small dc signal amplifier schematic need

[phoenix_1]

I need 0-5mV to 0-5V dc signal inverting or non inverting amplifier.
Op Amp must have single supply from 5 - 12 V range is ok.
Please any help.
It is for load cell sensor.
I was measure output is about 5mV if supply of cell is 5V DC.
If I put some load on cell ~ 10 kg output drop from 5mV to 4 mV.
If on cell isn't load 0kg out is 5mV.
Load 50kg on cell out is 0V.
If I want to measure with PicMicro ADC cell then I need to invert cell out
with opamp or software ...
I have a lot of TL072 SMD and if I can use it ?

Sorry for my bad English...

Regards
Robert

[mister_e]

so you need a gain of 100, with an op-amp.

http://www.radio-electronics.com/info/circuits/opamp_non_inverting/op_amp_non-inverting.php

just put the resistors value in the formula, and you're ready to go.

Your op-amp may/will have a dc offset, you'll need to compensate it in software. TL072 is not a rail-to rail one and will not work @5V (from what I remember of), so you'll need to use a higher voltage rail to make it work properly, or use a rail-to-rail one.

[mistergh]

My favorite Op Amp for those applications is the TLV2470 from Texas Instruments. This is a rail-to-rail unit and almost indestructible. The input impedance is in the Meg Ohm range and the output is a few ohms max. You can drive an ADC directly with it.
You can find a simple gain calculator at this address:
http://www-k.ext.ti.com/srvs/cgi-bin/webcgi.exe?Company={5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(32618),new
A calculator for gain and offset is here:
http://www-k.ext.ti.com/srvs/cgi-bin/webcgi.exe?Company={5761bcd8-11f5-4e08-84e0-8167176a4ed9},kb=analog,case=obj(35457),new

Good luck!

[mikendee]

Robert,
For amplifying the output of a load cell I think you should use an instrumentation amplifier. I have use an INA114 in a situation like yours. You can buy a descrete chip or you can construct one with 3 op-amps an some resistors.
The fact that the output voltage goes down as the weight increases maybe fixed by swapping the excitation voltage or turning the load cell the other way up. If not it shouldn't be hard to fix it in the software.

Hope this helps.
Mike

[mistergh]

Robert,
to really understand the working of an Op Amp, or Instrumentation Amp, you should read "Design Reference" from Texas Instruments. You can download it from ti.com, just search for SLOD006B. Also read SLAA068A and SLOA030A, etc.
The INA114 was a very good general purpose part years ago. It is not a rail-to-rail unit and is more than 10 years old, there are more modern Op (Instrumentation) Amps available from several manufacturers.
To have the output voltage (going to the ADC) going up or down when applying weight to the sensor is just a matter of switching the two outputs from the sensor (+ or-) going to the Op Amps. Of course you can also handle this in software.
I have used the TLV 2474 (Quad OpAmp) many times for those kind of applications successfully.

[mistergh]

Robert,
the TL072 you have is old technology and I don't think it can be used at all for your application.
The gain you would need for a span of 0 to 5000mV ( 5mV amplified to 5 Volt) is 1000! A gain of 1000 really needs to be done in two stages if you want any precision.
The gain needed also depends on the ADC you want to use. If you use a PIC with a 12bit ADC you could probably get away with less amplification then what you would need when using a 10bit ADC.
I hope I covered it all now.

[phoenix_1]

I will probe with LM358 and LM324.
Also with inverted amplifier version.
Apropos I use PicMicro 10bit ADC.

Regards
Robert

[mistergh]

Hi Robert,
The LM324 or LM358 can be used, but remember, they are not rail-to-rail, you have to design the circuit accordingly. Freescale Semiconductors has some very interesting "Application Notes": AN 1517 and AN 1325
http://www.freescale.com/files/sensors/doc/app_note/AN1517.pdf?fsrch=1
http://www.freescale.com/files/sensors/doc/app_note/AN1325.pdf?fsrch=1
there are many more on their web site. You might want to study those.
If you want to use a 10bit ADC I would suggest using it with a 2.048V reference voltage to get a decent resolution.

[phoenix_1]

Hi Robert,
The LM324 or LM358 can be used, but remember, they are not rail-to-rail, you have to design the circuit accordingly. Freescale Semiconductors has some very interesting "Application Notes": AN 1517 and AN 1325
http://www.freescale.com/files/sensors/doc/app_note/AN1517.pdf?fsrch=1
http://www.freescale.com/files/sensors/doc/app_note/AN1325.pdf?fsrch=1
there are many more on their web site. You might want to study those.
If you want to use a 10bit ADC I would suggest using it with a 2.048V reference voltage to get a decent resolution.

Thank's to all and you Misterg it was help 100%.
AN1517 and AN 1325 was final and the best help.
At these moment all is in test mode.

Regards and thank's again to all.

Robert

[mistergh]

Hi Robert,
I am glad I could help. Let me know how your project moves along.
Do videnja.