complete project Circuit diagram

[Tinkerer]

Tinkerer Hex file

found a hex file. Not sure if good, but worth a try.

[Tinkerer]

I like your board. Also the test point loops.
I am a bit surprised with the low PPs rate. Usually my preference is high rate 2k and up to 20k. This design is for an induction balanced coil. The bucking coil in series with the TX coil is wound in the opposite direction of the TX coil, around the RX coil. The number of turns (stated as 1 on the schematic) depend on the diameter of the RX coil.

[eclipse]

The mosfet is rated 650V and unrestricted went all the way up to 800V. I did not expect to see high heat build up (probably arround 50C) on the flyback control resistor (let's call it that).
Right now I've connected it to a regular mono coil 550uH as was impatient to turn it on and building a IB coil will take me a while.
I'm using the default timings 600PPS with 100uS TX provided by you. Some parts are kept tall as I want to be able to desolder them to be re-used as this build is more of a proof of concept test board where things will be swapped/desoldered and possibly destroyed
I took note and added copper pour can be connected to GND with J1 so I can actually see if/what improvement it gives. Also you will notice audio connector which can be connected to 2nd board with alternative audio solution possibly AD654 based.

[Tinkerer]

Changed it to 100 ohms and it looks better now, not too sure.. the voltage peak is 250V now.

It is OK to regulate the Flyback voltage with the resistor. The important thing is to avoid avalanching the Mosfet or overvoltage of the parts, capacitor and resistors. Avoid Wirewound resistors when possible.

What is the timing schedule you are using?

[eclipse]

Changed it to 100 ohms and it looks better now, not too sure.. the voltage peak is 250V now.

[eclipse]

On the TX part where the 420R - 1uF(500V) - 47R is located, the 420R resistor is getting quite bit of heat (I'm using 330R/3W there), is this okay or maybe I should lower the value to maybe 100R ? Without those components the voltage reaches nearly 700V with 15V supply and after I soldered them it went down to 450V, which is good, 1uF cap is rated at 500V.

[Tinkerer]

On the last post at 0:38 the audio stops for a while when the target is over the coil. It maybe appears when signal is too strong (object too close to the coil)?

The audio pitch or frequency increases for copper or non magnetic targets. For Magnetic/permeable targets, the pitch decreases. There comes the point where the frequency reaches sub-audio frequency, near zero Hz.

The no target frequency should be set at a frequency that is kind to the ear.

A good improvement to the design would be a proportional audio volume.

[eclipse]

On the last post at 0:38 the audio stops for a while when the target is over the coil. It maybe appears when signal is too strong (object too close to the coil)?

[Tinkerer]

There's also hole effect which also may need to be revisited and improved.

Thank you for the observation.

Please tell us more about the hole effect you have noticed.

[eclipse]

There's also hole effect which also may need to be revisited and improved.

[Monolith]

more...

That seems to do a decent job of iron discrimination. If that continuous audio tone was changing in volume when the target is near, it would be less tiring. For myself I would also lower the center frequency a bit. Instead of a center frequency, make it 20% low and 80% high frequency. The iron does not really need to have a great range, it could be more of a yes-no indication.

[Tinkerer]

You are right. I have blown some mosfet´s...

It took me some time to notice the problem, as I was using mosfets with zener gate protection which were quite immune.

[mschmahl]

These designs had a problem with the inrush current, because there was no inrush current limiting. Under certain conditions this could blow the mosfet gate.

You are right. I have blown some mosfet´s...

[waltr]

Wouldn't the ON/OFF switch need to connect to +B to turn on Q3 since +15 is zero when Q3 is off?

[eclipse]

Here's what I use. It adds some delay and also doesn't produce sparks when you switch on.
Plus overcurrent and reverse battery protection the lazy way.