Analog MIC

The Analog MIC input on the Axon board provides a flexible interface for acoustic sensing using a broad class of analog microphone technologies. Axon provides support for mics of different types and companies at the same time preserving dynamic range while minimizing noise.

Wiring and connectors

For Single ended mic:
- Mic output → ANALOG_MIC pin (+)
- Mic ground → GND (GPIO GND) on axon header
For Differential mic:
- Mic output → ANALOG_MIC pin (+)
- Mic ground → ANALOG_MIC pin (-)

How to Setup

Follow these steps to connect and use an analog microphone with the Axon board.

1. Connect the microphone

Connect your microphone to the Axon board:

If you are using single interface mic, just connect MIC_OUT to ANALOG_MIC PIN (+) and Microphone ground → Axon GND (Connect to GPIO GND)
Otherwise if you are using differential mic, connect MIC_OUT to ANALOG_MIC PIN (+) and MIC_GND to ANALOG_MIC PIN (-)

Refer to the Axon pinout documentation for exact pin locations Axon Pinouts

2. Detect the microphone

Boot the Axon board and open a terminal.

Run:

arecord -l

This will list available recording devices.

Example output:

  vicharak@vicharak:~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: rockchipes8388 [rockchip-es8388], device 0: dailink-multicodecs ES8323 HiFi-0 [dailink-multicodecs ES8323 HiFi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: rockchipdp0 [rockchip-dp0], device 0: rockchip-dp0 spdif-hifi-0 [rockchip-dp0 spdif-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: rockchipdp1 [rockchip-dp1], device 0: rockchip-dp1 spdif-hifi-0 [rockchip-dp1 spdif-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 3: rockchiphdmi0 [rockchip-hdmi0], device 0: rockchip-hdmi0 i2s-hifi-0 [rockchip-hdmi0 i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 4: rockchiphdmi1 [rockchip-hdmi1], device 0: rockchip-hdmi1 i2s-hifi-0 [rockchip-hdmi1 i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Look for rockchipes8388, it contains ES8388 which is an analog audio codec chip, which handles: audio.
Note down the device and card number to be used in below commands
In this example: card 0, device 0 → plughw:0,0 is used

3. Record Audio from Microphone

Prerequisites

Ensure:

Microphone is properly connected to the SBC
ALSA utilities are installed

Install if needed:

sudo apt install alsa-utils

Step 1: Record Audio

Record audio using:

arecord -D plughw:0,0 -f S16_LE -r 16000 -c 1 test.wav

Parameter Explanation

Parameter	Meaning
`-D plughw:0,0`	Select microphone device
`-f S16_LE`	16-bit signed little-endian format
`-r 16000`	Sampling rate (16 kHz)
`-c 1`	Mono recording
`test.wav`	Output file

Step 2: Stop Recording

Press:

Ctrl + C

The audio will be saved as test.wav

Step 3: Playback Recorded Audio

Verify recording:

aplay test.wav

Recommended Settings for Speech Applications

Use:

arecord -D plughw:0,0 -f S16_LE -r 16000 -c 1 speech.wav

This configuration is ideal for:

Speech recognition
Voice assistants
Embedded AI applications

Notes

Use plughw instead of hw to allow automatic format conversion
16 kHz mono is sufficient for most voice applications
Higher sample rates (e.g., 44100 Hz) may be used for higher quality audio

Example:

arecord -D plughw:0,0 -f S16_LE -r 44100 -c 2 audio.wav

Troubleshooting

Quick Diagnostic Commands

List supported hardware parameters:

arecord -D hw:0,0 --dump-hw-params

Check microphone levels:

alsamixer

Press F4 → Capture devices

Increase capture volume if needed.

—

No audio detected

Check the following:

Microphone is connected correctly
Ground connection is secure
Microphone output is connected to MIC input
Device is visible using:
```
arecord -l
```
Capture volume is not muted:
```
alsamixer
```
Press F4 and increase Capture volume.

—

Low audio volume

Possible solutions:

Increase microphone gain using:
```
alsamixer
```
Use a microphone module with built-in amplifier
Move closer to the microphone

—

Excessive noise or interference

Check the following:

Ensure proper grounding
Keep microphone wires short
Avoid routing microphone wires near power or digital signal lines
Use shielded cables if necessary

—

Hum or buzzing sound

Possible causes:

Ground loop issues
Poor shielding
Electrical interference from nearby components

Solutions:

Ensure common ground between microphone and Axon
Use shielded microphone cable
Keep microphone away from power sources and high-frequency components

—

Verification Checklist

Ensure the following:

Microphone is securely connected
Microphone appears in arecord -l
Audio recording works using arecord
Audio playback works using aplay
Capture volume is properly set using alsamixer

Speakers

Axon Video Interface