LED panel meter and transducer. How difficult?

[wsemajb]

Hello,
I've been trying to find a reasonably priced pair or LED DPMs for passively monitoring fahrenheit in a water cooling loop.

All I find are very expensive industrial or laboratory units.
I don't need programmability or control functions. Simply a thermometer.

I've found a few of this sort of unit
**broken link removed**

I've asked at three forums prior to this. I've asked each of the parts suppliers. I've searched deep into the web for information on how to mate a transducer to one of these DPMs for measuring temp.

I'm astonished and extremely frustrated that this seems so difficult to achieve. These led panels measure millivolts. A transducer produces millivolts. Some transducers are more linear than others. Some are more/less accurate. I don't need much accuracy. I'm trying to simply monitor gross changes in temp in this cooling loop. I have to use red LED dpms in this project - not LCD.

Can anyone help me figure out what type and value of transducer to use with the above unit and perhaps tell me if it's possible to simply wire them together? I'm not competent enough to design a circuit. It appears that the above unit is already a designed circuit for displaying voltage in four red led digits. Is this not correct?

I hope someone can help me. This seems like it should be so simple, it's driving me nuts!!!!!!

Thank you so much for any assistance.

 

[j.p.bill]

Take a look at an LM35. They are cheap, have an output that changes linearly with temp, and should be easy to scale for a cheapo DPM.

 

[picasm]

Here is an old article that shows how to interface various temperature sensors with voltmeters.
**broken link removed**

If I were making a thermometer though, I would use a microcontroller to drive a led display and either a precision thermistor or a DS1820 sensor chip so that it never needs calibrating.

 

[jbeng]

The LM35 is used for Centigrade (Celsius) measurements. To get a Fahrenheit reading, I would suggest the LM34, which outputs 10mV per degree F. Find the LM34 specs and datasheet **broken link removed**
Connect the output of that circuit to an appropriately scaled A/D converter/display circuit using an ICL7107 chip.
**broken link removed** to a page describing a panel meter built around the ICL7107.
Jeff

 

[TrevorP]

Are you trying to do something like this? Where as the temperature goes up a higher led would turn on? (and vice versa).

If so use one of the chips recommended bellow to get the temperature into an accurate current then use multiple LM3914's tied together to give a bar graph appearance.

EDIT: never mind you probably don't want this sort of thing because it won't give you numbers.

 

[wsemajb]

Wow,

Fantastic board you guys!

I got more help here in 24hrs than the combined efforts of two weeks worth of probing elsewhere.


Cheapslider. I'd like nothing better than to cannibalize an off the shelf room thermometer with remote sending unit. Indeed they are plentifully available. I'm not trying to do anything so noble as educate myself to circuit design - if I can help it. But they are all LCD. The project I'm working on uses red led meters already on its panel. I'd like to keep things consistant.

I've actually already tried LCDs for this and am sorely disappointed with their visibility, even the backlit ones (in comparison with the LED versions). LCDs are just so much easier on batteries in inexpensive room thermometers that LEDs are all but non existant in these devices anymore.

Jeff, I'm a complete novice with circuit design/analysis. I followed the last link you provided and do I understand correctly there are forty something components to that project? I'm just trying to be a little rational. If I can wire together the DPM that I linked in the first post to an LM34 with just a couple of connections and get within a couple of degrees accuracy, that's time well spent and I'll feel like I accomplished something.

My needs are for monitoring gross changes in temp between in/out on a water cooling loop. I'd like to take advantage of inexpensive readily available parts like the DPM I linked to and the LM34. Otherwise, I can simply purchase a pair of CyberDyne LED dash mounted water temp gauges with senders from Summit Racing online for about 110 USD. An eight dollar display along with a six dollar sender - wired together for me for 55 dollars - and I can't crack that mystery myself without an EE degree. Guess that goes right to the heart of my frustration.

Until I googled it a while back, I would have guessed that LED DPM thermometers would be as common as light bulbs. A digital display of fluid temp. Isn't this a somewhat fundamental and common need for an experimenter or hobbyist? LCDs suck for visibility by comparison - at least in this smaller form. And the affordable LCD aquarium and computer bay thermometers available are of breathtakingly poor quality - (i tried them).

Where ever I've asked about affordable panel thermometers it's as if I were inquiring into the grander mysteries of ghost particles in the universe. I'm just knocked out by this really. Why hasn't this been done a million times, by a million people, and documented at least dozens of times. Why don't parts suppliers have LED DPMs and transducers available cross-referenced with basic instructions for the most common applications - such as temperature or PSI?

Hasn't anyone else out there come across a situation where you were astonished by it's obscurity? Like, say, going to the hardware store for sandpaper and having the clerk stare blankly and call for assistance? The assistance comes and the guy says "yeah, we used to use that stuff at a shop I worked in. Like beach sand glued to hard paper - yeah I think that's the stuff. Haven't seen it around these parts. Have you looked online?"