Society of Robots - Robot Forum
Mechanics and Construction => Mechanics and Construction => Topic started by: mdaisl on January 25, 2011, 11:36:00 AM
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I have never built anything electronic before, but after glancing at the tutorials, i would very much like to build a temperature alarm with an adjustable set point. If temp. drops below set point, an alarm goes off. If i can accomplish this, would like to take it one step further. If temp. drops below set point, an alarm goes off and makes a telephone call to pre determined number. Any help getting started would be greatly appreciated, thanks.
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The first part is rather easy. A temperature sensor and a voltage comparator is all that is needed.
There are a number of different devices that can sense temperature. A Thermistor (temperature varying resistor) are cheap and easy to use. They don't have a linear response to temperature changes but that wouldn't be a problem.
The LM339 is a commonly available voltage comparator (there are others). One input is the reference voltage that is set from a pot (potentiometer) and the output go high or low depending on whither the input voltage is higher or lower than the reference voltage.
Search on the parts I mentioned for more info on how to use them. This is a good starting project.
The second part can be done but it isn't some thing I've done so other will need to help you.
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Hi,
I have never built anything electronic before, but after glancing at the tutorials, i would very much like to build a temperature alarm with an adjustable set point. If temp. drops below set point, an alarm goes off.
As waltr mentioned, this is quite easy.
What kind of alarm did you have in mind?
Is it just for fun, or do you have a need for it?
If i can accomplish this, would like to take it one step further. If temp. drops below set point, an alarm goes off and makes a telephone call to pre determined number. Any help getting started would be greatly appreciated, thanks.
A bit more work. Either consider using an old cell phone with a prepaid card (then it's fairly easy), or, if the application allows it, perhaps a cheap radio module could be used instead.
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Try using
- LM335 [directly calibrated in kelvins]
- LM35 [calibrated in centigrades]
after this, you can either feed its output to an ADC(analog-to-digital converter) or use a voltage comparator like LM324N to obtain your output with a set point voltage
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Hi,
Try using
- LM335 [directly calibrated in kelvins]
- LM35 [calibrated in centigrades]
That would be gross overkill, especially in the light of this being a first time project. An NTC is all it takes, no calibration is needed.
KISS
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I find using LM335s pretty easy to use myself, might not be the same for everybody, but I did do something like this for an arduino, and it worked pretty nicely.
http://www.societyofrobots.com/robotforum/index.php?topic=12196.0 (http://www.societyofrobots.com/robotforum/index.php?topic=12196.0)
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I'm sorry, i think i may have mis conveyed the message....they come 'pre-calibrated'... meaning the voltage change is directly proportional to the change in temperature in kelvins/centigrades.
and their response is fairly linear over a good range of temperature. yet you still may need the ambient temperature to calculate the error and subtract/add from the original value though...so maybe you are right , sir, for a beginner it may pose issues. :D
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Hi,
I'm sorry, i think i may have mis conveyed the message....they come 'pre-calibrated'... meaning the voltage change is directly proportional to the change in temperature in kelvins/centigrades.
and their response is fairly linear over a good range of temperature. yet you still may need the ambient temperature to calculate the error and subtract/add from the original value though...so maybe you are right , sir, for a beginner it may pose issues. :D
Don't get me wrong, I know they're both precise, calibrated and comparatively simple to use when you've got a bit of experience (I've been in this game for a wee bit of time and I used my first LM35 around the early eighties IIRC).
But... a thermostat doesn't need absolute temp readings and besides, the OP clearly states that this is his(/her?) first project and an NTC is beyond any doubt the easier one to both use and understand.
Starting simple there's a chance to comprehend the stuff and thus learn. Starting just a shade to complicated, there's a real chance of failure and quitting the hobby.
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Starting simple there's a chance to comprehend the stuff and thus learn. Starting just a shade to complicated, there's a real chance of failure and quitting the hobby.
+1 , sir i agree. :D
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I'm using this http://www.dealextreme.com/p/usb-digital-thermometer-dongle-software-displays-temperature-7003 (http://www.dealextreme.com/p/usb-digital-thermometer-dongle-software-displays-temperature-7003)