Bluetooth: Peripheral HIDS keyboard

The Peripheral HIDS keyboard sample demonstrates how to use the GATT Human Interface Device (HID) Service to implement a keyboard input device that you can connect to your computer.

The sample also shows how to perform LE Secure Connections Out-of-Band pairing using NFC.

Requirements

The sample supports the following development kits:

Hardware platforms	PCA	Board name	Build target
nRF54L15 PDK	PCA10156	nrf54l15pdk_nrf54l15	nrf54l15pdk_nrf54l15_cpuapp
nRF5340 DK	PCA10095	nrf5340dk_nrf5340	nrf5340dk_nrf5340_cpuapp_ns nrf5340dk_nrf5340_cpuapp
nRF52 DK	PCA10040	nrf52dk_nrf52832	nrf52dk_nrf52832
nRF52840 DK	PCA10056	nrf52840dk_nrf52840	nrf52840dk_nrf52840

When built for an _ns build target, the sample is configured to compile and run as a non-secure application with Cortex-M Security Extensions enabled. Therefore, it automatically includes Trusted Firmware-M that prepares the required peripherals and secure services to be available for the application.

Note

If you use nRF5340 DK, the additional configuration of the network core will be taken from the child_image directory. For more details, see Image-specific variables.

If the NFC_OOB_PAIRING feature is enabled, the sample requires a smartphone or a tablet with Android v8.0.0 or newer.

Overview

The sample uses the buttons on a development kit to simulate keys on a keyboard. One button simulates the letter keys by generating letter keystrokes for a predefined string. A second button simulates the Shift button and shows how to modify the letter keystrokes. An LED displays the Caps Lock state, which can be modified by another connected keyboard.

This sample exposes the HID GATT Service. It uses a report map for a generic keyboard.

LE Secure Out-of-Band pairing with NFC is enabled by default in this sample. You can disable this feature by clearing the NFC_OOB_PAIRING flag in the application configuration. The following paragraphs describe the application behavior when NFC pairing is enabled.

When the application starts, it initializes and starts the NFCT peripheral that is used for pairing. The application does not start advertising immediately, but only when the NFC tag is read by an NFC polling device, for example a smartphone or a tablet with NFC support. To trigger advertising without NFC, press Button 4. The NDEF message that the tag sends to the NFC device contains data required to initiate pairing. To start the NFC data transfer, the NFC device must touch the NFC antenna that is connected to the nRF52 device.

After reading the tag, the device can pair with the nRF52 device which is advertising. After connecting, the sample application behaves in the same way as the original HID Keyboard sample. Reading the NFC tag again when the application is in a connected state causes disconnection. When the connection is lost, advertising does not restart automatically.

User interface

Button 1:

Sends one character of the predefined input (“hello\n”) to the computer.

When pairing, press this button to confirm the passkey value that is printed on the COM listener to pair with the other device.

Button 2:

Simulates the Shift key.

When pairing, press this button to reject the passkey value which is printed on the COM listener to prevent pairing with the other device.

LED 1:

Blinks with a period of two seconds with the duty cycle set to 50% when the main loop is running and the device is advertising.

LED 2:

Lit when at least one device is connected.

LED 3:

Indicates if Caps Lock is enabled.

If the NFC_OOB_PAIRING feature is enabled:

Button 4:

Starts advertising.

LED 4:

Indicates if an NFC field is present.

Configuration

See Configuring and building an application for information about how to permanently or temporarily change the configuration.

Setup

The HID service specification does not require encryption (CONFIG_BT_HIDS_DEFAULT_PERM_RW_ENCRYPT), but some systems disconnect from the HID devices that do not support security.

Building and running

This sample can be found under samples/bluetooth/peripheral_hids_keyboard in the nRF Connect SDK folder structure.

When built as firmware image for the _ns build target, the sample has Cortex-M Security Extensions (CMSE) enabled and separates the firmware between Non-Secure Processing Environment (NSPE) and Secure Processing Environment (SPE). Because of this, it automatically includes the Trusted Firmware-M (TF-M). To read more about CMSE, see Processing environments.

To build the sample with Visual Studio Code, follow the steps listed on the How to build an application page in the nRF Connect for VS Code extension documentation. See Configuring and building an application for other building scenarios, Programming an application for programming steps, and Testing and optimization for general information about testing and debugging in the nRF Connect SDK.

Testing

After programming the sample to your development kit, you can test it either by connecting the kit as keyboard device to a Microsoft Windows computer or by connecting to it with nRF Connect for Desktop.

Testing with a Microsoft Windows computer

To test with a Microsoft Windows computer that has a Bluetooth® radio, complete the following steps:

1. Power on your development kit.

2. Press Button 4 on the kit if the device is not advertising. A blinking LED 1 indicates that the device is advertising.

3. Connect to the kit with a terminal emulator (for example, nRF Connect Serial Terminal). See Testing and optimization for the required settings and steps.

4. On your Windows computer, search for Bluetooth devices and connect to the device named “NCS HIDS keyboard”.

5. Observe that the connection state is indicated by LED 2.

6. Open a text editor (for example, Notepad).

7. Repeatedly press Button 1 on the kit. Every button press sends one character of the test message “hello” (the test message includes a carriage return) to the computer, and this will be displayed in the text editor.

