## Introduction: LED Display

I ordered a USB solar charger and torch from China on eBay and received a kit instead of a complete product.

There were missing parts that included missing wires and a missing reachable battery.

This gave me an idea. I would use the metal case and the screen from the torch to make my 12 LED display.

You need one red wire for the positive connection and 12 black wires for the negative connection. You also need resistors for each LED to make sure the LED voltage does not exceed 2 V and the current does not exceed 5 mA or 10 mA depending on the LED current rating.

A friend of mine also received the same kit and found a use for the bright LED panel from the torch:

## Supplies

Components: 20 LEDs, insulated wires, 100-ohm or 220-ohm resistors, wooden block, screws, washers, power source (3 V minimum - AAA/AA/C/D batteries, battery harness).

Optional components: solder.

Tools: electric drill, wire stripper, pliers, screwdriver (plus/minus, or both).

Optional tools: soldering iron.

## Step 1: Design the Circuit

Calculate the required resistance value for 5 mA current LEDs:

Rled = (Vs - Vled) / Iled = (3 V - 2 V) / 5 mA

= 200 ohms

(I chosen 220 ohms from E12 resistor series)

Calculate the required resistance value for 10 mA current LEDs:

Rled = (Vs - Vled) / Iled = (3 V - 2 V) / 10 mA

= 100 ohms

(I chosen 100 ohms from E12 resistor series)

Calculate the maximum resistor power dissipation:

Pmax5mA = Vrled * Iled

= 1 V * 5 mA = 0.005 Watts = 5 mW

Pmax10mA = Vrled * Iled
= 1 V * 10 mA = 0.01 Watts = 10 mW

Thus we can use 0.25 W or 250 mW resistors.

## Step 2: Simulations

PSpice software simulated LED currents are very similar to the predicted/calculated values.

## Step 3: Drill the Holes

I drill the holes in my wooden block.

## Step 4: Make the Circuit

I used yellow instead of red wire because I have a big spool of yellow wire. Also, I connected the yellow wire to each LED (you do not need to do that) to allow differential input control. My display can show the difference in magnitude between two inputs. However, the positive voltage must be at least 2 V greater than the negative to ensure that the LED turns ON.

You can see how the other side of the wooden block looks like in the second photo.

## Step 5: Testing Letters

Testing for Latin alphabet letters:

"H", "A", "L" and "T"

## Step 6: Testing Russian Letters

Testing for Cyrlic alphabet letters:

1. "Г" - Similar to Latin alphabet letter "G"

2. "П" - Similar to Latin alphabet letter "P"

## Step 7: Testing Numbers

Testing for Arabic and Roman numerals:

1. "0" - Zero

2. "II" - Two

## Step 8: Testing Pictures

Testing for pictures:

1. Rocket

2. Alien UFO

Participated in the
Lighting Challenge