Miniature Bat Signal - Incoming Call Indicator

I found a very old flash light, which was broken and didn't power up - got an idea to make a bat-signal light out of it!

Let's make a simple table top bat-signal which lights up and projects a bat symbol on the wall/surface near your worktable or roof during an incoming mobile phone call.

The device is powered through 5V via USB-C port. Device lights up around vicinity of 150-200 mm from the mobile phone to receive the signal. It works if your phone is next to this device in your worktable!

Circuit works on 2G (GSM/CDMA) network, will upgrade to 3G/4G in later versions.

"What are you waiting for? The Signal!"

―Commissioner Gordon [source]

What is a Bat-Signal? 

The Batsignal (or Bat-Signal) is a distress signal device appearing in the various interpretations of the Batman mythos. It is a specially modified Klieg searchlight with a stylized symbol of a bat attached to the light so that it projects a large Bat emblem on the sky or buildings of Gotham City.

In the stories, the signal is used by the Gotham City Police Department as a method of contacting and summoning Batman to their assistance in the event of a serious crisis and as a weapon of psychological intimidation to the numerous villains of Gotham City. [source]

For more info: 

https://en.wikipedia.org/wiki/Bat-Signal

https://batman.fandom.com/wiki/Batsignal

1. Old LED flash light (for led and reflector)
2. USB Type C breakout board
3. LM358 (DIP8)
4. BC547 (TO92)
5. 2G Helical antenna
6. 6MR resistor
7. 10K potentiometer
8. MEL7135 (on a breakout)
9. 0.1uF capacitor
10. 10K resistor
11. 1K resistor
12. M3 inserts
13. Glue gun
14. Adhesive
15. Hot air blower

Led and the reflector is used from an old flash light. Based on the shape and dimensions of the reflector external housing was designed for 3D printing. Reflector diameter from the flashlight was around 28mm.

You can download the model files for 3D printing from the below link.

link (Please read the post -processing info of the 3D printed files)

PCB is assembled on a protoboard of dimension 35 x 20 mm. Circuit is built and wired based on the available spacing .

All are wired up together and powered by 5V USB. 10K potentiometer is fine tuned to adjust the receiver sensitivity for incoming call.

Circuit is powered from an external 5V USB source. The 2G helical antenna receives a relatively higher amplitude signals during an incoming (or outgoing) phone call, this signal is amplified/compared to reference signal by LM358.

Output of the LM358 is connected to a BC547 transistor to drive the LED. LED is driven by a linear CC (constant current) -MEL7135.

Get ready when the signal arrives!!