I've just started experimenting with arduino, and am working towards building some data logging set ups.
I'm interested in logging from strain gauges and thermocouples and have started to experiment with Instrumentation amps to get my head around what is required.
I've built the circuit in the image attached, with the aim of connecting it to a K-type thermo after verifying that it works.
The voltage divider is just to provide a reference input (5mV) so that I can verify that everything is working.
I am trying to log the output of the INA126P using arduino analog input. I have set the gain resistor of the INA125P to 220 Ohm in order to give a gain of approx 370, and an INA126 output of 1.84V.
I have tried a few modifications but can't get anything other than 4.4V from the output.....
yetles:
The voltage divider is just to provide a reference input (5mV) so that I can verify that everything is working.
5mV won't work.
Common mode range of this opamp on a single 5volt supply is ~1volt to ~3.8volt.
See the shape inside the shape on Figure4/page 8 of the TI datasheet.
Pin4 of the chip should be connected to ground.
Instrumentation amps measure the difference between the two inputs.
With a gain of 370, the difference has to be within + or - 5mV to keep the output within it's limits.
Both inputs have to be within the common mode range of ~1volt to 3.8volt.
Load cells (strain gauges) can be measured with a HX711 breakout board.
And thermocouples with a MAX31855 board.
Leo..
Even if you biased the INA126 inputs to about mid-rail to get sensible readings , you still have to deal with cold junction compensation to get accurate readings from a thermocouple.
As post #2 mentioned there are many shields which do all this for you - I've used those based no the MAX6675, but there are many others. They all have easy to use drivers, so much of the hard work is done for you.
