S100 Slave - WiFi ESP-WROOM-02


The S100 Slave - WiFi ESP-WROOM-02 Module is a certified Rhomb.io module that delivers highly integrated Wi-Fi solution to meet users’ continuous demands for efficient power usage, compact design and reliable performance in the Internet of Things industry.

It mounts the well-known ESP-WROOM-02 module, which integrates the Espressif ESP8266EX SoC. With the complete and self-contained Wi-Fi networking capabilities, this Rhomb.io module can perform as a Wi-Fi adaptor to a host Master through SPI/SDIO or I2C/UART interfaces (other versions of this Rhomb.io Module can perform as a Master themselves for standalone applications).

The S100 Slave - WiFi ESP-WROOM-02 Module integrates a printed circuit antenna with its switches, RF balun, power amplifier, low noise receive amplifier and filters, all of them adjusted to get the best RF performance.

The next figure show a 3D view for the S100 Slave - WiFi ESP-WROOM-02 Module:

S100 Slave - WiFi ESP-WROOM-02 v1.0 (PR) - Top.png S100 Slave - WiFi ESP-WROOM-02 v1.0 (PR) - Bottom.png


  • Internet of Things
  • Home automation
  • Smart lighting
  • Security alarms
  • Monitor and scales
  • Mesh Networks
  • Industrial Wireless Control
  • Wereable electronics
  • WiFi Position System Beacons

Module specification

This module has been build around the ESP-WROOM-02 module from Espressif. Its complete and self-contained Wi-Fi networking capabilities can be controlled easily by AT commands through the UART interface. Aditionaly, a SPI interface is accesible.

The module implements TCP/IP, full 802.11 b/g/n WLAN MAC protocol and Wi-Fi Direct specification. It supports not only basic service set (BSS) operations under the distributed control function (DCF) but also P2P group operation compliant with the latest Wi-Fi P2P protocol. Low level protocol functions are handled automatically by the integrated ESP8266EX.

To facilitate the programing and debugging of the module, a reset button and a mode selection switch have been implemented.

The following figure identifies the main components onboard:

S100 Slave - WiFi ESP-WROOM-02 v1.0 (PR) - Top - Indic.png

The next figure shows the Block Diagram for the S100 Slave - WiFi ESP-WROOM-02 Module:

S100 Slave - WiFi ESP-WROOM-02 v1.0 (PR) - Diagram .png

WiFi ESP8266 Key Features
Espressif ESP-WROOM-02 WiFi module
2 MB Flash, 50 KB SRAM; 802.11b/g/n 2.4 GHz; up to 72.2 Mbps; FCC/CE(RED)/TELEC/MIC)/KCC/SRRC/IC/NCC; WPA/WPA2
Security: WEP/TKIP/AES
64 KB SPI Flash Memory
USB, UART and SPI interfaces
Op. Voltage: 2.8 V to 3.3 V
Op. Temperature: -40 ºC to +85 ºC


User interfaces

The following table indicates the available serial interfaces of the Rhomb.io standard used in this Module. First column shows the signal names of the Rhomb.io standard, and second column points out to which pin of the ESP-WROOM-02 these are connected.

Interface Rhomb.io Signal ESP-WROOM-02 Pin

  • UART: data transfers to/from UART interface can be implemented via hardware. The data transmission speed via UART interface reaches 115200 x 40 (4.5 Mbps). By default, UART outputs some printed information when the device is powered on and booting up.
  • SPI: functions of these pins can ve implemented via hardware. In the ESP-WROOM-02 module, this interface is known as HSPI.



The following table summarizes the GPIOs used on the S100 Slave - WiFi ESP-WROOM-02 Module. This table relates the signals of the Rhomb.io standard with the net names of the schematic and with the components to which they are connected.

Rhomb.io Signal Schematic Signal Component Component Pin
IO7 - -

IO2 Signal could be on-board connected to IO5/RESET Signal through the DEEP SLEEP Solder Jumper. When done this, ESP-WROOM-02 IO16 can be used for Deep-sleep wake-up.

For more details, check the Module Schematics and the ESP-WROOM-02 manufacturer documentation.


The S100 Slave - WiFi ESP-WROOM-02 Module uses only the 3V3 power rail. Make sure this rail is enabled on the motherboard you are going to plug this Module.

The average consumption of the Module is 80 mA, with peaks of 170 mA when transmitting and only 20 μA in deep-sleep mode.

WROOM Power Consumption.png

Getting started

By default, the internal Flash memory of the ESP-WROOM-02 is empty. To download the programs into the Flash follow the procedures below:

  1. First, you must set the module to work under UART Download Mode. The S100 Slave - WiFi ESP-WROOM-02 Module is pre-set to enter in this mode by just using the Mode Switch (SW2 in the schematic).

    Switching it to position 3 (L on board), the GPIO ESP-IO0 will be pulled-down to GND and the device will enter in UART Download Mode.

    WROOM Mode Select.png

  2. Download the programs into Flash with ESP Flash Tool.

  3. After downloading the programs into the Flash, you just have to switch the GPIO ESP-IO0 to position 1 (H on board) to pull it up to 3.3V. Once done this, the Module will shift from UART Download Mode to Flash Boot Mode.

  4. Each time you power on the Module, or after pressing the Reset Button, the programs will be read and executed from the Flash during the initialization.


Click the image below to download the schematic files.

Mechanical specifications


S100 Slave - WiFi ESP-WROOM-02 v1.0 (PR) - Dimension.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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