Dynamite Egg Timer


Now what the hell it this!?

This is an egg timer that looks like dynamite, however explosion is not implemented. It just displays a countdown. Many times, I get asked where I get such ideas from - Honestly, I have no idea, it just happens when I'm bored...

The dynamite rods behind the PCB are just decorative. The one in the middle contains 3 AA batteries for power supply, hence the cables coming out of it. All in all I invested huge effort in looks, since functionality is rather trivial.

And what can I do with it?

The timer doesn't count to zero, but to 00:01 instead, Hollywood style! And at 00:01 there is an alarm sound and additionally a beep sound every second. There is also a switch to deactivate the beeping. The timer can be set using the buttons.

How it's done

The underlaying microcontroller is an Arduino Mega 2560. It's the Mega, because the Arduino Uno is too small to mount all the components on. On top is a shield where the display and the other components are soldered on. Connecting wires are hidden on the back side (see the photos).

Each "dynamite" rod is a PVC tube covered in red paper and filled with brown plasticine. The middle one contains 3 AA batteries yielding about 5V (actually 4.5V) and cables attached to them, coming out of the top. However, you are pretty free when it comes to designing the body, as it is merely decorative and a container for the hidden power supply.

There's a photo below, showing how the components are connected together. This is not a step-by-step guide on how to build one yourself, but it should give you an approximate idea where to start. The Arduino code which I provided as download is pretty trivial, there's really not much to it. It just controls the buttons, the display and the buzzer.

I think the trickiest part is wiring up the 7-segment display. This is where I struggled a bit, to be honest, but there are plenty of guides online on how to set it up. I'm using a 4-digit 7-segment display with common anodes. You will need 8 resistors for the 7 segments plus the colon in the middle connected to the Arduino pins, and you need to connect the 4 digit pins to the Arduino and then multiplex the display. The buttons need to be connected like this. The rest is pretty much basic electronics.

If you're good with electronics, you will be able to build one yourself. Like I said, design is up to you, maybe you have cooler ideas for it?