ask about the design of PI metal detector

[DJSUOL]

I am learning and implementing a pulse induction metal detector now and I have some questions about it. 1. I found for some design only one sampling circuit is used to connect to an integrator circuit and for some design two sampling circuit are used with a differential amplifier. What is the difference between the two technology and which performance is better? in addition, how to determine the threshold value of the comparator. 2. For the delay circuit, could someone suggest some methods to achieve it? The design I learned now is from the book 'Inside the metal detector' and the CD74HC221 chip is used to delay the clock signal from the 555 timer. How to simulate this chip function in the simulation software such as ltspice and is there any equivalent method to perform the function? 3. when I built the circuit, I wanna used two coils as transmitter and receiver. How did I design the two coils? I wanna use a smaller size coil such as 12 cm since this is a student project and how could I improve the sensitivity of it since I found almost all the product use more than 20cm diameter coil for the better performance. 4. Did someone have the experience to make a PI metal detector combining with Arduino and analog circuit that can give me some advice about your design?I

I really need the help and I appreciate your time and advice.

[waltr]

All good basic questions. Read the ITMD book is a start but that book has very little PI info.
A better place is the Detect articles here:
https://www.geotech1.com/cgi-bin/pag...e=projects.dat

LTSpice is good but some of the complex timing type chips (555, etc) are tough to model. LTSpice is good for the other detector circuits so we use a 'voltage' source then set it up to do pulses to drive TX MOSFET and RX sampling switches. Keep reading all the threads on the forums here for lots of info and discussions.

A Simple PI circuit can use one sampling switch but then noise, Earth Field, etc will effect the output. Two switches and a differential integrator helps this IF the sample timing is correct (again read the threads for discussion.
Output Threshold should be operator adjustable since the settings varies with conditions.

Using a micro-controller is the best way to do timing. I use a PIC but nothing wrong with an Arduino. Check the 'programing' sub-forum and the code (yes its for a PIC but in C so portable to Arduino) in the ITMD book on simple way to code timing. I do not recommend using timing chips since they are hard to make changes and all can be replaced with a single u-controlller chip.

IB coils work great on a PI detector. I use a 20cm concentric or a 25cm DD coil on my PI. Lots of info on making these. Check my build thread for some details on the coils, timing code, etc.
https://www.geotech1.com/forums/show...ake-on-the-HH2

Build and experiment and you will become an expert.

[DJSUOL]

Thanks for your reply. Do you know how to simulate the delayed clock in a simulation software or can you advise me any software contains these chips? In addition, is the setting threshold should be equal to the differential amplifier output without metal nearby? My project requires to simulate and implement a detection system. But the circuit design from the book cannot perform well. In my design, I wanna use the Arduino to check the integrator output and make decisions

[waltr]

I already stated how to do timing pulses in LTSpice- Voltage source Advanced options.

Arduino is great to create all the timing pulses but to use it to make decisions is more difficult due to you needing to DEFINE what to do with what change of signal.

It could do what my PIC VCO does. Read the comments in the source code I posted for how it works.

Threshold would be the Integrator output Pulse or Minus a little. Think of this as a Voltage window. If the Voltage is within the window then NO detection (no target). If the Voltage goes out side the window (+ or -) then a target detected and create some indicator, audio Tone, LED, etc.

[DJSUOL]

Could you please tell me how long is suitable for the sampling delay clock?

[DJSUOL]

And could you please tell me some methods about how to make sampling clock using chips such as 74hc221?

[Andi68]

So many "experts" and no answer

[kt315]

And could you please tell me some methods about how to make sampling clock using chips such as 74hc221?
---
banner at top of this page is CLICKABLE. just click and find out there the article of Carl M. HAMMERHEAD - PULSE INDUCTION DETECTOR.
open the schematic. look on it. find 74HC221.

[kt315]

banner GEOTECH****

[DJSUOL]

can you tell me how does the 14093 chip circuit in surf pi design to achieve the delay clock? Have you tested the practical results using an oscilloscope?