We are a FIRST robotics team of students doing a project on Water Quality. We are trying to use the Particle Electron to create an inexpensive remote water quality meter.
Our plan is to emulate this arduino project using the Electron, but the assumptions in the project are difficult to translate to the Electron. The problem is the differences between the Electron and the Arduino.
Specifically, the project creator (M. Ratcliffe) has documented this diagram:
Vin = the voltage supplied to the sensor
Ra= the resistance of the digital pins (on the Arduino)
Vout = the voltage to be measured.
Rc = The resistance to be measured/calculated across the sensor
R1 = a fixed resistor (that we need to select for our design)
He then proceeds to calculate a value for R1 that will give good resolution to Vout (and subsequent calculations for Rc). A key assumption is that Vin is 5VDC, and Ra for the Arduino pins are 25ohms.
Would we use Vin of 3.3VDC for the Electron? What about Ra? What value for fixed resistor R1 should we choose to give good resolution for the expected range of Rc values? Note that we expect Rc to be between 114 ohms and 2195 ohms based on the temperature and dissolved solids in the water.
We can probably handle the programming if we can get the hardware worked out. Thanks in advance for helping out the newbies.