Simple, robust, touch sensitive electronic switch which can prevent vehicle theft even if thief has vehicles keys - see testimonials below....
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Step 1: Preparation
Gather together the necessary components, materials and tools.... the images below show the necessary electronic and mechanical components - you'll also need some epoxy resin (about 5ml), some lacquer, solder and a few tools - more information can be found on my website - http://home.clear.net.nz/pages/dandavies/parts_materials_tools.htm
Step 2: Assembly
Assemble the components according to my slightly antiquated and long winded animated instructions written for electronics students - if it is not easily viewed on your display, it may also be viewed here home.clear.net.nz/pages/dandavies/instructional_animation.htm
Step 3: Test Your G-Spot
Apply +ve power to the anode of the SCR, connect a load to the SCR's cathode and then earth the load... now touch the G-Spot as well as earth at the same time and the load should operate... see schematic below....
Step 4: Install Your G-Spot
Pop the vehicles hood/bonnet or boot/trunk. Locate the battery and follow the largest cable from the batteries +ve terminal to the vehicles starting solenoid. Disconnect one wire at a time (if more than one) from the starting solenoid until turning the key doesn't start vehicle. This is the wire you need to interrupt with your G-Spot so trace it to a point where it is far enough away from the engine heat and cut it - it can be under the hood/bonnet or under the dash in the passenger compartment. The end of your G-Spot with the wire coming from it (Anode of SCR) connects to the end coming from the ignition key, the other end (Cathode) connects to the end going to the starting solenoid. Crimp your G-Spot in place and then run the sensing wire to a screw or other conductive spot within easy reach of the driver - this must be isolated from the vehicles earth! Test your installation by turning the key to "Start" while simultaneously touching the vehicles G-Spot. Note: You must be earthed while doing this so if your keys are plastic coated you may have to slide a finger down onto the barrell of the ignition (usually earthed) or get an uncoated key cut. If it doesn't work and you're sure you're earthed, etc, try giving your fingers a lick otherwise a separate relay may need to be fitted due to the small voltage drop across the SCR. Casually check to ensure no one else is watching before operating any G-Spot! For more information see - home.clear.net.nz/pages/dandavies/known_limitations.htm