Threshold Pot doesn't work

[h9361]

OK, but then if you will get a negative response if:

1. you slightly lift the coil off the ground
2. you sweep the coil over uneven ground
3. you sweep over a negative hot rock
4. you sweep over a target (the "bounce-back" response)

I think the LED will be constantly flashing. I thought you added ground balance to the HHD, that should have solved this problem.

For this, i want to add a threshold for the LED.
According to my tests, a vacuum void decreasing is very very stronger than you mentioned above. The voltage will be at the lowest possible amount.

[Carl-NC]

Probably the best place to add it is at TP5. Add another opamp stage similar to IC8b (including threshold) and have it drive an LED. You will have to figure out all the details.

[h9361]

Probably the best place to add it is at TP5. Add another opamp stage similar to IC8b (including threshold) and have it drive an LED. You will have to figure out all the details.

I attached a schematic, is it possible to check it and if possible, suggest me correct values for tp5?
Thank you

[Carl-NC]

That's a good start but everything needs to use +5V/-5V, not +12V. I have no idea about component values, it will depend on the offset at TP5 and how strong the signal is.

[h9361]

That's a good start but everything needs to use +5V/-5V, not +12V. I have no idea about component values, it will depend on the offset at TP5 and how strong the signal is.

Hello Dear Carl
I hope you are in a good health.
Please see the attached, it is the MPS project (it is for DD coil). I used its DISC part for my HHD, it works without any problem.

As you see, the Disc part is using a separated coil for discriminating. Other words, it works like voodoo ( a mono coil for PI, a coil for Disc).
But my problem is for DD coil. I did Mr. dfbowers changing to for DD coil. But as soon as doing such changing, my TP4 form will be changed as follows:


I changed 5534 with tl081 in Disc part, no changing. I removed the 5534 from disc pcb, my TP4 is backed!
Do you have any suggestion for checking?
Thanks.

[h9361]

That's a good start but everything needs to use +5V/-5V, not +12V. I have no idea about component values, it will depend on the offset at TP5 and how strong the signal is.

Hello
Dear Carl
Please forgive me for my questions.
I need your help for adjusting delay of two pulse.
Please see attached, I want to adjust delay between S1 and S2 as 2us.
For this, i decrease R33 from 1K to 220R, but my pulse will be disappeared. I increase the R33 from 220R so that the pulse comes back.
I measured the minimum delay, it is 6us. Do you have any suggestion for decreasing the delay?!

[Carl-NC]

Seems like it should work unless that configuration has a minimum delay. Try changing C16 to 1n.

[h9361]

Seems like it should work unless that configuration has a minimum delay. Try changing C16 to 1n.

Hello dear carl
Thank you for you tip.
Today, my micro programing for timing is finished and it is work very nice.
I need to your help about the attached, please see the pic.
I want to connect rx coil Simultaneously to another 5534 as input.
As connecting as the second connection, my TP4 form will be changed, it will be like a simple pulse. Do you think the second 5534 consumes more current? Is better to add a capacitor between the two 5534…?

[Carl-NC]

I would probably connect to the other side of R12 and then swap the positions of D4-D5 and R8. The make R8 and R12 2k.
A better solution might be to switch the preamps to non-inverting types, then use one clamp circuit.

[h9361]

I would probably connect to the other side of R12 and then swap the positions of D4-D5 and R8. The make R8 and R12 2k.
A better solution might be to switch the preamps to non-inverting types, then use one clamp circuit.

Dear Carl
I have a problem about my HHD. The unit of my PI is metallic and i touch its body or its coil connector, my PI will detect my touching.
Do you have any idea about this problem?

[Carl-NC]

Did you attach a ground wire to the enclosure?

[h9361]

Did you attach a ground wire to the enclosure?

No, i checked.
But i have an external battery pack unit and i used a cable that has two wires + a shield for connecting to HHD unit.
I think i did not connect the cable shield to ground. Do you think that is?

[Carl-NC]

You need to ground the cable shield, plus the cable connector and the enclosure if they are metal.

[h9361]

You need to ground the cable shield, plus the cable connector and the enclosure if they are metal.

Thank you.
I connected coil connector to ground, the problem is solved.
Dear Carl, do you think the power part of HHD need yo any change if i use LM7805 and LM7905 instead of 78L05 and 79L05?

[Carl-NC]

No changes needed.