I intend to use air contaminants sensor TGS 2602. The internal resistance changes if a given gas is detected. It requires an input voltage
V_C = 5V to operate.
According to the specs, the basic measurement circuit is:
The problem I am facing is I want to read the measurements with digital IO pins, specifically I want to use Raspberry Pi for this. I found a simple solution to a similar problem here: Reading Analogue Sensors With One GPIO Pin. Essentially it involves using an RC circuit and measuring time lapsed until "high" voltage occurs on our digital pin.
In this case I would then be inclined to simply switch
R_L with a capacitor but by doing this I would quickly cut off the supply voltage for the sensor (it requires
V_C). I then thought I should maybe add the capacitor in parallel with
R_L. But the
R_L voltage drop is low, so I would never reach the "high" voltage on the capacitor to be able to read it with my digital pin. Should I perhaps use op-amp to drive the
V_RL up? But is it not over-complicating things?
My question is then how should I measure value of
R_S with a digital reader?