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Fishing NZ Style
To create your own
G-Spot
SS-1335 model (or similar), first you will need to gather together the following electronic
and mechanical components (not
drawn to scale) or their equivalents.
The semi-conductors have been chosen because of their compatibility with
the rest of the design, they're inexpensive and they are usually readily
available.
You
can use leaded components instead of the surface mount ones - they're easier to
handle for the less dexterous among us - but you may have to modify the
encapsulation process slightly. I've used surface mount one for their
cheapness, size and ease of drawing.
Summary of Electronic Components
The SCR. This is one optional output semi-conductor and controls the supply of power
to the load. Proper selection of this component is critical to the
reliability of the end product, especially if installing in the starting
solenoid circuit.
I have used the one pictured, which
handles a 200 Amp surge for 0.01 seconds, 13 Amps continuously and up to
400Volts - similar products have survived 90,000 + simulated engine starts
followed by 8 years field testing with no problems so I have no hesitancy in
using these. I'm no expert but perhaps MOSFET's would do a better job, providing they
incorporated ESD (Electro-static Discharge) Protection.
Theoretically almost any SCR with a continuous current rating of
at least 8 Amps or higher, in a
TO220 non-isolated tab style case as pictured, should suffice - providing it handles the surge
current of the throw winding inside the solenoid which can momentarily exceed 70
amps in some solenoids. I like to use an over-rated one for that little
extra peace of mind, especially as there's no thermal protection. The initial current in starting solenoids very
quickly drops as the throw winding is disconnected and the hold winding takes
over and in all the cases when I tested it, the starting solenoids became hotter than the
SS1335 model after two or three minutes of continuous operation.
Please ensure that if you are using a different SCR, one with the
pin configuration reversed, you must take this into
account when you solder it to the mini-circuit board.
Note: It may be possible to use an isolated tab type SCR if the
non-isolated one's are unavailable, but the anode will have to be connected to
the ring-crimp as this is where the supply comes into the rest of the circuit.
Farnell's code for the BT-152 400R is 362-608.
A PNP transistor. This amplifies the tiny current that flows through your body
when contacting your vehicles G-Spot
and triggers the SCR.
I use a general purpose, low power BC857C PNP type in a SOT 23 case.
Farnell's code is 934-239 - a BC 857B from RS 288-581 will probably work
too, along with a fairly wide range of other PNP transistors, just check on the pin
configuration and substrate type first - must be a PNP type for negatively
earthed vehicles, and silicon, which is the predominant variety. Check the
schematic for
pin-layout of BC857C.
A silicon diode. This provides reverse-polarity protection which may not
be required.
I use this one which is an ISS380 rated
at 100mA, 35V in a UMD2 package. RS stock code 263-6847. Virtually
any low power silicon type diode rated at 100mA or higher will suffice for a 12V
system.
Note : There may be a 'bug' in this design
with using a diode of this rating in a 24 volt system. In a 12V system, the 220 ohm
resistor between the SCR's gate and the transistors collector allows for a
maximum of about 64mA to flow, which along with a maximum of 1.5mA through the
base circuit - with the sensing point earthed - should ensure that the current
never exceeds about 70mA, well within the diodes rating. In a 24V system
however, the maximum current through the 220 ohm resistor doubles to 128mA,
which exceeds the diode's maximum rating. Going to a slightly larger
rating should remove any possibility of diode failure due to the prolonged operation
of the sensing point.
A 330 k/ohm resistor. Farnell # 614-002 - RS # 169-222.
This resistor 'ties' the base of the transistor high to prevent
false triggering and provides biasing for when the sensing point is contacted by
the skin of an earthed operator - see Operating Instructions for more detailed
information.
A 10 k/ohm resistor. Farnell # 613-824 - RS # 169-519
This resistor prevents the flow of current through the operator
from ever being able to exceed about 1mA (typically it's a few micro-amps) in a 12V vehicle. I have no idea how whether or not that
level of current may interfere with things like pacemakers, so please check with
the supplier of any electronic medical equipment you're using before using a
G-Spot.
A 220 ohm resistor. Farnell # 613-629 - RS # 169-064
This resistor must be low enough in value so enough current
flows through the gate of the SCR to ensure it is triggered. It must also
be high enough to ensure that too much current doesn't flow through the gate of
the SCR.
If using surface mounted ones for assembly by hand, use 1206 size for ease of
handling if you can.
I've experimented with other values and found
that this combination gives a very reliable operation over a wide voltage range
(at least 6V - 24V) when used in conjunction with the semi-conductors I have
mentioned.
Also, if you are using a different transistor, you may have to
experiment with the value of the 10 k/ohm and 330 k/ohm resistor(s) to ensure that both the
transistor is turned on sufficiently to activate the SCR and that it restricts
the flow of current through the base of the transistor sufficiently to negate any possibility of too
much tingling for
the G-Spot operator.
