NES front loader LEDs

[matt2]

I've successfully installed a LED into my controller, now I want to put some in the main casing, but I am not that good with electronics so I'm wondering if anyone knows a good detailed tutorial on adding LEDs to the case or if someone could explain it.

I want to hook up as many as possible green LEDs (once I purchase them at radio shack) and I found a few 12V connections on the main board but I want to know to how to know how many LEDs I can get off each 12V without interfering with the operation of the nintendo. Also would it be better to put them in series or parellel? Also whats the best method of hanging them in the case so it looks the best? Just gluing them to the side?

Thanks

[Aidan]

Green LEDs are pretty typical silicon diodes - they have a forward voltage drop of around 1.4V (check the forward voltage on your LEDs though, they may be different). That means you can get about 8 across a 12V supply, depending on the LED.

However, you need to include a resistor, as LEDs are current sensitive devices, rather than voltage sensitive devices, bearing in mind that each LED will 'waste' the foward voltage drop.

Just FYI, the forward voltage of the LEDs is the amount of voltage you have to put through them before they will start to conduct at all. You have to have at least the forward voltage of the LED across all LEDs that are in series, otherwise none of them will light up.

There's also a typical current that the LEDs are designed to work at. It's usually between 20mA and 50mA, but it depends on the LED. This is the allowable current though an LED or series of LEDs.

If you use ohms law, you can figure out the size of the resistor you need by adding up the forward voltage drop across each LED (1 LED = ~1.4V, 2 LED = ~2.8V, 3 LED= ~4.2V etc). You can then subtract the total forward voltage drop from the supply voltage to find out how much voltage is left over. (IE, 3 LED = 4.2V, supply = 12V, there's 7.8V 'spare'). Once you know how much is spare and what the typical current is for an LED, you can use Ohm's law to work out the resistance.

For a set of 3LEDs I have, we have 7.8V spare and a typical current of 40mA. We convert the current into Amps by dividing by 1000, so we end up with a typical current of 0.04A. Then we plug in the voltages, knowing the the resistance we need is calculated by dividing the spare voltage by the current.

So, for that 7.8V, we divide it by 0.04 to give 195 (7.8/0.04) ohms of resistance. We don't have a 195Ohm resistor, as the closest is 200Ohms. Sorted.

Obviously if the voltages, number of LEDs and current are all the same, the resistor value will remain the same.