linuxgeek: [nslu2-linux] Temperature sensors and A-D converters

--- In nslu2-linux@yahoogroups.com, Philip Tait <pjtait@...> wrote:
>
> 1-wire sensors: http://en.wikipedia.org/wiki/1-Wire

Ah, but that actually requires 2-wires :-( .

And it would seem that the idea is to put the A-D converter at the far end of some wire alongside the sensor.

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 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).
>
> On Thu, 2010-04-01 at 13:47 +0000, clerew5 wrote:

> > --- In nslu2-linux@yahoogroups.com, "Mike Westerhof (mwester)"
> > <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?