opamp

Archiver

hello all,

I have a lm35 temp sensor, and a adc0831. To use the adc at a optimum, i
want to amplify the output of the lm35 temp sensor, so that the range
becomes 0 to 5 volts instead of the range of the lm35. I thought of a opamp,
but how to use them? There amplify a lot is told me. i'm good in digital
electronics, analog is worse [noparse]:([/noparse]

thanks,

pieter
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Archiver

>I have a lm35 temp sensor, and a adc0831. To use the adc at a optimum, i
>want to amplify the output of the lm35 temp sensor, so that the range
>becomes 0 to 5 volts instead of the range of the lm35. I thought of a
opamp,
>but how to use them? There amplify a lot is told me. i'm good in digital
>electronics, analog is worse [noparse]:([/noparse]
>thanks,
>pieter

Hi Pieter,

Here is a circuit that amplifies times four. So the resolution with the
adc0831 becomes about 0.5 degrees C instead of 2 degrees, and the range is
0 to over 100 degrees C. The input from the LM35 is 10 mv per 'C and the
output from the op-amp is is 40 millivolts per 'C. If you want x8 gain,
then use 105kohms with 15kohms. Then the resolution would be about 0.25
degrees C and the range about 0-60 degrees C.


;

---

+9 volts
|\|
LM35

---

|+\
| >--o--adc0831
;

---

|-/ |
| |/| |
o--/\/\

---

o
| 30k | LM324 or LM358 or ...
\ (105k) |
/ 10k |
\ (15k) | gain=1+(30k/10k)=4
| | (gain=1+(105k/15k))=8
'

---

o

---

common

There are also op-amps that would allow you to run the op-amp off of a 5
volt power supply and still get 5 volts at the output (rail to rail
output).

-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com