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How to make a home-made thermal sensor??

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hokwunhongderek

New Member
Hello all, I am now doing a GCSE project, and I am stuck on my own idea about making a computer overheat detector. I dunno what thing to use to monitor the temperature, as my budget is limited I should not buy stuff but to make one myself. Is a bimetallic strip good enough to do the sensor job? What temperature should I set to turn on the alarm? And is it OK that I gonna put it on the back of the computer, just outside the computer fan?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
hokwunhongderek said:
Hello all, I am now doing a GCSE project, and I am stuck on my own idea about making a computer overheat detector. I dunno what thing to use to monitor the temperature, as my budget is limited I should not buy stuff but to make one myself. Is a bimetallic strip good enough to do the sensor job? What temperature should I set to turn on the alarm? And is it OK that I gonna put it on the back of the computer, just outside the computer fan?

A simple and cheap temperature probe can be made from a silicon diode, their forward voltage drop is temperature sensitive, you can amplify it with an op-amp. They have even been used as outdoor temperature sensors for cars.

The most temperature sensitive part of a computer is the CPU, that's probably where you need to be measuring. However, most modern motherboards already have a sensor built-in, plus they come with monitoring software - which usually has the option of slowing the CPU down, or shutting it down all together, if it gets too hot.
 

k7elp60

Active Member
Temperature sensor

I agree a cheap temperature sensor is a silicon diode. I like the 1N914 or 1N4148 as I have put the forward current around 5Ma and had good results. I am not familiar with the specifications of a bimetalic strip. They must be good as a lot of thermostats used them for years. Choosing
the trip temperature could be a difficult thing to determine as there are alot of factors to consider, including the placement of the sensor to the
sample point, the manufactures maximum temperature.
I have a temperature probe I use with my DVM to check the temperature of power semiconductors. One my be amazed on how much the temperature varies on the various places on a heatsink, when the device is dissipating power.
 

Optikon

New Member
hokwunhongderek said:
Hello all, I am now doing a GCSE project, and I am stuck on my own idea about making a computer overheat detector. I dunno what thing to use to monitor the temperature, as my budget is limited I should not buy stuff but to make one myself. Is a bimetallic strip good enough to do the sensor job? What temperature should I set to turn on the alarm? And is it OK that I gonna put it on the back of the computer, just outside the computer fan?

If the reason you want to make one is cost, then you are basically saying that you can spend 20 cents for a diode or some bi-metallix strip but cannot spend a 1.50 on an integrated circuit temp sensor with all the signal conditioning built in. IMHO, you should save yourself some headaches on fitting diode curves and get an IC temp sensor.
 

mozikluv

New Member
temp sensor

:D

have you tried using a 2N2222A as your sensor? :wink:
 

hokwunhongderek

New Member
Really thanx !!

Dear all,

Really thanx for the replies! Just another question, where can I buy those specific electric stuff?? 'cos I don't think the DT stall in my school has such thing... Also is it my so-call 'idea' really crap? (yes I know it is, but my DT teacher said yes when I told him this idea... :evil: ) And here is the whole thing, I gonna make the sensor next to the comp somewhere, then connect to a LED and a buzzer, should I connect to a comp fan too, so that it blows when it becomes overheat? Thanks for reading. ^^
 

plot

New Member
Re: Really thanx !!

hokwunhongderek said:
Dear all,

Really thanx for the replies! Just another question, where can I buy those specific electric stuff?? 'cos I don't think the DT stall in my school has such thing... Also is it my so-call 'idea' really crap? (yes I know it is, but my DT teacher said yes when I told him this idea... :evil: ) And here is the whole thing, I gonna make the sensor next to the comp somewhere, then connect to a LED and a buzzer, should I connect to a comp fan too, so that it blows when it becomes overheat? Thanks for reading. ^^

well, as someone already mentioned, pretty much all newer motherboards (probably anything 2 years or newer, and most before that), have built in temperature sensors. HOWEVER, alot of computer manufactors like emachines, Dell, HP, Gateway, etc... probably don't have temperature sensors on there motherboards (depending on the particular model of course). Any motherboard you buy for a computer yourself will have at least two temperature sensors, one for the processor, and one for the case in general, and in the BIOS options there will be a place to make it shut down your computer at a certain tempurature, go into standby, etc... There are also many tempurature monitoring programs out there that take advantage of these motherboard sensors such as Motherboard Monitor (google it).

that aside, have it send off a warning around 65C-70C (notice that's celsius), anything over that, and it get's critical for most AMD processors. Pentiums run alot cooler, but i'm sure there temperature range is around the same general area. That's what'd I personally recommend in any case.

Now, as for places to purchase these types of electrical components, assuming you are in the United States, i recommend the following:
www.jameco.com
www.digikey.com
and
www.mouser.com

in that order. I've never used the last one personally, but I know alot of people who swear by them.


...and for your last question, you can add a fan if you want too, or make the computer go into standby or something.. shouldn't just let it fry.
 

grrr_arrghh

New Member
If its for a GCSE project, you could try a thermister and an op-amp (i've got a diagram if you need one). If you used something like a 555IC as an osscilator to make a buzzar beep rapidly (as an alarm), it would be more than complicated enough for a GCSE project

Tim
 
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