"Gary's Pulse-AV, PI Detector"

This is Mainly Designed for use on "Conveyor Belts",

But may be useful for other Applications.

Preliminary article Created: April 12, 2011
Updated: June 1, 2011.

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I Do NOT give Any help to persons making my PI Detectors,
Unless they Buy at least the Basic Kit of parts from me.

Too many persons make Substitutions or Errors,
than expect me to solve their mistakes.

Warning: I Do Not Recommend this project for "Beginners", It Requires Good Soldering Skills and a reasonable working knowledge of electronics. Good Soldering is an Absolute Must!

This detector uses only a Single Coil.
It also uses just a Single "Threshold Control". This "THRESHOLD Control" sets the point of Triggering, Thus giving a "Precise and Sensitive" indication of metal detection.

It is best to just set this control with NO Metal near the Coil and Just on the Verge of tripping the LED and Sound.

It displays both an "Audio and Visual" Indication of a Metal Target. The Audio is a Fixed Tone from a Piezo Transducer, and a Visual Showing on an LED. This is a Non-Motion, "Go, No-Go" Detector.

Connecting an "Opto-Isolator" in series with the LED will allow for operation of a Relay to control other Circuits. This can be very useful when Detecting metal on Conveyor Belts.

The Present Frequency of Operation is 300 Hz. NOTE: I'm Still playing with this for best over-all performance.

I Recommend you use the "WATER BASED FLUX type of Solder" as Included in the Kit and that you Wash the board to Remove All the Solder Flux Residue. IT WILL NOT WORK CORRECTLY IF YOU DON'T remove this flux!

Before Inital Testing your Completed Unit:

I Recommended the use a Current Regulated Power Supply. Just for the first few minutes of testing this unit. (A Supply that is Limited to Less than 300 Ma. is quite satisfactory) NOTE: Excessive Current, will Distroy the REG1117A.

Failing a Regulated Supply, a 100 Watt/110 volt standard light bulb can be placed in series with the positive battery lead. Or a Constant Current Source using a LM317.
Either of these will limit current to a reasonable level, preventing any damage to parts.

SETUP: 1) Check all Supply Voltages. (-9.75, +5 and -5 Supplies) The -9.75 may read somewhat Low, when using the Light Bulb current limit. 2) With your Coil Attached, set VR1 so you get a reading of between 0 and .5 Volts on Pin 6 of IC9. 3) Adjust VR2 & VR3 as needed. Now it Should Detect Metal. "When your Sure the circuit is working OK, Remove this current Limit". 4) REPEAT Steps 1, 2 and 3.


1) For use On Conveyor Belts, you will probably need to make "Custom Coils. And since most conveyor belts also have Metal Parts, Coil Placement can be Tricky. Also, Rectangular shaped Coils can be better in some situations.

2) This metal Detector was Not designed to Detect Gold Nuggets. It Will detect larger Gold Nuggets, of around 1 gram with a suitable coil. But if your expecting to detect Tiny Nuggets or Flakes of Gold, FORGET IT!

** However, using one of my 8 inch Coils: My Prototype Detects a .177 "BB" at 1.75 Inches in Air. It Detects a 1 Gram Gold Nugget at 1.5 Inches in Air. My Gold Ring at 9.5 Inches.

My Recommended: "Optium Flat Coil Sizes". Depending on my current Stock, I may use a 20.5, 21 or 22 AWG Wire. And I can Supply these Flat Coils, Up to about 13 Inches OD:

For Really Small Objects: A 4 or 6 inch OD coil is good. Small Coils wound on Ferrite Rods are also good.

For Overall, GENERAL Detecting: Use an 8 inch Coil.

For Larger Objects: 10 inch or 12 inch Coils are good.

Or "YOU" can make even Larger Coils: For Really Large Objects: A 48 inch Square Coil with 8 to 10 turns will work.

This Detector is Quite Stable in many situations.

NOTE: The Kit of the parts, Water based flux type Solder and PCB is: "ONLY Available from me". And other than the PCB and coils, These parts are supplied at my Landed Cost.

The Schematic, Subject to changes.

An "Opto Isolator" Circuit, for use on
Conveyor Belts and possibly elsewhere.

A Detailed Picture Overlay of this Assembled PCB.

There are too many Variables in Coil Construction, as well as materials, shapes, sizes and soil conditions to try to predict exactially what your detector will do under various conditions.

ADDITIONALLY, Remember This:


All Imformation in this Article is "Copyright protected".


*Copyright © 2011*