White's AF108

[Carl-NC]

White's AF108 Mine Detector, pulse induction with bipolar TX.

[Geo]

Thanks Carl.
"Unit fault" works when there is not Tx Signal?????

Regards

[Qiaozhi]

Now I have to find which pot adjust the sample delay time I think.Im going to be looking at that schematic for a while.I think I will have big one printed at kinkos.Thanks a million Carl.

The signal driving the TX output stage can be monitored at TP5.
U6A and U6B are dual monostable multivibrators used to generate the main and secondary sample pulses. Without looking too closely, I think the pots are as follows:
VR1 = main sample delay
VR2 = main sample pulse width
VR3 = secondary sample delay
VR4 = secondary sample pulse width

[Brian Deese]

Awesome

The signal driving the TX output stage can be monitored at TP5.
U6A and U6B are dual monostable multivibrators used to generate the main and secondary sample pulses. Without looking too closely, I think the pots are as follows:
VR1 = main sample delay
VR2 = main sample pulse width
VR3 = secondary sample delay
VR4 = secondary sample pulse width

I have alot to learn about pi circuitry,thanksfor your help. If I connected the coil terminal to a scope I would only see the transmit pulse correct? I will have to pick up the sample pulse on another channel to actually see the sample pulse delay time on the screen,correct me if I am wrong.Secondary sample delay sounds new to me,since its bipolar I wonder if it samples on the positive and negative pulses?

[Qiaozhi]

I have alot to learn about pi circuitry,thanksfor your help. If I connected the coil terminal to a scope I would only see the transmit pulse correct? I will have to pick up the sample pulse on another channel to actually see the sample pulse delay time on the screen,correct me if I am wrong.Secondary sample delay sounds new to me,since its bipolar I wonder if it samples on the positive and negative pulses?

Yes, you will need a 2-channel scope to see the main sample delay relative to the TX pulse.

Have a look at the Hammerhead article here -> http://www.geotech1.com/cgi-bin/page...head/index.dat
It uses a similar arrangement for producing the main and secondary pulses. The secondary pulse is used to eliminate any signal from the Earth's magnetic field. In the AF106, U11a appears to be a differential integrator that amplifies the difference between the two samples.

[6666]

White's AF108 Mine Detector, pulse induction with bipolar TX.

Yep, I know this is ten years old, I guess this uses a centre tap coil, any coil info available, is it centre tapped with equal inductance per side ?

[Carl-NC]

Pretty sure it is.

[6666]

Pretty sure it is.

Great thanks.

[Altra]

Garrett has made the AF108 manual available. As someone mentioned the similarities to the PI1000, it uses the same 11" coil shell.

[dbanner]

"The signal driving the TX output stage can be monitored at TP5.
U6A and U6B are dual monostable multivibrators used to generate the main and secondary sample pulses. Without looking too closely, I think the pots are as follows:
VR1 = main sample delay
VR2 = main sample pulse width
VR3 = secondary sample delay
VR4 = secondary sample pulse width"

Can anyone help with these settings. Does anyone have info on the original timing scheme of the AF108.

I put together an ltSpice sim to play around with. timing control.zip

[GeoMax]

Hi DBanner,

The ICs CD4538B, CD4024B and CD4081B are missing when opening the file. From where do I get the IC's components for the simulation?

[GeoMax]

This is how it looks when opening the file...

[dbanner]

This is how it looks when opening the file...

I'll send it to you

[dbanner]

Link to large collection. simply unzip and replace entire lib folder. Everything is in there. Or you can pick through the specific ones needed and paste them in the appropriate ltspice lib file.
https://drive.google.com/file/d/1F3v...ew?usp=sharing

[dbanner]

i think there are two models for the 4538's in the collection. I used the one depicted in the pdf file.
timing control.pdf