The Ne5521 detector by BJBJ.

[BJBJ]

Also, this looks very similar to a design by Don Lancaster in one of his Hardware Hacker articles, but that used an NE5520 LVDT Signal Conditioner. I suppose there's an alternative somewhere. Perhaps the AD598?

As said before in another thread, Don Lancaster never did a design or built anything with the 5521 or the 5520,
he merely suggested a one chip detector to be built by somebody else. My design has nothing to do with
Don Lancaster suggestions in his private Hacker pages whatsoever. Don Lancaster is a person who never
gives away any designs he does to a open public especially if he can make some money out of it.

You can build a detector with the AD598, but why, the chip is very
expensive and you can do better stuff with semidiscrete components.

[Qiaozhi]

Also, this looks very similar to a design by Don Lancaster in one of his Hardware Hacker articles, but that used an NE5520 LVDT Signal Conditioner. I suppose there's an alternative somewhere. Perhaps the AD598?

Bomb Jack Bomb Jack...?

[Qiaozhi]

The wiring for S3 looks a bit odd. Pins 2 and 3 are already shorted out, so moving the switch to that position won't do anything.

[BJBJ]

I once did a simple detector back in 1999 with the Ne5521 chip, unfortunately i cant find the exact schematic for that detector however here are
a similar design i did at the time. The Ne5521 are a obsolete chip, the Phillips factory who manufactured the chip burnt down to the ground some
years ago and there are no second source. But if you come across the chip at some time you can build a quite decent detector with it.
Range are pretty good beats many pro machines.

However it have a rather interesting feature it can detect the full 360deg range, SW1 sets 0-180, and 180-360.
it uses a two tone circuit, one freq for ferrous and another for non ferrous.
There might be value errors and i cant remember the use of SW3, and it can be redesigned to run of one 9V battery for example.

http://thunting.com/geotech/forums/a...1&d=1180123869