Sampling frequency of the SparkFun Gator Microphone

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1

Hello there,

I am trying a physics experiment to measure the speed of sound.

I am using a microbit fitted with a SparkFun gator microphone sending its audio data either by USB cable / serial or preferably (for the experimental setting) by WiFi / OSC messaging.

Whatever the data transmission mode (USB serial or WiFi/OSC), with makecode, I am not able to call the audio envelope measurements (the ptx soundintensity function) at a sample frequency better than ~160 Hz (every 6.25 ms) which is not suffisant to get an accurate speed of sound estimation: I had read that the default sampling frequency was ten fold (1600 Hz) ? Is there a way to increase it to 3000 Hz ? Is it possible to test this sensor on Mu ? (in micropython)

Best,

Jean-François B.

2

Unfortunately we don’t have any documentation that shows how to change the sample rate and it doesn’t look like our Makecode extension has the ability to change it either. :frowning:

If you feel like writing your own extension, the ADC on the Gator Microphone can sample as fast as 3300 samples per second, check the data sheet in the link below for more information.

https://cdn.sparkfun.com/assets/6/5/6/2/a/ADS1015.pdf

3

Hello,

Thank you for the answer.

I read from your doc. (about the ADC) that:

7.5 Electrical Characteristics
At VDD = 3.3 V, data rate = 128 SPS, and full-scale input-voltage range (FSR) = ±2.048 V (unless otherwise noted)

So, using it with a bare micro:bit (3.3 V) will only enable to output @128 SPS and not 1600 SPS ?

In a first time, I can try with a VDD = 5 V to see if I can reach 1600 SPS.

If this is the case, I can try to make an extension juste changing

uint16_t _sampleRate = ADS1015_CONFIG_RATE_1600HZ;

by

uint16_t _sampleRate = ADS1015_CONFIG_RATE_3300HZ;

in SparkFun_ADS1015_Arduino_Library.cpp

4

Hi there,

I don’t think one can set the VDD at 5 V on the ADS1050 pin (to reach its default 1600 Hz data rate) in a simple manner ? (while maintaining the other parts of the circuitry ~3.3 V).

All the other Gator µphone components seems to have a maximum input voltage over 5 V: would the Gator µphone board withstand a 5 V input and still operate properly ? Or would it cause problems with the analog input levels of the ADS1050, or with the logic levels, I²C or other things ?

If it is not possible, does that mean that the data rate of the Gator µphone board is limited to a crude 128 Hz ? (not 3300 or even the default 1600 Hz)

5

The board was designed to work with a [micro:bit at 3.3 volts, I don’t know what problems you might run into (if any) if the board is run at 5 volts.](https://www.sparkfun.com/products/17287)

6

I have already ordered an Adafruit ADS1015 Breakout to be able to apply a VDD of 5 V to it, along with the Electret Microphone Amplifier board.

You should make your customers aware that your Gator Microphone board is limited to 128 SPS (the other data rates are not accessible @3.3 V).