Hello,
I have source I want to read voltage from. It varies between 1.5-4 volts. I only need reading from 1.5 to 2.5 volts, but i would like to have good resolution. So, is it possible to read it with gain setting of 4 (+-1volt) ?
You might be better helped if you posted a picture of a hand-drawn wiring diagram and all the source code. If possible, some serial monitor output showing the existing results with a statement of what is wanted.
Also try to put the code
I doubt you understand differential readings.
Differential is the difference between two voltages, but they both must be between Gnd and VCC.
For a single voltage up to 4volt, use PGA 1 (4.096volt max).
That will give you a 15-bit resolution, assuming you have a genuine ADS1115.
Leo..
I do not have any code nor wiring yet. I'm trying to find out if ads1115 is suitable for this.
So, If i use pga 4 setting then I will not get any reading? (As the voltage goes above the 1.024v?)
On PGA4, any voltage above 1.024volt will peg the A/D to it's maximum value.
PGA1 and 1.5volt to 4volt will give you a very high resolution (4.096volt / 32768 steps).
More than enough for e.g. battery measurements.
Leo..
For 4 volts I would need measuring accuracy of 0.05mv or greater. I have EMF sensor I want to measure.
4.096 / 32768 = 125uV steps.
Tell us more about this EMF sensor.
The ADS might be too slow for the frequency too.
Leo..
Okay. I did some miscalculations. Seems that it is enough.
Its old analytic balance with emf load cell. It's making voltage to change from 4 volts (0 grams) to 1.5 volts (60 grams)
Accuracy is 0.0001g for the scale, bit unfortunately the original pcb Don't have output for arduino, so I have to take the reading straight from the sensor.
24-bit HX711 breakout boards are commonly used for load cells, not ADS1115.
The HX711 also provides a stable excitation voltage (4.25volt) for the load cell.
Leo..
Since the ADS1115 resolution is 15 bits plus sign, there are 32767 steps between 0V and 4.096V or roughly 7 milligrams per ADC step. That seems hardly worth the effort.
24-bit HX711 breakout boards are commonly used for load cells, not ADS1115.
The HX711 also provides a stable excitation voltage (4.25volt) for the load cell.
Leo..
How do I connect the hx711 to scale? Can it read values from 1.5volts to 4 volts?
I looked datasheet and seems that maximum voltage is supply voltage minus 1.5 so 3.5 volts.
I did calculations and get result of 3 milligrams. How did tou calculate yours?
No, the HX711 is useless for your application.
You need a 24 bit ADC with an input range of at least 4V
The LTC2485 might be an option
It was recently co-developed and tested by @vitaliykrym here
So, if I have ground and two inputs 5v stable and 3-4 volt changing can I use the more accurate input? (Pga 2)
All the inputs have the same accuracy
I meant the voltage range. Voltage from ground is over 2v , but voltage difference is under 2 volts. So, is the pga 2 range from ground or difference between voltsges?
So set the gain for a FSR (Full Scale Range) of +/-512mV
Connect your 1.5-2.5V signal to AIN0 and connect 2V to AIN1.
The differential signal will be +/-500mV
The resolution will be 1.024V/(2^16) = 15.625uV
In your code add 32768 to make it positive
If you need higher resolution then you will need a 24 bit ADC
The ADS can only measure the difference between two physical points.
Leo..
Thank you!
I'm getting stable reading with this and will get my desired accuracy of 0.0005g I'm using +/-256mv range. It will suppress some of usable range from scale but I don't need it anyway, so not big deal.