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I am trying to create an induction loop detector by following this http://www.allaboutcircuits.com/projects/metal-detector-with-arduino/ but apparently something is wrong on my side or I missed something.

I have soldered a PCB with a BC338, resistors and capacitors and I bought ENAMELLED COPPER WIRE to create the loop.

Connected all together but when I try to get any metal close by, nothing happens, there is not actually "clock" sent to the Arduino. Only if I power at 12V and I short quickly the coil wire to the pin I get a pulse for a second.

At 3.3 and 5v I get nothing, the voltage across the two pins of the coil is 0.035V and nothing increase when a put a metal close by.

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    \$\begingroup\$ I take it you do not have an oscilloscope. Perhaps you have a multi-meter that can measure frequency. First you need to verify that the oscillator is working. \$\endgroup\$ – Marla Jan 14 '17 at 17:00
  • \$\begingroup\$ I have one at work, I will give a try it but did I use the wrong wire? What is the normal winding number? \$\endgroup\$ – max246 Jan 14 '17 at 17:49
  • \$\begingroup\$ The article you linked gives information on how to build the coil (50 turns). Be sure to scrape off the enamel insulation from the ends of the coil wire before you connect the coil to your circuit. \$\endgroup\$ – Marla Jan 14 '17 at 17:58
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    \$\begingroup\$ Also, if you connected 12 volts in place of the 4.5 volts, you destroyed your ATmega328. \$\endgroup\$ – Marla Jan 14 '17 at 18:01
  • \$\begingroup\$ I have scraped off the enamel as I checked the continues loop to make sure the connection was there. I soldered just the metal detection and connecting GND, 5V+ and output signal to my arduino. \$\endgroup\$ – max246 Jan 14 '17 at 18:32
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Re-Check all your connections. The peak sine output may exceed Vcc slightly.

Tune Inductance to match frequency in code. < Falstad simulator

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  • \$\begingroup\$ Nice simulator! \$\endgroup\$ – Jack Creasey Jan 14 '17 at 19:10
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    \$\begingroup\$ Yes it's my "go to" fave Sim for quick and dirty designs. hFE is adjustable but constant. Caps are ideal so ESR must be added if needed. Ctrl+ click can drag and stretch part ends, Click moves them, right mouse gives component option. hundreds of options. Slow motion with no scope trigger but time base is in options in sampling rate. Use this shortcut for frequency response falstad.com/circuit/e-filt-hipass-af.html or goo.gl/qVuzuK \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 14 '17 at 19:26
  • \$\begingroup\$ I have tried to put on a breadboard first then I just wasnt sure if the connection was secure and I soldered it. All seems to be fine, but cant understand what is not working. I think when I will hook it up to the oscilloscope I can give you more feedback \$\endgroup\$ – max246 Jan 14 '17 at 19:45
  • \$\begingroup\$ Check the DC and AC voltage on B,C,E \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 14 '17 at 23:21

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