So we're looking to sense temps in the ~~0-40C range, and wondered what to use. In the past I've used LM35's and would again, but all the cool kids seem to using this digital stuph, so I was wondering what's a roughly parallel sensor that has some ilk of digital output?
They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
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LM71, 3 wire SPI.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Depends whether you want an accurate sensor.
At the moment interchangeable glass-encapsulated thermistors leave everything else for dead at +/-0.2C (or better, if you are prepared to pay more).
You've got to put together a bridge and an A/D to turn the resistance into a digital number, which is going to be a non-linear function of temperature
but sorting out the Steinhart-Hart relationship won't overload a 32-bit CPU\.
-- Bill Sloman, Sydney
else for dead at +/-0.2C (or better, if you are prepared to pay more).
digital number, which is going to be a non-linear function of temperature
...Jim Thompson
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| James E.Thompson | mens |
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I love to cook with wine. Sometimes I even put it in the food.
else for dead at +/-0.2C (or better, if you are prepared to pay more).
digital number, which is going to be a non-linear function of temperature
There are simpler ways, methods of which I have posted multiple times on this newsgroup.
Slowman, You're a has-been... if you ever WERE in the first place. Go away. ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
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| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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I love to cook with wine. Sometimes I even put it in the food.
A few degrees won't matter....
-- A host is a host from coast to coast.................wb8foz@nrk.com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433
The hobby 8-bit microcontroller people seem to like the Dallas DS18B20/ DS18S20 and similar parts. They speak Dallas' "1-Wire" protocol, so you can string several of them on one I/O pin. The TO-92 case seems to be popular but you can also get them as SOIC. They claim +/- 0.5 C accuracy, and somewhere between 0.1 to 0.75 seconds per reading depending on how many (configurable) bits of resolution you want.
I think those parts are popular in that area because they are always short of I/O port pins, and because there are ready-made software libraries that will handle bit-banging the protocol for you.
These seem to be reasonably available 1 or 2 at a time (Digi-Key has them in minimum quantity 1), but they now come from Maxim. For other kinds of parts, I have heard varying things about Maxim's willingness to sell parts in small quantities, where "small" is defined as "less than 100,000 at a time".
When PC motherboards started sprouting temperature sensors, a lot of them seemed to be National (now TI) LM75 or similar. The LM75 speaks I2C, claims +/- 2 C and comes in a couple of surface-mount packages. There are similar parts all the way from LM63 to LM94; some of the options are SPI, different resolutions, programmable alarm points, lower power consumption, etc. You need more than one I/O pin to make these work.
These also seem to be reasonably available 1 or 2 at a time (Digi-Key). I haven't heard anything bad about TI's small-quantity availability.
Standard disclaimers apply; I don't get money or other consideration from any companies mentioned.
Matt Roberds
I'm all ears. TO92 case is nice, fanatical accuracy is not required, Price is part of the decision....we can always use just LM35's.....
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In the morning. It's quite trivial... and fundamental. ...Jim Thompson
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thing else for dead at +/-0.2C (or better, if you are prepared to pay more) .
to a digital number, which is going to be a non-linear function of temperat ure
Sure. Make the thermistor the frequency determining element in an astable, but then you have to cope with the temperature dependence of the reactive e lement.
I was recommending an accurate solution, rather than a simple one.
I may be a has-been, but I provided real - and potentially useful - informa tion. You've just claimed to know a "better" way (probably incorrectly), wi thout giving any indication of what it might be, and followed it up with gr atuitous personal abuse. Definitely an exhibition of psychopathology, thoug h you've skipped the criminal aspect on this particular occasion.
-- Bill Sloman, Sydney
So why bother measuring it at all?
-- Bill Sloman, Sydney
On a sunny day (Fri, 12 Apr 2013 02:41:04 +0000 (UTC)) it happened David Lesher wrote in :
I think some of those LM things also come with iic interface?
else for dead at +/-0.2C (or better, if you are prepared to pay more).
digital number, which is going to be a non-linear function of temperature
There are lots of simpler ways, they're just less accurate. Bill's right about thermistors, especially if you're interested in working near a single temperature. Junctions aren't in the same class, because parameters like doping density and beta aren't as well controlled. IC temperature sensors have crappy thermal time constants, their temperatures are dominated by conduction through the leads (which is sometimes what you want, but often not), and for accurate temperature control, they're strictly in the "just keep banging the rocks together, guys" class. (*)
Mixed technology wins again. ;)
For slightly wider ranges, platinum RTDs are all the go, especially if you pulse the excitation so you can use a higher voltage without horrible self-heating.
But AFAIK nobody makes thermistors with built-in I2C or one-wire or whatever the OP is looking for. So ICs are probably useful for something after all. ;)
Cheers
Phil Hobbs
(*) "So a big hello to all intelligent life-forms everywhere, and to anybody else, the secret is just keep banging the rocks together, guys." -- Douglas Adams, "The Hitchhiker's Guide to the Galaxy"
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
pay > >> more).
into > >>a digital number, which is going to be a non-linear function of te mperature
t
As I pointed out back in 1978
Sloman, A.W. "On microdegree thermostats", Journal of Physics E: Scientific Instruments, 11, 967-968 (1978).
platinum resistance thermometers have a lower thermal resistance to ambient than thermistors, which does compensate - to some extent - for the lower s ensitivity. Any place I'd have wanted to sue them I'd have had to use AC ex citation to get the sensitivity I wanted. Reversing DC will do - but a bifi lar wound Blumlein transformer bridge is a very neat way of setting up a ve ry stable bridge, and that usually takes a couple of kHz if you want to use a nice compact ferrite cored transformer.
Too true.
-- Bill Sloman, Sydney
For a bit more money I saw a project that had a whole bunch of DS18B20's that did a temperature profile of metal plate. (Maxim though...)
George H.
.highlandtechnology.com jlarkin at highlandtechnology dot com
I've been using the AD7414. With appropriate wiring and board stuffind, I can get eight on an I2C interface (used for thermal testing only).
Microchip has some pretty cheap ones. Like everything from Microchip they are a bit crappy but if accuracy isn't the prime goal...
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
everything else for dead at +/-0.2C (or better, if you are prepared to pay more).
digital number, which is going to be a non-linear function of temperature
CPU\.
There is an LM35 in a TO220 package. We use them to measure heatsink temperatures, part of running a realtime dynamic model of mosfet junction temps for a "smart" overload shutdown.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
rything else for dead at +/-0.2C (or better, if you are prepared to pay mor e).
into a digital number, which is going to be a non-linear function of temper ature
t CPU\.
t -
Not a digital solution, But I've been using diode connected transistors (in TO-220 packs) as temp sensors. I like that it comes with a mounting hole :^) I did a calibration run (versus a spendy lakeshore diode) and then a single point calibration after that. (all transistors with the same date code.) I've got to do another calibration in the near future, and it will be interesting to see how different the next batch is. How important are all the process variations for a diode connected transistor?
George H.
everything else for dead at +/-0.2C (or better, if you are prepared to pay more).
a digital number, which is going to be a non-linear function of temperature
CPU\.
temps
That's turning a bug into a feature, for sure. George has mentioned using TO220 transistor junctions for the same sort of job.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
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