How can Rpi Pico W control a GPIO pin connected, I2C digital MEMS microphone?

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Using the Raspberry Pico Pi, how can micropython be used to get the values from a MEMS microphone such as the Adafruit Silicon MEMS Microphone Breakout - SPW2430 link to ada fruit Product ID: 2716.

Can this be connected to a GPIO pin and then in a while true loop read the pin outputs which are then fed into a speaker? Since the breakout board should be returning digital signals then the CPIO pins can be used directly and if so how should it be implemented? If code directly is not provided some overall pseudo code would be great.

• audio
• pi-pico
• microphone
• micropython

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edited 11 mins ago

tlfong01

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asked Dec 30, 2022 at 22:29

Vass

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• 1I goggled :How to convert PDM to analog?” and got the following answer: The process of decoding a PDM signal into an analog one is simple: one only has to pass the PDM signal through a low-pass filter. This works because the function of a low-pass filter is essentially to average the signal. – tlfong01 Dec 31, 2022 at 3:50  
• 1Have you actually read the link you posted. This device outputs line-level analog. – Milliways Dec 31, 2022 at 5:05
• Converting PDM Data to analog – EESE, Asked 1 year, 11 months ago, Viewed 566 times electronics.stackexchange.com/questions/542348/… – tlfong01 Dec 31, 2022 at 5:46  
• electronics.stackexchange.com/questions/435996/… – tlfong01 Dec 31, 2022 at 5:50  
• There are 60+ PDM Q&A’s in EESE! – tlfong01 Dec 31, 2022 at 5:57  
• 1@Vass: It is not clear what sort of audio signal you wish to process. I would suggest to begin with experimenting with the simplest, say 1 kHz: 1k Hz Tone Test Tone – Sonic Electronix youtube.com/watch?v=TbPh0pmNjo8 – tlfong01 Dec 31, 2022 at 7:04  
• 1If you agree 1kHz tone signal is good to start with, I would then suggest how to connect the MEMS mic output to a PicoW GPIO pin and count the number of pulses, … – tlfong01 Dec 31, 2022 at 7:10  
• 1@tlfong01, that is a great recommendation, do you know the pseudo-code for that in micropython or C? – Vass Dec 31, 2022 at 15:35
• 1pseudo code is not specific to any programming language … for example, assign a loop variable – jsotola Dec 31, 2022 at 18:26 
• @Vass: Oh yes, I usually start with Chinese in my little head, then broken English, then pseudo code, then perhaps microPython, … – tlfong01 Jan 1 at 2:06  
• Let me first brainstorm a preliminary project spec, you counter suggest something, then we together scratch the pseudo code. – tlfong01 Jan 1 at 2:10  
• First thing first, our dream spec is a human speech recognition device: (1) Stupid human speaks to MEMS mic which outputs PDM signal fed to any PicoW GPIO pin. (2) For prototyping, we can perhaps start with two signals: (a) 1k tone, (b) 2k tone, … – tlfong01 Jan 1 at 2:16  
• 1picoW would would say, continuously count the bits per second. If count is a multiple of 1,000, then it should be 1kHz. If a multiple of 2,000, then it should be a 2k tone. Of course it is, as the Chinese saying goes, just first step of a one thousand miles long journey, … – tlfong01 Jan 1 at 2:21  
• I bought a couple of MEMS mic’s from TaoBao sometime ago (MP34DT01 麦克风模块 PDM MEMS Microphone ¥25.00), but I could no longer find them in my junk bin, item.taobao.com/…. Perhaps I would try harder searching, … – tlfong01 Jan 1 at 2:33   
• 1This whole exchange reminds me of my time as an engineering manager. I had a number of young engineers working for me. They loved solving problems (they reminded me of puppies with a ball) BUT they never actually defined the problem they were trying to solve. – Milliways Jan 1 at 2:42
• I googled another reference: PDM — Pulse density modulation interface – NordicSemi infocenter.nordicsemi.com/… – tlfong01 Jan 1 at 6:39  

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Question

How can PicoW read MEMS digital microphone output?

Answer

Update 2023jan19hkt1316

17.0 For the preliminary testing, I am only considering PLL A and Clock 0:

16.0 Using declarative programming tools to convert Si5351 flowchart/pseudo code to ADT (Abstract Data Type) for preventive/troubleshooting/newbie proof/friendly program development.

I found the Github libraries out there too powerful and comprehensive for newbie like me difficult to understand and use. So I am thinking to make to the six or seven pseudo as simple as possible. As a example/case study, I would start with the first pseudo statement:

15.0 Programming Considerations

I found the Si5351 Clock setup procedure straightforward, and therefore to translate it to pseudocode, and if I use functional programming technique, translate it further to a couple of high level programs. One problem is that the free Window 10 SkyClock’s Clock Builder app is no longer available, so I need to calculate parameters, using my always dodgy arithmetic.

