Tech help needed in building an LED display

[glotech]

Hello everyone, Am new to this site but have been an observer for a while now. A very intelligent audience indeed. I've no vast experience in electronics except a few basics. I've been trying to do some exciting projects but don't know how to begin. I want to learn how to do an LED display with my own ideas. It does seem cool but am getting frustrated on how to get started. I can't make a PCB, I can't seem to understand some components that seem vital to making the display reality. I only have limited ability in lighting an LED. I hope someone kind enough can give me the opportunity by explaining how I can go about this project and where I can get some of the components including LEDs. I wouldn't also mind having friends who live in the DMV area that also wouldn't mind hooking up some weekends to help in a project either mine or yours. Much luv to this community. Thanks.

 

[vne147]

Welcome glotech. When you say LED display do you mean that you want to light up multiple LEDs that you will arrange in a pattern to display a word or picture? Can you please be a little more specific about exactly what it is you want to do? If you're not sure and you want ideas in addition to assistance that's fine too.

 

[glotech]

Thanks vne147. I mean't LEDs that I will arrange in a pattern to dispaly a word. A picture seems cool tho. My problem is when the transistors and programing comes in; but I just want to get in the habit of doing these sorts of hobbies, so am willing to try. In the case of LEDs it becomes scary when the resistors, capacitors, transistors, and the programing components have to be integrated. Am learning somewhat on some sites and this site but i still need assistance in knowing how to size these components and notes i need to be aware of when trying to write words with Leds.
Thanks.

 

[vne147]

glotech,

Unless you plan to make the LEDs blink, turn on and off at different times, or have variable brightness the only parts you'll need will be the LEDs, some resistors, and a power source.

The sizing of resistors is easy. The resistors job is to limit the flow of current. The LED brightness will vary with the amount of current that's flowing through it. The more current, the brighter it is. The less current, the dimmer. This is only true up to a point as the LED can only withstand a certain amount of current before it burns out. That maximum current can usually be found in the data sheet. Just for the sake of this example let's say it is 25 mA or .025 A. The maximum current isn't the only thing you need to know. You also need to know what the forward voltage drop of the LED is. This is different for different color LEDs and once again ca be found in the LED's data sheet but for this example let's say it's 2V.

Let's use this simple circuit for the example:



So far we have:

Maximum current: I = .025 A
Forward Voltage: Vf = 2V

Next we need to determine what the voltage drop will be across the resistor. If the supply voltage is 5V and the voltage drop across the LED is 2V then the remainder:

5 - 2 = 3V must be dropped by the resistor.

The current going through the resistor and the LED will be the same because they are in series.

We use Ohm's law:

V= IR to find what value the resistor should be.

Solved for R:

R = V/I

R = 3/.025 = 120Ω

Remember that this resistance value was calculated for the maximum allowed current. To be conservative and to extend the life of the LED it would be best to bump it up a little. If you want a dimmer LED, bump it up a little more.