This looks like a pretty cool circuit:
http://www.redcircuits.com/Page55.htm
However, where would I purchase a set of ferrite rods? I checked
Jameco and Radio Shack, but no dice.
-or-
Would any ferrous metal rod work similarly? I.e. a simple steel nail
or bolt?
-and-
Anyone ever build this? Would increasing the voltage increase the
range?
thx
A bolt probably won't work. Eddy currents in the bolt would eat up a
lot of the energy making the range low assuming the transmitter
portion oscillated at all.
You do have some options however. Assuming you can't find some
ferrite rod material, you can stack a series of toroids or ferrite
beads together and treat it like a rod (use a dowel or nonconductive
center or just glue them together)
It oscillates at 35 KHZ which is relatively low and you could probably
get by with a bunch of thin iron wire. The iron should not conduct
well, so allow it to rust a little before packing the core.
I use steel fence (agricultural electric fence) wire for wire cores
since it is readily available and cheap. It is zinc coated to prevent
rusting and is very conductive. I cut the wires to the length I need
for my core then put them in a jar of vinegar for a few days - that
causes the zinc to oxidize and insulates the wires. I neutralize the
acid with a rinse of baking soda.
Craft stores are another source of thinner steel wire - but they can
be costly if you need a large core.
Alternatively you can just chuck them in a fire and burn the coating
off - the zinc vapor may be toxic so you'd want to avoid doing it
where you breath or under the chicken in the BBQ grill . . . Burning
it will or may cause it to anneal and that is desirable in a magnetic
core (easier to bend or straighten too)
You can make your own powdered iron cores that will work really well.
I started fooling with steel wool in an attempt to make a high
frequency core - it actually worked pretty well.
You can make a core to rival commercial ones by buying fine iron
powder - stay away from science shops, it costs too much - it is for
sale on line for pyrotechnic purposes in different sieve numbers
(particle sizes). Stuff is used to make bright white star burst
fireworks shells and roman candles.
My technique is to mix the powdered iron with epoxy thinned with a
smidgen of acetone (or get thin boat builders epoxy or polyester
resin) then pour it into a short length of PVC or CPVC pipe that has
been waxed inside with a coating of silicon grease as a mold release.
Pour it and cap it on both ends with greased PVC end caps pushed on,
store it vertically while the epoxy sets - or you will regret it - one
end cap will leave a shoulder in the molded product - it won't come
out from that side. Let harden for a day or two then push the iron
out (a dip in a pan of boiling water will help if it doesn't just
slide out - most won't with PVC, CPVC is smoother inside).
Voilà! a powdered iron core that didn't cost a mint.
A further refinement is to stack ring type ferrite magnets around the
mold while it hardens (stack has to be full length and you may have to
grind off the shoulder on top before you push it out)
I have a lot of old speaker magnets that work well for that - but
winding a coil and passing current through it may also work.
Magnets increase the permeability of the core by aligning the
particles of iron while it sets up. They also tend to cause the
mixture inside to try to walk out of the tube - so be sure to use two
end caps pushed on hard.
It may work to just stuff a tube with iron powder and glue the caps on
- I don't know. The wall thickness of the tube may work against you
for leakage inductance and the particles may move around while being
excited by the driver - I assume that would be a bad thing but I
haven't tried it.
cool circuit - haven't built it