I'm trying to figure out how to wire the ADS1115 ADC to work with a 4-20mA sensor, and reading the ADS1115 with a 5V arduino uno over I2C.
The sensor is for measuring water depth and the only specs the producer/seller provides is 24V, 4-20mA and 0-5m depth range, nothing about wiring. In normal operation the sensor will be at around 2m under water and the water level will vary about 0.5m from highest to lowest.
From what I've found on the internet, there needs to be a resistor between the A0 pin and GND to bring the voltage down to not fry the ADC.(see attached picture) I've found someone saying it should be 50 Ohm and someone else saying 250 Ohm, but does anyone know how big this resistor should be?
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250ohm for the analogue input of a 5volt Arduino on default Aref (20mA produces 2500.02= 5volt).
51ohm if you use the more stable internal 1.1volt Aref (510.02= 1.02volt).
Both above values are for using the Arduino 10-bit A/D, which could give you ~800 A/D values (steps) over that 5meter range.
If you plan to upgrade to a 16-bit 15-bit (single ended) ADS1115, then 100 ohm with a PGA gain of 2 could be used.
Googling "ADS1115 4-20 site:arduino.cc" might give you a head start.
Leo..
Wawa:
Googling "ADS1115 4-20 site:arduino.cc" might give you a head start.
Leo..
Ok. Thanks.