Project: Add external microphone to Home Mini

Talk about any modifications to Google Home
jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Project: Add external microphone to Home Mini

Post by jonathan »

A member has commissioned us to look into adding a microphone jack to the Home Mini so we will be using this thread as a project log. I will also be making a video of the progress. Stay tuned!

*Update* - We succeeded and the mod kit is now on sale here. https://www.snektek.com/shop/index.php? ... uct_id=108
curtdissel
Posts: 5
Joined: Sat Feb 03, 2018 7:40 pm

Re: Project: Add external microphone to Home Mini

Post by curtdissel »

Message from friend working on similar task:

Hello my name is bernie, thank you for your time. I have attached two pictures (Front and back) of the Alexa dot and google home. I am looking for a method to be able to tap into their circuit to add my own digital I2R signal. The problem im facing is that all of my wiring gauges are to big to tap in to the circuits. Would appreciate any input you may have.

Ps: Im not even shore this may be possible with out destroying the board with a soldering iron.
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jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Re: Project: Add external microphone to Home Mini

Post by jonathan »

Hi Curt. We are taking a similar approach. We will de-solder the microphones with a hot air station and tap into the signals with small wire. It is doable, with the right equipment. I don't suggest you attempt this if you don't have hot air ability.

PS. Those are some nice pictures.

Jon.
curtdissel
Posts: 5
Joined: Sat Feb 03, 2018 7:40 pm

Re: Project: Add external microphone to Home Mini

Post by curtdissel »

Hi Jon,

My friend is having issues picking a hot air station for this task. any recommendations? we see some for 40 dollars, some for 60 dollar and others over 100 dollars. We didn't want to grab a cheap one that wont even get the job done.
jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Re: Project: Add external microphone to Home Mini

Post by jonathan »

curtdissel wrote:
Mon Feb 05, 2018 11:23 pm
Hi Jon,

My friend is having issues picking a hot air station for this task. any recommendations? we see some for 40 dollars, some for 60 dollar and others over 100 dollars. We didn't want to grab a cheap one that wont even get the job done.
I use one that looks like this and it works pretty well, although the switch broke and I had to replace the fan once.
hotair.jpg
Any model with adjustable air temp should work though.

On my end, I bought the ADC analog to I2S breakout boards a few days ago, now it's a waiting game until they show up.

Jon.
curtdissel
Posts: 5
Joined: Sat Feb 03, 2018 7:40 pm

Re: Project: Add external microphone to Home Mini

Post by curtdissel »

thanks, we were actually ripping apart analog digital converters, but the breakout board is a not cleaner of a solution. Do you think this one will suffice? Seems to be cheap. ~$5 dollars. http://www.kr4.us/Breakout-Board-for-MC ... gJi9vD_BwE
Attachments
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jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Re: Project: Add external microphone to Home Mini

Post by jonathan »

curtdissel wrote:
Mon Feb 05, 2018 11:37 pm
thanks, we were actually ripping apart analog digital converters, but the breakout board is a not cleaner of a solution. Do you think this one will suffice? Seems to be cheap. ~$5 dollars. http://www.kr4.us/Breakout-Board-for-MC ... gJi9vD_BwE
No that won't work, that is an Digital-to-Analog converter (DAC), so more for analog signal generation. And even then it's not really suitable for audio (and incompatible with home mini and echo) since it's not I2S capable.

I ordered this:

https://www.ebay.ca/itm/112679662396
pcm1808.JPG
jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Re: Project: Add external microphone to Home Mini

Post by jonathan »

I have received the ADC breakouts, will proceed with experiments
jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Re: Project: Add external microphone to Home Mini

Post by jonathan »

So David and I took apart the mini and desoldered a microphone. Here's what that looked like
20180306_011623_HDR.jpg
By taking the microphone off we were able to identify the model number by comparing the various datsheets to the PCB footprint.

Turns out we were wrong about the microphone being i2s, it is actually a PDM microphone. PDM is a digital signal where a high frequency pulse density represents the frequency of the audio wave.

We verified this with the oscilloscope and saw the PDM waveform.

Now we need a way to convert a line in signal to PDM. From our research this far, we were not able to find an IC that does this. The closest thing we found is an electret Mic preamp which is not ideal but should work. We would take the line in signal and divide it using a voltage divider to get the millivolt signal expected by the preamp.

David is looking into alternative solutions.

Stay tuned.
jonathan
Posts: 189
Joined: Thu Feb 01, 2018 1:12 am

Re: Project: Add external microphone to Home Mini

Post by jonathan »

David's been working on generating the PDM on an STM32F103, will update on that soon.
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