I'm seeking assistance with a project that involves the Tracker ONE (523MEA). My goal is to publish real-time data from a 5v analog type sensor, specifically a pressure sensor (https://www.amazon.com/Pressure-Transducer-Sender-Sensor-Stainless/dp/B07W98P6NV). The first step should be to solder the 3-pin sensor to the M8 cable. Which pins should I use for 5v power and data reception? From the diagram, it appears that I should use Analog A3 (3); CAN 5v (6); CAN - (7); however, I read that: 'Note that Serial, I2C, GPIO, and ADC on the Tracker SoM can only be used at 3.3V maximum. The pins are not 5V tolerant!' Isn't A3 a GPIO?
You can power from CAN_PWR and GND, which will be 5V when CAN_PWR is enabled.
However, if the sensor actually outputs 0 - 5V, you will need a voltage divider to make a maximum of 3.3V on A3. The maximum voltage on any nRF52 digital or analog input pin is 3.3V.
CAN+ and CAN- are not GPIO; they're differential and connected to a CAN transceiver.
Thank you for the clarification!
My concern is that the sensor uses output voltage to measure pressure. For instance, if the sensor has a range of 0 to 10 bar, and the output voltage reads at 2.5V, then the pressure would be calculated as: Pressure = (2.5V / 5V) * 10 bar = 5 bar, approximately. If I limit A3 to a maximum of 3.3V, this could potentially limit the sensor's functionality. What alternative solutions could be pursued? I know 3v3 pressure transducers do exist, but they are as scarce as water in the desert. I could use an ADC, in that case which pins should I use?
What would you recommend?
@martin.iot, @rickkas7 suggests a voltage divider (using 2 resistors) to scale the 0-5v range to a 0-3.3v range. The ideal ratio is 1.52 or so. So at the 2.5v output of the sensor, the voltage input to the ADC is 1.67v, well within the ADC's range and not constraining the sensor's output.
What peekay123 said. I like to use 10K on the high side and 18K on the low side, which leaves a little safety margin and uses standard resistor values. It has a maximum of 3.214V.
The other thing I like to add is a D1213A dataline protection diode and TVS. It protects both against transients and also if the input exceeds 3.3V. The D1213 saved me once when I was using a 12V powered sensor with a 0-5V output with a similar voltage divider. I discovered if the sensor ground was loose it would output close to 12V on the 5V output, which would have fried the ADC if not for the protection diode.
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