Design Challenge

[Skippy]

"The BLUE signal is the pulse that generates the slope"
So you know when the slope will occur. So, as per my previous suggestion, start a negatively sloping waveform generator at the correct rate, sum it with the actual rising slope, and you have a near-flat waveform. Use a later trigger to see if the 'flat' voltage is the same near the end of the ramp-time as it was at the beginning. Maybe a sample-hold is needed at the beginning, to compare against?

[Sean_Goddard]

I assumed so. You can't discriminate without a reactive component.

Definitely on the right track there Carl, I suspect Qiaozhi is too. It's one of those "OH FFS" moments when you realise there is a LOT more information in the Tx signal of a PI than was previously realised, and you wonder why no one spotted this before. I had a major face-palm moment when, whilst trying to achieve something entirely different, quite by accident I stumbled across this method.

I was trying to gate the Tx pulse to give maximum power with any coil fitted, but when I adjusted some timings, the steel washer I was using was no longer picked up but when I reached across to turn the machine off, my wedding ring gave a signal. I thought "No way", then tried some other targets and sure enough my suspicions about what was happening were confirmed. It's not perfected and the circuit is on 3 breadboards atm so I'm going to try to reduce it down. Dave Emery says the PD only has 4 op-amps in it and I'm trying to get down to less that the dozen or so I have atm.

[Carl-NC]

Sure, there's just as much info during a PI transmit as there is during a VLF transmit. Including lots of ground signal. Quite a number of people, including here on Geotech, have explored this but either got nowhere with it, or they did and kept their mouth shut. At White's I figured out how to combine the TX-time response with the flyback response to cancel ground and discriminate. It had the unique property that when GB was enabled, the detector got more depth.

[eclipse]

Here's a link to Tinkerer's IB-PI thread

[Sean_Goddard]

It had the unique property that when GB was enabled, the detector got more depth.

Spoke to Dave Emery this week about just that very property. The pulse devil depth INCREASES when there is ferrous near the target and when the GEB is turned on.

Also US10,181,720 B1. I have been using this method in my PI design (with Daves permission) which is why I cannot go commercial with it. he refuses to grant license to use it for commercial designs even to me .

[rickb]

Which of those 29 threads are you referring to?