The idea came looking at other Instructable:
I have chose the design with the 555 because I had several 555 around and I like build small projects, like this other credit card sized project.
Step 1: The Circuit and Components
This is a screenshot from the project of :
The Component are:
- 555 Timer
- Credit card
- battery holders (recycled)
- 2032 coin batteries
- 10 kΩ resistor
- 220 Ω resistor
- 4,7 μF electrolytic capacitor
- copper tape (antenna)
- epoxidic glue (few drops)
Step 2: First Prototype
As you can see in the photo, pretty ugly.
But it was working, so I started to work to the final version.
Step 3: Final Version
As you can see in the video it is working and with good sensitivity, actually I had to keep the antenna very short due to the high sensitivity.
I used a 1kΩ resistor instead of 220Ωto reduce the sound of the buzzer .
This is an entry in the
Pocket Sized Contest