Cache Detector

<body topmargin=0 leftmargin=0 marginheight=0 marginwidth=0> <table cellpadding=0 cellspacing=0 border=0><tr> <td valign="top" height=90 BGCOLOR="#006699" TEXT="#080000" background="1fcfd5a3.jpg"> <div> <FONT SIZE="5" COLOR="#000000" FACE="Arial" ><B>BIT Company</B></FONT><B>    </B><B> |     </B><A HREF="index.htm" TARGET="_top" TITLE="BIT Company"><U><B>home</B></U></A></div> <bR> <div> </div> </td> </tr><tr> <td valign="top" height=390 BGCOLOR="#FFFFCC" TEXT="#080000"> <div> <I>Cache Detector</I></div> <div> <IMG SRC="255e0080.jpg" border=0 width="480" height="8" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <div> added 24 January, 2003</div> <bR> <div> This device was first built in 1991 just out of curiosity but mostly because my wife thought someone might have buried a jar of coins around here! </div> <bR> <div> <IMG SRC="23a22ee0.jpg" border=0 width="290" height="238" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"> Fat chance of that, the last folk to live down here in the jungle before me was back in 1843 and they moved to South Florida!</div> <bR> <div> The design is simple and straight forward and uses readily available components with lots of latitude in the design for substitutions. Operating frequency in this unit is 40 kHz and is somewhat arbitrary. I've ran it from 10 to 40 kHz with no particular effect on sensitivity, just a slightly sharper localizing response at the higher frequency. </div> <bR> <div> The transmit and receiving coils are wound on forms made from stacked 1/10" acrylic sheet, the outer sections 9" x 12" and the center section 8" x 11". Originally, the heads were 12" x 12" but were broken when a mob of 6 month-old GSD pups came roaring in the shop one afternoon and crashed into the gadget!  I didn't have any more 12" material, hence the 9" width. You can build any size you wish, round, square, or rectangular, and space them as far apart as you are comfortable but for best results, the spacing should be on the order of twice the coils' largest dimension.</div> <bR> <div> Principle of operation is simplicity itself, the transmit and receive coils form the primary and secondary of a transformer but due to being orthoginal to each other, have very low mutual coupling. Anything metallic that appears between or beneath them allows coupling the transmitted signal to the receive coil. The large black knob seen toward the front of the transmit coil allows vernier tilting of the coil in order to null local fixed coupling. The 3/4" PVC schedule 40 frame is tapped for 1/4"-20 and a threaded rod secured to the transmit coil with captive nuts with a rear mount (not shown) consisting of a 10-24 screw tapped into the frame floating on a rubber grommet. I had a series of photos ready for this page but somehow the floppy disk they were on became corrupted. I'll re-shoot them in the near future. </div> <bR> <div> <IMG SRC="23cc4930.jpg" border=0 width="196" height="147" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></div> <bR> <div> The following circuitry and component lists are based on the transmit coil having 25 turns of #26 enameled magnet wire and the receive coil 40 turns center-tapped of #30 enameled magnet wire.</div> <bR> <div> <A HREF="id63.htm" TARGET="_top" TITLE="Cache Detector Driver layout"><U><IMG SRC="23d0e850.jpg" border=0 width="270" height="133" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <div> Cache Detector Driver layout</div> <div> Click for larger image</div> <bR> <div> <A HREF="id64.htm" TARGET="_top" TITLE="Cache Detector Driver schematic"><U><IMG SRC="23ed2850.jpg" border=0 width="210" height="133" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <div> Cache Detector Driver schematic</div> <div> Click for larger image</div> <bR> <div> <A HREF="id67.htm" TARGET="_top" TITLE="Cache Detector Driver parts list"><U><U>Cache Detector Driver parts list</U></U></A></div> <bR> <div> <A HREF="id65.htm" TARGET="_top" TITLE="Cache Detector Receiver layout"><U><IMG SRC="23f0d850.jpg" border=0 width="269" height="133" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <div> Cache Detector Receiver layout</div> <div> Click for larger image</div> <bR> <div> <A HREF="id66.htm" TARGET="_top" TITLE="Cache Detector Receiver schematic"><U><IMG SRC="240ec850.jpg" border=0 width="236" height="133" ALIGN="BOTTOM" HSPACE="0" VSPACE="0"></U></A></div> <div> Cache Detector Receiver schematic</div> <div> Click for larger image</div> <bR> <div> <A HREF="id68.htm" TARGET="_top" TITLE="Cache Detector Receiver parts list"><U><U>Cache Detector Receiver parts list</U></U></A></div> <bR> <div> <A HREF="index.htm" TARGET="_top" TITLE="BIT Company"><U><U>Home</U></U></A></div> <bR> <bR> </td> </tr></table></body>