How to use AD to measure the resistance of a single chip microcomputer, and how to detect the voltag

Ignoring the influence of temperature and other factors, the method of measuring voltage by series resistance can be directly adopted.

The principle is to use a high-precision resistor with a known resistance value [assuming r0], connect a measured resistor [r1] in series, and add a stable DC power supply [v0] to both ends of the series resistor, and use a single-chip microcomputer.

AD detects the voltage across R1 [v1], via Ohm's law.

The formula can calculate the resistance.

r1v1=———x v0

r1+r0)

Convert: v1

r1=———x r0

v1+v0)

v0 and r0 are known, and r1 can be calculated for the value detected by v1 bit AD.

Schematic diagram of the circuit.

The internal AD of the single-chip microcomputer can only measure the voltage, if there is a constant current source, the resistance to be measured can be connected to the constant current source, measure the voltage at both ends, and calculate its resistance, or it can be connected in series with a known resistance, add a stable voltage at both ends of them, measure the voltage at both ends of the measured resistance, and also know the voltage on the other resistor, according to the voltage division relationship of the two resistors, the measured resistance can be obtained.

As upstairs, you'll need to determine the approximate range first. I'm going to talk about the process and the idea. The measuring resistor must first have a stable standard voltage and a resistor, and then connect it in series with the resistance to be measured on the standard voltage. Then obtain the voltage values at both ends of the resistor and calculate.

According to the data given to you by the thermistor manufacturer, write it yourself and put it in the ROM, and there is an example table lookup program in the MCU book.

1；The positive capacitive pole of the solar cell and the positive pole of the battery are connected together, and the two negative poles are charged through the MOS switch, so the ground is not supplied;

2；The VBAT in the figure below is the 12-24V solar cathode and the battery cathode, and the Vat is the solar voltage; VGND is the voltage of the solar negative electrode to the ground of the single-chip microcomputer, and PV-VO is the voltage of the IO port of the single-chip microcomputer.

3；Some people may ask if the voltage of the battery changes, isn't the voltage of the detected solar cell also changing? Rest assured, because all the voltages in the formula are based on the single-chip microcomputer ground as the reference 0 point level, because the positive pole of the solar cell and the positive pole of the battery are connected together, we change the angle, take the vbat as the reference 0 level, the ground of the single-chip microcomputer and the ground of the solar energy are both negative levels, and the battery voltage decreases, indicating that the ground of the single-chip microcomputer is closer to the 0 level, VGND will not change, and the PV-VO voltage will also be closer to the 0 level, and the final V will not change.

That can use the AD converter chip with I2C interface, so that it can be detected by opto-decoupling isolation.

Introduce a reference ground, but the voltage has to be processed.

Multiple differential operational amplifiers are used to access multiple differential voltage signals, so the voltage signal output by the differential op amp is generally co-ground with the single-chip microcomputer or AD chip, which solves this problem. Undertaking, single-chip microcomputer, circuit board, controller development and customization.

Is this problem solved?,I don't know exactly what the principle is.。

There are many ways to measure resistance:

1. Constant current source: Some chips, such as LM334, are themselves a constant current source. Let the constant current flow through the measured resistor, and then use AD to measure the voltage (the voltage is too small, use a proportional amplification circuit composed of an operational amplifier to amplify it), send it to the microcontroller for analysis, and calculate it upside down.

Assuming that the current is 1mA (this current is what you know when designing the constant current source), and the measured resistance is assumed to be about 100 ohms, then the voltage generated after the current flows is about 100mV, but this voltage is too small, AD detection is not very convenient, you can take a magnification of 20 times the amplifier (the multiple of the amplifier is also calculated according to the circuit in advance, belongs to the known quantity), and amplify the voltage to about 2V. After detecting the result (e.g., and then working backwards, divide by 20 and then divide by 1mA) to calculate a more accurate resistance value.

2. Bridge method: This is a little troublesome, to use bridge balance, differential amplification and other circuits, you need to check the network information, not a few words can be clear.