My questions are: - What is the function of the 3k3 resistors (R3, R6, R12, R9) on the input of the analog pins of the ADS1115DGS ADC?- Is this circuit more advantageous compared to just measuring the voltage drop of a 250/150 Ohm resistor with the ADS1115DGS ADC?
I need to read a 4 - 20 ma signal from a pressure transducer using an Arduino Mega. I've considered using a 250 Ohm resistor, and measure the voltage drop with the Mega's analog pins, but the 10 bit resolution of the Mega's ADC is not high enough for this particular application.
Referring to channel A0:R3 and C3 are input filtering for the ADS1115's AIN0 inputR1 and R2 form a 150ohm load to ground for the input 0..30mAAt 30mA, there will be 4.5V across R1+R2, and 3v across R2 which is what the ADC will read.It looks like they divided the input to provide a 0v - 3v input to the ADC because there is a 'Power supply selection' jumper giving the option of running this from a 3.3v supply.If you are powering the ADC at 5v and you want to read 4 - 20mA, you can replace R2 with 250ohm and remove R1. Keep R3,C3 for filtering.Yours, TonyWilk
Did you read the datasheet of the pressure sensor.Most of them have a total possible error of 1-2.5%. Way more than a 10-bit A/D (0.1%).You will get more numbers with a 16-bit A/D, but do they mean anything.You could use a 120ohm current sense resistor and the Mega's buildin 2.56volt reference.Add an RC filter between that sense resistor and the analogue pin for protection (like in the module).Leo..
I am sorry, but did you mean they don't ship to Europe or they do ship to Europe. Because I have tried, and they are willing to ship what you need to where I live (Belgium) I don't have a clue where you live though.