S100 Slave - Sensing Mix-1


The Sensing MixOne Module is a certified Rhomb.io module that includes a wide variety of sensors. This module has been designed in order to gather on a single board lots of sensing capabilities, giving the opportunity to use the imagination to create sensing-based products.

The module contains the following sensors: movement, temperature, barometer, Heart-Rate and Pulse Oximeter. The movement sensor is a powerful 9-axis IMU that integrates a gyroscope, an accelerometer, and a compass.

The Sensing MixOne Module works as a typical slave Rhomb.io module. All the sensors are managed through I2C.

On the next two figures, it is shown the top and the bottom side of the module.

Sensing MixOne 3D view Top v2.jpg Sensing MixOne 3D view Bottom v2.jpg

General specifications

The Sensing MixOne Module has been designed in order to provide to the user a wide variety of sensors. The following figure identifies the five integrated circuits (IC) onboard. It is possible to communicate with each one by using the I2C serial bus, working at 400 kbps.

There are two pull-ups resistors for the I2C, but normally those resistors are not assembled. If so, ensure that there are I2C pull-ups on the system, otherwise the Sensing MIX Module will not work. Configure the I2C speed to 400kbps.

Module description v3.jpg

Two different source voltages are present on the board: 3.3 V and 1.8 V. Note that there is no power management nor regulators on the PCB, that's because the supply power comes directly from the rhom standard connectors. Look at the Schematics section for more information regarding the supply voltage for each IC.

Key features

Block Diagram

The next figure shows the Block Diagram for the Sensing MixOne Module. The five integrated circuits are shown with its corresponding part number and the I2C slave address. The I2C interface should be configured at 400 kbps.

The module only uses four GPIO from the standard Rhomb.io connectors. GPIO1, GPIO2, and GPIO3 should be treated as interruption inputs. See the sensor description for more details.

Note that there are interrupt signals on the movement sensor, the HR + PO sensor, and the barometer. Those signals are conneted to the GPIO1, GPIO2 and GPIO3, respectively. Those GPIOs should be treated as interrupts inputs. For more details look at the sensor descriptions beneath.

Diagrama de bloques v5.jpg

The following table shows the main features for each integrated circuit and its corresponding I2C address.

IC Sensing Features I2C address
MPU9250 Accel +-(2, 4, 8 and 16) g 0x68
Gyro +-(250, 500, 1000 and 2000) deg/s
Compass 0,6 or 15 μT/LSB 0x0C
TMP103A Temperature -40°C to 125°C; 1°C resolution 0x70
TMP103B Temperature -40°C to 125°C; 1°C resolution 0x71
MAX30101 Heart Rate Integrates internal LEDs and optical elements 0x57
Pulse Oximeter
LPS25HTR Barometer 260 hPa to 1260 hPa 0x5C

A basic description for each sensor can be found below. Please refer to the Manufacturer IC documentation for a detailed information.

Temp A and B

Note that there are two temperature TMP103 sensors. Both ICs have the same specifications, except for the I2C slave address. This allows to use simultaneously the two temperature sensors but with two different configurations. The I2C address for the Temp A sensor is 0x70, while for the Temp B sensor is 0x71.


The MPU-9250 is a 9-axis Motion Tracking which includes a 3-axis accelerometer, 3-axis gyroscope and a 3-axis magnetometer. From the I2C point of view, the IC works as two devices. One device is the magnetometer and has the 0x0C address. The other device is the accelerometer and the gyroscope, and its I2C address is 0x68. There is a lot of source code available on the most widely spread platforms such as Arduino and mbed.

The device allows selecting different resolutions by writing on the configuration registers. For the accelerometer, the available resolutions are: +-2g, +-4g, +-8g and +-16g. The gyroscope can be configured as 250 °/s, 500 °/s, 1000 °/s and 2000 °/s. The magnetometer should be configured as 0,6 μT/LSB or 15 μT/LSB. Each device has its own specific configuration registers, so the resolution is fixed independently for each one.

The sample rate can be configured through I2C in order to accomplish the system requirements. Furthermore, the samples can be stored on an internal FIFO. It is possible to store on it only 3-axis, 6-axis or the entire 9-axis.

An external signal connected to the frame synchronization pin (FSYNC) can be used to fix the time from which the device will start to take samples at the fixed sample rate. The FSYNC pin is connected to the Rhomb.io standard GPIO pin 0 (GPIO0).

The MPU-9250 has different interrupt sources that should be configured by writing on its corresponding registers. When the programed interruption event occurs, the logic level on the INT pin changes, according to the selected interrupt configuration. For example, if the FIFO is being used, a typical interrupt event could arise when the FIFO overflows.

The INT pin is connected to the Rhomb.io standard GPIO pin 1 (GPIO1). To see more interruption sources, look at the "Connections-GPIO" section.

