There are times when you want to control a LED indicator light through
the side of a plastic box, without wires and without drilling a hole in
the box. One example where this may be needed is in data collection
systems. These are often used out of doors in harsh environments and
have to be hermetically sealed. Holes drilled in the side of the box for
panel mounted LEDs or light pipes can often leak.
Wireless LED Driver Circuit Diagram :
The circuit below solves this problem by sending power to the LED through the plastic, using a magnetic coupling technique. The circuit below can route power through plastic enclosures as thick as ¼ inch. The circuit will not work through metal boxes. An expensive inductor, driven by a series resonant mode 125KHz oscillator, forms the power transmitter. A similar inductor, wired as a 125KHz parallel resonant circuit, forms the power receiver. A voltage doubler circuit at the receiver efficiently converts the collected AC into DC. The circuit will operate over a wide 3v to 6v supply range.
With a 5v supply, the circuit draws about 25ma of current. However, by gating the oscillator on for a brief 20ms period, with a 0.5Hz rate, the average power can be reduced to about 250 micro amps. If you want to extend the range of operation out to ½ inch, try using a 74C14 (CD4069) with a 12v supply. Using surface mounted components; the complete LED assembly can be encapsulated and glued to the outside surface of the box. Tiny unshielded surface mounted inductors can be used to reduce the size of the transmitter and receiver. However, smaller parts will reduce the power transfer range to perhaps only a 1/8 inch separation.
A very nice bright green LED, which works great for this circuit, is one from King bright, available from Digikey, part number 754-1089-1.
Wireless LED Driver Circuit Diagram :
The circuit below solves this problem by sending power to the LED through the plastic, using a magnetic coupling technique. The circuit below can route power through plastic enclosures as thick as ¼ inch. The circuit will not work through metal boxes. An expensive inductor, driven by a series resonant mode 125KHz oscillator, forms the power transmitter. A similar inductor, wired as a 125KHz parallel resonant circuit, forms the power receiver. A voltage doubler circuit at the receiver efficiently converts the collected AC into DC. The circuit will operate over a wide 3v to 6v supply range.
With a 5v supply, the circuit draws about 25ma of current. However, by gating the oscillator on for a brief 20ms period, with a 0.5Hz rate, the average power can be reduced to about 250 micro amps. If you want to extend the range of operation out to ½ inch, try using a 74C14 (CD4069) with a 12v supply. Using surface mounted components; the complete LED assembly can be encapsulated and glued to the outside surface of the box. Tiny unshielded surface mounted inductors can be used to reduce the size of the transmitter and receiver. However, smaller parts will reduce the power transfer range to perhaps only a 1/8 inch separation.
A very nice bright green LED, which works great for this circuit, is one from King bright, available from Digikey, part number 754-1089-1.
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