WELCOME!!

[Qiaozhi]

I'll take the Tx stage, who wants the front end amp and first stage buffer amp?

Unfortunately I have no time to be involved in this interesting project, as I'm up to my eye balls in real work.

Hope you have your project manager's hat at the ready. You're probably going to need it!

[soverey]

Unfortunately I have no time to be involved in this interesting project, as I'm up to my eye balls in real work.

Hope you have your project manager's hat at the ready. You're probably going to need it!

Ooh , I was hopping we could just start and build what Sean had designed and at least see how it works. I think Ivconic is right in his approach - if he wants ,to build a single sided pcb with more available components , and to compare it to the standard 4 layers pcb and more modern components it is ok.

I don't want to be critical in any way , but I have seen many start-up projects on this forum , started and not finished, and when I saw suggestions like ... lets make it modular, add wireless charge .. I thought ooh here we go again ..Sean's projects will be lenghten again..and probably will end up like others ... which I really don't want to happen...

I'm waiting for the chance to start to build something more advanced for some time , if you remember , It was me who tried to convince Moodz to publish his detector project, and he did start to make a build document some time ago, but unfortunately there was no progress lately, probably he is busy. So please lets build something first.

[ivconic]

EXCELLENT POINTS ALL!!

I've NEVer yconsidered you an "amateur" Ivconic, quite the opposite in fact. I greatly value your input on all parts of this forum. Same with the other who are on this thread.

OK lets make THIS the first modular project.

Who wants what part to play with? I'm thinking a TX with blanking on the output to stop front end saturation for a start. The best part is the power supply, too many switching PSU's in existing designs, ssynchronous or not they generate NOISE (shouts) so lets put a whisper on those supply rails.

Of copurse no point in havinga silent PSU if the other stages chuck out a load of guff instead so each person who takes up will have the rsponsibility of making sure THEIR stage stage shtum (quiet) too. Ah you thought you were going to get off lightly? NO chance! ;-P.

Right, according to Dave (Guess who) the supplies can be as lowe as +/- 2V5 but I prefer +/- 4V so can we work from that?

I'll take the Tx stage, who wants the front end amp and first stage buffer amp?

This is going to be FUN ;-))

In the past i made ultra low noise guitar preamp and was impressed with gained results.
I tried to adapt that circuit for detector's front end. Just done it without precise calculating.
Would be good if someone skilled with simulators check this, because that's my proposal for front end:



P.S.
Circuit is working with low voltages, +/- 4,5V .

[Davor]

With BF862 this circuit's noise may go below 1nV/sqrt(Hz)
Unfortunately it is also a bit misleading, because of a problematic settling time (those 1000uF capacitors), and the fact that this is a PI front end.
There are differential pair solutions that may prove better in settling time sense, and that may keep the good noise performance of a discrete front end.

[ivconic]

With BF862 this circuit's noise may go below 1nV/sqrt(Hz)
Unfortunately it is also a bit misleading, because of a problematic settling time (those 1000uF capacitors), and the fact that this is a PI front end.
There are differential pair solutions that may prove better in settling time sense, and that may keep the good noise performance of a discrete front end.

Caps can be omitted or changed. Depends on power supply stage and how it is designed.
I put them only principally.
Differential pairs are exotic thing here in local shops! Kinda "say what!!??" reaction that you will get from a seller.
For guitar pickups is not problem to chose a fet. Here... i am not sure.
Yup, that's the misty part in schematic, i am scratching my head right now!

[Qiaozhi]

I don't want to be critical in any way , but I have seen many start-up projects on this forum , started and not finished, and when I saw suggestions like ... lets make it modular, add wireless charge .. I thought ooh here we go again ..Sean's projects will be lenghten again..and probably will end up like others ... which I really don't want to happen...

Hence my comment about the project engineer's hat.

The very valid comments you made (above) are nearly always true when something is designed by committee.

Sean - I would seriously suggest that you take complete charge of this project, and then it will be up to you if you include any of the suggestions or not. Otherwise, as soverey quite rightly said, the project will drag on forever with no ending in sight. Communal projects can seem a good idea at the start, but even with the best of intentions, it will inevitably come unravelled.

