It has been many years since my brother, who is an awesome graphic designer and a pixel-art fan, asked me to make an "LED grid" for him to have his pixel art sketches hanging on the wall. The goal was to create something which is easy to use and fast to "draw" with, and good looking enough to hang on the wall of coarse. at the time, I was 16 years old and not really into electronics, so nothing happened with this project.
A few weeks ago, approximately 10 years later (!), I had some free time and decided to give my brothers' challenge a try.
I thought that the simplest design would be to control each LED separately, and as I didn't want to use a microcontroller and multiplexing, I decided to use a switch for each LED. I figured that an 8X8 grid should be enough for a nice adjustable LED box and for that it will require 64 LED's and 64 switches.
Well, things turned up not to be that simple. I went to the electronics shop, only to find out that even the simplest switches are quite expensive!
So, I decided to buy only the LED's, and to figure something out instead of the expensive switches.
The indestructible you are about to read utilizes the solution I came up with- it is not ideal, but if you have some screws laying around in your shop, it is probably the cheapest rout to a controllable LED grid.
The basic concept is as follows:
64 LED's connected in parallel, are attached through 64 resistors to ground, and 64 screws which act as a switch are connected to 5V. When a screw is tightened, it touches a conducting point on the prototyping board which closes an electric circuit with the LED and current flows through the LED, and there shell be light!
Step 1: Tools and Materials
Tools you will need:
2.7mm drill bit (or a drill bit that drills a hole which will fit your screws after tapping)
5mm dril bit
Fine M3 tap or similar size tap that fits the screws you chose.
Sand paper (120 grit)
Materials you will need:
Standard prototyping board, 2.54 mm hole spacing
UHU all purpose glue
Fast curing (5-10 min) epoxy glue
123 primer or similar
4mm Balsa wood
4mm aircraft plywood
Laboratory filter paper or similar
73 M3X12mm screws
18 M3 nuts
Some electrical wires (sparkfun 22 AWG or similar)
64 LED's (I chose red, make sure you know what is the voltage drop of your LED of choice)
64 220 ohm resistors
Female DC cord connector
5V power supply (1-2 Amps is fine)
Step 2: Assembling the Prototyping Area
My prototyping board came in a peculiar elongated rectangular shape. It was about 11X50 cm with the standard 2.54 mm hole spacing. I guess these dimensions make some sense when one uses the imperial system...
Anyway, I decided on a 15X15 cm grid to accommodate my 64 LED's, with about 1.7 cm between each LED.
In order to obtain a prototyping board of these dimensions, I had to assemble the board from two pieces (15X10cm and 5X15 cm) which were cut using a sharp blade and a ruler, and glued together using cyanoacrylate glue.
Step 3: Laying Out the Electronics and Soldering
I started laying out the LED's.
I positioned them so that they are all evenly separated from one another making sure that they all have their long positive leg (the anode) facing the same side. This side was marked with a piece of blue duck tape. When I was happy with the layout, and after double checking the polarity, I used some clear tape to hold the LED's in place and turned he prototyping board upside down.
And then I started soldering...
After a good 20 min of soldering this is what I got.
And then, it was resistors time!
Each red LED causes a 1.8 voltage drop, so assuming an LED's typical current drew is 10-20 milliamps, and a 5V power source, 220 ohm resistors in series with the LED's should result in ~15 milliamps of current through each led.
So each LED had a 220 ohm resistor attached to its cathode (negative, short leg) in series. When soldering, make sure you cut only one of the resistor's legs (cut the one closer to the LED’s cathode) as you will use the other one to create the circuit.
Now that the resistor is soldered in place, band the resistor's remaining leg at 90 degrees, so it reaches the next resistor- this way we will get 8 rows of 8 LED's each connected in series to a resistor, and each resistor-LED couple is connected in parallel to the other LED-resistor couples. When you’re happy with the result, solder it al up.
It is now time to connect all 8 rows of parallel LED-resistor couples to a common ground. To do so, I used a small piece of wire, soldered perpendicular to the previously soldered rows.
