I want to make this project to meassure the weight is being applied to the load cell and show it in a LCD, but i didn't find any of this instrumentation amplifier i have all the neccesary except the amplifier. Im using a 5KG load cellhttp://www.robotshop.com/blog/en/files/5-kg-micro-load-cell-500x500.jpg, and the arduino uno, i don't need accuracy, also i didn't find yet the LM741 it is possible I may find it later but i only have a few days to complete the project, what can i do in both cases if i find the LM741 or not? thanks in advance for your help. I also heard someone to say that i could use an arduino pro mini and the load cell and this will avoid using an amplifier but i don't know if it is possible.
Ordering online an instrumentation amplifier isn't an option due to the arrival date of the piece and the time i have to finish the project.
If this is for a class, you need to re-read your notes and the datasheet. That load cell has a miniscule sensitivity. You need an amplifier of some sort...either a stand-alone amp or something like the HX711 with integral PGA.
Or, if you happen to have a Mega2560, you could use its ADC in differential mode, with its PGA set to 200, and with the internal reference voltage. See page 268 of the datasheet. Oops - I see you said you have an Uno. It doesn't have that capability. Oh well.......
MXBR7:
...also i didn't find yet the LM741 it is possible I may find it later but i only have a few days to complete the project, what can i do in both cases if i find the LM741 or not?
You can use an ADS123x also but sourcing would be more difficult as HX711. In case you have some luck: Some electronic stores sell HX711 breakouts. Did you buy the load cell alone? In some cases thsi load cell is soled in a kit with a HX711 breakout. So have a look perhaps you have this breakout alreadx, see Gravity HX711 Load Cell / Wheatstone Bridge Interface - RobotShop
Indeed, its a dinosaur, great in its day, but pretty miserable in performance compared to today's
good opamps. And it needs a lot more than 5V supply to work.
For a load cell you want a precision instrumentation amplier. You can build your
own from two precision opamps with good CMRR and a third opamp (no special properties needed)
Its much easier to buy one pre-packaged - then you don't need to get the <0.1% resistors needed for
the discrete version.
eg HX711 instrumentation amp based shields are cheap and good.
741's , apart from needing +/- supply volts, have ghastly input offset and current , plus poor temperature stability specs compared to many modern offerings.