Tag Archives: RMS microphone

The Hacky Super Loop Arduino Nano 33 BLE Sense Example You Have Been Waiting For

The Arduino Nano 33 BLE Sense was released in July 2019 and was a real step up for Arduino! Using the Arm Cortex-M4F based nRF52840, the Nano 33 BLE’s arrival made the days of Atmel based 8-bit microcontrollers seem numbered. With the proliferation of dirt cheap Arduino clones this was probably the result of Arduino seeing the writing on the wall that keeping it simple was probably not going to bring in the dough anymore. In the end the sheer amounts of fairly useless Arduino projects seem a bit dull these days, and with more complex offerings such as the Nano 33 series, a new era of seriously cool projects may be on the horizon.

A common complaint about the Nano 33 BLE Sense is the lack of working examples available for the board. Only a simple PDM Serial Plotter example exists when you install the board package, and this seems to have caused some confusion among users who were expecting an example to exist that uses all of the available on board sensors. In fact examples do exist for all the on board sensors, however they are available only on the individual sensor library repositories.

Below is a table including each sensor, it’s component name, a brief description, and a link to the example code.

SensorNameDescriptionExample Code Link
IMU LSM9DS1 3 acceleration channels, 3 angular rate channels, 3 magnetic field channels Arduino_LSM9DS1
Microphone MP34DT05PDM omnidirectional digital microphonePDM
IR APDS9960  Gesture, light, proximityArduino_APDS9960
Barometric Pressure LPS22HB  Barometric pressureArduino_LPS22HB
Temperature/Humidity HTS221  Temperature/Humidity Arduino_HTS221

Let’s Be Honest About What We Really Wanted

We wanted a super loop that would read all the values from the sensors and print them on the serial monitor/plotter. We wanted to be able to buy this board, fire it up, and to be able to look cool to all our friends immediately. We didn’t want to have to think. In fact we didn’t want to have to do anything. It did not matter that the actual values would probably be useless, we just wanted it to be there.

Perhaps the reason this super loop example we want is so terrible is because of the fact that the Nano 33 BLE Sense can utilise Mbed OS. Finally, a reasonably performant and relatively deterministic way of arranging our more complex Arduino projects! We can finally bid farewell to the almighty super loop!

Alas, I understand the RTOS can be a new and scary venture for some. And having just got my Nano 33 BLE sense, I decided to create a simple example program that can display all the available sensor data on serial plotter to check with the sensors are at least powered on and outputting semi-meaningful data without any of the BLE functionality.

The Example Project

The repository for nano-33-sense-serial-example can be found here. The data itself might be fairly useless for most applications, as it is mostly raw digital values pulled straight from the sensors which need to be converted to useful metrics before being meaningful. It plots the following raw data:

  • x/y/z acceleration data
  • x/y/z gyroscope data
  • x/y/z magnetic data
  • RMS microphone data
  • left/right/up/down gesture data
  • r/g/b light data
  • proximity data
  • Barometric pressure data
  • Temperature/Humidity data

Some of the difficulty in displaying this data in a coherent way is the different sampling frequencies in which sensor data is obtained. The table below shows these sampling frequencies.

Data TypeSampling Frequency
x/y/z acceleration data 109Hz
x/y/z gyroscope data 109Hz
x/y/z magnetic data 20Hz
16mS RMS microphone data 62.5Hz
left/right/up/down gesture data
Undefined
r/g/b light data
Undefined
proximity data
Undefined
Barometric pressure data
On request (1Hz in example)
Temperature/Humidity data On request (1Hz in example)

Because of this, all data is plotted with a frequency of 20Hz in an attempt to display the data in a way where the values will somewhat correlate to each other. There are some simple macro based configuration options available to allow some control over what data is actually outputted.

What the Output Looks Like

All Sensors

IMU Sensor

Gesture/Light/Proximity Sensor

Barometric Pressure Sensor

RMS Microphone Output

Temperature/Humidity Sensor

Conclusion

The nano-33-sense-serial-example is a great way to visualise all of the onboard sensors on the Nano 33 BLE sense. In the future I hope to recreate this project using Mbed OS in an effort to create a simple, low power alternative that can be used as the base for many projects that use the Nano 33 BLE sense.