# Path of least resistance right?

#### VictoryLap

Joined Oct 3, 2019
5
So I've built a buffer using:
- 3.3V power supply module
- 1 Yellow LED(left)
- 1 White LED(right)
- 2 220 Ohm resistors
- 1 1k Ohm resistor
- 1 2N3904 NPN transistor
- 1 jerry-rigged button (push to close)

But for some reason, I can't understand the white LED won't turn on when the transistor turns on.

thanks,
a circuit newb

#### MrChips

Joined Oct 2, 2009
21,647
The white LED requires more than 3.3V to turn on.

#### MrChips

Joined Oct 2, 2009
21,647
The two LEDs and two resistors are all in series. You do not need two resistors.
You need to show where the -VE side of the first battery is connected.

#### VictoryLap

Joined Oct 3, 2019
5
Thank you MrChips! I guess my math was wrong? I just tested the positive rail with that leads into the white LED(ultimately into the collector) w/ 5V and works like a charm!

but when you say I don't need 2 resistors are you referring to the fact that I could use a 1.2k ohm resistor instead of a 220 and 1k?

#### MrChips

Joined Oct 2, 2009
21,647
Why do you need the transistor?

Try battery, switch, 220Ω resistor and one LED first.

#### VictoryLap

Joined Oct 3, 2019
5
I was looking to show off on youtube my "perfect" understanding of building logic gates using transistors lol

#### VictoryLap

Joined Oct 3, 2019
5
Thanks again, I gotta look at some data sheets and crunch some numbers to make sense of this mathematically.

#### MrChips

Joined Oct 2, 2009
21,647
Ok.
Use one LED on the collector of the transistor.
The 1kΩ resistor on the base is ok.

You can increase the 220Ω resistor to make the LED less bright.