I have a device that produces a signal at +/-12V which I want to connect to a ADS1115, I have drawn up 3 different circuits but I am not sure which one would give the best result. The right and bottom circuit would be measured in differential mode.
Or am I just wrong on everything?
The voltage applied to an ADS1115 input must be >= 0 and <= Vcc at all times, where Vcc = ADS1115 supply voltage. That applies to differential measurements as well as single-ended.
Negative input voltages will instantly destroy the ADS1115. It may not a good choice for your project.
What are you trying to measure and how fast to you need to read it. What is your accuracy requirements.
In the above 3 circuits the voltages at the output are all 0 to 4v if I did everything right.
If so, then any of them will work. What does "best result" mean to you?
Its connected to an analouge display of a old piece of metrology equipment, the voltage will be stable so would not have to be read fast.
Giving me the most accurate voltage reading, im not sure which would do that.
That would depend on whether you choose precision resistors. 0.1% precision is the minimum recommended for accurate voltage division.
The resolution of the ADS1115 is overkill even in that case.
Thanks.
-12V to +12V can be reduced to 0-5volt with a three-resistor voltage divider.
Ask Google for online calculators.
The average Arduino A/D will give you about 1000 steps across that 24volt span.
An ADS1115 could in theory do 32 times better than that.
Question is if you need that.
Leo..
