i need your help!!!!!!

[deah]

i'm a senior physics student from philippines and i need help of how will i make my undergraduate thesis.. my instructor suggests to do the thermometer sensor.. if i can't make it,, can i ask from any of you to give a back-up topic..
hope for your good response..
thank you..

 

[A.Anand Srinivasan]

just tell us what domain you are working on... so that we can post some good topics of that domain....

 

[deah]

actually I'm working on what my instructor has been suggesting..
i feel good on that topic, the one thermometer sensor but i just don't know what to do first.
it's like, we're making a display thermometer..
that thermometer should measure the temperature of the desired area,, and everyone can see it just like a digital clock..
do you get me?
what will be my first step?

 

[A.Anand Srinivasan]

the first step would be to design a temperature sensitive circuit... for that you may use a thermistor which is biased properly to give a current or voltage output proportional to the temperature....
or you can exploit the eber moll equation and measure temperature using the temperature dependence of collector current of bjt or current of a diode...

you can then convert this to digital format using a ADC and display it...

 

[deah]

thank you very much..
but can you give me background of how will i do the "design a temperature sensitive circuit"....
or just teach me how to..

 

[A.Anand Srinivasan]

are you working on some IC layout or are you planning on a temperature sensing circuit using discrete components.....

because temperature sensing circuits using discrete components is very hard to make... the one main thing is that the power dissipation also causes heating and this leads to difference between the internal temperature and the surrounding temperature which we want to measure also the temperature distribution is not uniform....

 

[deah]

what about IC layout?
how about doing on 'temperature sensing circuits using discrete components',, how long will it take me to do it?
is it too expensive?

 

[johnyaya]

Measuring air temperature requires:
1) Decide on budget/cost.
2) Decide on accuracy required. Balance budget vs. accuracy. For best accuracy you will need to ventillate your sensor when making air temperature measurements.
3) Select an appropriate sensor, data acquisition, and display.
4) Draw schematic. Prototype sections that you are unsure of.
5) Layout PCB. There are free software packages available, just look...
6) Assemble and troubleshoot if there are PCB layout mistakes.

For a simple, yet accurate temperature measurement you could use a thermistor like the YSI44031 (0.1 deg C interchangable) in a half-bridge configuration. I would select a micro that has an integrated ADC to do the data acquisition. There are many options for the display, kinda depends on what you want the thing to look like, and your budget.

Another option is to select a solid-state temperature sensor like the LM35 which already has a linearized output, but would not be as accurate as the YSI thermistor. Analog Devices makes some solid-state temperature sensors that are very accurate, but they cost a lot. You may be able to acquire samples though.

So many options... Start with #1 and #2 above.

 

[deah]

thank you.....
but what if i can't find thermistor like the YSI44031 here in our town?:|

 

[A.Anand Srinivasan]

there are many thermistors with different values and different sensitivities available... you can go to some company sites and search and download their datasheets to check things out...

 

[johnyaya]

Yup, MANY different thermistors out there. Which one you chose and how you implement it's use will determine accuracy. Thermistors are also very inexpensive.