reading load cell signal using PIC

[kobre98]

Hi
I have a project in which I use load cell to measure up to 250 Kilogram
the load cell has 4 wires and output values in Millivolts
I want to read the voltage and convert it to weight using PIC and display it on LCD
I've been told that this can be done using ADC in PIC by adjusting the +-Vref to make it read small values
or use amplifier to amplify the signal from the load cell.
I need specific details on how to do such thing in any programming language. C language MikroC would be good

Thanks in Advance

 

[paulfjujo]

hello,

What is the voltage output of your load cells
usually industrial load cells give 2mV/V excitation for the full scale
ex: load cell of 250Kg
if excitation (power supply for the load cell) is 10V,
then you get 2mv* 10= 20mV for the full load of 250Kgf
with PIC ADC is 10 or 12 bits for any .. poor resolution

Maybe you can use external ADC like MCP3424 17 bits or others similars devices...
with differential inputs
include a PGA analogue amplifier..
you can see some test on Microchip MCP3424 evaluation borad on my web page
ex: full scale 128mV with Gain=8 15 bits 7.8µV resolution

up to 2µV/point with 17 bits and G=8

 

[kobre98]

can't I just amplify the signal then deal with it using PIC ?!
wouldn't that be easier ?!?!

 

[paulfjujo]

hello,


Yes you can !
but you need a big amplification and manage the offset
so to choose a good Instrument amplifier to avoid drift of measure.

Easier ? not sure..
but it is my opinion only...
wait for other advice .

 

[kobre98]

can You give me more in how to use MCP3424 and is there any other IC that I can use if I couldn't find this IC
?!

 

[paulfjujo]

hello

**broken link removed**
but for only one chanel you can use MCP3421 instead off.
other type of ADC
AD7715 (old) , AD7730 .. etc ...


look at similar threads !