14.0 Writing a MicroPython program to set up Si5153 2MHz Clock

The I2C read/write registers function seem OK, Next step is to setup a 2MHz clock for the digital PDM microphone module MT40DT01. I am following the following programming procedure.

13.0 Si5153 Read/Write Reg 3 program listing

12.0 Testing writing to si5351 registers

https://penzu.com/p/b57eefc0

11.0 Using PicoW I2C1 (GP6, 7) to control Si5351 (address 0x60)

10.0 Si5351 HF Clock Gen Wiring

0.9 Si5351 testing notes

I found Si5351 HF square wave sig gen seemingly flexible and easy to use (There are quite a number of AdaFruit and Arduino tutorials around!). So I have begun reading the datasheet and trying to write a simple PicoW micropython python to test it.

(1) I2C Programmable Any Frequency CMOS Clock Generator + VCXO Datasheet – Silicon Labs

(2) Programming si5351 with the PyBoard (micropython) YouTube Tutorial

0.8 1MHz to 3.5MHz Clock for MT40DT01

The 1MHz Clock works for MT40DT01. However it is expensive and awkward to handle. So I am looking for an alternative. The following looks good.

5351 Si5351A High Frequency Square Wave Signal Generator – AliExpress HKD21

0.7 MT40DT01 now with external 1 MHz clock outputs something

0.6 Microphone not working because input frequency to low, < 1MHz

Earlier I used 200kHz as clock frequency but found nothing happening. I checked the datasheet and found that the minimum frequency is 1 MHz (Max 3.5MHz). Now I have a problem, because it seems that the PicoW’s system timers are software timers and so could not support too many clocks at high frequency higher than 500 KHz. So now I need to check if an external clock > 1MHz can solve the problem.

0.5 Real time test setup

mt40dt01 test program listing – https://penzu.com/p/2f213cb6

0.4 Creating 4 PicoW system clocks, two for real time tone signals, two for MT34DT01 MEMS digital microphone clock inputs

PicoW Mems Digi Mic v13.0 Program Listing

# PicoW Mems Digi Mic v16.0 - tlfong01 2023jan07hkt2138

import machine
import utime
from machine import Pin, Timer, RTC

print('MemsDigiMicV16.0, 2023jan07hkt2138')

redFreq     = 20000  # DigiMic #1 Clock signal
grnFreq     = 4      # For troubleshooting

redLed      = Pin(0, Pin.OUT, value = 1) # Create Red LED object, init On
grnLed      = Pin(1, Pin.OUT, value = 1) # Create grn LED object, init On

redTimer    = Timer() # Red LED timer, callback toggleRedLed
grnTimer    = Timer() # Grn LED timer, callback toggleGrnLed

def toggleRedLed(dummy): #ISR RedLed
    redLed.toggle()
    return

def togglegrnLed(dummy): #ISR grnLed
    grnLed.toggle()
    return

redTimer.init(freq = redFreq, mode = Timer.PERIODIC, callback = toggleRedLed)
grnTimer.init(freq = grnFreq, mode = Timer.PERIODIC, callback = togglegrnLed)

utime.sleep(10)
redTimer.deinit()
grnTimer.deinit()
redLed.off()
grnLed.off()

# *** End of program ***

0.3 Using MT34DT01 MEMS Digital Microphone for Very simple Speech Recognition

The MP34DT01-M MEMS digital microphone datashheet says it can be used for AI applications such as speech recognition, (Ref 1). Now I am thinking of exploring the fisibility of doing very simple speech recognition, say, for a very, very small subset of audio signals, denoting doggie commands like “Sit”, “Eat”, “OK” etc.

I read that it is practical to use Rpi python to do Alphabet reqognition of 26 handwritten patterns A to Z, using CNN (Convolutional Neural Network), for example, Glezer, Ref 2. In CNN application usually represent one visual paatern, say one alphabet, by a liner list of bits. For audio patterns, I think we can also similarly represent doggie commends “Sit”, “Eat” etc, each by a list of bits.

The MEMS digital microphone MP34DT01 seems ideal for our simple application. This is what will explored in the subsquent sections.

(1) MP34DT01-M MEMS audio sensor omnidirectional digital microphone – STM 2014

(2) Running a Convolutional Neural Network on Raspberry PI – Marcelo Glezer, 2020oct01

0.2 Tone Generator and Frequency Counter Schematic

0.1 MEMS PDM Digital Microphone MT34DT01 Test Setup V0.1

1. Introduction.

We can connect the MEMS microphone output pin to a PicoW GPIO pin and read signal, into a list for later processing.

