Introduction: Availability Indicator

Since i work at my home office, my wife asked me a way to quickly know if i'm available or not.

So i built a small availability indicator, controlled remotly by Bluetooth.

For this, i used :

  • Teensy v2
  • a HC-05 (Linvor) bluetooth module
  • a servo motor
  • some wires
  • a piece of wood
  • paper, scissor, glue, tape etc...

Step 1: Hardware

It's quite simple, just connect as shown.

I used a Teensy without header pins, so the wires are directly soldered on the board

Step 2: Frame

The servo is blocked by nails, on the top of the wooden piece.

Use the attached pdf file, print it, and glue it on a piece of cardboard, then cut . On the top the board, a hole was digged to allow the servo axis.

Same for the arrow (print, glue, cut), and it was fixed on the servo arm with tape.

Step 3: Software

There is two pieces of code : one for the Teensy, and one for the computer


The Teensy code is Arduino compatible. We manage the Bluetooth module with the HardwareSerial library

#define MOTOR_PIN  4

HardwareSerial bt = HardwareSerial();
Servo myservo;

char c;
int pos = 0;
char intBuffer[12];
String intData = "";
int delimiter = (int) '\n';

void setup()

  myservo.attach(MOTOR_PIN);  // attaches the servo on pin 9 to the servo object
  bt.println("Start !!");
  myservo.write(130); // Force 'Free' position at startup

void loop()
      while (bt.available() ) {
        int ch =;
        if (ch == -1) {
            // Handle error
            Serial.println("No Data");
        else if (ch == delimiter) {
            Serial.println("delimiter -> break");
        else {
            intData += (char) ch;

      if (intData.length() > 0) {
        // Copy read data into a char array for use by atoi
        // Include room for the null terminator
        int intLength = intData.length() + 1;
        intData.toCharArray(intBuffer, intLength);
        // Reinitialize intData for use next time around the loop
        intData = "";   
        // Convert ASCII-encoded integer to an int
        int pos = atoi(intBuffer);

        if(( pos > 0 ) && (pos <= 200 ) ) {
           //Serial.print ("go to pos : ");
           //Serial.println(int(pos) );
           pos = 200;


I've built a small app in Python / Gtk, using the bluetooth librairy. It's rn under Linux box.

I sent the servo position manually from the python code. Mine was 130 for 'Free' position, 70 for 'Work', and '25' for 'Phone'. You can calibrate it using a serial app (like cutecom).

You must insert your Bluetooth module MAC adress. You can obtain it with hcitool command

user@laptop:~ > hcitool scan
Scanning ...
        00:xx:xx:xx:12:80       HC-05
user@laptop:~ >

As we use RFCOMM, we need to setup the linux box

user@laptop:~ > cat /etc/bluetooth/rfcomm.conf
# RFCOMM configuration file.
rfcomm0 {                                                                                                                                                                                                                                              
   bind yes;                                                                                                                                                                                                                                           
   device 00:13:03:19:12:80;                                                                                                                                                                                                                           
   channel 1;                                                                                                                                                                                                                                          
   comment "BT-001";                                                                                                                                                                                                                                    
user@laptop:~ >

user@laptop:~ > cat /var/lib/bluetooth/<your_BT_adapter_addr>/pincodes
00:13:03:19:12:80 1234
user@laptop:~ >

Step 4: Final

The indicator is action !