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You probably have a bias issue, not gain. If you using the Adafruit Max4466 microphone module (https://www.adafruit.com/product/1063), the two 1Meg resistors bias the input from the mic module to mid supply, meaning that the output of the MAX4466 will be also at mid supply. With something like...

I'm no longer producing the assembled microphone models, but you can order the bare boards on Oshpark: https://oshpark.com/shared_projects/BxlkfMrh Thanks! Leon

Something a little different from my prior audio/LED projects - an inexpensive 241 LED circular array, driven by a Teensy 3.2 to create a pseudo plasma effect. I printed an enclosure with translucent PLA and the infill pattern diffuses the LEDs such that the light smears out in interesting...

Yes, I ran out of the original batch of 45 and decided to retire the mic modules. The demand was good in the beginning but dropped to about one a month toward the end. I figured out that I would have to produce around 200 of them to make this work out and it looked like that would give me a...

I think I understand your question. Yes, mic sounds create an internal voltage that is compared to the voltage on pin 14, TH, or Threshold. When the sound is loud enough, the ACG does reduce the gain in . Table 1 and Table 2 in the datasheet show how you can change the time constants. I used...

Yes, I know that I can simultaneous stream two ADC channels to USB and they show up as left & right to Audacity - that's how I test the mics. Stereo recording to a file on the SD Card is something I haven't tried. Hopefully someone can weigh in on this!

That's have the fun!! "What can I do with these things?!?"

I'd say "Happily, you live in New Zealand!" I've never been there but understand that it's beautiful!! Tindie wants me to create country-specific profiles in order to add shipping costs to orders based on the ship-to location. Given my lack of experience in this, I originally decided to...

I hadn't read up on the differential pairs of ADC inputs. Seems interesting. Are you thinking of an conventional microphone input with phantom power and everything? I'm probably not going to tackle the uSD card reader - I would prefer to keep all digital off the microphone board. I suppose I...

Thank you so much!!!

The signal levels are lower then my set-up - nice low noise floor! Yes, long wires between the Analog Shield and the microphone element will pick-up noise. On my set-up, the mic element is soldered directly to the Shield at a right angle so it points straight off the end. As for the card, I'm...

I recorded a few seconds of "silence" from each. No 172Hz component. I can't get a truly silent recording given my wife is watching the Emmys in the other room! A touch more 60Hz noise on the I2S mic.

Update: I reran the testing using a little test speaker and white noise. Actually, it's a small wooden box with the speaker mounted on the outside pointing in and a small hole on the other side. This lets me generate sounds inside that chamber without a ton of external influence...

I2S mic spectrum Analog mic spectrum Nope - don't see anything like that. Here is the recorder sketch using the I2S microphone: // Record sound as raw data to a SD card, and play it back. // // Requires the audio shield: // http://www.pjrc.com/store/teensy3_audio.html // // Three...

I'm not sure I understand what that second audio input "AudioInputUSB usb1; " is doing. Looking like you're taking audio input from the USB connection and also streaming it back out. Can you simplify the audio blocks as a test to just stream the I2S into the USB? // GUItool...

Okay, I created two "recorder" sketches, one using the adc1 input connected to the analog mic and one with the I2S mic. This obviously means that I can't simultaneously record from both sources but will create two separate .RAW files. Importing these into Audacity and playing them back, I...

Using the recorder sketch seems like a straightforward way to check. It looks to be mono not stereo so I won't be able to get side-by-side recordings on the left and right channels, but should be able to get two files - one with the I2S mic and one with the analog mic. I do have a uSD card -...

Sound better? I'm not sure I have the equipment to judge this based on accurate measurements but here is my setup and results: - Teensy 3.2 with Audio board - microphone element soldered to the Audio Board and tested to confirm pass through to the USB port and Audacity - one of my analog...

That is a fine question and one that I can't readily find the answer to! I'm would guess its the same as the Teensy 3.X series given it uses the same Cortex family but maybe Paul or someone that knows can weigh in. I don't actually have an LC or I'd run a quick test.

It should work pretty well, as long as you use mini-coax cable between the mic element and the amplifier board.

For jpk and endless_harmonics (<cool name BTW), I have added the cost for postage to your countries. It's a shame that the postage is more than the mic!!! If you know of less expensive methods of shipping from US to your country, please let me know!

Changed the sample code to use tft.drawFastVLine to draw filled boxes - got slightly fast refresh times: //****************************************************************************** LCD OUTPUT for (byte i = 0; i < 16; i++){ // cycle through the 16 channels int line1 = level[i]...

Thank for measuring the current draw. I meant to get around to that!!

If it's the capacitor connected to pin 15, that's filtering the optional volume control analog input. If you're not using that, then you should be good.

Glad to hear that it's working fine. I'll go try that speed-up trick with the SPI clock!

If I'm lucky enough to get one, first thing I'm going to do is whistle the "The Bridge on the River Kwai" song into it and have it whistle it back, MIDI style!

