Hardware design-audio circuit and headphone interface line control principle
1. Take the CJC6811A chip as an example to introduce the analog audio circuit part
The analog pins are as follows:
20PIN, MIC_BIAS: DC bias voltage of MIC;Output, also used for button detection voltage
a> 21PIN, MIC_IN: MIC input signal; input 0.1UF capacitor isolation
22PIN, ADC_IN: analog-to-digital conversion signal; used Button detection
25PIN, HP_L: left channel;Sound output, 100U capacitor is connected to the headset, which can simulate the switch and output to the speaker through the insertion detection of the headset. , the audio is amplified through the power amplifier in the middle.
26PIN, HP_VCOM: left and right channel reference voltage; 2.2uF capacitor to ground
27PIN, HP_R; right channel; For sound output, a 100U capacitor is connected to the earphones, which can simulate a switch and output to the speaker through the insertion detection of the earphones, and the audio is amplified through the power amplifier.
28PIN, Codec_Vmid: encoder-decoder reference voltage; 2.2uF capacitor to ground
30PIN, USB_DM: USB2.0 signal;
31PIN, USB_DP: USB2.0 signal;
The above picture shows the analog switch for channel switching through headphone insertion detection.
GPI02---->Headphone insertion detection
GPIO0–> Output 1 when the headset is not inserted, output 0 after inserting the headset
GPIO3–> Output 0 when headphones are not plugged in, output 1 when headphones are plugged in
2. Principle of headphone interface
2. 1 Headphone insertion detection principle
The schematic is as follows. GPIO2 is the MCU detection pin. When the headset is not plugged in, gpio2 is pulled high. When it is plugged in, it passes through the coil of the left channel in the headset to ground, and is pulled low at this time. MCU can identify and detect.
2. 2 mic principle input
The mic is DC biased through MICBIAS, and the sound signal is converted into a voltage signal by the MIC sensor through vibration, and then is blocked by a capacitor, and the MCU obtains the sound waveform.
2. 3 Button recognition principle
There will be three buttons on the headset. Here is a brief introduction to their recognition principle. As shown in the figure below, the key recognition is through the MIC pin, which is connected to the ADC_IN pin of the MCU to identify voltage changes. This is achieved by using different resistors to short-circuit the mic line. If a resistor of about 220 ohms is used to short-circuit the mic, the volume will be reduced. If a resistor of about 1k ohm is used to short-circuit the mic, the volume will be increased.