8. Press Button 2 and hold it while pressing Button 1. Observe that the next letter of the “hello” message appears as capital letter. This is because Button 2 simulates the Shift key.

9. Turn on Caps Lock on the computer. Observe that LED 3 turns on. This confirms that the output report characteristic has been written successfully on the HID device.

10. Turn Caps Lock off on the computer. Observe that LED 3 turns off.

11. Disconnect the computer from the device by removing the device from the computer’s devices list.

Testing with nRF Connect for Desktop

To test with nRF Connect for Desktop, complete the following steps:

1. Power on your development kit.

2. Press Button 4 on the kit if the device is not advertising. A blinking LED 1 indicates that the device is advertising.

3. Connect to the kit with a terminal emulator (for example, nRF Connect Serial Terminal). See Testing and optimization for the required settings and steps.

4. Start nRF Connect for Desktop.

5. Open the Bluetooth Low Energy app.

6. Connect to the device from the app. The device is advertising as “NCS HIDS keyboard”.

7. Pair the devices:

   1. Click the Settings button for the device in the app.

   2. Select Pair.

   3. Optionally, select Perform Bonding.

   Optionally, check Enable MITM protection to pair with MITM protection and use a button on the device to confirm or reject the passkey value.

   Wait until the bond is established before you continue.

8. Observe that the connection state is indicated by LED 2.

9. Observe that the services of the connected device are shown.

10. Enable notifications for all HID characteristics.

11. Press Button 1 on the kit. Observe that two notifications are received on one of the HID Report characteristics, denoting press and release for one character of the test message.

    The first notification has the value 00000B0000000000, the second has the value 0000000000000000. The received values correspond to press and release of character “h”. The format used for keyboard reports is the following byte array: [modifier, reserved, Key1, Key2, Key3, Key4, Key5, Key6].

    Similarly, further press and release events will result in press and release notifications of subsequent characters of the test string. Therefore, pressing Button 1 again will result in notification of press and release reports for character “e”.

12. Press Button 2 and hold it while pressing Button 1. Pressing Button 2 changes the modifier bit to 02, which simulates pressing the Shift key on a keyboard.

    Observe that two notifications are received on one of the HID Report characteristics, denoting press and release for one character of the test message. The first one has the value 02000F0000000000, the second has the value 0200000000000000. These values correspond to press and release of character “l” with the Shift key pressed.

13. In the Bluetooth Low Energy app, select the HID Report (which has UUID 0x2A4D and the properties Read, WriteWithoutResponse, and Write). Enter 02 in the text box and click the tick mark button. This sets the modifier bit of the Output Report to 02, which simulates turning Caps Lock ON.

    Observe that LED 3 is lit.

14. Select the same HID Report again. Enter 00 in the text box and click Write. This sets the modifier bit to 00, which simulates turning Caps Lock OFF.

    Observe that LED 3 turns off.

15. Disconnect the device in the Bluetooth Low Energy app. Observe that no new notifications are received.

16. If the advertising did not start automatically, press Button 4 to continue advertising.

17. As bond information is preserved by the Bluetooth Low Energy app, you can immediately reconnect to the device by clicking the Connect button again.

Testing with Android using NFC for pairing

To test with an Android smartphone/tablet, complete the following steps:

1. Touch the NFC antenna with the smartphone or tablet and observe that LED 4 is lit.

2. Observe that the device is advertising, as indicated by blinking LED 1.

3. Confirm pairing with ‘Nordic_HIDS_keyboard’ in a pop-up window on the smartphone/tablet.

4. Observe that the connection state is indicated by LED 2.

5. Repeatedly press Button 1 on the kit. Every button press sends one character of the test message “hello” to the smartphone (the test message includes a carriage return).

6. Press Button 2 and hold it while pressing Button 1. Observe that the next letter of the “hello” message appears as a capital letter. This is because Button 2 simulates the Shift key.

7. Touch the NFC antenna with the same central device again.

8. Observe that devices disconnect.

Dependencies

This sample uses the following nRF Connect SDK libraries:

• GATT Human Interface Device (HID) Service

• Messages and records (if the NFC_OOB_PAIRING option is enabled)

• Bluetooth LE OOB records (if the NFC_OOB_PAIRING option is enabled)

When the NFC_OOB_PAIRING feature is enabled, it also uses the Type 2 Tag library from sdk-nrfxlib:

• API documentation

• DK Buttons and LEDs

The sample uses the following Zephyr libraries:

• include/zephyr/types.h

• include/sys/printk.h

• include/sys/byteorder.h

• GPIO Interface

• Settings

• Bluetooth APIs:

  • include/bluetooth/bluetooth.h

  • include/bluetooth/hci.h

  • include/bluetooth/conn.h

  • include/bluetooth/uuid.h

  • include/bluetooth/gatt.h

  • samples/bluetooth/gatt/bas.h

References

• HID Service Specification

• HID usage tables

• Bluetooth Secure Simple Pairing Using NFC

• Bluetooth Core Specification Volume 3 Part H Chapter 2

The sample also uses the following secure firmware component:

• Trusted Firmware-M