Switches = cost, which is why I didn't add them. I figure you'll configure it once and use it that way forever, so the switches add no value after the initial setting. It would be possible to wire up separate external switches but be careful of noise. Long wires going to sensitive parts of a...

Great! Given that I don't test that on every board, there was a chance that it didn't work. I, like Microsoft, let my customers find the bugs.

Wow! That is much faster! Thanks for the tip!! //*************************************************** // Spectrum Analyzer using a Teensy 3.2, TJCTM24028-SPI TFT module w/ 9341 driver chip // Test microphone is connected to A2 //**************************************************** #define...

Instructions for the Microphone Module -

Insert a simple R/C filter on the 5V supply to see what happens. I used 100 ohms and 100uF as approximate values but the goal is to turn that 5V supply into a super quiet reference voltage. Ideally, you'd use an actual precision reference.

With an amplifier between the Teensy pin and the speaker, correct?!? I can recommend the Audio Adapter board, using the Line Out pins to an audio amplifier.

Agreed - you might be able to do this in one stage. The input cap will let you bias the +/- 5V input to 0.6V, with the positive input to the op-amp also biased to 0.6V and then you can scale the op-amp gain to 8.33. This is an LTSpice schematic that should show what I'm thinking.

Wicky21 was asking about sample code using a 240x320 LCD with the 9341 driver. Here is my first pass. The rectangle fill method I use seems slow, so I'll be playing with options to speed it up. If you know of the fastest method to draw filled rectangles, please let me know...

1) Longer cables - I haven't tested with any longer than 20cm (9") but seems like a good thing to try! I'll use a chunk of shielded headphone cable; shield = GND, Red = 3.3V and White = mic signal. This won't be ideal because noise from the 3.3V will get onto the mic signal, but it'll still be...

By the way, I'll be testing every microphone using the test set-up described in this YouTube video: https://youtu.be/Vb1vDsfh-GY Thanks! Leon

The first production batch just came in today and work fine! I'm very impressed with PCBway as a manufacturer - great communication, good component pricing and faster delivery than I was expecting. Anyway, you can find them on Tindie...

I'm going from memory but isn't the gain for a non-inverting op-amp 1 + Rf / Rin = 1 + 100K / 1.5K = 67.66. Can someone check my math?? I like that little virtual ground part!! Gotta play with that! Great project!!

I'm not sure - that's probably buried in the MK20DX256VLH7 datasheet somewhere. Otherwise, Wikipedia says: Conceptually the Cortex-M4 is a Cortex-M3 plus DSP instructions, and optional floating-point unit (FPU). If a core contains an FPU, it is known as a Cortex-M4F, otherwise it is a...

I'm assuming that you're trying to create some type of portable analysis system using a Teensy and are keen on making it small, battery powered and need to make decisions based on what sounds you hear. Otherwise a good laptop plus a instrumentation microphone and Mathlab would work better for...

Boards on order! I'm using PCBway for the first time. Costs seem reasonable so now we'll see what their production and shipping times are like. I'll update again when I have some concrete dates.

You know that I am!!

By the way, I'll be putting them up for sale on Tindie as soon as I get a batch made. When they're available, I'll post a shameless plug. For sure, in time for the holidays and they'll make a wonderful stocking stuffer for that special Teensy hacker on your list! Thanks to all the Alpha and...

I would suggest not filtering the mosquito buzzing sound until you've capture sufficient audio samples to confirm that you have all the interesting frequencies. Don't trust your ears - sample fast and then analyze the frequency content. I'll bet the Teensy 3.2 is fast enough that you can run...

Sounds good - I just sent you a private message via the forum board. You can do the same by clicking on my forum name and selecting private message.

Qty Parts Value Description DigiKey Manufacturer 3 C1, C2, C9 0.1uF CAPACITOR, American symbol 399-1170-1-ND Kemet 1 C3 100uF POLARIZED CAPACITOR, American symbol 478-8156-1-ND* AVX 1 C4 0.022uF CAPACITOR, American symbol 399-1163-1-ND Kemet 1 C5 2.2uF CAPACITOR, American symbol 399-3522-1-ND*...

The ferrite along with C1 and C3 act as a fairly heavy filter for noise coming from the Teensy. Most of the holes are vias to connect the ground plane on the bottom to grounds on the top side to help reduce noise. I removed the mounting holes from the board because I was running out of room :)

Adding the schematic to help show the design:

YouTube video - code // Spectrum Analyzer using a Teensy 3.2 & the Adafruit 1.8" TFT module w/ ST7735S chip // Test microphone is connected to A3 // Adding some FastLED code to test interaction //*********************************************************************************** INIT //...

A quick test of the Auto Gain Control circuit. Top waveform has it enabled and the bottom has it defeated by shorting out a level set resistor. Based on popular feedback, I need to add a convenient way to shut that AGC off. // Teensy 3.2 to stream audio from analog channels to USB // Test...