Level reading problem

tangwei8802429

Level reading problem [Copy link]

IO is the input read level value

maychang

I don't know why the original poster wants to use such a circuit. The IO port of the microcontroller can only read high and low levels, in other words, it can only read digital quantities, so P9 must also be digital quantities (high and low levels). P9 may be a dry contact (no power supply, just a contact), relying on the 3.3V power supply to determine whether the contact is closed. If so, there is no need to use a transistor, a resistor is enough. If you are afraid of interference, you can add a capacitor to form a first-order RC low-pass.

tangwei8802429

At that time, I didn't know how serious the interference was, and I didn't know whether the capacitors were clean enough. I wanted to use the unidirectional conduction of the PN junction to prevent the interference source from burning the microcontroller.

maychang

tangwei8802429 posted on 2018-10-17 10:07 At that time, I didn’t know how strong the interference was, and I didn’t know if the capacitors were clean; I wanted to use the unidirectional conduction of the PN junction to prevent the interference source from burning the microcontroller.

How strong the interference is can be estimated from the source of the input signal, the type and length of the wire, the surrounding electromagnetic environment, etc.

曹伟1993

This circuit is designed so that the transistor is always turned on. In principle, the voltage of P9 is always measured. However, this is an ideal situation because the transistor has a voltage drop. Therefore, what you actually measure is not the voltage of P9.

chunyang

Circuit design error, what function do you want to achieve? First figure out the function and make the correct design. For interference problem, first figure out the nature, intensity, spectrum, etc. of the interference, and then take targeted measures.

熊仔饼干

I think this circuit is great. It's pretty good. You should test it. Looking forward to your test results.