2. Simulation

For prototyping, we can simulate the microphone output signal as a GPIO output pin connected blinking LED, and use another GPIO input pin to read the blinking LED pin.

3. Trying Blink rates 1kHz, 2kHx, to simulate 1kHz, 2kHz tones

*4. The OP wishes to connect the MEMS digital mic output to PicoW. So now I am looking at the real thing.

5. MP34DT01-M MEMS audio sensor omnidirectional digital microphone

(5.1) MP34DT01-M MEMS audio sensor omnidirectional digital microphone – ST

(5.2) PDM Microphont: PDM Signal Definition – ST Video

6. MT34DT01 MEMS Digital Microphone

9. / to continue, …

References

(1) Adafruit PDM Microphone Breakout 1

(2) Adafruit PDM Microphone Breakout 2

(3) AliExpress Digital MP34DT01 Microphone Module Simple Pulse Density Modulation Output PDM Digital MEMS Microphone Module – HK$27

(4) TaoBao MP34DT01 MEMS PDM Microphone – ¥25

(5) 1000 Hz Test Tone – Sonic Electronix

(6) Using a Digital Microphone (MT34DT01) on STM32 – Dario Petrillo, Hackster, 2022jul14

Appendices

Appendix A – MicroPython program blinking two LEDs simulating two MEMS digital microphone output signals

# Pico W Blink Two LEDs - tlfong01 2023jan01hkt1941

# *** Modules ***
import machine
from machine import Pin, Timer

# *** Configuration***
redLed      = Pin(0, Pin.OUT)
greenLed    = Pin(1, Pin.OUT)

redFreq     = 2
greenFreq   = 4

redTimer    = Timer()
greenTimer  = Timer()

# *** Callbacks ***
def blinkRedLed(dummy):
    redLed.toggle()
    return

def blinkGreenLed(dummy):
    greenLed.toggle()
    return

# *** Main ***
redTimer.init(freq = redFreq, mode = Timer.PERIODIC, callback = blinkRedLed)
greenTimer.init(freq = greenFreq, mode = Timer.PERIODIC, callback = blinkGreenLed)

# *** End of program ***

Appendix B – Blinking LEDs Video

PicoW blinking two LEDS

Appendix C – MEMS Mic, PicoW GPIO Eval Brd Setup

# PicoW GPIO Input Testing v7.0 - tlfong01 2023jan02hkt1410

# *** 1.0 Modules ***
import machine
import utime
from machine import Pin, Timer

# *** 2.0 Configuration and Functions ***

# 2.1 Blinking LED Configurations and Functions
redFreq     = 6 # Red LED blinking frequency
greenFreq   = 3 # Green LED blinking frequency

redLed      = Pin(0, Pin.OUT, value = 1) # Create Red LED object, init On
greenLed    = Pin(1, Pin.OUT, value = 1) # Create Green LED object, init On

redTimer    = Timer() # Red LED timer, callback blinkRedLed
greenTimer  = Timer() # Greed LED timer, callback blinkGreenLed

# 2.2 Blinking LED Callbacks
def blinkRedLed(dummy):
    redLed.toggle()
    return

def blinkGreenLed(dummy):
    greenLed.toggle()
    return

# *** 3.0 GPIO Input Configurations and Functions ***

readGpioPin2 = Pin(2, Pin.IN, Pin.PULL_UP) # Create GPIO input pin object
readGpioPin3 = Pin(3, Pin.IN, Pin.PULL_UP) # Create GPIO input pin object

def readRedLed():
    ledStatus = readGpioPin2()
    if ledStatus == 1:
        return "High"
    else:
        return "Low"

def readGreenLed():
    ledStatus = readGpioPin3()
    if ledStatus == 1:
        return "High"
    else:

        return "Low"

def readPrintRedGreenLedStatus():
    redLedStatus = readRedLed()
    greenLedStatus = readGreenLed()
    print('RedLedStatus   =', redLedStatus)
    print('GreenLedStatus =', greenLedStatus)
    return

### *** 4.0 / to continue, ... ***

# *** 9.0 Main ***

# 9.1 Run Red/Green Timer for 2 seconds

redTimer.init(freq = redFreq, mode = Timer.PERIODIC, callback = blinkRedLed)
greenTimer.init(freq = greenFreq, mode = Timer.PERIODIC, callback = blinkGreenLed)
utime.sleep(2)
redTimer.deinit()
greenTimer.deinit()

# 9.2 Set/Read/Print Red/Green LED status

redLed.on()
greenLed.on()

readPrintRedGreenLedStatus()

# *** End of program ***

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edited 20 mins ago

answered Jan 1 at 12:29

tlfong01

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• 2thanks alot for this and the links with the great video – Vass Jan 1 at 19:42

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