If those values specified are not available, resistors with
similar values should be suitable.
A capacitor. This helps prevent 'false triggering' of the unit by
'de-coupling' any induced electrical impulses from nearby power surges.
I use a 0.01uf, 50V in an 0805 case as it get's a little tight on the
board where this one's mounted. Farnell # 755-722 - RS #
264-4371.
A capacitor of a similar size and rating should
serve the same purpose.
Summary of Mechanical Components
A ring crimp terminal with a 3mm (1/8") diameter mounting hole and sleeve
to fit a cable diameter of 4mm2 cross sectional area.
I use a Utilux H3132
model but if you know of one with a longer sleeve, use it and please tell
me! It doesn't matter if it is insulated or not.
A butt-splicing crimp connection to fit a cable diameter of 4mm2
cross sectional area. I recommend an un-insulated one and use a Burndy
BS04 link from Ideal Electrical. Farnell equiv. # is 488-227.
I've not tried an insulated one of these yet as I imagine it
could get messy when sealing with the solder after being crimped to the cathode.
I imagine the plastic would melt but otherwise it should be fine providing you
ensure a full seal is formed with the heat-shrink part of the process too - that
resin is messy when it leaks!
A 35mm x 10mm length of flat copper at least 1mm thick, with slightly rounded
corners . Drill a 3mm hole (1/8") at the top of one end using your SCR's
mounting hole as a guide - the top of the SCR should be in line with the top of
the copper strip when assembled. Instead of copper you could use aluminium
or flat steel at a pinch. Whichever metal you're using, make sure it has a
nice flat surface so the SCR makes good contact for heat-sinking purposes.
Keep in mind that this is connected to the
power source when riveted to the SCR's tab.
A 10mm wide strip of card, heavy paper or other thin insulating material
about 20mm long.
A 3mm (1/8") diameter short barreled pop rivet.
2 - 3 meters of thin (preferably) black hook-up wire.
A section of Vero Board 2 holes wide by 7 holes long.
A 70mm long length of (preferably) black heat shrink tubing. Ideally it
should be of the adhesive lined variety and should have an internal diameter of
at least 9mm and shrink up to approx. 5mm. I've used Raychem's 9/3 DWP125
3/8". It has an inside diameter of 9.5mm which is gives a
perfect fit to the SCR's 10mm width when slightly compressed.
If you can not get hold of the adhesive lined variety, you will
need to use a small amount of glue or other sealant around the butt-splice crimp connector when
assembling to ensure a thorough seal - or else the resin will leak out of any
small holes.
WARNING! Use of
a thin walled type of heat
shrink for manufacture with subsequent installation in the engine bay of a vehicle,
especially a high
performance one, is definitely not recommended. The heat shrink
may split after prolonged exposure to the heat from the engine. Obviously,
the amount of heat generated will depend largely on the way the vehicle is
driven. The amount of heat the heat shrink is exposed to will depend on
the efficiency of the engine bay to dissipate the heat and the proximity of the
installed control unit to the heat source.
A small amount of lacquer or varnish - preferably of the aerosol spray on type
for electronic circuits. I use Electrolubes™
Clear Protective Lacquer
CPL200H - available from Dick Smith's, but ordinary wood varnish or even clear nail
polish should work just as
well. This provides a conformal coating to the assembled circuit board
which acts as an extra layer of protection against the ingress of moisture, which may cause the unit to falsely
trigger.
A small amount of resin and the
associated hardener - about 10ml (two teaspoons) is ample for the right diameter
heat-shrink. I've successfully used either Hi-Tech's 9000 series fiberglass
resin and a polyester resin - whose origin I'm not too sure of - along with some
black dye, but so long as it doesn't shrink too much during curing,
or chemically react with the dry lacquer, just about any fiberglass or polyester
resin should suffice.
A plastic bottle you can squeeze, with a nozzle is ideally suited for the pouring of the resin
past the ring-crimp and into the heat shrink during the final stages.
A small amount of emery paper and an ink eraser come in handy for cleaning the
vero-board.
A small length of tape - preferably electrical.
A small amount of heat-sink paste (preferable - but not essential).
Flux remover (preferable - but not essential).
A small amount of isopropyl alcohol (preferable - but not essential)
A small amount of solder.
The tools required
are as follows :-
A fine-tipped soldering iron.
Side-cutters.
A sharp object such as a large needle - for threading the wire through the side
of the heat-shrink.
A pop-rivet gun.
A vice, vice grips or terminal crimps, for crimping the butt-splice onto cathode.
A source of heat - heat-shrink gun, lighter, Bunsen or methelated spirits burner.
A small hacksaw or a 3 - 6mm drill are handy for breaking the tracks on the Vero
board.
A file.
A 12V D.C. power supply and connections.
A 12V load, typically a lamp of suitably low resistance.
My handy animated assembly instructions.
