Pi power supply

[Carl-NC]

It's differential in the sense that most opamps are used as differential amplifiers. Yes, I know this is commonly called a single-ended configuration but the opamp amplifies the difference between ground and the other side of the coil, which decays to ground. It is obvious that at full decay any noise on ground is common-moded and does not show up at the output, assuming good CMRR. But this is also true during the entire decay. So whatever problem liudengyuan is having, it's probably not what he thinks unless it is due to a bad layout. And without some circuit drawings from him I doubt he'll get much more help in figuring it out.

[liudengyuan]

Thank you for your guidance, thank you for your selfless dedication, I like to use single chip microcomputer to replace waveform generation and delay, but I have not found a suitable file

[eclipse]

Always use synchronization of the voltage converters in the circuit to reduce noise, also use decoupling caps next to each IC.
For example LT1054 which is often seen to provide +5V or -5V if left un-synchronized pours alot of noise which can be hardly fixed.

[waltr]

Thank you for your guidance, thank you for your selfless dedication, I like to use single chip microcomputer to replace waveform generation and delay, but I have not found a suitable file

Did you look in the Hammer Head II projects???
The thread "My take on the HH2" uses a PIC processor and has the source code posted.
Did you look in the "Inside the Metal Detector" forum?? It also has PIC code.
Did you look in the Programming" forum?? It has various info and code using PIC and Atmel processors??
Did you try the Forum Search feature to find info????????

All you have asked for is in the forums here...Search and Read...

[liudengyuan]

thank you

[liudengyuan]

I searched HH2 but I didn't find its URL, please send a link, thank you

[waltr]

I searched HH2 but I didn't find its URL, please send a link, thank you

https://www.geotech1.com/forums/foru...mmerhead-II-PI

[green]

It's differential in the sense that most opamps are used as differential amplifiers. Yes, I know this is commonly called a single-ended configuration but the opamp amplifies the difference between ground and the other side of the coil, which decays to ground. It is obvious that at full decay any noise on ground is common-moded and does not show up at the output, assuming good CMRR. But this is also true during the entire decay. So whatever problem liudengyuan is having, it's probably not what he thinks unless it is due to a bad layout. And without some circuit drawings from him I doubt he'll get much more help in figuring it out.

Thanks for the replies. Trying to understand any noise on ground. Made a spice simulation. Ground is half way between the supplies. Common is noise reference to ground. Single ended tracks common, diff amp cancels common reference to ground. Don't know which is better. Maybe not what your suggesting.

[Carl-NC]

Ugh, my mistake, you are correct. I forgot there is a gain-of-1 pass-through on the common-mode signal. Thanks for the catch.

[liudengyuan]

So what is true differential amplification? Do I need to isolate the power supply?

[liudengyuan]

In order to cope with the influence of the high-voltage line on the instrument, is it useful to process the frequency filter behind the pre-amplifier circuit? Has anyone studied?

[liudengyuan]

Can pulse detectors use double D coils to discriminate against iron? What are the advantages of double D coils?

[waltr]

Can pulse detectors use double D coils to discriminate against iron? What are the advantages of double D coils?

Yes, PI can use DD coils but this does NOT in itself help with iron discrimination.
Did you READ my HH2 Thread???? It has info on the DD coil I use.............

Advantages of DD is possible shorter delay to first sample by reducing the Fly-Back and pre-amp overload recovery.
A DD has a different magnetic field pattern that has advantages in some locations.

[liudengyuan]

Is there any other way to discriminate against iron

[waltr]

Is there any other way to discriminate against iron

That has been the Holy Grail of PI detector design and no one has yet demonstrated a PI that does iron disc reliably.
READ the Forums here.

This one has possibilities but we are waiting for real testing.
https://www.geotech1.com/forums/show...Metal-detector