reaches the same or greater value of the potential applied
to run the microcontroller, it locks on to that frequency. If
you construct the coils close to the specifications given,
the primary will induce a great deal of power with a
considerable bandwidth of about 3 kHz or greater on
either side of the resonant frequency. You should notice
wireless power to the CFL starting as low as 700 kHz and
as high as 3 MHz.
Circuit Construction
The entire circuit can be made to easily fit on a
raised platform that supports the primary and
secondary coils. To construct a design like the one
shown here, you will need the following pieces of
hardware and tools. Start the design by cutting a
3. 5 inch square piece of prototyping board and drill
1/8” holes in the corners as shown in Figure 7.
The base for the design is made from 1/8” Lexan
or similar plastic material. Cut two pieces of the Lexan
into one 3. 5” square and one 3. 5” x 5” size, and drill
1/8” holes in the corners by using the printed circuit
board (PCB) as a guide. Using eight one inch
threaded aluminum standoffs, mock assemble the
PCB and Lexan squares as shown in Figure 8 to make
sure everything aligns properly.
The one most important consideration is the
inclusion of the power supply. I designed the
prototype for this design with an onboard transformer
which requires tall enough standoffs that provide
clearance. I also made provisions for an off-board
supply by using a rectified input jack as noted in the
schematic. This allows you to experiment with
different supplies to the circuit. The tube for the
secondary coil is mounted to the upper Lexan piece
by gluing one of the end caps to the 1.5” hole cut in
the plastic as shown in Figure 9.
Drill a small hole in the bottom of the tube cap
and feed the six inch length of wire through it for
connection to the PCB. I used a SIP male and female
connector pair for convenient connection to the
circuit board. I constructed the toroid for the coil
from the bottom of two soda cans. To create the
toroid, saw one inch of the bottom of two aluminum
cans and sand off the labels from both halves along
with the plastic coating from the insides. Drill a hole
; FIGURE 9.
; FIGURE 8.
; FIGURE 7.
24 April 2014
