On the left side of the figure is a chemical sensor, with current flowing between the 2 pins. Ask experts to teach the working principle of the schematic diagram, whether R19 needs to use a high-precision sampling resistor. Thank you very much!
Jessica postato su August 12, 2020
This is an oscillating circuit, the chemical sensor composition changes, causing the oscillation frequency to change.
The size of R19 affects the sensitivity of the sensor. This circuit should have a calibrated (positive) adjustable resistance.
Samantha postato su August 12, 2020
This is a sensor amplifier circuit. The voltage signal output by the sensor is amplified by the operational amplifier at pin 3.
Ella postato su August 12, 2020
Amplifier 2 and 3 pins are GND, the sensor current flows through the network composed of C8, R15, R14 and R17, the current signal is converted into a voltage signal, R18 and C16 form an RC low-pass filter output.
Sarah postato su August 12, 2020
Coincidentally, the circuit used in a project I have recently used is similar to yours. When I was making a carbon monoxide sensor, the carbon monoxide sensor used was a current source. The current was converted into a voltage through the transconductance of the operational amplifier and output to the AD port of the microcontroller.
