Pi zero analogaudio

Pi-Zero-Analogaudio

The Pi-Zero is a stripped down board, there is no analog audio jack like on the bigger Pis. But it is no problem to add it using a few simple and cheap components.

The schematic

shows the necessary parts and the wiring. Basically, you configure the Zero to output pwm-signals, then you use a combination of a lowpass and highpass filter to clean the signal on every channel.

The audio quality is ok, but not on hifi level. The filters limit the frequency range and the signal is still not absolutely clean afterwards. If you really need high-quality audio-output, use HDMI, bluetooth or attach an audio-hat based on I2S using a DAC.

Hardware

Required parts:

• two resistors 270 Ohm
• two resistors 150 Ohm
• two capacitors 33nF
• two capacitors 10µF
• an 3.5mm audio-jack (e.g. STX-3120-5B from Adafruit)
• some jumper-wires

In the folder kicad you can find a complete pcb, designed for the above throughhole components. You will need to adapt the design if you use a different audio-jack.

Software and System Configuration

You don't need special software, just use aplay to play wav-files or e.g. mpg123 for mp3-files.

You can configure the system manually, or you can clone the repository and just run the install command:

git clone https://github.com/bablokb/pi-zero-analogaudio.git
cd pi-zero-analogaudio
sudo tools/install

The install command will add the following lines to your /boot/config.txt:

dtparam=audio=on
dtoverlay=pwm-2chan,pin=12,func=4,pin2=13,func2=4

This configures analog-audio for the physical pins 32 and 33. Other pin-combinations are possible, see the file /boot/overlays/README for a complete list.

In addition, the install command runs

amixer cset numid=3 1

This switches the audio-output from auto (0) or HDMI (2) to analog-out (1). You can also use raspi-config for this task (or for switching back).