3pin Bi-colour led

Hi everyone
I’m having difficulty finding a 2colour led with 3 pins of which the common pin connects the anode of the one colour and the cathode of the other colour? A led like this would work perfectly for a hi/low state signal without having to use additional transistor.
Or even a 2colour led with 4 pin where I could manually solder anode/cathode together would work, but also nothing?
Maybe if I new the name for it, I would find it, or don’t one get them like this?

Why do you think that this strange combination is specially helpful?
Can you present your intended circuit diagram?

I have seen leds connected as you describe only once, years ago, on an old Japanese apparate … never found them as spare part, anyway … but if a simple “1/0” status indicator for a circuit is that what you want to build, you can simply use an inverter gate for each led (actually they are available also in SMD single pieces, no more need to use a 6-ports DIP just for one gate as in the past) … just use a bicolor 2-pin led (the ones with chips in antiparallel) and connect one pin of the led to the out of the inverter, and the other with the input (with a resistor) :wink:

A single inverter gate can be used with any 3-pin bicolor LED for an on/off indicator.

Sorry, but my circuit diagram would make you ether laugh or cry!! Basically I want the led to signal me when the signal pin of a 555timer is ether 1/0. If the cathode and anode of both colors were connected, the 1/0 signal could go to that pin and v+ and gr. to the other 2 pins without the need of a inverter gate. Less components is basically the aim of the game!

If you can’t get the desired combination in one case you can do whatever you like with 2 discrete LEDs instead.

Yes, that is how I originally designed it, and then I stumbled upon bi-coloured LEDs. They would make any display that much nicer. So I’ll have to stick with a inverter gate then.
Thanks everyone fir your time

There are also single bi-colour leds with 4 independent pins, but afaik are all SMD … if you can work with SMD is easy to find them, but for passthrough pin components, sorry, i don’t know any …

If you can (or want to) control it from the software, you can simply add a #define in the code.

#define LED_ON LOW
...
...
digitalWrite(ledPin, LED_ON);

And you can change the define to #define LED_ON HIGH if it’s common cathode.

Sterretje, you have me, I actually don’t use an arduino for this project, only a 555timer.
Sorry for using this forum, but my thoughts were that most people here would have the led knowledge I need.
Thanks everyone, my seed blockage monitor is coming along nicely!

It doesn’t work. An LED is still also a diode. The series leds would be between the power rails, and they’d both be illuminated all the time. Unless you adjust the voltage really carefully.

Most of the bi-color chip LEDs have 4 poles, don’t have a common.

But there is a problem pointed out by westfw posted. :joy:

Westfw, I’m quite new at this so please correct me where I go wrong. If led 1and 2 have there own resistors, and no resistor on 1/0pin would current not take the path of least resistance when 1/0pin is low, therefore red led stays off?

1 Like

You constructed a 3-state indicator :slight_smile:

Green means LOW, Red means HIGH, and both together mean high impedance (input) if Vcc is 5V or more, else both go off.

@arduinofarmer in reply #14. But that will not be possible with a three pin bi-colour LED :wink:

If I can’t find one with the anode and cathode connected to one leg, then no!

It would if the LED actually had one cathode and one anode to the common. But that is extremely unusual.

Well, technically, if you have a 2-pins bicolour led (the ones with led chips in antiparallel) and you don’t care if there is a small current consumption also with led turned off (high impedance state), you can do what you want with 2 resistors only (and the led ofcourse) … connect the 2 resistors (say, 2 x 1K or similar value) in serie, one end of the serie to VCC, the other end to GND, the middle point to one pin of the led, the other pin of the led to your output … if the output is high, the chip with the cathode at the middle point of the serie turns on through the resistor to GND, if is low, is the chip with the anode at the middle of the serie that turns on through resistor to VCC, if HI-Z, no leds on … but this also means that you have a consumption of current (2.5mA with 5V) also when the led is off, through the 2 resistors in serie, you decide if this is a problem or not :wink:

Interesting, could you draw the circuitry?