Any proper spy will find the need on occasion to pass secret information along to an ally securely. There are many techniques to do so — sometimes, they can be highly technical, such as an encrypted digital message, but other times they may need to be decidedly simple and low tech -- hiding information just outside of plain sight can be very effective.
For example, you can write an innocuous-looking letter that will pass scrutiny should it be seen by enemy eyes, yet have top secret information written in invisible fluorescent ink! Your intended recipient can use an ultraviolet (UV) light to read the message!!
In this project we'll use your Gemma M0 to create a touch-sensitive UV light illuminator. Plus, you'll learn a little coding with maker.makecode.com so this is a great way to make your first spy project
You'll need some paper and an invisible UV marking pen, as well as the parts listed below.
Additionally, you'll use two M3 x 8mm screws and nuts to connect the LED to the Gemma M0.