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.

  • 1
    I 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
  • 1
    Have you actually read the link you posted. This device outputs line-level analog.
    – Milliways
    Dec 31, 2022 at 5:05
  • 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
  • 1
    If 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

1 Answer 1



How can PicoW read MEMS digital microphone output?


Update 2023jan19hkt1316

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

si5351a block diagram

MicroPython Si5351 GitHub

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:

pseudo statement 1

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.

enter image description here

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.

si5351 prog procedure

13.0 Si5153 Read/Write Reg 3 program listing

12.0 Testing writing to si5351 registers


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

si5353 ajn1301

i2c detect 01

10.0 Si5351 HF Clock Gen Wiring

si5353 hf clock gen

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.

si5351 01

(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

mic test 0901

mic test 02

mic test 0903

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

realtime test 01

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

mt34dt01 test 1

mt34dt01 test 2

mt34dt01 test 3

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

def togglegrnLed(dummy): #ISR grnLed

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


# *** 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

tone gen and freq ctr

0.1 MEMS PDM Digital Microphone MT34DT01 Test Setup V0.1

mt34dt01 v0.2

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

1k, 1k led blinking tones

1k, 2k tones 2

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

ada fruit mems digi mic

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

pdm interface

6. MT34DT01 MEMS Digital Microphone

mt34dt01 mems digi mic

9. / to continue, ...


(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


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):

def blinkGreenLed(dummy):

# *** 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

gpio eval brd

# 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):

def blinkGreenLed(dummy):

# *** 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"
        return "Low"

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

        return "Low"

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

### *** 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)

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



# *** End of program ***

  • 2
    thanks alot for this and the links with the great video
    – Vass
    Jan 1, 2023 at 19:42

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