BT Click is a compact add-on board targeted for applications that require both Bluetooth Smart and Classic connectivity. This board features the BT121, a dual-mode Bluetooth Smart Ready module solution that gives unparalleled flexibility to integrate both Bluetooth Smart and Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) wireless technologies from Silicon Labs. It contains a high-performance Bluetooth radio, a low-power ARM Cortex MCU, and a Bluegiga Bluetooth Smart Ready stack software marking it an extremely easy-to-use device. This Click board™ can be used in a wide variety of applications such as cable replacement, HID devices, health and fitness, PoS (point-of-sale), industrial and home automation gateways, and others.

BT Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.

BT Click is based on the BT121, a dual-mode Bluetooth Smart Ready module solution that gives unparalleled flexibility to integrate both Bluetooth Smart and Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) wireless technologies from Silicon Labs. It contains a high-performance Bluetooth radio, a low-power ARM Cortex MCU, and a Bluegiga Bluetooth Smart Ready stack software marking it an extremely easy-to-use device. Also, it contains two configurable power-saving modes. Power Mode 1 is a shallow sleep state with all clocks and peripherals running but with the processor core stopped, while Power Mode 2 is a deep sleep state in which most peripheral devices and system clocks are Power-Down states.

The BT121 module generates all the required clock signals internally. The clocks used by the internal MCU and external peripherals are synchronized to an internal 32.768kHz crystal connected to the internal RTC, always available to Wake-Up the module. It will take approximately two seconds for the RTC oscillator to stabilize after power is connected. To avoid this delay it's recommended not to turn off the power supply of the BT121 but to set the module into the lowest power mode providing the smallest current consumption.

This Click board™ uses the UART communication interface as its default communication protocol that supports all standard baud rates up to 4 Mbps. It is also left the option for the user to use the I2C interface if he wants to configure the module and write the library by himself. In addition to standard UART TX/RX pins, it also has UART RTS/CTS pins routed on the CS and PWM pins of the mikroBUS™ socket recommended for every application for reliable data transfer.

It is necessary to mention the way this Click board™ works so that the user can use it correctly. In the example code that Mikroe offers to its users, the Serial Bluetooth Terminal Android application was used. By clicking on the given link, the user is directed to the free Android application on the Play Store that needs to be downloaded and installed so that he can pair his device with BT Click. Only after successful pairing, the BT Click will be visible in the Serial Bluetooth Terminal Android application.

The BT121 module comes with built-in firmware that provides the ability to use the module Update feature. The module can be updated through the UART interface by holding the built-in ARM® Cortex® MCU of the BT121 module in a Reset state via RST pin, which typically will free the UART communication lines to be used by the Device Firmware Update protocol (DFU). DFU protocol contains commands and events that are related to controlling firmware update over the configured host interface and are available only when the module has been booted into DFU Mode. The user can find all the necessary commands in the attached API reference document.

The Update function consists of the following steps:

Boot device to DFU mode with DFU Reset Command. Wait for the DFU Boot Event. Send command Flash Set Address to start the firmware update. Upload the firmware with Flash Upload Commands until all the data has been uploaded. Send Flash Upload Finish command when all the data has been uploaded. Finalize the DFU firmware update with the Reset command. In addition to all features, the BT Click also has additional components such as 2 LED indicators as well as several onboard pushbuttons. Based on the example code, the blue LED labeled as LED1 is used to visually indicate the successfully established connection, and the red LED labeled as LED 2 reports when establishing the connection is unsuccessful. The onboard pushbuttons don’t have a precisely defined function. It can be configured to operate as a standard general-purpose digital I/O’s, and they are left to the user to configure them according to their needs.

This Click board™ is designed to be operated only with a 3.3V logic voltage level. A proper logic voltage level conversion should be performed before the Click board™ is used with MCUs with different logic levels. However, the Click board™ comes equipped with a library that contains easy to use functions and an example code that can be used as a reference for further development.

• Interface: Analog, I²C, UART
• Compatibility: mikroBUS™
• Dimensions: 42.9 x 25.4mm
• Input Voltage: 3.3V
• Supply Voltage: Min. -0.3V, Typ. 3.3V, Max. 3.6V
• Frequency Range: Min. 2402MHz, Max. 2480MHz
• Operating Range: Min. 200m, Max. 400m
• Operating Temperature Range: Min. -40°C, Max. +85°C

• Schematic
• BT121 Datasheet
• Bluetooth Smart Ready API Reference
• mikroSDK
• GitHub