A closer look at the AF108 bi-polar drive circuit

[dbanner]

I just opened up my ltspiceIV program and to my pleasant surprise, I found a vast library of third party models in a folder labeled as "EXTRA", including CD4538, CD4024.
So I have everything needed to simulate the drive and sample pulses. I have never done anything like this before, so its going to be a steep learning curve. Stay tuned.

[6666]

No, it is not my file. porkluvr posted a screenshot here:
https://www.geotech1.com/forums/show...ighlight=xl500

Thanks for the thread link, yes thats the one I was thinking of, gee 2009, but no .asc file, mr pork does not post here now, oh well maybe one day.

[sinclairuser]

The AF108 was specifically designed as a mine detector, but in the end it failed qualifications (as I recall) and so the limited number made were sold off. Many were bought for the beach.

I think the AF109 is strictly a utility model, an unfortunate naming similarity to the '108.

For those unaware, White's UK often design their own machines and sell models not available in the US. They still make old models like the 1970s Beachcomber.

yes carl, that link i posted has some of the beachcomber machines two from memory, they must still sell or they wouldn't still stock them.
one interesting thing i noticed when looking at the different machines was one which looked like a coil with a control box mounted on a 3" stem was said to operate at 0.3 khz.

[dbanner]

Can somebody please have a look at the AF108 schematic I posted and tell me that there is a quad nand gate chip(4011) mislabeled as CD4069?
Or am I missing something?

[waltr]

Can somebody please have a look at the AF108 schematic I posted and tell me that there is a quad nand gate chip(4011) mislabeled as CD4069?
Or am I missing something?

Yes, a CD4069 is a hex inverter. The schematic for U8 is definitely a quad AND (not NAND since the output pin does not have a small circle to indicate inverted, Negation).
So probably a CD4081.
https://en.wikipedia.org/wiki/List_o...rated_circuits

[dbanner]

Yes, a CD4069 is a hex inverter. The schematic for U8 is definitely a quad AND (not NAND since the output pin does not have a small circle to indicate inverted, Negation).
So probably a CD4081.
https://en.wikipedia.org/wiki/List_o...rated_circuits

Thanks waltr, you just have to love those logic symbols, and yes I see these are AND gates, without the little circle. Thanks for pointing that out.
Now here is my next problem. I'm trying to run a simulation in ltspice, but I just don't know where to put the ground or 0V node. Here is the ASC file on what I've got so far. I'll have to change those gates around to AND. But I need to know where to put the power supply ground or common. Or maybe I need to use a single supply for VC and just make VE the ground or common? Any help would be appreciated.

[Andi68]

0V ist Battery Socket A

[waltr]

0V ist Battery Socket A

Correct.

The AND gate chip, CD4081, is powered from VC & VE, the + and - power supplies.
Ground in between these, 0V on schematic.

[Carl-NC]

yes carl, that link i posted has some of the beachcomber machines two from memory, they must still sell or they wouldn't still stock them.
one interesting thing i noticed when looking at the different machines was one which looked like a coil with a control box mounted on a 3" stem was said to operate at 0.3 khz.

"whiteselectronics.com" takes you to 2 different web sites depending on whether you're on the left side or right side of the Atlantic. So I cannot see what you see. Used to be I could select the UK web site in the upper-right corner, but that no longer works.

[Altra]

"whiteselectronics.com" takes you to 2 different web sites depending on whether you're on the left side or right side of the Atlantic. So I cannot see what you see. Used to be I could select the UK web site in the upper-right corner, but that no longer works.

Carl try this it works for me

https://www.whiteselectronics.com/pr...ctors/?lang=gb

[dbanner]

edited

[dbanner]

edited

[dbanner]

Correct.

The AND gate chip, CD4081, is powered from VC & VE, the + and - power supplies.
Ground in between these, 0V on schematic.

0V on schematic, yes, but no 0V rail on the part of the schematic I wish to simulate. Only VE and VC. What this means is that I'll need to make VC into common or ground, and VE set at negative 5V.

[dbanner]

From the RX preamp all the way through to the audio, this circuit is very much the same as the whites PI1000 machine.
My simulation of the tx and gate pulses is now working, just need to analyze the data, take some screenshots and post the spice file. Then its on to the actual build. I'm not sure what benefits bipolar pulsing can bring to a beach machine, if any.

[dbanner]

Upon closer inspection of the audio output stages, the AF108 appears to have the option of selecting between two audio outputs. First, a monotone audio derived from the CD4024, and secondly, a VCO type audio "click click" generator.
Can anybody confirm this?