Hobby Hybrid MD1

[Detectorist#1]

Hi all MD enthusiasts! Now, I propose one more schematic of hybrid MD. This design is based on the schematic of DFBowers and previous my designs. First, this design uses ready search 15"x12"DD coil of SEF type. This avoid the manufacturing of the search coil - the hardest work for me and maybe for many hobbyists. Discrimination Fe/non Fe is made during ON pulse time and is very reliable. Indication is done by two LEDs. The "ALL" channel uses sound generator with controlled frequency proportional to the level of the signal. This design uses only two control potentiometers - "DELAY" and "SENSITIVITY". The sure discrimination is not possible for too big signals (big targets very close to the coil). This necessitates sensitivity adjustment. For now, the design uses 4 separate boards. My future work is to design only one board with all parts. It will be good if some body will help in this.
The schematic is attached.

[Op04]

So this using N-channel MOSFET. Thank you for sharing Detectorist#1!

[Detectorist#1]

Basically, using of direct sampling of the signals on the outputs of the input amplifiers of "ALL" and "DISK" channels will give possibility to essential reducing of the number of parts in this design. Real-time signal processing specialists with microprocessors have a say. I'm not one of them.

[Detectorist#1]

Why the power voltages of the OpaAmps are +3V/-3V instead of +5V/-5V? The reason is using of contemporary OpAmps with low input offset voltages and low input bias currents. Yes, this increase the price of the parts but for singe production it is not essential.

[Detectorist#1]

To be honest, my hope is that Ivconic will help significantly with the PCB project. Hi is a real master in PCB design!

[ivconic]

I thought the same thing today when I saw the schematic. But something strange is happening with me.
For a couple of months, I feel a very sharp pain in my right upper arm, which goes to my neck.
It resembles a nerve under inflammation. Or on a twisted "fiber".
I guess it's from the position I'm sitting in while holding the mouse with my right hand.
I've tried Brufen, I've tried Paracetamol, massage... nothing helps. I've been in terrible pain all day today.
And it prevents me from doing my favorite hobby during the winter days; and that's drawing...
First, I would redraw the schematic in the ExpressSch program. And then I would try to draw the pcb.
But for now I am unable because of the terrible pain.
Maybe the outside weather affects it too?
Ten days ago, the temperature here is very low and even the heating in the house does not manage to insulate me enough from it.
The first thing I plan to do this year is install insulation on this part of the house... which (Murphy) is the only one left uninsulated.
The schematic is interesting. I took a cursory glance.

[Detectorist#1]

Hi ivconic,
Take your time to curry your health. We need your advises in MD area.

[andon80]

Is there a company code or link for the 15"X12" SEF coil?

[Detectorist#1]

Hi Andon80,
https://www.detech-metaldetectors.com/contacts.html
https://www.detech-metaldetectors.com/products/coils/52-15-x-12q-sef-search-coil.html

[Detectorist#1]

I'm very surprised from discrimination possibilities of this design - the beer's cap is surely discriminate as Fe target on 25cm. Previous my design with DOD search coil (more more complex) recognizes the same beer's cap as Fe target only at 15cm distance. Good reduction of the dig efforts!

[Altair]

I'm very surprised from discrimination possibilities of this design - the beer's cap is surely discriminate as Fe target on 25cm. Previous my design with DOD search coil (more more complex) recognizes the same beer's cap as Fe target only at 15cm distance. Good reduction of the dig efforts!

Interesting project! Thank you for sharing.
Could you provide some video?

[GeoMax]

Hello Detectorist#1

nice circuit... I would split your design into two parts (PCBs). If you don't plan to replace the timing with an MC later, I would stick with this concept. The first PCB board should run as a standalone PI circuit and the hybrid part is built as an add-on board. This minimizes the number of PCBs. But before I would make a board, I would first choose a suitable housing, then check whether everything fits in it (including the battery). The PCB design is not very complex to make. Do you have in mind to have a 2 or 4-layer design for your detector? Further should it be a discrete or SMD board design?

[Detectorist#1]

Hi GeoMax,

The first assembly of this design starts with using of 2pcs. of standard PI MD. One of these boards was modified to be used as discrimination channel and on additional board was soldered final modules of the DISC channel (with LM393 and CD14538BE). The first tests showed big noise of 50Hz on the outputs of ALL and DISC channels. After reducing of the values of the capacitors in sample-hold parts from 220nF to 4.7nF, this 50Hz noise almost disappear. Next, essential reducing of the noise on the output of the DISC channel was achieved by assembling of the first stage of DISC channel on separate mini board and connecting this stage on the same solder points as the first stage of ALL channel. Thus, using of two separate boards for ALL and DISC channels have to be made with caution.
Concerning the PCBs - this project is proposed as hobby project. I think, 2-layer PCB design is more suitable. The same for THD-SMD parts - THD is more suitable according me. For SMD OpAmp in SOIC-8, I think have to be used SOIC-8 to DIP8 small adapter board - popular and cheap solution.
The solution of power supply source as usual is very important. Now, I design modification of the schematic of the supply with using of 2pcs. 18650 LiPo cells. Also they will be charged from any 5V 1A USB source. I'm close to the finish of this variant.

[Riss]

I thought the same thing today when I saw the schematic. But something strange is happening with me.
For a couple of months, I feel a very sharp pain in my right upper arm, which goes to my neck.
It resembles a nerve under inflammation. Or on a twisted "fiber".
I guess it's from the position I'm sitting in while holding the mouse with my right hand.
I've tried Brufen, I've tried Paracetamol, massage... nothing helps. I've been in terrible pain all day today.
And it prevents me from doing my favorite hobby during the winter days; and that's drawing...
First, I would redraw the schematic in the ExpressSch program. And then I would try to draw the pcb.
But for now I am unable because of the terrible pain.
Maybe the outside weather affects it too?
Ten days ago, the temperature here is very low and even the heating in the house does not manage to insulate me enough from it.
The first thing I plan to do this year is install insulation on this part of the house... which (Murphy) is the only one left uninsulated.
The schematic is interesting. I took a cursory glance.

ivconic, Dr. Riss recommends: massages, mineral water baths, microelements ( Magnesium ) , feet in warm water and sea salt, warming compresses and walks - they improve blood circulation. Cold nerves worsen blood circulation, which worsens the condition of the nerves...Your neck should be wrapped in a woolen scarf. in your city there are mineral springs with a temperature of about 29 degrees. There is a lot of information on the Internet about treating inflamed nerves. If you do not start treatment, your condition will worsen.

[ivconic]

Thanks for the tips. The situation is getting worse.
Because it's winter, it's snowing, I have nothing else to do, so I sit in front of the computer for many hours during the day and my right hand is always on the mouse.
The worst is the first 20 minutes every morning. During the day things calm down a bit.