General discussion

How to interface digital thermometers to a pc?

I need to record maybe 50 readings from 6 digital thermometers with wired probes. This is close to datalogging, but I can't do the expense of buying a true datalogger, especially 6 of them. Neither do I really want to get into arduino etc scratch-builds. There has to be a real simple way do do this.

Who carries (cheap) multichannel analog pc boards anymore? Or, can this be done using either serial or printer port?

I don't mind hacking into the thermos if I had an idea that the actual temp readings were available inside, in some form I could use directly, such as a voltage level.

At this level of thinking, I'd sure appreciate a shove in the right direction. Maybe someone else has gone down this road before and would like to share, or maybe just give me a few brainstorm ideas to look into. Any help would be appreciated.
st

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Comments
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Think simple.

Place the digital displays on a board and take a picture of them the required 50 times.

Done! It meets the specification given in your post. Maybe you wanted ready to use numbers in a spreadsheet but years ago I did it this way since PCs didn't exist in 1980.
Bob

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pics work...

Hi, R!

Ya, I know what you mean. I just completed an analysis of my power usage this way, 3 month's worth of pics, written numbers and date/times, and entering into excel. I was looking for a way of getting these temperature numbers into the pc without having to do the manual stuff, not that it is horrific.
Thanks
st

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good idea, bad support!

Well, THAT was a waste of time and money. I got my 6 oregon scientific digital in/out thermos and set about testing my solar fins, hoping to lay out the thermos close together and take pics for documentation. First, I rubberbanded all the sensors together and waited a bit. None of the thermos read the same! Thinking, what the heck, I tried them attached to a single piece of metal in the sun for 'calibration'(used wood pinchy clothespins). Range was 4 degrees different, and on top of that, the lcd readouts were crappy. On half of them, the turned-off segments were just as bright as the segments for the readings, so I had trouble reading them off and on... the effect kept changing. Yes, all had new hi-power batteries.

Being a glutton for punishment, I took them inside and retested for cal with all sensors in a glass of water. After temp stabilized, still different by sometimes 1, sometimes 3 degrees f. Each time the things re-read, the numbers were different.
This dint work out well at all. OS thermos are crap.
Maybe I'll just go to RS and pick up a few sensors and just compare resistances. Hopefully, the sensors are made to better tolerances than the OS thermos I tried.
Any other ideas?
st

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After years of testing.

I've learned that such things are best given about 1 degree Celsius tolerance. Or you calibrate it out by doing the ice and boiling water tests and put the correction factors on a note for each thermocouple.

Be sure to take into consideration the current air pressure during the calibration runs.
Bob

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just a bad implementation...

Problem with trying correction factors is this: same-pipe readings have no repeatability within reason. EG, one pipe reads 111.5, 110.7, 113.0 120.0 at one minute intervals. Can't correct for that.

I think these things are ok to look at and say 'it's hot outside', or not, but to compare temps in multiple rooms, or outside different windows is meaningless.

tom

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Not long ago I picked up the IP Power 9212
http://www.google.com/search?q=ip+power+9212+-delux

This is NOT the newer delux version. I can accommodate 8 temperature probes. But you may find that cheap indoor/outdoor things usually are good enough. I read what yours did but here the ones I picked up over the years are not that bad.

I wonder if there is some mag/electrical noise in the area such as motors or such. There is that old trick of twisting the cable pair to help reject the noise and pickup.
Bob
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crappy is as crappy does

Hi, R.

I have a couple radio shark-branded units that I've been using for several years. I kept 2 of them close to my tests as a reference. The 2 rs devices maintained .1 deg of each other I bought the new ones online thru Amazon, from somebody 'out there'... I suspect these are 2nds because of the way the displays keep lighting up unused segments at random.

At this point, I'm heading towards setting up a rig like the arduino, and using sensor devices that have tolerances that are specced. Was hoping for quickndirty, but that's how life is, huh?

Anyhow, I've been wanting to try out these arm gizmos, so I guess now's the time.

st

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Keep me posted.

My past is with embedded from 1802, many versions of the 8051, MicroChip PIC, TI DSPs and well the list is far too long.
Bob

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1802?

Many moons ago I worked for RCA memory and microprocessor div in Fl. I was a tech writing programs for the testing of the 'cosmac' series 1802 microprocessors on automated test systems, from wafer level to final qa testing. Is this the same device you mentioned as '1802'? They had a cosmac one-board system that I got schematics for, and built one up using wire-wrap connections. Dern thing actually worked! Might even still have it laying around here somewhere.

funny coincidence, eh?
st

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My involvement was too deep on that one.

Yep. That one. I can still write code for in, in hex without an assembler.

71 00 7b 7a 30 00

Bob

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hex input...

I wonder how many of the now-folks even understand what it means to code on a hex pad?
Even before working the 1802 circuit, I built/tested mainframes for RCA, their Spectra-70 series. And I do remember entering code directly into the machines on a bunch of lighted switches that predated the keypads. All the work was done in ebcdic... remember that word?
Gawds, that brings back memories of some pretty wonderful days in the field.
st

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Use Arduino for temperature

I know it may sound complex, but it's not.

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Arduino Books

Sorry bad link on that last post.

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