Bluetooth Vibration Sensor - RuuviTag Pro

We get every now than then questions if RuuviTag could be used to monitor vibrations from rotating machines. RuuviTag Pro can be as a Bluetooth vibration sensor and we have created a custom firmware version to measure vibrations. Some of our customers have already started proof on concept projects with the RuuviTag Pro sensors. Collecting the vibration sensor data needs a custom setup which can be for example a RaspberryPi or data can be collected using the Ruuvi Gateway and send data to a private server.

Scroll down for downloading the custom firmware for vibration measurement. Please note that firmware is a beta version and it’s not comprehensively tested. Note also that might not be possible to flash standard firmware again without Ruuvi Development Kit.

RuuviTag Bluetooth Vibration Sensor Data Formats

Simple Vibration Data Format AC for Bluetooth Vibration Sensors

RuuviTag can run both simple and complex measurements on acceleration. At its easiest, the acceleration measurement can be just a peak-to-peak value.

Vibration Measurement Basics - RMS, Amplitude, and Peak-to-Peak — Vibration Measurement Basics – RMS, Amplitude, and Peak-to-Peak

The peak to peak tells essentially how hard acceleration Bluetooth vibration sensor has seen. Another simple measurement is root mean square value and it tells how much power acceleration has. Since RuuviTag Pro has a 3-axis accelerometer, a separate value is reported along each axis.

RuuviTag Special Vibration firmware Simple Data Format

Byte	Name	Range	Note
0	HEADER	0xAC
1	VERSION	0x02
2	P2P_X_MSB	0 … 32767	Signed, mG.
3	P2P_X_LSB		Limited by accelerometer amplitude, 4 – 32 G
4	P2P_Y_MSB	0 … 32767	Signed, mG.
5	P2P_Y_LSB		Limited by accelerometer amplitude, 4 – 32 G
6	P2P_Z_MSB	0 … 32767	Signed, mG.
7	P2P_Z_LSB		Limited by accelerometer amplitude, 4 – 32 G
8	RMS_X_MSB	0 … 32767	Signed, mG.
9	RMS_X_LSB		Limited by accelerometer amplitude, 2 – 16 G
10	RMS_Y_MSB	0 … 32767	Signed, mG.
11	RMS_Y_LSB		Limited by accelerometer amplitude, 2 – 16 G
12	RMS_Z_MSB	0 … 32767	Signed, mG.
13	RMS_Z_LSB		Limited by accelerometer amplitude, 2 – 16 G
14	RESERVED0	N/A	Reserved for future
15	RESERVED1	N/A	Reserved for future
16	RESERVED2	N/A	Reserved for future
17	RESERVED3	N/A	Reserved for future
18	RESERVED4	N/A	Reserved for future
19	RESERVED5	N/A	Reserved for future
20	VOLTAGE_MSB	0 … 254	Calculate as: 1600 mV + 8 * VOLTAGE mV
21	TEMPERATURE_MSB	-125 … 125	In celcius, 1C resolution
22	SEQUENCE_COUNTER_MSB	0 … 65534	Incremented for each measurement, rolls over to zero
23	SEQUENCE_COUNTER_LSB

Special Data Format for Simple RMS vibration data by Ruuvi

Dataformat 0xAC version 2 specification. For signed values lowest possible value means error, for signed values highest possible value means error.

Complex Vibration Data Format AF for Bluetooth Vibration Sensors

The brains of RuuviTag Pro is a quite capable nRF52832 from Nordic Semiconductor. It comes with an ability to run a Fast Fourier Transform to calculate frequency components of acceleration.

Comblex Vibration Measurement - FFT Fast Fourier Transform — Image credit to https://en.wikipedia.org/wiki/Fast_Fourier_transform

The Fourier transform can differentiate between frequencies of acceleration RuuviTag Pro is measuring. By default, the FFT is calculated out of 1024 samples taken at 1344 Hz at 12 bits and 2 G amplitude.

This gives 512 frequency bins where one bin is 1344 / 2 / 512 = 1.3 Hz wide. However, broadcasting every bin is not feasible, so bins are summed together into 16 frequency
buckets and the power of the bucket is calculated for broadcasting. This gives output with 16 buckets of power per frequency.

Since the scale between buckets can vary a lot, it is not meaningful to use a fixed scale for frequency data. Instead, acceleration is normalized to the highest value and the rest of the values are scaled accordingly. Scaling information is sent in the broadcast.

Learn more about the FFT from Wikipedia https://en.wikipedia.org/wiki/Fast_Fourier_transform

RuuviTag Special Vibration Firmware Complex Data Format

An example on how to decode the vibration sensor data, please see https://github.com/ojousima/ojousima.ruuvi_endpoints.ts/blob/master/src/ojousima_endpoint_af.ts

Byte	Name	Range	Note
0	HEADER	0xAF
1	VERSION	0x01
2	TYPE	0 … 2	0 – X-axis, 1 – Y-axis, 2 – Z-axis
3	SCALE_MSB	0 … 255	8.8 Fixed-point value
4	SCALE_LSB		Divide value by 256 to get a scaling float
5	FREQ_MSB	0 … 65534	Highest frequency bucket.
6	FREQ_LSB		Limited to ~5 kHz by accelerometer. In Hz.
7	BUCKET_1	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
8	BUCKET_2	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
9	BUCKET_3	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
10	BUCKET_4	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
11	BUCKET_5	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
12	BUCKET_6	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
13	BUCKET_7	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
14	BUCKET_8	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
15	BUCKET_9	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
16	BUCKET_10	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
17	BUCKET_11	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
18	BUCKET_12	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
19	BUCKET_13	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
20	BUCKET_14	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
21	BUCKET_15	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
22	BUCKET_16	0 … 255	Divide by scale to get original value in G(rms)^2/Hz
23	SEQUENCE	0.254	Rolls over to 0, increments by one for each measurement

Special Data Format for Complex FFT Vibration data by Ruuvi

RuuviTag Pro Bluetooth Vibration Sensor Firmware

We have made a proof-of-concept firmware which broadcasts in above formats and original Ruuvi RAWv2 (0x05) format. You can download and run it on any RuuviTag or Ruuvitag Pro up to hardware version B8. Special firmware can be downloaded here https://github.com/ojousima/ojousima.acceleration_bcast.c/releases/tag/v1.0.3. Flashing can be done using Nordic Semiconductor nRF Connect and instructions can be found here.

The firmware broadcasts in one-minute cycle, with each cycle having 5 distinct broadcasts:

Original RAWv2
“Simple” Vibration Data Format AC
“Complex” Vibration Data Format AF, once per each axis

Each broadcast is repeated 5 times at 1285 ms interval, so the one-minute cycle has about 32 seconds of broadcasting and another half minute of quiet time. All measurements are taken from same acceleration sample.

RuuviTag Pro Bluetooth Sensor

Test Ruuvi's beta firmware for Vibration Measurement

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