A closer look at the AF108 bi-polar drive circuit

[dbanner]

Here is the layout for the power supply module. On we go. Next up, the duck's guts.

[dbanner]

Now about the simulations. After finally figuring out simple and basic how to add third party models to LTspice, well, simulating the timing and sampling was somewhat stupid, since I can't know the values of those trimmer pots, I can only verify that the simulation works, impossible to know the precise nature of the pulses generated by the actual device( the sample delays and sample widths and tx drive pulses, etc.), now I feel somewhat like mild idiot.
Carl will have to dig out his unit and put oscilloscope to the circuit
On the upside, the timing and control module can serve as sort of universal pulse controller, as it has the possibility of adjustment of several of the critical parameters of the drive and sampling pulses.
Tinkering with the simulation clearly shows the tx1 and tx2 pulses interspersed by the sample pulses, but impossible to know how those trimpots were setup in the original circuit. Oh well, at least I learnt how to import 3rd party models into LTspice IV.

[dbanner]

I've come too far to turn back now. So I will continue on with making a pcb for the bipolar drive circuit and then the "ducks guts" rest of the thing. Experimentation with the timing and control is a bridge I'll have to cross when I get there.

[Andi68]

Which transistor do you want to replace the BUY92?
I would think that before I create a layout

[waltr]

dbanner,
Yes, simulating the timing chips is tough when trim values and timing requirements are unknown.

You could replace the timing chips with Pulsed Voltage sources in LTSPICE then play with the parameters to see what effect various timing has of the analog sections.

[dbanner]

dbanner,
Yes, simulating the timing chips is tough when trim values and timing requirements are unknown.

You could replace the timing chips with Pulsed Voltage sources in LTSPICE then play with the parameters to see what effect various timing has of the analog sections.

I hadn't intended to go that far, I feel foolish as it is, any further endeavor with spice and my ego will be crushed. I need to go slow, baby steps.
Besides, I prefer to tinker with the real circuit, at least I'll have a chance to make a working machine instead of a spectacularly complex but useless simulation.

[kt315]

Which transistor do you want to replace the BUY92?
I would think that before I create a layout

simple rule PNP one is changed on P-channel mosfet. or, Darlington one you see in Bara.

[DeborahJ]

There is a AF-108 PI Military Metal Mine Detector listed on ebay, if anyone is interested.

[dbanner]

Having done some more digging and research, I realized that there was also a PI 150 pipe locator which is a totally different circuit(although it does have similarities).
This was the circuit which was back engineered by Ivconic, and not the AF-108.
I also found a photo of the PCB of the AF-108 mine detector. Note that the quad AND gate is a 4081 just as waltr had speculated(on the schematic it is mislabeled as CD4069). And also have a look at those lovely BUY92's, with there custom heatsinks. Wow! that's fantastic.

[waltr]

Great to see a picture of this board and the nice construction.

Those heat sinks were off the shelf back in the day.
No idea if they can still be bought.

[Andi68]

These heat sinks are easy to turn on the lathe.
But due to lack of availability of the BUY92 this is not necessary

[kt315]

http://shemopedia.ru/radiatoryi.html

[dbanner]

OH LORD,THAT'S TERRIBLE MURIEL!
Won't the solder melt before the magic smoke appears? OK, that will surely work, but not the prettiest sight.
The BUY92 is nothing special(TO-39 package). Easily replaced by something in a TO-126 package. This is least of the worries.
The biggest challenge here is adjusting those trimmers in the pulse generator circuitry.
I have almost completed the remainder of the layout. Will be starting construction soon.
Hope to have a working prototype in about two weeks or so.

[Andi68]

Man can indeed solder the sheet without transistor
Adjust the settings of the trimmer with the oscilloscope

[waltr]

The issue with adjusting the timing pots is not knowing what the timing should be since there seems to be no documentation on this.

dbanner will need to make some guesses as to timing then a lot of experimenting to determine best timing.