Pulse Induction Metal Detector | Gary Chemelec

The first homemade metal detector that I successfully constructed is Gary's Pulse Induction (PI) Metal Detector. 

It is actually not for beginners because it involves a lot of electronic components that must be properly connected on the PCB circuit board.

I went through a lot of trouble in building the project where it took me almost two months of troubleshooting for it to properly work and achieve the best setting adjustments. 

Although, when it comes to the sensitivity and accuracy, the problem really isn't from the electronic circuit part but the search coil.

Search Coil of Pulse Inductive Metal Detector

The search coil of a pulse inductive metal detector may consist of a single coil which act as the transmitter and receiver. 

Some search coils may have two or three coils working together for a more efficient processing of the signal.

So how does it work?

Taken from the name Pulse Induction MD, a pulsating current goes through the wire of the search coil. 

And as a result, a pulse of electromagnetic field is produced which travels way down into the ground. 

When the generated pulse reached the end, the magnetic field will reverse in polarity and at the time, collapses very suddenly. 

This reaction causes a sharp electrical spike. The electrical spike will only last for a few microseconds before another current will run through the coil for a repeated process.

Commercial PI metal detectors sticks to the standards of about 100 pulses per second.

If it happens that the transmitted pulse of electromagnetic field came contact to a certain metallic object, the pulse will create an opposite magnetic field around the target. 

Then when the pulses collapses resulting into a reflected pulse, the generated magnetic field around the object will cause a longer delay of the reflected pulse before it will completely disappear.

Assuming that a certain object has caused a delay on the reflected pulse, the "sampling circuit" will pass the signal into the monitoring device called "integrator". 

The integrator will then interpret the signal which will be amplified and then converted into a direct current (DC). 

This DC current signal will be processed into the audio circuit where it will be finally converted into an audible sound that alerts the operator.

Gary Chemelec's PI Metal Detector Design

I will not be sharing Gary's PI metal detector on this post where I suggest that you should visit his own website to get a copy of his circuit-schematic diagram.

This is the link to his website:

http://chemelec.com/Projects/Metal-1a/Metal.htm
http://chemelec.com/Projects/Metal-2a/Metal-2.htm

If you are not quite good at building electronic projects, I suggest that you should purchase the complete kit. 

Gary's complete PI metal detector kit already consists of all the necessary parts that you need. All you just have to do is to follow the instruction from the manual in order to properly assemble it.

You can also ask help from Gary if you have trouble in building the kit.

Overall, pulse induction metal detectors performs great on high conductive soil or ground. It is actually quite good at detecting deep buried objects as compared to any other designs. 

However, PI detectors are not good with discrimination which is the major draw-down of the equipment. The reason is that, the reflected pulse length of various metals are really hard to separate.