Bipolar PI design

[eduardo1979]

Hello again.
As promised, I have updated the schematic today with all the modifications suggested by the participants in this project.
The 74HCT4066 is connected between +5V and GND as Carl recommended me. In the end I have chosen to use the LM386 in the audio amplifier, just like Carl in his original project. For the preamplifier, in the end I have opted for the two-stage amplification, because if you want to use only one stage, with a few small modifications, you would have it and in this way we can test the two variants. I have replaced the two LT1112s with a TL064, since it is a cheaper operational amplifier. I have also replaced the LMH6646 with a NE5532, because it is cheaper and Carl recommended it to me that way and his recommendation seems very coherent to me. I hope you can review the schematic and if anything else needs to be added or modified, it will be modified.
Best rehards,
Eduardo.

[Carl-NC]

The 74HCT4066 is connected between +5V and GND as Carl recommended me.

No, not what I meant. The 4066 has to be powered from +5V/-5V. By making R42,R47 = 0 then one side of each switch is connected to the virtual ground inputs of the opamps (U10) and the switches will behave more consistently.

[eduardo1979]

Hi Carl.
Thanks for your quick reply. I am attaching the corrected diagram. Please let me know when you can if everything is correct.

[Detectorist#1]

Hi Eduardo,
Unfortunately, this schematic also is full of problems, but we will help:
1. 4066 have to be supplied from +5V and -5V volts. No problem to use CD4066B. This will allows to be managed analog voltages in range +5v to -5V. Voltage translators from CPU to 4066 with transistors are OK.
2.Pot R4 have to be connected in series with R55 and the value of R56 have to be increased to 47K. This will preserve cut-off frequency of this stage to be independent from SENS setting.
3.No problem for D17 to be removed - no problem for Q13 to work with minus 5V at Base electrode.
4. Max signal to pin 3 of LM386 have to be limited as +0.4V. Voltage amplifying in this connection is 20 and max output voltage will be +8V.
5. The load of LM386 - SP1 have to be connected via electrolytic capacitor for stopping of DC current without the signal.
6. The diodes D18 and D19 have to be replaced with resistor with 22-47ohms. It is not possible to use diodes as filters - the dynamic resistance of the diodes is very low when a current flow via them.

[eduardo1979]

Hello @Detectorist#1.
Once again, my haste has led me to new mistakes.
Of course, the 4066 has to be powered from +5v to -5v, and the output of the LM386 has to be connected to the speaker through an electrolytic capacitor. Of course it does. Another thing I want to make clear is that if I change the location of the P4 as you say, we will have a problem with the Threshold adjustment, which is the P5. By modifying the value of the P4, the Threshold will be affected. In this way, as it is shown in the diagram, the Threshold will remain constant despite modifying the sensitivity of the detector with the P4. I perfectly understand what you mean about the filter, but it is the harsh reality.
Attached is the diagram with the relevant modifications.
I look forward to your comments.
Regards,
Eduardo.

[Carl-NC]

Another thing I want to make clear is that if I change the location of the P4 as you say, we will have a problem with the Threshold adjustment, which is the P5.

I think there is confusion because the part numbers keep changing. He's talking about the gain resistors on U12d, which are now labeled R53 & R54. You can put the Sens pot in series with either one. If you put it in series with R54 (as you have it) then the sensitivity adjustment is linear but the bandwidth changes with setting. This is not usually a terrible thing because you normally need to reduce the BW at high gains and not so much at low gains. If you put P4 in series with R53 the the sensitivity adjustment is non-linear but the BW is constant. In the future, it helps to keep part numbers constant until the design is finalized, then rename them if you like.

4. Max signal to pin 3 of LM386 have to be limited as +0.4V. Voltage amplifying in this connection is 20 and max output voltage will be +8V.

You can overdrive the LM386 input, no problem.

[Detectorist#1]

Hi Carl,

No reason for different linearity in regulation if the SENS POT P4 is connected in series with R53. In this case the value of R54 have to be increased to 51K. If the POT is connected in series with R53 without change of the value of R54, the gain of the stage will be regulated from 2 to 1.02

[Carl-NC]

Here are the gain curves with the pot in both places. I've reduced the pot to 10k instead of 50k. With the pot in series with R54 the gain is very linear [G = (R54+P4)/R53]. With the pot in series with R53 (and R54 = 10k) it is very non-linear [G = R54/(R53+P4)]. If you do this with a 50k pot it becomes even more non-linear.

[Detectorist#1]

Hi Carl,
Sorry, you are right - with POT connected in series with the input resistor, the curve is very non linear. The gain when POT is zero and is connected in series with the backward 1K resistor is not 1 but 2 but this not changes the total curve of dependence. Sorry again!

[algan]

Hello, Carl, I would like to ask, there is another diagram of the bipolar generator shown in the book, and the diagram actually shows what is on the oscilloscope, and could you post the diagram of the generator that is pictured in the book, so that we can do it to this diagram. Thanks.

[Carl-NC]

I don't understand what you are requesting. Also, Fig 23-11 has an error. See the Errata thread for the correction.

[algan]

Yes, thanks, I thought it was just according to the diagram in the book, I missed reading this topic.

[pechkata]

Hello everyone.
Works just as described in the book.
Not a bad idea - I've never made a detector with this pumping before.
Something like multi-frequency.
I like it.

[algan]

Hi Carl, here the two impulses to are high, and for example if one is low and the other is high, then the picture will be the same as in the book, but won't the bugs then disappear, have you tested it this way? Thanks.

[ivconic]

I didn't just randomly choose this project around which I started the topic, but for a good reason.
Unfortunately, I still don't have the conditions to make it.
A friend sent me a PIC from a neighboring country, but the package did not arrive.
A frequent occurrence with Serbian post offices and customs.
So I have nothing new to post except to follow what other colleagues are doing.



Porting the code to the AVR won't be a difficult task, but it will take time. But it also entails redesigning the pcb. And so the tasks pile up.