|
DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, November 29, 2011 08:14 PM
Hobby Circuits'
Category List
The contents &
graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
SITE server |
 |
|
|
|
|
|
|
More
LED circuits
Driver circuits |
|
Wireless
LED Driver
Nov. 2, 2008
designed by David A. Johnson, P.E. |
|
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. |
|
|
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 microamps. 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 Kingbright, available from Digikey, part
number 754-1089-1. |
|
|
Click on Drawing Below to view PDF version of Schematic |
|
 |
|
|
More
LED circuits Driver circuits
Hobby Circuits'
Category List
eMail David A.
Johnson, P.E. about this circuit |
|
