Loading ...
Sorry, an error occurred while loading the content.

Temperature sensors and A-D converters

Expand Messages
  • clerew5
    ... 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.
    Message 1 of 16 , Apr 2, 2010
    • 0 Attachment
      --- 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?
    • Mike Westerhof
      ... 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
      Message 2 of 16 , Apr 2, 2010
      • 0 Attachment
        clerew5 wrote:
        > --- 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 :-( .
        >

        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-boards.com/catalog/product_info.php?cPath=23&products_id=1503

        > 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@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?
        >>>
        >
        >
        >
        >
        > ------------------------------------
        >
        > Yahoo! Groups Links
        >
        >
        >
        >
        >
      • clerew5
        ... Yes, there seems to be some neat stuff there. But I am already well down the i2c route. Actually, I have now reached the conclusion that the easiest way to
        Message 3 of 16 , Apr 5, 2010
        • 0 Attachment
          --- In nslu2-linux@yahoogroups.com, Mike Westerhof <mwester@...> wrote:

          > > 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.

          Yes, there seems to be some neat stuff there. But I am already well down the i2c route.

          Actually, I have now reached the conclusion that the easiest way to embed surface mounted chips (even the very small ones) is to manufacture a one-off PCB. This turns out to be much easier that one might have thought. Google turns up lots of advice. All you need is a laser printer, some suitable transfer paper (old glossy magazines are recommended), and a willingness to handle ferric chloride etch (which is pretty messy stuff by all accounts).
        • Thomas Cooper
          It s much easier to buy what you need ready to go from Spark Fun Electronics, or some place similar... They cost about a buck or so. A bottle of ferric cloride
          Message 4 of 16 , Apr 5, 2010
          • 0 Attachment
            It's much easier to buy what you need ready to go from Spark Fun Electronics, or some place similar... They cost about a buck or so. A bottle of ferric cloride will cost you more than that.

            On Mon, Apr 5, 2010 at 4:09 AM, clerew5 <clerew5@...> wrote:
             


            --- In nslu2-linux@yahoogroups.com, Mike Westerhof <mwester@...> wrote:

            > > 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.

            Yes, there seems to be some neat stuff there. But I am already well down the i2c route.

            Actually, I have now reached the conclusion that the easiest way to embed surface mounted chips (even the very small ones) is to manufacture a one-off PCB. This turns out to be much easier that one might have thought. Google turns up lots of advice. All you need is a laser printer, some suitable transfer paper (old glossy magazines are recommended), and a willingness to handle ferric chloride etch (which is pretty messy stuff by all accounts).


          Your message has been successfully submitted and would be delivered to recipients shortly.