Analog to digital conversion problems, the process of analog to digital conversion

The core principle of these is to read the voltage signal with an AD converter and send it to the microcontroller for processing and display. But the specifics are different.

1. Voltmeter, voltmeter is basically a series sampling circuit, that is, 2-3 precision resistors form a series circuit, and then read the voltage from both ends of the lowest resistance (one end of the resistance is grounded), the resistance value is different according to AD and the measurement range, but at least to ensure that the maximum voltage read can not exceed the reference voltage VREF value of AD.

For example, if the range is 20V, and the sampling network is formed with two resistors, the upper resistor may be 30K and the lower one is 10K, so that the maximum voltage on the bottom resistor is 5V (normally). Of course, it also has a protection circuit design, and the difference between different multimeters is here.

2. An ammeter. The ammeter needs a precision resistor (known resistance value, and high power) as the sampling resistance, when the current flows through the resistor, the voltage drop will occur at both ends of the resistor, read this voltage, using Ohm's theorem, i=u r, you can know the current intensity.

3. Digital thermometer. This is the use of a temperature sensor, which is often a thermistor, and when the temperature changes, the resistance value is not the same. Using the bridge and instrument amplification circuit, the voltage at both ends of the thermistor is amplified N times (n has to be calculated, and it is also a definite value), and sent to AD, when the voltage U is detected, the resistance value of the resistor is calculated by using the amplification circuit and the bridge circuit structure.

Then, according to the list of the relationship between temperature and resistance that is known in advance, the current temperature is obtained by looking up the table.

The principle is basically these, but if you want to do it specifically, there is still a long way to go, under different indicators, the circuit may be very different, if the analog circuit, circuit foundation, single-chip microcomputer capacity is not enough, it is very difficult to do.

Digital voltmeter, digital ammeter, and digital thermometer are all composed of single-chip microcomputer as the core device, plus display circuits.

It is circuitically inexplicable to think of modular electricity.

Digital voltmeters, digital ammeters, and digital thermometers all have one thing in common:

1. Set the comparison value (standard value); Given a comparative voltage on the special foot of the single-chip microcomputer, such as 1V, etc., this voltage must be stable; On the dedicated feet of the microcontroller.

2. Sampling; Input the voltage to be measured (including the voltage drop caused by the current flowing through the resistor, the output voltage of the temperature sensor, etc.) on the special pin of the microcontroller.

3. Comparison; By comparing the standard value with the measured value, the specific value of the measured voltage, current, or temperature can be obtained.

As for the internal calculations, the software does the work.

<> analog-to-digital conversion generally goes through steps such as sampling, holding, quantization, and encoding.

1. Sampling: Sampling refers to the hand-leakage conversion of the high four bits in parallel mode as the converted high four-bit output, and then the digital output is converted to D or A to restore the analog voltage.

2. Maintain and quantize: Maintain and quantize the original input voltage with D or A converter.

The analog voltage of the output is subtracted, and the difference is converted to A or D in the lower quadruple. The digital output of the above-mentioned two-stage A or D converter is then paralleled into the nuclear shed as the total output. The conversion speed has been adjusted to solve the contradiction between increasing the resolution and increasing the number of components.

3. Coding: The coding selection of ADC should not only consider the main indicators such as the accuracy and speed of the application, but also consider the input letter.

The digital quantity at the input side changes by 1 and only causes a change in the relative quantity of the output 1 2 = 1 8, and this value is called a digital-to-analog converter.

resolution. The more bits, the higher the resolution and the higher the accuracy of the conversion.

The digital-to-analog converter resolution can be used as both input binary numbers.

The significant number of digits is given (e.g., if the input signal is a 2-digit binary number, the resolution of the digital-to-analog converter is 2), and it can also be given by the ratio of the minimum output voltage that the digital-to-analog converter can distinguish ("the input binary number - only the lowest digit is 1 and the other is 0" decimal number) and the maximum output voltage ("the input binary number - all 1" decimal number representation).

The resolution of a matter is defined as the value when the smallest bit is 1 and the rest of the bits are 0 divided by the value when all bits are 1. So according to the definition, you have 8 digits, the minimum value is 1, and the maximum value is of course 2 8-1, for example, if you have 3 digits on the mountain, then the maximum value is 7, 2 3-1, right, so there's nothing wrong with subtracting 1.

I hope mine can help you.

The technical requirements for analog-to-digital conversion of software defined radio include the following aspects:

1) The sampling method should satisfy the sampling theorem, and an anti-aliasing filter should be added appropriately;

2) Broadband, such as digitizing analog signals in the intermediate frequency, the bandwidth of the Shinga Burning Signal is usually in the tens to tens of megahertz;

3) Maintain a high dynamic range of the signal;

4) High sampling rate, should try to work in the medium frequency or radio frequency, in order to ensure the softwareization of the whole machine as much as possible;

5) Reduce quantization noise.

The analog-to-digital conversion is mainly to sample the analog Xinzenzi signal, and then the volume segment search is encoded into a binary digital signal. Digital-to-analog conversion is the inverse process of analog-to-digital transformation, which mainly reconstructs the current digital signal into an analog signal. The following describes the methods of sampling and reconstruction.

1 Low-pass sampling.

2 Interpolation formulas.

3 Bandpass sampling.

4 Oversampling.

A converter (also known as digital-to-analog converter, DAC for short) is a converter that converts a discrete signal in the form of binary digital into an analog quantity based on a standard quantity (or reference quantity), and its function is to convert digital quantities into analog devices.

A D converter (also known as an analog-to-digital converter, or ADC) is a circuit that converts an analog signal into a digital signal. The function of the AD conversion is to convert an analog quantity that is continuous in time and continuous in amplitude into a digital signal that is discrete in time and discrete in amplitude.

A D conversion generally goes through four processes: sampling, holding, quantifying and coding. In actual circuits, some of these processes are combined and coarse, e.g., sampling and holding, quantization and encoding are often implemented simultaneously during the conversion process.

The differences between digital-to-analog conversion and analog-to-digital conversion are as follows:

1. The concept is different. In analog-to-digital conversion, the analog signal can only be processed by software after it has been converted to a digital signal by a converter, and it is all achieved through the converter. Digital-to-analog conversion is the conversion of discrete digital quantities into analog quantities of connection changes.

2. Different directions. Corresponding to analog-to-digital conversion is digital-to-analog conversion, which is the inverse process of analog-to-digital conversion. In the same way, the digital-to-analog conversion corresponds to the analog-to-digital conversion, and the analog-to-digital conversion is the inverse process of the digital-to-analog conversion.

3. The object is different. Analog-to-digital conversion is mainly to sample an analog signal and then quantize and encode it into a binary digital signal. Guess Qingye's digital-to-analog transformation is the inverse process of analog-to-digital transformation, which is mainly to reconstruct the current digital spike shouting into a modulus.