Helios v1.0

This document shows the documentation for the Rhomb.io Helios board.

Preliminary version, use only for data updating or corrections.


The Helios board is a certified Rhomb.io PCB that integrates the rhomb modular ecosystem in a preceding boards. Helios is immediately useful, you only need a Rhomb.io master module plugged on the board to start to develop your projects quickly and easily. Is not a simple preceding boards, it is the most upgradable device you will find on the market. It gives the opportunity to easily assemble your machine according not only to your needs, but to your imagination.

The most common interfaces such USB, UART, I2C, SPI, digital inputs/outputs are available on board. But there are no limits on the Helios capabilities: LoRa, ZigBee, movement sensing, GPS..., all those are available on standard rhomb modules. The only thing you need is connect them on the corresponding slots. Furthermore, several microcontrollers of differets manufacturers are compatibles thanks to Rhomb.io modular technology. If there is a need for more processing power: you don't need to replace the Helios, the only thing you have to do is replace the master module for another more powerful. Helios board is fully compatible with Arduino and all its shields with extra features.

The next figure show a 3D view for the Helios board.

Helios 3D Top v1.png Helios 3D Bottom v1.png

As a summary, the following table indicates the main features:

Helios features
USB 2 x USB type B
SD micro-SD
Expansion headers 112 pines
Rhomb.io modules 1 Master Module slot
1 Generic Module slot


  • Prototyping tool
  • Industrial automation
  • Home automation
  • Internet of Things
  • Energy efficiency
  • Monitoring
  • Data acquisition
  • Technology for artists

Board specifications

Key features

The Helios board has been designed for working only with Rhomb.io standard modules, so a Rhomb.io core is not needed, only a master module. This board offers a huge amount of communications interfaces with easy access such as I2C, SPI, UART, USB. But it is not limited only to these features, the board also includes one socket for standard Rhomb.io modules. This brings a countless amount of customization options. The block diagram shows the parts that make it possible.

Helios Block Diagram v1.png

The following figure identify the main parts of the board. The most important parts will be explained with more details in the next sections.

Helios Description Top v1.png

Rhomb.io Core

The Helios board has no core sockets.

Rhomb.io modules

Lots of Rhomb.io modules focused in different areas such as communications, sensing or storage, are available. The Helios board allows to connect a one standard Rhomb.io master module and one slave module. Look at here [Añadir enlace a la tienda, sección modulos] to chose the desired module to convert your Helios in the device you want.

Modules v2.jpg


Two memory options are available for the Helios board: a micro SD card and a Memory eMMCXX Module.



There are available 2 USB 2.0 ports on the Helios. One of then (J9) works as a host. The other one (J10) works as On-The-Go. The OTG port also is routed to the pins 17 and 19 of the H6 header. The USB ports can be used as a supply source too. See the "Power" section for more datails.

There are ICSP and JTAG connectors for programming and debugging the Rhomb.io master module plugged on the board. The following tables shows the pinout of the these connectors.

Pin Function Pin Function
Pin Funtion Pin Function

It is also six headers with a total of 122 pins. Four of these headers have the Arduino standar disposition, so you can use in the Helios board all shields compatible with Arduino. The other two headers allow to access to all Rhomb.io master module signals. The following table shows the pinout of all headers.

H3 H1
Pin Function Pin Function
1 - 1 SCL0
4 3V3 4 GND
9 IO9
10 IO8
H4 H2
Pin Function Pin Function
1 AD0 1 IO7
2 AD1 2 IO6
3 AD2 3 IO5
4 AD3 4 IO4
5 AD4 5 IO3
6 AD5 6 IO2
7 TXD0
8 RXD0
H6 H5
Pin Function Pin Function Pin Function Pin Function
1 AD11 2 VIN 1 IO47 2 IO0
3 AD10 4 GND 3 IO46 4 IO1
5 AD9 6 AD6 5 IO45 6
7 AD8 8 AD7 7 IO44 8
9 IO35 10 9 IO43 10
11 IO34 12 11 IO42 12
13 IO33 14 13 IO41 14
15 IO32 16 RXD1 15 IO40 16
17 USB2_P 18 TXD1 17 IO39 18 Master_ID
19 USB2_N 20 19 IO38 20 GND
21 USB_ID 22 CLK_32KHz 21 IO37 22 IO10
23 BAT_RTC 24 GND 23 IO36 24 IO11
25 IO31 26 IO16 25 VSYS 26 IO12
27 IO30 28 IO17 27 3V3 28 IO13
29 IO29 30 IO18 29 2V8 30 IO14
31 IO28 32 IO19 31 1V8 32 IO15
33 IO27 34 IO20 33 GND 34
35 IO26 36 IO21 35 AD14 36
37 IO25 38 IO22 37 AD13 38
39 IO24 40 IO23 39 AD12 40

Helios Wired v1.png


The Helios board has nos wireless interfaces.


