The first question: This should be a simple second-order low-pass active filter, right? The second question: the actual output voltage of the amplifier should not be independent of the power supply voltage, but what I have measured now is that when LM358 is powered by 12V, when CT1, CT2, CT3, and CT4 have no input voltage, the corresponding FB1 The voltage is 0V, which should be normal, but the FB2, FB3, and FB4 ports have a voltage of about 10V. Is this abnormal? But I don't know what is going on?
After filtering, it is directly connected to the ADC port of the microcontroller. At this time, the 10V voltage is very high, and the microcontroller immediately starts to heat up, and the 3.3V voltage supplying the microcontroller rises, slowly reaching about 3.8V. This is horrible, please help me analyze and analyze what went wrong, now I am at a loss
Eman Posted on January 12, 2021
CT1~CT4 cannot be left floating, but a resistor can be pulled down to GND. It is necessary to limit the four input voltages not to exceed the power supply of the MCD, otherwise the output of the op amp must be connected to the port after a series resistance.
Hubert Posted on January 12, 2021
When you experimented, where did CT1～CT4 go? What does "no input voltage" mean? Is it floating or grounded?
Arvin Posted on January 12, 2021
Well, I made two boards, but they didn't connect together during the test, so they were left in the air.
Kanye Posted on January 12, 2021
It is possible that your external signal source is different. If it is low level, it means that there is no input voltage, then any one of them must output 0V. If you just leave it open, it means that there is no input, then the value of the output is basically normal. of.
Each CT terminal connects a relatively large such as 100K resistor to the ground, it must be normal.
By the way, for the simple circuit without amplitude limitation, it is not acceptable to directly send the MCU to the MCU. Once the output exceeds the MCU VCC, the lighter one will not work properly, the heavy one will burn the MCU. A suitable current-limiting resistor must be added, preferably a voltage regulator tube clamp, before it can be sent to the MCU for processing.
