I have recently bought a batman key chain from amazon. There is a small button in the key chain, when pressed it lights the batman's eye and sounds a pathetic tune. So I thought of customising it a bit.

The key chain will be able to produce a pacman monotone with a customizable light from the batman's eye. The tune is customizable. I chose pacman tone because it was easy to generate the monotone. If anybody can come up with a batman monotone I am happy to replace the tone.

Things needed.

ESP8266 01
3.7 V LiPo Battery
USB LiPo Charger
Old earphone speaker
LEDs
220 resistor

Step 1: Open the Keychain

The above video shows how it behaves when I got the key chain. Now open the key chain. There is enough room to put some custom electronic parts.

Step 2: Find an Old Earphone and Take One of Its Speaker

Earphone speakers are small and if you are going to generate some monotone sound, it is loud enough to be used in our purpose.

Step 3: Connection

Make the connection as per the circuit diagram. I have used 3 SMD (Red, Green, and Blue) LEDs. I soldered it to a small protoboard with 220 ohm resistor in series with the LEDs. You can use any LEDs, but SMD will save you a lot of space.

Connect the LiPo charger to the battery.

Step 4: Program the ESP

Program the ESP01 using a USBtoSerial converter. You can use arduino IDE for programming ESP8266.

keychain.ino
Download

Step 5: Put Everything Back Inside the Keychain

Make some space using your dremel tool to put everything inside the key chain.

Step 6: Test Your Keychain & Future Additions

Things that can be added in the futuree

Pressing for a long time will enable a hotspot
Option to change the tone by writing it to EEPROM on the go (ESP8266 has 512 bytes of EEPROM).
Option to play PCM encoded 8 bit WAV file.