The Helios board has nos audio and video interfaces.

LEDs and Button

3 LEDs are assembled on the Helios board in order to give status feedback to the user. The functionality is explained next:

  • Red LED: Turned on when the power supply (from DC connector or USBs connectors) is ready.
  • Yellow LED: Turned on when the battery is being charging. Turned off when the battery is fully charged.
  • Green LED: Turned on when the battery is fully charged.

The Reset button is used to reset the microcontroller of the master module. The User button is connected to the IO2 signal from master module and can be programmed as you want. By default, this button is disconneted in order to mantain the integrity of IO2 signal. If you want to use it, you have to bridge the solder jumper SJ1 located next to the button.

Helios LEDsandButton v1.png


Master module auxialiary connectors

The following table summarizes the standard signals of the Rhomb.io master module socket and where they are used in the Helios. These signals may not have functionality depending of the microcontrolled plugged on the board.

Pin Signal Used by Pin Signal Used by
1 IO47, SDA1 H5 pin 1 50 IO0 H5 pin 2
2 IO46, SCL1 H5 pin 3 49 IO1 H5 pin 4
3 IO45, LPUART.RX/RXD2, SPIFI_IO3 H5 pin 5 48 IO2 H2 pin 6, Slave Module I2C_INT, user button
4 IO44, LOPUART.TX/TX2, SPIFI_IO2 H5 pin 7 47 IO3 H2 pin 5, Slave Module SPI_INT
5 IO43, SPI1_MOSI, SPIFI_IO1 H5 pin 9 46 IO4 H2 pin 4, Slave Module GPIO0
6 IO42, SPI1_MISO, SPIFI_IO2 H5 pin 11 45 IO5 H2 pin 3, Slave Module PWM_OUT0
7 IO41, SPI1_CLK, SPIFI_CLK H5 pin 13 44 IO6 H2 pin 2, Salve Module GPIO1
8 IO40, SPI1_SS, SPIFI_CS H5 pin 15 43 IO7 H2 pin 1, Slave Module GPIO2
10 IO39, TMS/SWDIO H5 pin 17, JTAG/SWD 41 IO8 H1 pin 10, Slave Module GPIO3
11 IO38, TCK/SWCLK H5 pin 19, JTAG/SWD 40 IO9 H1 pin 9, Slave Module GPIO4
12 IO37, TDO/SWO H5 pin 21, JTAG/SWD 39 IO19 H5 pin 22, Slave Module GPIO5
13 IO36, TDI H5 pin 23, JTAG/SW 38 IO11 H5 pin 24
14 1V8 1.8 V 37 IO12 H5 pin 26
15 2V8 2.8 V 36 IO13 H5 pin 28
16 35 IO14 H5 pin 30, Slave Module GPIO6
17 3V3 3.3 V 34 IO15 H5 pin 32, Slave Module GPIO7
19 32
20 VIO_REF H3 pin 2, VIO_REF 31
21 AREF H1 pin 3, AREF 30 GND GND
22 GND GND 29 AD0 H4 pin 1, Slave Module AD_IN
23 AD14 H5 pin 35, Slave Module UART0_CTSN 28 AD1 H4 pin 2
24 AD13 H5 pin 37, Slave Module UART0_RTSN 27 AD2 H4 pin 3
25 AD12 H5 pin 39 26 AD3 H4 pin 4
1 AD11 H6 pin 1 50 AD4 H4 pin 5
2 AD10 H6 pin 3 59 AD5 H4 pin 6
3 AD9 H6 pin 5 48 AD6 H6 pin 6
4 AD8 H6 pin 8 47 AD7 H6 pin 8
6 IO35, TRST H6 pin 9 45 RXD0 H2 pin 8, Slave Module UART0_RXD
7 IO34, CAN1_RX H6 pin 11 44 TXD0 H2 pin 7, Slave Module UART0_TXD
8 IO33, CAN1_TX H6 pin 13 43 RXD1 H6 pin 16
9 IO32, 1-WIRE/SWP H6 pin 15, Slave Module ID 42 TXD1 H6 pin 18
10 USB2_P H6 pin 17, Slave Module USB 41 SDA0 H1 pin 2, Slave Module I2C_SDA
11 USB2_N H6 pin 19, Slave Module USB 40 SCL0 H1 pin 1, Slave Module I2C_SCL
12 USB_ID H6 pin 21 39 SPI0_MOSI H1 pin 7, ICSP, Slave Module SPI_MOSI
13 CLK_32KHz H6 pin 22, Slave Module CLK_32KH 38 SPI0_MISO H1 pin 6, ICSP, Slave Module SPI_MISO
14 BAT_RTC H6 pin 23 37 SPI0_SCK H1 pin 5, ICSP, Slave Module SPI_SCK
15 VBAT Battery 36 SPI0_SS H1 pin 8, ICSP, Slave Module SPI_SS
16 35 RESET H3 pin 3, ICSP, JTAG/SWD
17 34 GND GND
18 IO31, SDIO0_DATA1 H6 pin 25, SD card, Slave Module SDIO0_DATA1 33 IO16, I2S_SDI H6 pin 26
19 IO30, SDIO0_DATA0 H6 pin 27, SD card, Slave Module SDIO0_DATA0 32 IO17, I2S_SDO, SDIO1_DATA1 H6 pin 27, Slave Module SDIO1_DATA1
20 IO29, SDIO0_CLK H6 pin 29, SD card, Slave Module SDIO0_CLK 31 IO18, I2S_SCLK, SDIO1_DATA0 H6 pin 30, Slave Module SDIO1_DATA0
21 IO28, SDIO0_CDN H6 pin 31, SD card, Slave Module SDIO0_CLK 30 IO19, I2S_LRCK, SDIO1_CLK H6 pin 32, Slave Module SDIO1_CLK
22 IO27, SDIO0_CMD H6 pin 33, SD card, Slave Module SDIO0_CMD 29 IO20, I2S_CDCLK, SDIO1_CDN H6 pin 34, Slave Module SDIO1_CDN
23 IO26, SDIO0_DATA3 H6 pin 35, SD card, Slave Module SDIO0_DATA3 28 IO21, CAN2_RX, SDIO1_CMD H6 pin 36, Slave Module SDIO_CMD
24 IO25, SDIO0_DATA2 H6 pin 37, SD card, Slave Module SDIO0_DATA2 27 IO22, CAN2_RX, SDIO1_DATA3 H6 pin 38, Slave Module SDIO1_DATA3
25 IO24, DAC1 H6 pin 39 26 IO23, DAC0, SDIO1_DATA2 H6 pin 40, Slave Module SDIO1_DATA2

