than the parts. So I purchased a dozen
of the temperature sensors from a taiwan-based supplier (via eBay).
Each part is in a small transistor package, and were very easy to solder
to short (8 inches approx) twisted pair.
Each "pigtail" was tested, and the network address recorded. I attached
a label with the network address to the pigtail as well -- otherwise you
have no idea which sensor is which (they are, of course, wired up to
the same twisted pair).
I wired the building up with ordinary telephone twisted pair, running a
length through the first-floor rooms, then dragging it through the
crawlspace beneath the building to get a sensor down where the plumbing
is at most risk of freezing.
I estimate the total cost for that part of the system to be about USD 3
per sensor, by the time I was done with the sensors, solder, and
telephone wire. Hard to beat that for price.
-Mike (mwester)
>> On Thu, 2010-04-01 at 13:47 +0000, clerew5 wrote:
>>
>
>
>>> --- In nslu2-linux@
>>> <mwester@> wrote:
>>>
>>>
>>>> I have a slug installed at an old house I have been working to
>>>> refurbish. It uses a network of one-wire sensors to monitor
>>>>
>>> temperature.
>>>
>>> Eh? What sort of sensor uses one wire?
>>>
>
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>
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