Hi - I have an existing Pi Zero project in the car that uses a MAX31856 SPI thermocouple board to measure exhaust gas temps and pulls boost, RPM and temp data from the existing OBD2 system.
I’d like to add an independent boost pressure sensor using a generic 3 wire pressure transducer that outputs 0.4-4.5V, so I need an appropriate ADC. Would the ADS1015 (I2C) be appropriate?
That might be a little tricky as your Raspberry Pi will be expecting digital logic levels of 3.3V and the full-scale measurement range of the ADC depends on the supply voltage. Powering the ADC at 5V will give you the measurement range you need but the digital output will also scale accordingly and be too much for the Pi.
If you use a logic level shifter between the ADC and the Pi it should work ok.
I’ve included the section of the datasheet below which outlines the limitations.
Thanks Trent -
My sensor will have a full scale reading of 100psi, but in my application will only need 0-30psi. So the max sensor voltage will be around 2V.
So, if I power the ADC at 5V, does that mean I should get away without the level shifter?
While that may work for the Analog side of the ADC it won’t bode well for the digital side that connects to the Pi. The digital output from the ADC can be anywhere between 0.7 x VDD up to VDD, so if you run the ADC at 5 volts you may have a 5-volt digital signal being fed into your Pis digital inputs which will damage them.
Thanks Trent - understand. I found a post suggesting that these pressure transducers still provide a linear signal voltage at 3.3V, so just ordered the ADS1015 ADC and will try running the whole setup at 3.3v. I may need to calibrate to a known reference pressure - will see how I go.