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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.


    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.  

Copyright July 30th, 2001, Daniel Davies
G-Spot was a Trademark of Daniel Davies (aka Daniel Morgan)
Manufacturing Rights as per my Instructional Animation Now Licensed 
to Students Attending an Educational Institution or Individuals in a Private Dwelling, 
Subject to My Terms & Conditions and Disclaimer All Other Rights Reserved

NZ Patent Application # 510157
Last Modified 14th May, 2011

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