Hi Gene,
I would not be at all surprised if a device is already
available to do exactly what i want.
I assume you have read this thread,
and you know i want to vary the current through a car
headlamp using some kind of pressure sensitive device.
By vary, i dont mean switch on or off,
i mean increase or decrease smoothly.
I do not know of a lamp dimmer for 12 volt operation,
unless you mean a Headlamp Dipper Switch,
That would not control current smoothly,
it switches it around between lamps.
I dont know what 'Wally World' is, but my guess is
that its a motor car accessory shop,
and you mean a headlamp dip switch.
I have been drying out some fine sand and making a
unit to hold it with a plunger, a bit like a pump.
I have bolted on washers to the stationary part
and to the moving part, and connected wires to them.
The mixture will go in it later, after ive ground up
some carbon for it. Its about an inch diameter and
about two inches long.
I expect the compression to take about a millimetre,
but i dont know yet.
I want it to vary between from roughly 800 ohms down
to about 4 or 5 ohms or maybe better.
It would have to be lower than 1 ohm to light a 60 watt
headlamp even poorly.
But for test purposes i would be happy with lower
single figures.
It is not intended to be a one-shot device, it is
intended to return to the high resistance state after
compression.
The activation device will be a bar from a nearby
assembly, the current i want to control would be as
much as i can get away with, i expect about 2 Amps
would make the unit quite warm, when i get suitable
materials i expect it to run hot.
Eventually i hope to make units controlling 10 Amps,
These would be somewhat larger, and hot running.
Meanwhile, i just want to make a fairly small version.
I had considered sliding contacts on solid carbon parts,
but this was not practical.
The nearest thing i have found readily available is the
old pressure sensors fitted to some cars.
But i havent been able to get hold of one yet.
As mentioned before, i mean the electrical sensors that
work a gauge not a light.
I may try breaking the carbon up rather than using
filings, maybe a pile of bits like sand wont clump up
into a lump.
Cheers, John