Line-In/AUX Input to a Dragonboard

For my next project, I really wanted to do something based on audio, something like a visualizer. But… How to you take audio input on boards that have just audio output that too via HDMI.

After thinking for a bit an idea sparked, the Dragonbord(s) have mic input, so why not plug the Aux into that? Well, as it turns out the voltage levels of line-out and mic are fairly different, about +/- 2v for line in and +/- 1.6v for the mic input.

But How?

Not an electronics guy… so i went to the forums…

• Step 1: Have a problem?
• Step 2: Ask on the 96Boards forum…
• Step 3: Get questions answered…
• Step 4: ???
• Step 5: Profit!

And i ended up with this schematic to bring the Line-In levels down…

• R1: 22K Ohms
• R2 R3: 2.7K Ohms
• C1: 22uF

Note: 1.8v Mic Bias pin on the audio header is not enabled by default, but you can use the 1.bv pin on the Low-Speed header

… and it looks something like this:

And finally I am able to record Line-In audio on a dragon-board using audacity!

I have just tested this on a DragonBoard410c, but since the 820c also has an audio header it should work as well…