# Author: darius

## LEDs – No Datasheet, no problem

Spoiler: All you need to do is connect a potentiometer in series with the LED and measure the current. Adjust the potentiometer until the light intensity and current are as you want them – say 20mA. Then measure the voltage dropped on the LED pins and you’ll have the LED’s forward voltage. Now you have all the necessary information to calculate the limiting resistors and other parameters of your LED circuit. All the details are explained in the article below. Happy reading!   There may be times when you want to use one or more LEDs in your project,...

## Power multiple LEDs from a single Arduino pin

Before we begin, I want to mention that this article is about powering multiple LEDs at once from a single Arduino pin. If you wish to separately control each of the LED, an article on that matter will be available soon. What you need: Arduino board Power supply (9V battery, etc), other than your Arduino’s 5V VCC pin. 1x LM7805 or anything that can supply/regulate 5V 1x NPN transistor. I’m using BC141 but any general purpose NPN will probably work. 1x 470 Ohm Resistor – or any resistor in this ballpark 10x LED – or as many as you want....

## Light up multiple LEDs at once

Connecting LEDs in series vs parallel Basically there are two ways in which you can connect LEDs in a circuit. Series or Parallel. Series Connecting them in Series means daisy-chaning You start with one, then add a second one, connecting its (+) to the (-) of the previous one, then a third one, connecting its (+) to the minus of the previous one, and so on. If you look at this image, you can notice that the voltage of the supply is much higher that the common 5V or 9V. Well, assuming that all leds that are depicted here have a forward voltage of 2V, it is easy to understand why a 20V supply is necessary for the 9 leds in the image. When connecting them in series, the total voltage drop between the (+) of the first one and the (-) of the last one is the sum of voltage drops for all leds. You can use various types of leds with different forward voltages, but the total voltage that is needed is the sum of all forward voltages. Considering this, 2Volt x 9LED = 18V total necessary voltage for the leds to power up. However you still have to limit the current going through them, so you have to add a limiting resitor. Choose a small voltage drop to have over the resistor, for example 2V and calculate the required resistance,...

## LED Voltages by Color

Find the “Led Voltages By Color” by scrolling to the bottom Below you can find a table that you can use as a guidance on LED Voltages when you don’t have a datasheet at hand. It’s probably good to use the lower voltage value for calculation purposes, and if the LED light is not bright enough, use a lower value resistor. This way the risk of damaging the it is lower. Consider this example: Assuming lower value: VCC = 5V assume 1.6V for red LED voltage across resistor = 5V – 1.6V = 3.4V resistance of limiting resistor = 3.4V / 0.02A = 170 Ohm Now if the real LED voltage is not 1.6V but 2V, this means: real voltage across resistor = 5V – 2V = 3V real current through resistor = 3V / 170 Ohm = 0.017A = 17mA, lower than the maximum rating of 20mA, so no damage occurs. the led will be dimmer but now you can choose a resistor with a higher value to make the LED brighter Assuming higher value: VCC = 5V assume 2V for red LED voltage across resistor = 5V – 2V = 3V resistance of limiting resistor = 3V / 0.02A = 150 Ohm. Now if the real voltage over the led is not 2V, but 1.6V for your LED, this means: real voltage across Resistor = 5V –...

## LED – Light Emitting Diodes – The basics

Hi everyone, this is a general overview on LED basics and how to use them in your projects. I’m not going to go very deep into technical details but after reading this I hope you will be able to quickly get up and running with a Light Emitting Diode. This article is mostly aimed at DIP LEDs – the type that you can see in the below image (a hard plastic case with two connecting pins), and not the small surface mounted (SMD) type. If you want to read more detailed information on the physics of a these devices,...