Teensy Hearing Aid

I made an enclosure for our device. Enclosures are hard!

Basically, I had to give up on making something attractive and I simply had to focus on making it functional.

Enclosed Tympan in Hand.png

More pictures and a link to CAD files: http://openaudio.blogspot.com/2017/05/enclosing-electronics.html

It sure does take special skills to make something both functional and attractive. Electronics and software is way easier than industrial design. Wow.

Chip
 
I tested the Tympan with three different microphones.

three mics.png

I measured their frequency response and scale factor. It was interesting to see how the microphones performed similarly and how they performed differently.

Calibration for All Mics.png

If you want more details on how I did the calibration (including Arduino sketches, spectrograms and whatnot), you can check it out here: http://openaudio.blogspot.com/2017/05/calibrating-microphones-with-tympan.html

What other kinds of microphones might people find interesting?

Chip
 
That PCB mic looks worthy of a test buy, Thanks for the info. Can you show the parts and circuit on the output to get the gain of 20?
 
defragster said:
That PCB mic looks worthy of a test buy, Thanks for the info. Can you show the parts and circuit on the output to get the gain of 20?
Click to expand...

The mic is connected directly to our audio codec (TI 3206). The codec has a built-in PGA that you simply command to +20 dB and you're done. Codecs are a pain to setup but, man, they sure do integrate a ton of good functionality.

The schematic is here: https://github.com/Tympan/Tympan_Library/tree/master/hardware/Tympan_PCB

Chip
 
After calibrating the system with different microphones, I turned to look at the output side of things. So, I calibrated the output of the system with a pair of my earbuds (inexpensive Klipsch S4). I used an ANSI-standard 2cc coupler and got the following response:

Klipsch Earphone Calibration.png

More details: http://openaudio.blogspot.com/2017/05/calibrating-my-earphones-with-tympan.html

Does anyone have any experience calibrating earbuds? What kind of test fixture did you use? 2cc coupler? Artificial ear? Some sort of homebrew thing?

Chip
 
Hi,

In your circuit you have directly connected the mic to the line in pins. I wanted to know if there is a requirement of pre-amplification stage for that or connecting the mic to line in directly gives a good quality output?
 
Kavyashree said:
Hi,

In your circuit you have directly connected the mic to the line in pins. I wanted to know if there is a requirement of pre-amplification stage for that or connecting the mic to line in directly gives a good quality output?
Click to expand...

The Texas Instruments AIC3206 has a programmable gain pre-amp. So, yes, you can connect a microphone directly to this chip without any additional amplification. For electret microphones, you do need to be sure that you provide a microphone bias (which can be either from the AIC or from your own bias voltage supply), but no additional amplification is needed.

Chip
 
chipaudette said:
The Texas Instruments AIC3206 has a programmable gain pre-amp. So, yes, you can connect a microphone directly to this chip without any additional amplification. For electret microphones, you do need to be sure that you provide a microphone bias (which can be either from the AIC or from your own bias voltage supply), but no additional amplification is needed.

Chip
Click to expand...
Hi

The invensense ICS-40730 has about 9db more SNR than you're PCB mic, but listens from the bottom.
 
If you haven't done so already, check to ensure the audio caps used in teensy are the NP0 types or if you can use film capacitors. Regular ceramics will be noisy.
 
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