Modular Metal Detector

[Carl-NC]

Here is a schematic of the motherboard:



You can see why I led with a block diagram, as the schematic is just a bunch of connectors with mostly label-based routing. Hard to read.
And here is the layout:



It's very simplistic, only 2 layers and most of the routing is for power. The selection options are intended to be 0.1" male pins with suitcase jumpers. Clock and control pins are simply routed to 0.1" headers next to the modules, with the intent that jumper wires are used to connect them to a micro eval board like an STM Nucleo.

Below are a schematic PDF and Gerber zip file for the layout.

MainBoard.pdf
MainBoard.zip

[Carl-NC]

Here is a simplified diagram of the MMD system:



It is simplified in that it does not include the "ground" signals or the module control/clock inputs. There is a transmit module for driving a single TX coil. There can be (2) RX coils and (2) preamp modules; either preamp can be connected to either RX coil, so these are possible:

• RXA drives both PreampA and PreampB
• RXB drives both PreampA and PreampB
• RXA drives PreampA, RXB drives PreampB
• RXB drives PreampA, RXA drives PreampB

There are (4) complete X/R channels, each channel has a demod module and a filter/gain module. Each channel can be selected to read from either PreampA or PreampB. The X&R outputs of the filter modules are routed to a header to feed an off-board ADC.

The purpose of the MMD design is to compare different preamp, demod, and filter topologies. For example, you could use RXA and PreampA to drive 4 different demod designs and look at all 4 at the same time, to compare performances.Or, you could run it as a multifrequency design with up to 4 frequencies.

[Carl-NC]

For my purposes, the MMD project is already complete. I have a motherboard and numerous modules already designed and PCBs fabricated. It really began as a VLF investigative tool but can be used for PI as well. It is less easily adaptable to complex designs like AMX or stuff moodz is working on, those require more dedicated hardware.

[Daves]

Why don't we use the cheap PCB 100x100mm / 3.9x3.9 Inches, from JLPCB https://jlcpcb.com/ as standard? In post #9 I show my bi-polar Square current Wave TX board. These boards were designed to be stacked vertically.
For development work on the bench it is better to use the boards placed side by side, so that one has access to every part with the oscilloscope.
The TX board from post #9 is working good, only small changes to the layout would be needed to optimize it with a back plane.

The preamp at post #62 as now been tested on a breadboard. It works really well. This is really the preamp of the AMX Project.

https://www.geotech1.com/forums/foru...387#post419387

So I propose we merge this Modular Metal Detector Project with the AMX Project.

Is this schematic for only PI RX preamp

[Daves]

Sorry, this completely fell off my radar. I'll post more as soon as I can.

Thanks, waiting.

[Tinkerer]

Sorry, this completely fell off my radar. I'll post more as soon as I can.

Why don't we use the cheap PCB 100x100mm / 3.9x3.9 Inches, from JLPCB https://jlcpcb.com/ as standard? In post #9 I show my bi-polar Square current Wave TX board. These boards were designed to be stacked vertically.
For development work on the bench it is better to use the boards placed side by side, so that one has access to every part with the oscilloscope.
The TX board from post #9 is working good, only small changes to the layout would be needed to optimize it with a back plane.

The preamp at post #62 as now been tested on a breadboard. It works really well. This is really the preamp of the AMX Project.

https://www.geotech1.com/forums/foru...387#post419387

So I propose we merge this Modular Metal Detector Project with the AMX Project.

[Carl-NC]

Sorry, this completely fell off my radar. I'll post more as soon as I can.

[Daves]

I tried that approach a long time ago but never could get the backplane figured out in a way I liked. Looks like you got it solved.



I think what I'll do is move this to the Projects section and start posting schematics and Gerbers.

Hi Carl, do you have a date planned?

[Tinkerer]

I use that same blue silicone map to lay out the parts to be soldered.
When I order the PCB I also order the stencil for the PCB.
With the Stencil I apply the solder paste. For quick and dirty I use low temperature Sn42 Bi58 solder paste (Aliexpress). that makes it easy to remove the parts if I want to change. Place all the parts on their places on the solder paste.
Then I set the PCB on a thick aluminum plate and heat the plate with a clothes iron until the solder paste starts to run.
Then I run over it with the hot air, not on the components, just around them. As the PCB is already pre-heated, the solder fuses immediately.

[ivconic]

Do you have a hot air soldering tool? If yes, I can show you and anybody else interested, my crude and simple SMD reflow method. Not good, but good enough for initial POC assembly. The whole board soldered in 5 minutes. I like 1206. The 0604 only under the microscope for placement, at great sacrifice.
Having separate modules, we have some liberty for the individual modules as long as the connections to the motherboard are respected.

I have one. Please do tell, do show.
At the moment Mancha is exploring it:

[Tinkerer]

Good!
I might convert some parts into through-hole for my own experiments.
I don't prefer such tiny "invisible" components.
1206 is the all I can do.
Not only bad eyesight but also shaking hands too.
Schematics and Gerbers will do.

Do you have a hot air soldering tool? If yes, I can show you and anybody else interested, my crude and simple SMD reflow method. Not good, but good enough for initial POC assembly. The whole board soldered in 5 minutes. I like 1206. The 0604 only under the microscope for placement, at great sacrifice.
Having separate modules, we have some liberty for the individual modules as long as the connections to the motherboard are respected.

[ivconic]

At half sampling rate than what you used; there is ADS1256 ready modules, affordable here:

https://www.aliexpress.com/item/4001058364470.html?spm=a2g0o.detail.1000014.5.4cd63f1645XkEV&gps-id=pcDetailBottomMoreOtherSeller&scm=1007.40000.320564.0&scm_id=1007.40000.320564.0&scm-url=1007.40000.320564.0&pvid=9fd4440a-91bf-437b-97db-f806ad7b7180&_t=gps-id:pcDetailBottomMoreOtherSeller,scm-url:1007.40000.320564.0,pvid:9fd4440a-91bf-437b-97db-f806ad7b7180,tpp_buckets:668%232846%238107%2381&pdp_ext_f=%7B%22sku_id%22%3A%2210000013902200146%22%2C%22sceneId%22%3A%2230050%22%7D&pdp_npi=2%40dis%21RSD%211338.02%211070.85%21%21%21%21%21%402101c84f16747360339116587e395f%2110000013902200146%21rec

[ivconic]

I tried that approach a long time ago but never could get the backplane figured out in a way I liked. Looks like you got it solved.
I think what I'll do is move this to the Projects section and start posting schematics and Gerbers.

Good!
I might convert some parts into through-hole for my own experiments.
I don't prefer such tiny "invisible" components.
1206 is the all I can do.
Not only bad eyesight but also shaking hands too.
Schematics and Gerbers will do.

[Carl-NC]

My take on a modular platform.
Post 10.

https://www.geotech1.com/forums/forum/technology/tech-forum/16875-new-member

Steve

I tried that approach a long time ago but never could get the backplane figured out in a way I liked. Looks like you got it solved.

Hi Carl,
I would be very keen to purhase and evaluate your modular concept. I have an SMD reflow oven so all I need are the PCB's and BOM.
Cheers

I think what I'll do is move this to the Projects section and start posting schematics and Gerbers.

[Dean Sarelius]

Hi Carl,
I would be very keen to purhase and evaluate your modular concept. I have an SMD reflow oven so all I need are the PCB's and BOM.
Cheers