ESP8266 Community Forum

- Sat Aug 15, 2020 6:16 pm #88329 I used a 150 ohm resistor, i was using 3.3V pin on esp8266 board. My multimeter wasn't able to detect the current, granted it will only show as low as 0.01A. But it stayed at constant 0.00A, only jumping to 0.01A every 5 seconds or so. The LED is plenty bright for my needs, i could even make it less bright but its ok for now.

- Sun Aug 16, 2020 4:17 am #88330 This cloud based calculator will calculate everything for you regarding LED current limiting: http://led.linear1.org/1led.wiz

It says that for a red led (Vf 2.0) and passing 20 mA, an 68 Ohm resistor will suffice.

You can calculate this yourself if your adventureous:
- subtract the Vf from the supply current (in this case that would be 1.3 V)
- this is the voltage that needs to be over the resistor (so LED + resistor will be add up to 3.3 V)
- Ohm's Law says I = V / R, let's fill it in: 0.020 = 1.3 / R -> R = 65 Ohms.

Microcontroller's GPIOs are almost never a true connect-through to Vcc or GND, it's more like a current source, so you might get away leaving the resistor out, if you're using a LED that has a sufficient high Vf regarding to Vcc. But I'd really rather add a $ 0.01 resistor.

- Sun Aug 16, 2020 5:42 am #88331 Each led is happy with its own 150 ohm resistor. But it makes me wonder how bright those LEDs can get .. like i said, i am barely using any current now, my multimeter will not show it. And it is plenty bright for my needs (i need the led to simply tell me if something is working or not). I am wondering if i used less resistance and use 20mA per LED .. i could actualy make a bicycle light out of a bunch of this i think

- Sun Aug 16, 2020 6:05 am #88332 Especially with blue and white LEDs, which are very bright, I tend to use a 10 kOhm resistor. They will only use << 1 mA then, but still clearly visible. For red/green/orange/yellow LEDs a 1 kOhm resistor is still fine.