Replies to Minipulse Plus

[liudengyuan]

George's view of the same,

[Qiaozhi]

Yes I agree there is terrible marketing hype surrounding detectors. Have you noticed that even the buyers of this hype largley help propagate the hype too lo.
Many years ago I owned a garret ads deepseeker vlf. With it I could ping a coin at about 35cm in air and the reality is that there is not much improvement since then. All the current vlf detectors that I see today would be no better than that, most are probably worse. In air there wouldn't be many PI's that can beat that either.
The laws of physics can't be overcome.

Good GB and as you say lower noise front end is were improvements can be found.

Unfortunately air tests do not equate to depth in the ground. Modern motion detectors have an advantage over the older designs (such as the Garrett ADS) with better target separation and recovery, plus target ID.
Also, it's worth noting that PI detectors generally will not do so well in an air test when compared to VLFs, but in real soil the situation is different. VLFs can lose a third of their air test depth (and often much worse), whereas the PI detector's loss is small. Today's designs seem to be optimized more towards detection of targets in contaminated soil, so comparisons with older designs (using air or non-mineralized/homogeneous soil tests) will show little improvement in depth. Plus, as you say, the laws of physics haven't changed.

[josewashere]

Yes I agree there is terrible marketing hype surrounding detectors. Have you noticed that even the buyers of this hype largley help propagate the hype too lo.
Many years ago I owned a garret ads deepseeker vlf. With it I could ping a coin at about 35cm in air and the reality is that there is not much improvement since then. All the current vlf detectors that I see today would be no better than that, most are probably worse. In air there wouldn't be many PI's that can beat that either.
The laws of physics can't be overcome.

Good GB and as you say lower noise front end is were improvements can be found.

I certainly hope so. The other PI projects can benefit from this approach as well, but I'll have to see where to put what to make them tick.
In essence there is no difference between any of the simple projects against the much more expensive commercial ones. Except for the preamp noise and the ways of reducing it. MPP is limited with the coil damping resistance to 4nV/sqrt(Hz) or so. A select few of the commercial products take care of input noise in a meaningful way. QED for example. Everything else is just a clever play of marketing wits and front panel presentation.

[liudengyuan]

I did not use LT1054, I am using other modules, Tucker converted into a plus or minus 24V 5V, and with isolation

[Qiaozhi]

I've built a mini. The effect is not very good, increasing the power supply to the I 24V, the effect is not ideal

You cannot run the MPP from 24V. The LT1054 has an operating supply voltage range from 3.5V to 15V.

[josewashere]

Also with the revised timings on this unit a 500uH inductance is probably too much for the mpp. 350uH probably a much better choice but yes if the damping resistor value is too high you will see ringing on the preamp output waveform and even on the coil connections too with a scope. You aim for the highest value before it starts to ring. Too low a value and you loose sensitivity. Every different coil will use a different value but the standard 470ohm resistor will work with most coils that I tried.

[joop]

Calculating is not an option... Watch the output of the NE5532 (TP3) as you change the damping resistor. When the damping resistor is to low, the decay curve will have spikes. I have a 360 uH coil and use around 300 Ohms. The original minipulse coil uses 500 uH with 470 Ohms. So you will need to know the inductance of your coil.

[CAS]

Just a quick question - what is the best way of calculating the optimum value of damping resistor (R1)?

[liudengyuan]

I've built a mini. The effect is not very good, increasing the power supply to the I 24V, the effect is not ideal

[6666]

Drats I found the fault with my MPP a short circuit 78l05 reg, no real reason for it to fail, was working fine.
I will record current readings as I put the machine back together as an aid for construction.

Here is a tip LOAD test your voltage regs before construction.

[liudengyuan]

Who pulse detector for iron-discrimination programs and technology? I think discrimination iron is necessary, because the whole world is garbage, if we may expand the topic of discrimination iron a discussion. We need to progress

[Davor]

I certainly hope so. The other PI projects can benefit from this approach as well, but I'll have to see where to put what to make them tick.
In essence there is no difference between any of the simple projects against the much more expensive commercial ones. Except for the preamp noise and the ways of reducing it. MPP is limited with the coil damping resistance to 4nV/sqrt(Hz) or so. A select few of the commercial products take care of input noise in a meaningful way. QED for example. Everything else is just a clever play of marketing wits and front panel presentation.

[josewashere]

Excellent work! The GB mod is going to make this detector really nice.

[Davor]

Great work! Do you have a plain circuit diagram for the GB mod? and were it connects to the existing circuit? In my day we just used spice on the roast chicken lol.

I already placed labels C and D on the diagram to follow on the MPP logic. Here is the latest, only slightly modified circuit to facilitate using MC14538 sockets for a simple plug-in solution. Border between MPP and a add-on board is a dashed grey line. So the idea is to pull MC14538-s out, and plug the add-on board in. Connections B, C, D, -5V, and GND are taken from the MC14538 sockets, exactly where they are already.

There will be 2 potentiometers, one for time base (same function as "reject"), and another for GB. The MPP "reject" potentiometer loses its function and becomes replaced with time base (sample duration) potentiometer.
"First pulse delay" is a GB potentiometer. Because this delay is set to be relative to the sample duration, the GB solution position on a potentiometer is largely independent from sample duration. Hence you may shift sample duration left, right and sideways, and your GB setting will remain virtually the same. This gives me some nasty ideas on elimination of the hole ... later on.

[Qiaozhi]

Until now, no one can be better than Delta Pulse Pulse, whether or stability detection range, so for the average DIY, I think the best option is delta pulse

Delta Pulse is (as WM6 stated) a brute force approach. It is a good detector for finding huge buried items using large search frames. It can also be used with smaller coils of course, but it is not designed to work with early sampling, and therefore cannot find small low conductivity items. So in your case, where you're searching for larger items at great depth, then Delta Pulse will be better. However, you could modify the MPP to create a larger brute force TX pulse (same as the DP), but remember to add a heatsink to the mosfet. You would also need to disable the SAT, as discussed earlier in this thread. The modifications required are small to make the MPP work like the DP, but if you already have a DP then go with that. You cannot simply say that one is better than the other. It's horses for courses.