Bipolar PI design

[Detectorist#1]

Also, the using of smaller size of DD coils have to be useful for searching of smaller nuggets as you well know.

[Detectorist#1]

Hi eduardo1979,
Let to assembly my schematic in "Bipolar PI MD with GB and DD coil" and to make serious tests in real different ground conditions. All other comments are only words.

[eduardo1979]

Hi Eduardo, you can do this test on the bipolar circuit with the MAX4066ACPD integrated circuit and not use translators, but you have to change the power supply of the bipolar circuit to be like the ITM3 GB-PI, but then GND will be +12 like in TDI and you know that you have to adjust the circuit, the power supply of the PIC16F18426 chip, the source of the IRF740 transistors to be -12 volts and I'm thinking about the sound, which is GND, and where else you need to, but you understand that you also need this new bipolar board.

Hi Algan.
Using voltage level translators hasn't been a big problem for me. The voltage level translators solved the problem with the 4316 IC, and I was able to use the CD4066 instead without any problems. My full-bridge bipolar PI detector works perfectly. On the other hand, I'd like to make a half-bridge bipolar PI detector because I could use any commercially available PI coil. It would also be a better detector for searching for small gold nuggets. I'm still figuring out where to start.

[pechkata]

Hello
Has anyone besides Karl-NC worked on this scheme?
I like how it works.
And how did you know it wasn't working?

[algan]

Hi Eduardo, you can do this test on the bipolar circuit with the MAX4066ACPD integrated circuit and not use translators, but you have to change the power supply of the bipolar circuit to be like the ITM3 GB-PI, but then GND will be +12 like in TDI and you know that you have to adjust the circuit, the power supply of the PIC16F18426 chip, the source of the IRF740 transistors to be -12 volts and I'm thinking about the sound, which is GND, and where else you need to, but you understand that you also need this new bipolar board.

[eduardo1979]

Hello Detectorist #1. Sorry for the misunderstanding.

[Detectorist#1]

Hi eduardo1979,
The question of pechkata in post #388 is concerned only for right connection of 74HCT4316 in the schematic of the Bipolar-PI design in ITMD3. My answer is concerned only with this. The other problems in this design are not discussed in my answer.

[eduardo1979]

I have completed testing the Bipolar PI design and posted new firmware. I changed the timing to use 1 timer and is now all interrupt-driven, there are no polling delays. This gives the delay adjustments more resolution and more consistency.

Two things I don't like about the design. One is that the demods are a bit glitchy in that they pass through some transients. I don't know if this is a particular problem with the 4316 switches or what. I have not seen this in other designs I've done. Second is that the audio is not all that great. The 555 VCO does not have as much frequency range as I recall from when I breadboarded the circuit. And the transient glitches from the demods gives the audio a little it of a raspy sound. With a little tinkering, both might be solvable but I don't have the time right now.

[Detectorist#1]

Hi pechkata,
Nothing wrong in this schematic. 74HCT4316 will work OK. The error in the controlling of 74HCT4316 was only in the schematic of PI-GB design in the first version of ITMD3 book.
In my post #387, I mean the best variant of 4066 (MAX4066ACPD) without need of level translators (when the micro is supplied from 0V and -5V) and with lowest leakage current for all 4066 type analog switches.

[pechkata]

What's wrong with the 74HCT4316 - from the schematic?

[Detectorist#1]

The best choice for analog switches in MD designs with +/-5V power of analog part and 0V/-5V supply voltage for control uP is MAX4066ACPD+. This IC needs only +4V high level of control voltage for switches for 12V supply voltage and the leakage current of open switches is below 100pA at 25oC. This current is 10 times lower than the typical leakage current (1nA) and 1000 times lower than max leakage current (100nA) at 25oC for popular 4066 switches. But the price is more than 6.60USD 1+

[Detectorist#1]

But this pleasure haves a price - appr. 7.50USD 1+

[Detectorist#1]

MAX4612-4616 works only at supply voltage 2.0-5.5V. You have to use MAX4610CPD+. This IC works OK with only 4V level of high voltage on the control inputs at 10V supply.

[algan]

And this one is a bit more expensive MAX4616, but it should work without translators, maybe it's better than 74HC4066.

[Carl-NC]

Yes, that would work, with really no difference in performance. However, there is still the issue of getting enough logic swing on the 4066. If the 4066 is powered by +/- 5V then per the data sheet it needs a 7V logic swing. I have run these on 5V logic swing but it is not guaranteed to work with all chip producers.