[Davor]

...Differential pairs are exotic thing here in local shops! Kinda "say what!!??" ...

Not at all. You need to match a pair of FETs and that's about it. FETs are quite forgiving when it comes to matching.

[ivconic]

Not at all. You need to match a pair of FETs and that's about it. FETs are quite forgiving when it comes to matching.

Ah so. I though you are referring on special monolithic differential pair.
I saw those only on picture...

[localbug]

I like the schematic, especially attention to supply filtering/bypass. And shift towards using 4066 or similar instead of fets for gating. And the I also like the thoughts on a "LEGO" type concept. Have thought about the idea too, as it would be easier to experiment with changes to a particular section or "block". And it would become very easy to create a model following the pattern of any older or well known design using generic "blocks" or modules. You can find on places like thingyverse, generic opamp layouts/modules etc. Could be a useful way to learn about practical layout placement, and mixing manhattan and ugly style construction too.

can't agree more for stack-up design, finally someone brought this to the surface.
will save plenty of time redesigning PI... power supply block, oscillators, front end, sampling, integrator,etc.
universal dimension need to be figured out..

[Sean_Goddard]

Right I'm back, here goes.

Two coil or mono or option? Let's go Mono to start and work from there.

Davor and Ivconic, can you take on the front end ampl please between you as a team as you BOTH have excellent ideas and I think that 1nv/Hz would be just about dandy ;-)). Keep the gain low so as to avoid ground problems and watch for saturation and recovery times.

Can you also look as active blanking or can we get away with not needing that? Suggestions please?

I'm going to task Old Cart with the PSU, nothing complicated, but rock solid stable and quiet.

I need someone to take on the integrators so I might have a go at that (EEK!)

Oscillator and pulse timing ANYONE please? Max of 2KHz and everything else variable too. One thing I want to try / ask about is a SUPER LONG ground integration time. Like can we sample the ground for 250uS and integrate it until JUST before the Tx pulse? Surely this would give us the best ground immunity or am I missing something?

Coil design, nothing hard to make just FAST (like 8uS) so we can get that thin yellow stuff.

Let me know if you're happy with these assignments.

[Sean_Goddard]

You can find on places like thingyverse, generic opamp layouts/modules etc. Could be a useful way to learn about practical layout placement, and mixing manhattan and ugly style construction too.

Tell us more please. Can you investigate this for the project, in fact what about reference designs for op amps etc.

Invonic, What about the OP series amps, can you get those in DIP where you live? They are low noise and quite good.

[Old cart]

Power supply

Ok I will do the power supply. Assuming we stay close to your original design I suggest we either we use the design you proposed or the following design.

I am having problems attaching an image, will try in next response.

This can be proceeded by a 11-15 volt battery and can produce any +/- voltages desired. Some samples are shown. The coil MOSFET will be driven either the battery directly OR the pre regulator that would feed this. The pre regulator is not critical and can be an ordinary 78 or 79 series TO220 style. By choosing the correct pre regulator I think this will work with either a N or P channel MOSFET. It should be able to source plenty of current, requires no adjustment, provides a very clean low impedance ground for the analog sections, and always give an perfectly symmetrical supply that tracks the input voltage.
I have NOT built this circuit but it is used in high end audio equipment where clean supplies are critical. It contains absolutely no switcher so could be built on the main board or as a separate module.

[Old cart]

Oh it actually worked, just did not look that way! Anyway this supply is flexible. Easy to change supply voltage ranges etc. It basically splits whatever you give it so if you apply regulated 9 volt you get regulated +/-4.5 Volts. Since you would normally use a pre regulator of say 10 volts this would give a clean 10 volts to run transmitter driver stages and also be a clean source for the split supply. Not shown here is the extra bypassing that should be added, much as Sean has done. I think 100, 1 and .1uf ( film) should work well for C4 and C5. C1 Should be on the the order of 2200uF low ESR type. Coil should be fed with source as close as possible to this cap, star arrangement.

[Thomas]

Here is a front end that caught my eye recently.

[WM6]

Very nice symmetric PS proposal Old Cart. Thanks.
Probably both 1N4002 are connected to ground too?