HELP - Odd waveform on TP4?

[barwildi]

Still trying to complete my HH1 Rev. D build. But I have a strange waveform on TP4 (compared to docs). The preamp output almost looks inverted and includes other pulses. This is with Q3 and R11 installed and no coil attached as in photo (also, C10 is on solder-side). Is this normal?

I have included a photo of my board and the scope traces respectively. The top trace is TP10 at 6.5V p-p, and the bottom is TP4 at about 8V p-p (same traces as would be in fig.29 of docs).




I would sincerely appreciate any assistance.

- Barry

[porkluvr]

I looked over the drawing but could not find a TP10. Where is that?

[barwildi]

I looked over the drawing but could not find a TP10. Where is that?

Hello porkluvr,

TP10 is actually pin 2 of IC7. On the PCB, it's to the right of R50.

- Barry

[porkluvr]

I don't have a Hammerhead to dissect so I can't actually duplicate your "problem", but I have to suggest that what you are seeing at TP4 and TP10 is probably normal.

In the Hammerhead, the preamp's output (TP4) will normally swing high as the tx pulse is generated, even though there is no coil. There are also switching transients generated by the switching of IC7, caused by by the signals at IC7-13 and IC7-5 feeding through, being seen "upstream". Nothing abnormal about that.

Admittedly I don't understand why you are seeing three (instead of only two) glitches on the TP4 waveform, but I suggest that you not worry about it. Go ahead and install a good coil into the system and then see if the system works.

IF there is a problem, THEN you can worry about fixing it, but you might be just chasing your tail otherwise.

edit: but I am a little curious about why you are seeing those three glitches instead of only two, and I wonder where the third glitch is originating

[barwildi]

...I suggest that you not worry about it. Go ahead and install a good coil into the system and then see if the system works.

IF there is a problem, THEN you can worry about fixing it, but you might be just chasing your tail otherwise.

Porkluvr,

You were correct - it IS working. I guess I WAS chasing my tail.

I made a 10-inch test coil similar to the one suggested in the HH article and wired it up. Though the coil is still unshielded, it can detect a set of pliers at about 6 to 8 inches. That is probably not optimum. But it can be tweaked for better performance now that I know I have a working board.

My only problem now is that I somehow have non-VCO audio in spite of the fact that I have configured the board for the VCO option. I get an off-to-on, tone (about 1khz) when the pliers are brought within about 6 or 8 inches above the coil. The tone does NOT change in regard to the distance. If I hold the pliers steady, the tone goes from on-to-off after about 2 seconds or less. This is non-VCO operation, no?

So I guess I may be due for some more forum searching once again to find a solution. That is, unless you see something wrong in my PCB photo that sticks out like a sore thumb? Before you look, I must say that I did make 2 changes that are not in the photo (and obviously did NOT resolve the problem) - attempting to fix today:

1) removed R51
2) installed R50

Regardless, I thank you for pushing me to take a "leap of faith" and move on to the live coil test. It proved successful so far. Now for the audio issue...

- Barry

[Silver Dollar]

I had some confusion about the VCO/NonVCO option too. In this thread is some info I received;
http://www.geotech1.com/forums/showt...343-VCO-NonVCO

I stuffed my board, missing a few parts I didn't have, then got lost when I went back to it.
I got some 24 gauge wire today to maybe make a new coil and go at it again...

[barwildi]

Just wanted to provide some closure for the discussions within this thread - mainly for any future, first-time HH1 builders like myself.

Porluvr,


Short story: I found that the source of the glitches on TP4 appear to have been generated from IC1, back-feeding from the sync pin (7) of IC1 via C11 and R37.

Long story: I was originally using an ICL7660 which is only rated for 10v input. Since I'm using a 12v battery, I suspected there may be an issue there. I was able to get my hands on a few LT1054 chips (drop-in replacement, but 15v max input rating) to try. Trying every one that I had, the results were consistent, but different from the 7660. The 1054s produced interference that appeared as a small triangle wave riding on top of the main oscillator square waves on TP1 (think of Bart Simpson's hair-do). Tired of de-soldering and since I socketed IC1, I bent pin 7 outward temporarily to disable the sync. The result was ZERO glitches on TP4 and that triangle wave was gone, looking very clean on TP1. Finally, I removed R37/C11 to permanently resolve the issue.

All said and done, the 7660 or the 1054 could be used as the 7660 exhibited no issues except for the glitches that were easily resolved by removing R37 and/or C11.


Silver Dollar,

Thanks for the info. But I discovered I really did not have an audio issue after all. Ultimately, I only needed to take the beast outside away from all of the noise to see that I really had no issue at all. My board quieted down a good bit once I took it outdoors.

Before I did that, I tried configuring it for non-VCO. That is when I realized there was a very big difference from what I thought I was hearing, since the non-VCO config was behaving in a VERY different way. So then I figured the issue is probably due to the indoor noise, and it was. My HH1 is now working as intended, though still incomplete. Still need to make another coil and put everything together.


- Barry