New Project - MPS PI - Iron discriminating metal detector.

[GeoMax]

Hi,

the oscillator around U12 (D3/D4) is also not correct. Detectorist#1 mention it also. I do not why you have not corrected this. I told you about this error before.

[old_gingerbeer]

Hi old_gingerbeer,

The schematic 1.22.2 is full of errors in comparison with 1.22.1.
1. Common connection of D3 and R19 have to be connected to the anode of D4
2. Left end of R21 have to be connected to the cathode of D17, not to the anode
3. The lower ends of C45, U14 and C46 have to be connected to GND, not to -5VA
4. Capacitor C2 have to be moved on the place of R6. R6 have to be removed.
5. The value of R7 have to be reduced from 100K to 10K
6. Common connection of C28 and R30 have to be connected to GND
7. The lower end of R30 have to be connected to pin4 of U9B
8. The left end of C47 have to be connected to pin7 of of U10B
9. The resistor R36 have to be removed
10. On the pin2 of RV4 have to added capacitor 1uF to GND
11. To left unused parts of U1 with floating inputs is not good idea. These parts is possible to switch unpredictable from capacitive connections with near parts of the board and this will add additional noise on the board

Thanks for all proof readers .....must be close to have duplicated cct in KiCad

[old_gingerbeer]

The Gerber files are for ver 1.09 Are there geber files for ver 1.22.1

[old_gingerbeer]

Hi Diy's
Please find attached the latest cct version Need to learn how to manually route .... this will take sometime. If some who is experienced with Kicad routing and wants to do a pcb layout please PM me Condition is gerber files are to be published on this site. My future plan is to revise the Pi front end with a view to significantly improve sensitivity

[Detectorist#1]

Hi old_gingerbeer,
The last cct have errors:
1. The left end of R21 have to be connected to the anode of D17
2. The connection of the internal diode of Q2 have to be inverted
3. The type of D9 is zener diode with 6.8V or 7.5V

[GeoMax]

Hello old_gingerbeer,

R24 and R26 make no sense. You can never adjust the 100k potentiometer RV1 fully clockwise or counterclockwise. Also, you have to connect pins 1 and 3 of the headphone jack. Otherwise, you'll only get the target signal on one side of your headphones.

[Detectorist#1]

Hello old_gingerbeer and GeoMax,
All nulling parts for 5534 in this design are non-sense. The max input offset voltage of 5534 is 5mV. Voltage gain in this design is 221. The max output offset voltage is 5x221=1.105V. The capacitor C14 stops that DC voltage.

[nejdet]

Thanks for all proof readers .....must be close to have duplicated cct in KiCad

Few errors

[Detectorist#1]

This project is only very good start point for many our experiments - optimizing of the DISC channel, optimizing of the ALL channel, how to combine the output signals from these two channels and how to make indication to the user. According me, different sound tones only are more convenient in practice - not additional LED indication. But it is my own opinion.

[h9361]

Not true MPS like Minelab I guess
One Disc sample, one main sample, one EFE sample.

Hello
Dear dfbowers.
I tested your DISC schematic on my HHD, it works without any problem if i use it as concentric mode ( on mono coil for HHD and on coil for DISC schematic).
But i have a problem for using DD coil. As soon as connecting DISC schematic to DD coil ( according to your tips on scop), my HHD will be unstable ( its audio).
Do you know which point is problem?
I adjusted it very nice and it discriminate Iron and my HHD will detect nice depth, but its audio is unstable only in using DD mode for DISC PCB.
Thanks

[remi007]

If Carl's bi-polar TX were added to the scheme, it would be even better.

instead of an H-bridge, can a bifilar TX coil be used, driven by two drivers in opposition?

[pechkata]

instead of an H-bridge, can a bifilar TX coil be used, driven by two drivers in opposition?

Yes, but you would need to use the PMOS devices to drive the coils.

[remi007]

Thank you very much. I don't know why, but I'm tempted to use the SG3525 and two IRF740 chips for the MD transmitter.

[remi007]

And another question: Will I achieve greater sensitivity by using two receiver coils and two input amplifiers? One coil is reversed, meaning in antiphase to the other. The signals from the preamplifiers would be combined in a differential amplifier. Sampling during TX. What are your thoughts on this?

[pechkata]

Everyone has the right to a sample test.
What will happen is another question.