# LED issue

Hi,

I got a "1 inch 7 segment Blue LED display common cathode" LED from ebay. But when I connect it the a b and c sections of the LED is very very dim I can barely see it. So I tried taking out the 91 ohms resistors and still it was really dim. The LED is Voltage:3.2V Current:160mA. Wondering if I am missing anything?

The 3 and 8 pin on the LED is ground so I am connecting both of them to ground. Any suggestion?

160 mA is way too much for an Arduino pin to supply. You will need a driver of some kind.

Wondering if I am missing anything?

You will be missing your arduino if you take more than 40mA from a pin. It will kill it.

You didn’t set your pins to OUTPUT and/or as the other suggest, you’re drawing to much current out of the pins.

thanks guys, yea looks like it was taking up too much current. In the specs it said 160mA so I thought that means it is the total current but maybe it’s 7 * 160. I emailed the seller to find out what exactly is 160mA.

160 mA <---- milli Amps or 0.16 A per segments

7 * 0.16 = 1.12 A ← That will happen when a 8 is light up. ( all segments on )

jat421: I got a "1 inch 7 segment Blue LED display common cathode" LED from ebay.

eBay sellers are well known for their selection of high quality components.

jat421: But when I connect it the a b and c sections of the LED is very very dim I can barely see it. So I tried taking out the 91 ohms resistors and still it was really dim. The LED is Voltage:3.2V Current:160mA.

5-3.2V = 1.8 1.8V / 91ohms = 20mA

When you "take out" the resistor, how is the LED connected? If connected to an I/O pin, you're only going to get about 45mA out of the pin (before it dies). If connected directly to 5V, the segment should be very bright for a few seconds (before it dies).

jat421: yea looks like it was taking up too much current.[/qutote] An LED will only "take up" as much current as you give it. If you are using a current limiting resistor, THAT limits the current, not the LED.

160mA sounds more like the total current draw if all segments are on, not each individual segment. Typically LEDs draw around 20-30mA. So 20mA * 7 = 140mA.

You're doing something else wrong or the segment is bad. Describe your setup in more detail. (e.g. are you connecting to an I/O pin or are you connected directly to 5V?)