Confused about how to connect a bicolour diode

I am really confused about how to connect the bicolour diode in the following spec.

The test lead is connected to one end of my coil and the other end of the coil is connected to GND of my circuit.

The spec shows two leads on the bicolour diode.

But the one I have (from an old tv set) has 3 leads.

I can't get the bicolour LED to do anything.

If I replace the bicolour LED with 2 x ordinary red LEDs, connected as in the spec, then I can get them to light up a little.
But I have no idea if 2 x red LEDs behave the same as a bicolour LED in this circuit.

Could some one show me how they would connect a bicolour LED in this circuit but clearly showing all 3 leads.

**broken link removed**

The spec shows two leads on the bicolour diode.

But the one I have (from an old tv set) has 3 leads.

Click to expand...

A three-pin (common cathode) type doesn't work in this circuit.
Next question?

FvM said:

A three-pin (common cathode) type doesn't work in this circuit.
Next question?

Click to expand...

Oh!

From this: **broken link removed**

I think what I have is a tricolour LED.

Well does that mean two ordinary LEDs connected in reverse parallel will do the same job?

I used two normal red diodes and, with the other end of the tesla secondary connected to the wall socket earth, it works brilliantly.

I get a resonant frequency value of around 114kHz, measured with my multimeter.

It is so anti intuitive to have no obvious complete circuit, i.e. the other end of the tesla connected to the GND of the test circuit rather than the wall plug earth.

Usually. two leg bi-colour LEDs are wired head to tail so one or the other lights, depending on the polarity you apply. Three leg LEDs are still two diodes but one side of each is joined to the middle leg. You can get common cathode and common anode types. The advantage of three legs is you can light both LEDs simultaneously to get a third colour. Unfortunately, you can't connect across the outside two pins of a three leg device because one of the diodes will be reverse connected and they don't like that at all!

Brian.

betwixt said:

Usually. two leg bi-colour LEDs are wired head to tail so one or the other lights, depending on the polarity you apply. Three leg LEDs are still two diodes but one side of each is joined to the middle leg. You can get common cathode and common anode types. The advantage of three legs is you can light both LEDs simultaneously to get a third colour. Unfortunately, you can't connect across the outside two pins of a three leg device because one of the diodes will be reverse connected and they don't like that at all!

Brian.

Click to expand...

Actually I am getting some variations between readings - not surprising given that we are dealing with nano or micro amps and the resonance can be effected by environmental conditions.

My soldered circuit gave me a reading of about 156kHz and my bread board circuit gave me a reading of about 134kHz this time.

Might have to take some readings over a few days and then use the average as my resonance frequency.

You started with a single ended driver using 555 now are talking about tesla coils which is unrelated but operates on stray magnetism leaked to the open lead acting as an antenna.

1st both the 2 pin and 3 pin dual LEDs can be operated in 3 colours but not from the same driver. the 2 pin reversed LED pair must be driven by complementary signals which results in bipolar or AC -alternating 2 colours. to blend a 3rd colour. They can still be driven to any of the 3 colours. static voltage +,0 0,- or alternating dual drivers +-+-+-+- Naturally some current limiting resistance is needed.

In the case of the 3 pinned LEDs as you indicated you have. If they are Common Anode (CA) The Anode is tied to Vcc and either or both Cathode is switched down near 0V via separate current limiting resistors. such as 330R resistor when using 5V.

If they are a Common Cathode (CC) pair. then the Cathode is grounded and either or both Anode on the outside is driven high via separate current limiting resistors.

In the case of discrete back to back LEDs any stray AC will dimly illuminate both LEDs with 100uA such as a tesla coil nearby spewing out magnetic energy. But this fails to give you control to select any of 3 colours without additional circuits.

Any more relevant questions?

`With a proper bicolour LED I seem to be getting a resonant frequency value for my coil of 95-105kHz.

With the twin normal LEDs both were illuminated at the resonant frequency but obviously the colours didn't blend. In some cases one LED was on more than the other. They seemed to be giving me resonant frequency value a little higher than with the proper bicolour LED. So I suppose the slightly different electrical properties of the twin normal LEDs were having a stray effect on the device.