For more details, look at the specifications for the Rhomb.io standard.


The Helios board provides the needed voltages on the Rhomb.io sockets. For doing so, Low Dropout Regulators (LDO) has been included for supplying the "1V8 150mA", "2V8 150mA", "Buck8" and "Buck9" voltages. The "VSYS" voltage is switched in between 5V from a DC connector, 5V from USB connectors and VBAT (battery voltage) according to the following cases:

  • There is battery but the USBs or DC connector are not connected: VSYS = VBAT
  • There is battery and the USBs or DC connector are connected: VSYS = 5V
  • There is no battery and the USBs or DC connector is connected: VSYS = 5V
  • There is no battery and the USBs or DC connector is not connected: VSYS = 0V.

As per the above, the Helios board can work connected to a USB 5V source, connected to a DC source or with a battery. In this last case, only single cell Li-Po or Li-Ion batteries are supported. The charging rate is fixed to 100mA.

The input voltage range for the DC connector is 3V to 40V.

The following table summarizes the power supply signals on the Helios board and indicates where are used.

Signal (Rhomb.io) Voltage (V) Device
5V 5 VSYS line
5V_USB 5
VSYS 3 - 5.5 Rhomb.io modules, headers
3V3 3.3
2V8 2.8
1V8 1.8

Getting started


The schematics are available here.

Bill of materials

The BOM is available here.

Gerber files

Ther gerber files are available here

Mechanical specifications


Helios Dimensions v1.png


  • 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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