Applications of Microcontroller DAC Analog-to-Digital Conversion

Hello everyone, I am Da Yi! Today, I will introduce the topic of the application of microcontroller DAC analog-to-digital conversion. What does analog-to-digital conversion mean? Most of the signals we encounter in daily life are analog signals, such as the amplitude of sound and temperature levels. However, the internal operations of a microcontroller are based on digital signals, which are binary codes consisting of 0s and 1s. Therefore, we need a method to convert analog signals into digital signals, which is the function provided by an Analog-to-Digital Converter (ADC). Digital-to-Analog Conversion (DAC) is the opposite; it converts digital signals into analog outputs.
Basic Concept
The working principle of a Digital-to-Analog Converter is quite simple. It has multiple digital input terminals, each corresponding to different voltage outputs. For example, if we use three input lines, we can create a maximum of eight states (000, 001, 010…111), corresponding to eight different output voltages. Generally, the precision of a microcontroller DAC ranges from 8 to 12 bits, meaning it can output 256 to 4096 levels of analog voltage.
Hardware Circuit
I will take a 12-bit DAC chip as an example. It operates at a voltage of 5V and can output any analog voltage between 0 and 4.095V. The chip’s analog output is connected to the load through a low-pass filter circuit to eliminate high-frequency noise generated during operation. The microcontroller controls the DAC output level through a parallel or SPI interface.
Code Example

#include <regx51.h>

// Parallel 12-bit DAC
sbit DAC_D0 = P2^0;
sbit DAC_D1 = P2^1;
...
sbit DAC_D11 = P2^11;

void DAC_Output(unsigned int value) 
{
    DAC_D0 = value & 0x01;
    DAC_D1 = (value >> 1) & 0x01;
    ...
    DAC_D11 = (value >> 11) & 0x01;
}

void main()
{
    unsigned int dac_value = 0;
    while(1)
    {
        for(dac_value=0; dac_value<4095; dac_value++)
        {
            DAC_Output(dac_value);
            // You can insert some delay here to control the output change rate
        }
    }
}

Application Cases
Digital-to-Analog Conversion is very common in practical applications, such as generating waveform signals, setting reference voltages, and analog output. Here, I will give an example of an application in the field of audio amplification. We can connect the DAC output to the input of an audio amplifier to generate various waveform signals. For example, if we want to play the vowel “ah,” we only need to store the sampled waveform corresponding to the vowel “ah” in the code and then output it point by point to the DAC. If we use 4096 levels with 12-bit precision, it sounds quite good.
Of course, the microcontroller has limited memory and processing capacity. If we want to play streaming audio, we also need to use technologies like DMA and interrupts to enhance real-time data transfer capabilities. However, this part belongs to the domain of audio codec, and we won’t expand on it for now.
Common Questions

1. What should I do if the output waveform has a sawtooth or noise?

   This indicates that your DAC output contains high-frequency components. You can appropriately increase the clock of the filter circuit or raise the DAC operating frequency to output a smoother waveform.

2. What should I do if the DAC output amplitude does not match the set value?

   This may be due to inaccurate reference voltage, circuit malfunction, or zero drift. You need to check the hardware connections and the chip manual, and calibrate or power on again as necessary.

If you want to learn more DAC application techniques, just accumulate experience. That’s all I want to share for now, and I hope it helps you. If you have any questions, feel free to continue the conversation!

Practical Exercises

1. Implement sine wave output through programming.
2. Combine analog signal acquisition and digital-to-analog conversion to output sound and light effects.