LEDs, or light-emitting diodes, are current functioning devices that, when connected the wrong way, have almost an infinite resistance. Learn about using integrated circuits for multiple LEDs with help from a science teacher in this free video on circuits and LEDs.
Hi, I'm Steve Jones and I'm going to explain how to build a circuit with multiple LEDs. These are the LEDs, light emitting diodes. In various colors, and if you want to make a set of traffic lights, it's nice to have more than one. So you would have a red an amber and a green, or a red, yellow and a green. The first thing you have to remember is that the light emitting diode is a current functioning device. So the current of 30 milliamps or so is normal for an LED to work. Therefore, if we have a 5 volt supply, we have to work out the resistance we require to limit that current because the light emitting diode has very little resistance itself. If you connect it the wrong way around it has almost an infinite resistance. But, connected the correct way around it has virtually no resistance and therefore, we have to work out the rough resistance, about 166 OHMs. Well, I used 200 OHMs. It doesn't actually matter too much, this would be fine. So, what you do, because resistors only have certain standard values, you select the one nearest to the value you wish for your particular light emitting diode. Now you have a common strip between 5 volts and a common earth strip, 0 volts. To connect the LED, first of all check that it's going the right way around. Obviously, if it doesn't work, turn it around. It's a simple way. Here we connect the LED in a series with a resistant and that will light up immediately as you wish. You can of course add a switch if you wish, on this or that side, or anywhere you like within that to break that circuit. So there can be a separate switch included for each of these devices. Here, I have just drawn three of them connected into this circuit and you can see I can add a switch there and then I can control each of these devices. I could also control them with an integrated circuit. If I want to actually build this, I would actually go and get a piece of this strip board, we call it. It's got copper strips with little holes in. Very thin copper strips on the top of an insulating board. Be very careful when using this because you don't want to get it too hot, otherwise it will all fall to pieces. But, if you wanted to create a circuit like this, on a board of this kind, you would assign one to be 5 volts and assign another to be 0 volts and try and make it look like the circuit diagram. Then you can arrange the components always on the inside side so if you have a light emitting diode, it's got two long legs and there is the LED on the end of it. You put one leg through here, one leg through here and solder it. Remember though, that this leg is now connected to all of the holes along here so if you want to put a resistor in now, then you put your resistor through that hole say, and you put it through that hole and there's your resistor connected in between those two holes. Sorry, I shouldn't have drawn that in that way. So, you solder here, solder here, solder there, solder there. So, the LED is now connected to the resistor. And finally, you solder say, to this point here, and to this point here, your switch. If you solder it between those two points, then you will find you have from the 0 volts it goes through the switch, through the resistor, through the LED, and out to the other side. So, that is a complete circuit when you connect these two to your power supply. That is like this circuit. When connecting the next one, obviously you can't use these two because these two strips are for this one. There are two things you can do. You can break the circuit here, literally cut those strips there, and then do the same in this part because these remain the same. And you can do that three times, if you wished. Or, you can get a piece of strip board which is wider and use two different strips on the board for the other LEDs. So, that is very simply how to design and make a circuit for multiple LEDs.