After soldering everything in place your board should look something like the last picture
Step 4: Cutting the Base and Drilling the Holes
A 15X15cm square base was cut from 4mm aircraft plywood using a sharp modelling knife and a ruler.
To drill the holes properly, a grid was drawn on the plywood using a pencil and a ruler. The line spacing should be about 1.7 cm.
Each line cross section indicates the position of an LED.
Bear in mind that as the LED's cathode is approximately 2.5 mm from the centre of the LED, the holes actually need to be shifted 3-4 mm from the pencil mark.
I used a 2.7 mm drill bit and drilled 64 holes, all of them shifted ~3 mm down from the pencil mark.
After the holes were drilled, a fine metric M3 tap was used to thread the holes.
Step 5: Weaving the 5v Wire Around the Screws
So now that the holes were all drilled and the screws were all in place, I used a standard 22 AWG (Sparkfun) wire to "weave" all the screws together to have them all connected to the 5V source.
After removing the plastic insulation from the wire, I started weaving the wire around the screws. As the work went along I removed more of the red insulating plastic until I got to the last screw, where I left 15 cm of wire with the insulation still on, to be soldered later to the 5V of the power supply
In order to hold the wire in place and make sure it doesn't move later I used a few spots of 5 min epoxy.
The final result should look something like the picture attached
Step 6: Mounting the Electronics on the Wooden Base and Building the Balsa Walls
The prototyping board, now with all the electronics soldered to it was fitted on the wooden base, and 9 holes were drilled through both boards using the same 2.7mm drill bit as before. The holes were threaded and the boards were assembled together, using M3 screws (12mm long) and two M3 nuts as separators between the boards.
You can see the screws holding this LED sandwich together in the first picture
To build the walls, I used some 4mm thick balsa which I had laying around my shop.
I used a sharp blade and ruler to cut two 15X3.5 cm and two 15.8X3.5cm balsa strips and drilled a 5mm hole in one of the shorter ones (for the power cord), then I glued them to the plywood using cyanoacrylate.
Before gluing the sides, make sure the "switch" screws are screwed away from the electronics board (see picture) so that their bottom end is flush with the plywood base.
remember that the way this LED frame works is by closing an electric circuit when you tighten up the relevant screw (turning on the LED), and it is important to make sure there is enough room for the screw's head between the wall and the frame to allow the LED to be in an “off” state.
Step 7: Attaching the Power Cord and the DC Connector
The box was now assembled, and all I had to do was to provide some extra juice for box to light up.
I used a screwdriver to disassembled the circuit board from the plywood base and untightening all 9 screws that held it in place (remember the nuts) to remove it from the base.
For the power cord, I used an old PC power cord and cut it to about 15cm. I then soldered a female DC connector to one end. The blue wire was soldered to the circuit board, to the common ground line, and the brown wire was soldered to the red 5V wire which was attached to the plywood base with all the screws.
I didn't have any shrink tubing, so I used a piece of electricity tape to cover the soldered joint.
After soldering, I re-assembled the circuit board to the box housing and made sure everything works.
Step 8: Painting the Box and Covering It With Paper
The box was painted twice with a 123 primer I had laying around, and sanded between coats with a 120 grit sand paper. Make sure you let the primer dry for a few hours before sanding.
This gave a nice white matt finish which I liked, so I decided to leave it as is.
Next, I used some clean laboratory filter paper to cover the open face of the box.
I placed the sheet of paper on a clean table and covered the edge of the box with a thin coat of "UHU all purpose glue". I then pressed the box against the sheet of paper, and let the glue dry for an hour or two.
When the glue dried, a razor blade was used to trim the access paper.
Step 9: Final Remarks
The frame works nicely, it is pretty easy and straight forward to design any drawing that is 8X8 (8 bytes) and it looks pretty neat on the wall.
There is a small bug with the on/off mechanism though, when the screw is tightened, it pushes the prototyping board and this sometimes causes the LED's in vicinity to turn off. All you have to do is tighten the other screws a little more.
Grinding the solder contact point on the prototyping board and levelling it with a Dremel tool helps a lot with this issue.
Thanks for reading this far, I hope you liked this instructable!