The following picture show the axis direction of the accelerometer (ax, ay, az), the gyroscope (gx, gy, gz) and the magnetometer (mx, my, mz).
Sensing MixOne Axis v3.jpg


The MAX30101 is an integrated pulse oximetry and heart-rate monitor sensor. It includes internal LEDs, photodetectors, optical elements, and low-noise electronics with ambient light rejection. This device has been included in order to give the user more capabilities in new designs for fitness applications. The device is managed through the 0x57 I2C address.

An interruption source can be configured in order to warn events such as: new data on the FIFO, proximity threshold reached or device ready to collect data. When some of those previously configured interrupt sources are being reached, the !INT pin is tied to low level. This pin is connected to the Rhomb.io standard GPIO pin 2 (GPIO2). Note that an external pull-up resistor should be connected to this pin, so a firmware-level pull-up resistor should be configured on the MCU (where the GPIO2 will be connected).


The last sensor is the LPS25H, a piezo-resistive pressure sensor capable to detect absolute pressure from 260 hPa to 1260 hPa. The device allows to store the measures on a FIFO.

It is also possible to configure a high and low pressure threshold in order to create an interrupt event when the pressure is outside those two values. When there is an interrupt event, a change on the INT pin logic level occures, according to the selected interrupt configuration. The INT pin is connected to the rhom standard GPIO pin 3 (GPIO3).

The communications should be done through the I2C 0xBD address.



The following table summarizes the GPIOs used Sensing MixOne Module. Note that three of them should be configured as interrupt sources.

Device Name Rhomb.io pinout Interruption
MPU-9250 MPU-9250.INT# GPIO1 Yes
MAX30101 MAX30101.INT# GPIO2 Yes

Serial interfaces

The following table indicates the available serial interfaces on the Rhomb.io standard and which ones are used. The table also shows the nomenclature used on the schematic and its corresponding on the Rhomb.io standard. There are two pull-ups resistors for the I2C, but normally those resistors are not assembled. If so, ensure that there are I2C pull-ups on the system, otherwise the Sensing MIX Module will not work. Configure the I2C speed to 400 kbps.

Signal (Rhomb.io) Signal (module) Used by
I2C.SDA I2C.SDA All the ICs
I2C.SCL I2C.SCL All the ICs


The Secure Digital Input Output (SDIO) interfaces are not used on the Sensing MixOne Module.


As per the supply lines used on the board, there is a summary on the next table.

Signal (Rhomb.io) Signal (module) Voltage (V) Used
1V8 150mA 1V8 1.8 Yes
2V8 150mA 2V8 300mA 2.8 No
VSYS VSYS 3 - 5.5 No
Buck8 3V2 3.3 Yes
Buck9 Buck9 3.3 No

Other signals

The CLK_32KH, AD_OUT and PWM_INT signals are not used on the Sensing MixOne Module. More information regarding these signals can be found at the specifications for the Rhomb.io standard.


Click the image below to download the schematic files.

Sensing MixOne Arturo schemes v4.jpg

Bill of materials

Click the image below to download the BOM files.

Fabrication files

Click the image below to download the fabrication files.

Mechanical specifications


Sensing MixOne Dimensions v1.jpg


  • Precaution against Electrostatic Discharge. When handling Rhomb.io products, ensure that the environment is protected against static electricity. Follow the next recommendations:
  1. The users should wear anti-static clothing and use earth band when manipulating the device.
  2. All objects that come in direct contact with devices should be made of materials that do not produce static electricity that would cause damage.
  3. Equipment and work table must be earthed.
  4. Ionizer is recommended to remove electron charge.
  • Contamination. Be sure to use semiconductor products in the environment that may not be exposed to dust or dirt adhesion.
  • Temperature/Humidity. Semiconductor devices are sensitive to environment temperature and humidity. High temperature or humidity may deteriorate semiconductor devices characteristics. Therefore avoid storage or usage in such conditions.
  • Mechanical Shock. Care should be exercised not to apply excessive mechanical shock or force on the connectors and semiconductors devices.
  • Chemical. Do not expose semiconductor device to chemical because reaction to chemical may cause deterioration of device characteristics.
  • Light Protection. In case of non-EMC (Epoxy Molding Compound) package, do not expose semiconductor IC to strong light. It may cause devices malfunction. Some special products which utilize the light or have security function are excepted from this specification.
  • Radioactive, Cosmic and X-ray. Semiconductor devices can be influenced by radioactive, cosmic ray or X-ray. Radioactive, cosmic and X-ray may cause soft error during device operation. Therefore semiconductor devices must be shielded under environment that may be exposed to radioactive, cosmic ray or X-ray.
  • EMS (Electromagnetic Susceptibility). Note that semiconductor devices characteristics may be affected by strong electromagnetic waves or magnetic field during operation.


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