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Indi-Link and the Benefits That Open New Markets for LED Devices


Light emitting diodes are incredibly useful devices for signalling and indicating all manner of electrical conditions. They have properties of speed, high efficiency, long life and very high levels of reliability with a wide choice of colour wavelengths. They give information directly to the eye and offer a means to electrically isolate signals through optical coupling means at very low cost. Above a certain threshold of voltage (Vf rating) they act as pure current devices displaying little in the way of resistance. However having said that they are quite vulnerable devices, being easily destroyed by modest forward and reverse over-current or over-voltage. It is usual to incorporate a resistor in series with an LED to act as a means of protection but this reduces the device to a’ voltage mode’ of operation only, and limits its functionality to puny applications. LED’s also exhibit a relatively high forward volts requirement that manifests as a power loss (V*A = Heat in Watts) that also contributes to limit its application area.


Formerly this was true until an invention called Indi-link was born that attracted the attention of Judges at the International Invention Fair, Geneva Switzerland. They were so impressed as to award a Silver Medal for invention for its novel application as a bipolar current Detector / Indicator.


To explain the inventor describes his invention as a two terminal device that has the properties of an almost solid piece of connecting wire with the exception that it visibly lights up on detecting the presence of current passing through its terminals and without a separate power supply. It is bipolar and discriminates the polarity of the current via two different colour LED’s (which can be of any colour from red to white as desired). The current detection threshold is in the order of 0.003 Amps, but then Indi-Link can pass up > 10 Amperes if required in either direction. It is an LED device, truly being used in its Current Mode and over a huge range. Furthermore, being used in current mode, it will operate regardless of the line voltage (tested at> 11 K Volts) reliably in AC or DC circuits, transparently revealing the kinetic electrical events occurring within a circuit.


Such a device will not operate without parasitically taking power form the line, to which Indi-Link does, but at such low magnitude as to keep power dissipation to a bare minimum. The conducting medium between Indi-Links terminals has the property of a negative-impedance limiting the parasitic loss to between 0.35 and 1.1 volts, over 0.003 and 10 Amperes respectively. That accords to an impedance of between 115 and 0.11 Ohms over the full current range.


In furtherance to Indi-Links utility as an indicator, a pair of infrared type LED’s can be fitted in series with the indication LED’s. These devices form the transmitting part of opto-isolator devices that can return volt free outputs, repeating information to further machinery such as a PLC control system. Any of the various different opto-isolation technologies from Photovoltaic, to Photo–triac etc. can be put too good use. Armed with these devices, many and varied solutions are possible to provide a condition monitoring, closed loop feedback, signalling and signal isolation at low cost while adding functionality.


Indi-Link can also be powered by a non-invasive magnetic coupling means in order to monitor extreme currents or phase loss/ imbalance on multiphase supplies through the use of a current transformer.


Indi-Link Technology gives LED devices a protective suit of ’ bullet proof’ armour while simultaneously lowering their forward volts requirement to less than 0.4 volts. The result will provision ‘built in test equipment’ and give electrical transparency through the medium of light and in just about any circuit.


The advantages that Indi-Link technology will provision


1.  It gives an LED a suit of armour that protects and allows them to be used at currents > 500 times their usual ratings.

2.  It lowers their forward voltage requirements by up to 10 times (threshold 0.35 Volts regardless of colour type).

3.  Indi-Links 4 LED's form a bi-directional current sensor / indicator that discriminates the polarity of current flowing in a circuit and having a

     detection threshold of 3 milliamps but can also pass in excess of 10 amperes.

4.  Useful in AC or DC applications while being self powered.

5.  The device can signal via 2 optically isolated channels, four different conditions within a single circuit when powered by an AC.

6.  The line voltage of the circuit has no consequence to the reliability to the LED's employed above 0.35 V to thousands of Volts.

7.  Control Circuits employing Indi-Link gain operational transparency for both man and machine making conditions visible and detectable. i.e. 

    no hidden faults.

8.  The functionality of simple hardwired control circuits can be multiplied by a factor of 8 times usual.

9.  Control circuits using this technology can be reduced in complexity and offer high levels of fault tolerance at low cost.

10. Ideal solution for test and proving control circuits without process disruption.


Indi- Link is a current to light converter, a condition monitor, a current detector, a signal isolator and can multiply functionality of single wire I/O control circuits.



Collaboration sought: collaborate with an interested party who wishes to benefit from the commercialization of this versatile, informative and robust technology that despite its simplicity can bring many advantages to otherwise complex signaling and control problems while saving on cost.





Mr Robert Gardner

The Featherings

3 Heol-y-Bryn


CF62 6SY, UK


Mobile +44(0)7887705480






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