Controlling a robot with The Tactigon sensors over BLE

In this article we’re going to learn how to use simple Tactigon’s functions to send accelerometer data and quaternions over Bluetooth Low Energy.
alphabot2

Overview

This post will show how to take advantages of The Tactigon’s BLE Central capabilities. We wanted to control our robot by using The Tactigon as a “3D steering wheel” controlling speed with pitch and steering with roll. We made so few changes in the Alphabot2 original Bluetooth example code and wrote a sketch for The Tactigon to connect to the robot’s BLE characteristic and write in wheels speeds.

What we need

The Tactigon with a configured Arduino IDE
Robot. We used a 2 wheels robot with Arduino board and BLE radio interfaced with UART. Other kind of robots or custom ones can work as well.
Robot BLE MAC Address and Characteristic
Fun

Gathering BLE MAC Address and Characteristic

After our environment is configured and our boards are ON, we need to gather BLE MAC Address and Characteristic. To do so we used a free android application called BLE Scanner.

Scanning

Few seconds after the application should show the robot’s BLE:

MAC Address

As we see, all BLE devices around us are showed in this section. We need to write down the Waveshare_BLE MAC address: in this instance it is: 00:0E:0B:0C:4A:00
By clicking on the CONNECT button we access to device’s informations as attribute, service and custom characteristic.

Characteristic

Here we need to write down the CUSTOM CHARACTERISTIC UUID, in this case: 0000ffe1-0000-1000-8000-00805f9b34fb .
With this items we can set our Tactigon BLE to act as BLE Central in the setup() section of the code.

The Tactigon sketch

loop()

In this section we have the core of the sketch. At a frequency of 50Hz, we update quaternions and euler angles.

loop_quaternion_euler

Analizyng pitch angle provided by Tactigon library, we can determine steering radius by slowing internal wheel and accelerating external wheel.

pitch_steering_radius

Analizying roll, instead, we can determine travel speed of the robot.

roll_travel_speed

With a sprintf we prepare the buffer to write in the characteristic.

sprintf_buffer

Robot sketch

Since our Bluetooth sends received data over UART, we get wheels speed directly in the serial buffer.
We have set robot pins as follows, all as output:

robot_pins

To parse the command we first read all the serial buffer and verify if it is longer than 0:

loop_parse1

If the command contains “Wh” we can so parse the string and gather leftSpeed and rightSpeed.

robot_parse_wheel

The direct_motor function assign the speed transmitted by The Tactigon to each wheel of the robot. By doing so The Tactigon will act as a virtual-steering wheel!

direct_motor

Final Considerations

This sketch shows a potential application of The Tactigon, with the BLE Central mode is possible to connect to existing BLE devices and gather informations or control them.

Stay tuned for more Tactigon’s code!

Download Code:

Related Posts