INA125P is connected to 5v.
32u4's VREF is 5volt due to other sensors , so I wish a 0...~5v output.
Schematic is attached.
Regardless of gain, the max output is only 0 to 0,24v
Vref , measured at INA125 pin 4/15 is 3,7v
The load cell is a 1mV/V type, pretty common.
Why is the output voltage so low ? - Is there a faster way to adapt it to output 0..5v for the 10bit ADC or 32u4 - or should I just order a 24bit SPI ADC that can work on a diferent Vref ? - but then, why is INA125 VREF so far from it's output ?
These chips really need a dual supply rail, so you can leave grounds connected to ground.
As you have connected it now, you're trying to make 5volt Vref from Arduino's 5volt supply.
Not possible.
The IC needs 1.25volt more to do that, so 2.5volt Vref is the maximum from a 5volt supply.
Leo..
Datasheet states the specs at +15 and -15volt supply.
If you run it on a single 5volt rail, expect some performance degradation.
e.g. worst case output range is 1.7volt from the top, and 1volt from the bottom.
So expect to use only half of the A/D converter. 9-bits. A resolution of 1/500 of the weight.
Vref must be lower than the supply, so the next one down is 2.5volt.
Less Vref on the sensor, less output from the sensor.
But, I never actually worked with these chips, so don't take my word for it.
I only have some experience with almost the same chips for microphone preamps.
Leo..
looking at http://www.ti.com/lit/ds/symlink/ina125.pdf
it seems to me output is equally low in both +5v and -+15v specifications.
Could adding a resistor to "sense" pin11 increase output ?
also, looking at the PDF, disconnecting pin 15, scould increase output ?
Hi,
Page 12 of this data sheet shows how to connect to 3V single supply.
Note the comments about the two inputs must be more than 1V above ground to get linear performance.
They show 1.5V when the cell is at rest, to allow one input to decrease as the other increases and still stay more than 1V above ground.
AndreK:
32u4's VREF is 5volt due to other sensors , so I wish a 0...~5v output.
The output of the IC can only reach 0volt if there is a negative supply on pin 3.
If not, 0.15volt (0.3volt worst case) is the minimum.
Page 3, bottom of the page, output voltage.
The output of the IC can only reach 5volt if the supply is 5.8volt (6.2volt worst case).
Page 3, bottom of the page, output voltage.
See the graph on page5, bottom right.
It shows the output range on a 5volt supply.
AndreK:
Vref , measured at INA125 pin 4/15 is 3,7v
To generate 5volt Vref, the IC needs at least a supply that is 1.25volt higher than Vref.
Page 11, just above figure 3.
I see now that you are not using INA's Vref to supply the load cell.
The load cell is supplied directly from 5volt.
Connect pin4 to pin14, so Vref becomes 2.5volt.
It is not used.
If it's not working, measure the voltages on pins 6 and 7.
They should be almost equal.
load cell ina125 has output voltage 0 to 2.7 at loading max.10kg having Rg=300 ohms.I want to increase output voltage of ina125 0 to 5 volt.So how can i achieve this?
