Questions around sound reative project I'm designing - Page 1
Forum section: electronics / beginners

author: szenk
author_rank: Newbie
timestamp: July 25, 2022, 04:42:34 am
content: Good evening, all. Let me start by stating I hope I'm posting this in the appropriate area, and I apologize if that's not the case.I'm currently designing a project that is intended to be worn at music festivals and light up (dance) with the music being played. The board will need to stay as small as possible so there are some constraints on what all I can fit on there. I am fairly experienced in designing PCBs but for whatever reason, have a hard time designing audio circuits. It feels like for me the more research I do, the more questions I have.I'll start with my component selection first as it stands now:-200mAh Li-Ion battery-ATMEGA328P-MU microcontroller (luckily I have a small stockpile from before the insane price hikes)-MAX4466 Amplifier-CMA-4544PF-W Electret microphone-MCP73831/2 single-cell Li-Ion charger-14 APA102 2020 RGB LED'sMost of my selection has been based on products I've found on Adafruit's website. The fact that they share their schematics and PCB design on their products can be really helpful in getting a project started but of course, if better selections can be had, I'm open to changing them.the questions I have revolve around their Electret Microphone Amplifier - MAX4466 with Adjustable Gain product.looking at their schematic I see they've included an HPF C4 & R5 (which they've mislabeled as an LPF) I'm curious if a BPF would be better suited as I'm more concerned with frequencies between 20hz to 3khz?As for C2, I'm assuming that is meant to only allow positive AC cycles through to be amplified. If that is the case, shouldn't it be a polarized capacitor? also, what would be the best way to allow the full signal through without hurting the ATMEGA328 Analog input? Bias resistors? Is that what R3 & R4 are doing, or is that only providing a MIC bias?The two ferrite beads don't have any specifications listed. What should I look for? Are they even necessary in a low-power battery-powered amp circuit? as a general rule I always try to provide as large as possible ground planes, would this be sufficient or should I double down and look into something like a pi-filter?and lastly, The CMA-4544. Would it be recommended to try and source a better option with a lower frequency response? as I stated, I am more concerned with the lower frequencies, and with the trials I've done so far it seems like the circuit has a hard time picking up on the sub-bass/bass frequencies (kicks/808s)This has turned out to be a lot more verbose than I was initially anticipatingI just wanted to be as concise as possible and provide all the details I thought would be important. As always any feedback is greatly appreciated, thank you!

author: ledtester
author_rank: Super Contributor
timestamp: July 25, 2022, 08:07:25 am
content: Quote from: szenk on July 25, 2022, 04:42:34 amBtw - the Adafruit schematic is basically the same as "Figure 2" in the MAX4466 datasheet:https://datasheets.maximintegrated.com/en/ds/MAX4465-MAX4469.pdfQuoteThis is a standard AC coupling of the microphone signal. The DC offset is changed from whatever it is on the electret side to 1/2 AVcc so both positive and negative excursions of the signal will be within the common mode range of the MAX4466.QuoteI think this helps keep digital signals from your microcontroller out of the analog circuitry. See, for instance:https://electronics.stackexchange.com/questions/527213/selection-of-ferrite-bead-for-analog-and-digital-supply-isolationUpdate:QuoteFrom what I gather electret mics in general are not good at picking up low frequencies.Here is a reddit discussion of what seems like a similar project to what you're trying to do:https://www.reddit.com/r/arduino/comments/pa50s/beat_detection_for_led_club_outfit/and here's another:https://chrisgagne.com/1877/a-sound-sensitive-led-disco-suit-part-1/https://github.com/chrisgagne/ColorCyclingLEDsbut unfortunately no details on the sound input - perhaps you can ask him.