voltage divider question

I am in need of something like a voltage divider. Maybe something like this exists as an IC or something but here is my problem.

I have a adc hooked up to a thermistor and the voltage on the thermistor is in the range 2400-2700 ohms. I want it to use the maximum range of 5V from the lowest thermistor value and the highest thermistor value. 2400 ohms=5V and 2700 ohms=0V. The best I could do was use another resistor (2550 ohms) and use it and the thermistor as a voltage divider and the values I got were 2.5757-2.4285 which is a difference of .1471 for the whole range. I have a 12-bit ADC which means it is one increment for every .00122 V (5 / 4095). So for the whole range of 2400-2700, the ADC will only change 120 increments. I just want to have a better resolution.

Is there something I can make that will use the entire range of 0V-5V instead of 2.42V-2.57V?

Hi dreed75
First:
You must not apply high voltage eg 2-3 Volts to thermistor .
becaus it produce self (extera) heating and change measured accuracy!
Second:
You can use one op-amp to produce 0-5Volt output, for example use OP262.
put input (+) to voltage divider (max. 0.5 are sufficient).
connect input (-) to output via resistor R1
connect input (-) to voltage reference via R2, which it's voltage is minimum voltage of voltage divider.
choose R2 10K
and R1 so that R1/R2=5/(voltage diference in divider node)

Regards,
Davood.

first rest 2.42V to your signal that gives you
0-0.12V will result

then amplify this signal by a Gain of =5/0.12=41.67

you actually don't need a voltage divider instead you need a amplifying stage, using op-amp, with a Gain=41.67 (as Miguel Gaspar suggested). if u still don't get it tell me i'll send you the diagram.

yeah, I am a newbie, can you please send me the diagram? Thanks to everyone for their help so far.

Hi dreed75

Try with attached circuit.
use multi turn potentiometer for RV1 and RV2.
and it is better to use 1% tolerance for resistors.
for op-amp you can use any type of rail-to-rail one.

regards,
Davood.

thanks, I let you know how it works out.

Hi dreed75

RV1, R2 and R3 make voltage reference for pin (+) op-amp
R3 voltage adjusted near to thermistor voltage when it's values is about 2K5.
it would Vth= (Rth*VCC)/ (R1+Rth) = (2.5 * 5)/(2.5+10) = 1Volt
RV1 used to adjust DC shift at output.
minimum and maxixmum voltage change at thermistor pin (when op-amp not present):
Vmin= (2K4*5)/(2K4+10)= 0.968
Vmax=(2K7*5)/(2K7+10)= 1.063
Input swing = Vmax-Vmin = 0.095
output swing = 5-0 =5Volt
op-amp gain= output swing/input swing
Av= 5/0.095=52.6
equivalent resistor for R1 and Rth = R1*Rth/R1+Rth= 2K
R4+RV2=2K * Av= 2K * 52.6 = 105.2
as you can see; 129K > (R4+RV2) > 82K
also you can use combination of R4=92K and RV2=22K

Regards,
Davood.

What electronics simulator do you use or do you? I tried crocodile clips but it is very limited and only gives me one op-amp and probably not the kind I need to use in real life. Thanks.

I dont use simulator for this type of design!
just i design circuit then calculate components values.

Regards,
Davood.

what do you use to draw it then? Also, I would like to be able to do this sort of thing in my head too. Is there any books or courses that you would recommend? thanks

Its schematic diagram drwan by protel.
in university it's cource would be Electronics level 1, 2 and 3.
that cources used electronics books such as boylestad (and nashelesky)and
"microelectronics" by millman and
"Anallog integrated circuits" by Gray & meyer and some other books.

regards,
Davood.