https://www.youtube.com/watch?v=dtoTy4uD9vI
We used a low-cost Arduino Uno micro-controller to prototype our device (mechanical IoT-enabled switch flipper) together with a HC-05 bluetooth module and a TowerPro SG90 servo.
A 3d-printed housing is used to secure the servo onto the switch surface and a custom arduino shield was soldered on a breadboard to reduce the overall profile of our setup.
warning It is recommended to regulate the signal voltage down to a manageble 3.3V for the HC-05 module as the RX pin on the module is not rated for the 5V signal Arduino sends by default.
Hooked up to a wall switch.
To enable AT-Mode with your HC-05 module, press and hold the button on the module (when it is powered off) and power it on. If the blinking is roughly once every 3s, you're good to go in AT-Mode, otherwise, the module will blink rapidly (power it off and retry).
Once in AT-Mode, load the hc05_config program which is simply a read/write channel to the module.
//Adjust the parameters as neccessary to your setup
SoftwareSerial BTserial(3, 2); //RX pin | TX pin (relative to the Arduino)
Out-of-the-box, the HC-05 module has a default password like 1234 (totally insecure) and a default name. You should change it!!
important! Open the Serial Monitor and select "Both NL & CR" at the default 9600baud before attempting communication with the module.
First, try a "AT" command, you should get a "OK" response. Next we want to rename our module into something more friendly:
AT+NAME="LUMOS"
Now if you try a "AT+NAME?" command, you should get "+NAME: LUMOS" response (or sth similar).
Next we want to setup our password.
AT+PSWD="1234"
Obviously you should change it to something more secure. In any case, you can use "AT+PSWD?" to view the set password if you forget.
Power off the module and power it back on to escape AT-mode. Now we're ready to pair with our backend/bluetooth controller!
Here's a full list of AT commands.
You can use the Bluetooth Terminal app on play store to quickly pair with your HC-05 module and test it out. If you still have your serial monitor up, you should be able to see the messages your phone is sending to the HC-05 module :D
Particular bluetooth commands are hard-coded into the firmware as triggers to move the servo. A 'contact sensor' (two pieces of conductive metal touching) is used to give feedback to the current switch position.
U -> 'Up' Movement of servo
D -> 'Down' Movement of servo
T -> Flicker lights in a certain order to signal device connection
Closed circuit -> C //Switch sensor detects one position
Open circuit -> O //Switch sensor detects the other position
blue_shield -> Arduino firmware driving the switch
hc05_config -> Code to allow Arduino serial terminal to configure hc-05 bluetooth module
servo_housing.stl -> Stl file to 3d-print servo housing