Bipolar PI design

[pechkata]

Thank you GeoMax - you are great...
I drew it too - but you beat me to it...
Well done good job...
Schemes speak all languages…

[pechkata]

Hello Karl can we apply this scheme to this project...?
What would you suggest - how many coils...?
The AF 108 coil - can we use it...?

[Carl-NC]

Yes, but you would need to use the PMOS devices to drive the coils. The AF108 coil should work.

[Riss]

A cheap alternative to the 74HC4316 is the 4053 or HEF4053 . they have level translation - see pdf. I have used them in this mode

[Carl-NC]

A cheap alternative to the 74HC4316 is the 4053 or HEF4053 . they have level translation - see pdf. I have used them in this mode

True, but the 4053 is a triple and we need 4 switches, so you would have to use 2 chips. IC1 has an unused switch but in my layout it's not very convenient.

[dbanner]

As what? As level translator?

for driving 4066? can it not be powered to provide +/-5V drive

[Detectorist#1]

Hi dbanner,
Please, draw your's idea how to use 4011 in this case.

[eduardo1979]

Hello everyone.
First of all, I congratulate Carl on this great project.
I've tried to add some fuel to the fire, as there is always room for improvement in any project.
Now the preamplifier is two-stage, using the OPA1612AID, the audio VCO is made with the famous 4046, the demodulators have been modified, as they were a bit problematic, the microcontroller power supply is independent, because I've added another voltage regulator (U3) and so we manage to isolate the digital power supply from the analog power supply, I've also added a 10V voltage regulator (U5) for the power supply of the Mosfets and the 4053, I've improved the Threshold using the same absolute value amplification circuit used in TDI, etc, etc. I want your opinion and collaboration, so that together we can get a very powerful PI and also very sensitive to small nuggets of gold. I listen to your opinions.
Regards,
Eduardo.

[algan]

Hello, colleagues, what programmer do you program the chip with, I tried a little way with pickit3 Chinese version, everything was successful, then I tried to launch only the controller, but there are no pulses, which programmer would you recommend. .Thank you.

[Detectorist#1]

Hi Eduardo,
Yes. I agree with you - this is great project from Carl. Also I congratulate you for efforts to improve this project. Carl have to be satisfied - the aim of ITMD3 is in action - we together made efforts to design more good DIY projects!
My comments for your variant of the schematic:
1. First, 16V power supply source is very inconvenient. How you imagine this source? 10 pcs of AA batteries starts as 15V but have to be used until 1.0V per cell - 10x1=10V and the 7810 stabilizer will not work totally. The variant with 4xLiPo accus starts with 14.4V and ends as 4x3=12V. But this variant needs special charge source with voltage equalization - expensive option. Now, I design some variants for PI MD supply with using of two LiPo cells and DC-DC converters from 6-7.4V to stable 12V. At this moment my design have 84% efficiency. I continue to look for the solution with improved efficiency.
2. The original schematic of the demodulators is a bit problematic as you mention in post #63 and my post #67.
3. For adding of 10V stabilizer - at first look this stabilize supply voltage of the TX part -good idea. But the deepness of target's recognition depends in PI with power of 6 from TX power. In reality - reduction in TX power voltage as the voltage of the batteries go down, influences very little on the deepness (next compromise in the design of PI MD).
My dream at last time - to add to this design additional channel with TX ON-time analysis for sure Fe/non-Fe recognition. Have to be used balanced additional RX coil.

[dbanner]

Any reason why FETs can't be used instead of 4066? Can they not be switched directly by the pic. Seems like much less components.

[Detectorist#1]

Hi dbanner,

Yes, have at least one reason against using of J-FET as J113 as switches in similar projects - the voltage Ugs must not to be more than +/- 0.4V when switch have to be in ON state. Plus 0.4V is the border of conducting of a current on direct direction of P-N junction. Minus 0.4V is the border when P-N junction (gate-source) of J113 transistor starts to be closed - but the switch have to be closed in this situation. In short - it is possible to use J113 as good switch only if Ugs in ON state is not more than +/- 0.4V. In some projects this is possible but not in all projects. Using of 4066 not suffers from this problem.
Four transistors haves total 4x3=12points in PCB. CD4066 haves 14points in PCB. Not serious reduction for PCB tracing.

[Detectorist#1]

Hi Eduardo,
Your variant of the schematic needs to use in decoder's part OpAmps with very little Vos. This is true for LT1112 but convenient case DIP8 is obsolete. And SOIC8 case for DIY projects is not convenient and the price in MOUSER is 10.31USD 1+. Every real project is full of compromises!
BTW, for improving of the stability of the decoders in original schematic of Carl, 10K resistors have to be added in IC7c and IC7d in series of diodes D9 and D10 to the negative inputs of OpAmps.

[Detectorist#1]

Hi Eduardo,
Also dividing of the first RX stage in two stages with OPA1612AID not improves useful MIN delay in PI design. This idea is useful in old designs with NE5534 - NE5532. OPA1611AID is fast enough for real fast RX stage at real practice with additional sources of problems as ground and wet grace influence.

[eduardo1979]

Hello Detectorist#1.
To power the detector I would use a 16.8V/3400mAh LI-ION battery pack. I have used this type of battery for many years and they give very good results. I would leave the 10V voltage regulator there, because it helps a lot when the voltage level of the batteries drops significantly. In order not to lose depth, I would not increase the voltage, but rather try to increase the pulse width and leave the voltage at 10V. LT1112 operational amplifiers in SOIC8 format I have more than 50 units bought at Mouser a year ago and I would like to use them in my projects, since they cost me a lot of money. That is why I used the LT1112. I think your idea of using a single stage in the preamplifier is good and thus we save some additional components. I attach the corrected schematic. I really like your idea of adding an additional channel to be able to discriminate between ferrous and non-ferrous. I would like you to make a drawing so I can add it to the original scheme.