This week, I am going to show you how to make
a LED matrix dessert tray. This will let you light up and animate your cakes and other
snacks. The first thing that you need to do is build
a large LED matrix. Start by cutting out a 10 inch by 10 inch square of card stock and
dividing it into a grid of 2 inch squares. Next we need to attach a set of LEDs in each
square. To do this, take a pin and make two holes for the leads of each LED. Then insert
the LEDs so that all the cathodes are on one side and the anodes are on the other.
We need the LEDs in each square to be connected in parallel. So I bent the cathodes in one
direction and I bent the anodes in the opposite direction. Where they overlap, I soldered
the leads together and wrapped them in heat shrink tubing.
Now we need to connect the individual squares together into rows and columns. First I connected
the anodes in each row together with a large piece of copper wire. Then I applied tape
over it to help insulate it. Next I connected all the cathodes in each column together.
And I applied more tape to insulate these connections. You should now have a functioning
LED matrix. To test it, take a 3V battery pack and connect
the positive wire to one of the rows and connect the negative wire to one of the columns. The
LEDs in the intersecting square should light up.
To help keep the light in each square from diffusing into the adjacent squares, I added
a set of dividers that I made from folded paper. Now you need to construct the plastic cover
plate that will hold the dessert. To do this, I started by cutting out a 16 inch by 16 inch
piece of clear plastic. Then I cut some 3 inch wide pieces of foam board and glued them
around the outside. When you are done, the cover plate should perfectly fit around the
LED matrix. The last thing that you need to do is setup
a control circuit for the LEDs. I am using an Arduino microcontroller. The easiest way
to use an Arduino to control an LED matrix is to send a HIGH signal to the anode and
a LOW signal to the cathode. This will turn on the LED. Unfortunately, the LEDs that I
am using require more power than the digital pins can output. So I am using a set of power
transistors to control the switching. In this configuration, I have an NPN transistor connected
between each set of cathodes and ground and a PNP transistor connected between each set
of anodes and the positive supply. The base of each transistor is then connected to the
digital pins with a 1 k resistor. Now your LED matrix dessert tray is complete.
All you need to add is the dessert. The best things to use are snacks that let a lot of
light through such as white cake or rice crispy treats. Set your dessert on top of the tray
and turn it on. There is a link in the description box where you can download some example code
to animate your LEDs. Well that is how to make an LED matrix dessert
tray. Thanks for watching.