ARDUINO PROJECT: OPAMP AMPLIFIER
Posted by kll on February 21 2013 22:51:58

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opamp amplifier for mV input to ARDUINO



using the opamp LM324N, a 4 channel version.


datasheet






data



with this simple circuit it is possible to use a range between

4 and 40mV to about 1V and 3V output




circuit



but actually i want to build a so called instrument amplifier

what i order already as a INA121

but first i try to build it with my existing LM324N,

using 3 opamps from it.




circuit



selecting R = 50k, R* = 25k, and Pg= 2k

should also give me a good range for 0 .. 50 mV

but using any Pg, from non resistor gain = 1 to any high value get only gain 1.7

with IN- to GND and IN+ to a voltage devider from 0 .. 0.050V .. 5V



with a new voltage devider GND_R81k_P10k_R81k_V5

i got better data







so its very usefull for a bridge application



Here now the test of the INA 121


datasheet










in general the use of offset or bridge or bipolar powersource is required to amplify mV signals

i will use a offset of 2.5V by voltage divider between the ARDUINO and OPAMP GND and 5V

to shift up the GND of a other powersupply where i want to read Volt (6 ..9VDC)

and Amp ( 0 .. 40ADC ) by a 50mV shunt ( at 50A)



Rm = 46K poti, RV = 82k resistor

tested on a breadboard still looks like that:





next is to build it on a ARDUINO proto typ shield

on top of the ethernet shield




the TMP36 is on a socket so it could be extended by a short 3 wire cable



and testing the mV and V inputs









but have a problem with the RJ45 on the ethernetboard





thats the arduino with ethernet shield and TMP_mV_shield on top