POSSIBLE PROJECT LAP TOP METAL DETECTOR

		Quote:			Posted by xavier
	Dam that sounds interesting so I guess that I could use it on my VLF to see where the settings are at there best? Where should I place the test probe? And by the way I had Spectrum Lab on my PC must have downloaded it some time ago to have a look at but forgot about it. Regards Xavier

One thing I will mention here and it is important. Make sure you protect your PC by using an active probe - not just a wire. The input level should be the same as a microphone or headphone signal which, as you know, is very, very weak. You need to be sure it's an isolated signal and not something that has 5 or 12 volts on it. Use a capacitive coupled probe and a phonograph preamp to isolate your laptop (or desktop) from harmful signals. This is a precaution for when you are using it as circuit testing equipment.

When you use it as an analyzer for an audio signal (speaker or headphone level), direct coupling is fine. To answer your question, the best way to use it is to monitor the audio signal direct from your headphone jack. Just make a 3.5mm stereo to 6.5mm stereo cable from parts or buy one.

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		Quote:			Posted by xavier
	Hi GD The probe that I use for my PC Scope only has a 15M resistor on it and from what you tell me that?s not good enough although I have had no problems yet and have been using it for about a year. Could you send me the proper active probe design (specs). Regards Xavier

Xavier, it's not a matter of good enough or not good enough. The input levels are way different. One is a direct audio input (the PC Sound Card) and the other is a 10M or better, capacitive coupled input. No matter how large the series resistor is, all it can ever do is limit the input current while not affecting the voltage one whit. If you stick your probe on a 15 volt location, all of it goes into the sound card.

In order to avoid damaging your sound card, you have to ensure that the level of input is shifted down to an audio level. Or, you can use an active AC probe which is normally capacitive coupled.

I already gave you an active design spec when I said you should use a phonograph preamplifier as a probe level shifter. Single chip designs abound on the web. That's the best, lowest cost input filter I can suggest.

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Xavier, pardon me while I have a forehead slapping moment.


Ok. That's better. I've been giving this some thought and the answer is just too obvious. For the purposes of playing with the software, simply take your headphone jack and plug a cable from that to your audio-in on the sound card. Start with the volume down low and adjust.

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I look forward to your findings. I'll be taking your parts list with me to the shed today. Wish me luck.

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It's DOS software so a dual processor won't make any difference. The project I am working on uses an eoscope (diy oscilloscope) and doesn't have fourier. I have always wondered about how fourier would go with PI methods, is the sample rate fast enough?

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