Replies to Minipulse Plus

[Silver Dollar]

Ya those power supplies are always a bit tricky on the PI units so getting the 4016 to work is a bit tough...

It will be a challenge to get a shield to work too as the micro ground as to match up to the rest of the circuit.

The minipulse 3 used a few opto's to solve this problem
(see schematic at #4);

http://www.geotech1.com/forums/showthread.php?19418-my-Dual-field-coil-plus-small-mono&highlight=Mini+pulse

[CAS]

Thanks for that. It was more of a theoretical question as I am going to use the basic design to make a shield for a chipkit uno - with a few mods anyway. With any luck I will have time this week to try the GB circuit you came up with.

[Davor]

Yes, but not with digital supplies arranged as they are now. 4066 or 4016 are bilateral switches, and as such their charge injection is reduced against a simple FET. To achieve that you'd need to have 4066 power rails symmetrical (above and below) the average analogue signal voltage. If analogue signal is constantly close to any of the rails the charge injection becomes even worse than FET.

[CAS]

Just wondering if there would be any advantage to replacing Q3 and Q4 with a couple of gates in a 4016?

[johnandles]

johnandles, I am so sorry I addressed the wrong name is previous post. And I couldn't edit my post.

Thanks Chet,I knew you where replying to me.

[Chet]

johnandles, I am so sorry I addressed the wrong name is previous post. And I couldn't edit my post.

[Chet]

josewashere, sounds like you found your problem. I am using a "High Voltage 2KV 2000V Oscilloscope Scope Passive Clip Probe 100MHz 100X P4100" from eBay. Search for P4100 as low as $15.85 US.

[johnandles]

Its hard to imagine not getting a higher fly back voltage if those components checked out ok.

I think my problem is my usb scope, just doing some reading about it and it appears the input is limited to 5v.(then it internally clips).
So with probes at 10x attenuation it only measures <50v,I need to make an 100x attenuator to measure to 500v.(or buy a decent scope).
My new coil is tin plated stranded hookup wire , wound into a spiral.
Cheers
John

[josewashere]

About 9 inches is what I get with most of the coils I have made except for 2 home made coils (out of 15 or so) and a commercial Coiltek coil. I think you said you used magnet wire, I had very bad results with magnet wire. The best wire so far for me has been stranded teflon coated wire. followed by stranded pvc coated wire. Stranded being the key word!

Its hard to imagine not getting a higher fly back voltage if those components checked out ok. The prime suspect now would be the mosfet or your cro is not reading the flyback voltage correctly. Anyway its all part of the fun of building stuff I guess.

I have checked the resistors, all ok.
a 20c coin at about 9".
Haven't replaced Q1 yet.(but that's where I am heading, but need to order some)
Thanks for your offer.
More investigating to do.
Cheers

[Qiaozhi]

Ok, I made a new coil,300 uh,but still the same issue.
BUT...I did find something that's been causing a very noisy TP3, with a coil plugged in.
When I started my build I printed out both Rev B and Rev C build documents.
I must have got some of the printed sheets mixed up as I fitted C19 to my Rev B board..(as per Rev C document for rev C board.)
The C19 should not be fitted to the early board, as noted in the "B" build document.
This caused TP3 to show crazy patterns and noise. But dissapeared once the cap was removed.
So maybe other builders out there may have done the same.
I noticed JOOP's build picture shows C19 fitted to his Rev B board, (he was having noise issues at TP3 also....)
Hope that helps.
Cheers
John

On the REV-B board, C19 has its positive wire connected to -5V, and the negative wire connected to pin 1 of U10. In other words, it's connected across R37. This is (of course) incorrect, and the simple solution is to leave out C19. All this is mentioned in the REV-B Build Document. However, if you want to fit C19 correctly, then wire it between U10 pin1 (negative wire) and U10 pins 4/8 (positive wire).

[johnandles]

Have you tried another Q1 fet? also check the value of R1 and R3 Is the cable between your coil and the detector thick enough? Check the value of R12. What distance are you getting on a 20c coin (Aus)
I'm happy to check any voltage you are not sure about on mine for you.

I have checked the resistors, all ok.
a 20c coin at about 9".
Haven't replaced Q1 yet.(but that's where I am heading, but need to order some)
Thanks for your offer.
More investigating to do.
Cheers

[josewashere]

Have you tried another Q1 fet? also check the value of R1 and R3 Is the cable between your coil and the detector thick enough? Check the value of R12. What distance are you getting on a 20c coin (Aus)
I'm happy to check any voltage you are not sure about on mine for you.

Ok, I made a new coil,300 uh,but still the same issue.
BUT...I did find something that's been causing a very noisy TP3, with a coil plugged in.
When I started my build I printed out both Rev B and Rev C build documents.
I must have got some of the printed sheets mixed up as I fitted C19 to my Rev B board..(as per Rev C document for rev C board.)
The C19 should not be fitted to the early board, as noted in the "B" build document.
This caused TP3 to show crazy patterns and noise. But dissapeared once the cap was removed.
So maybe other builders out there may have done the same.
I noticed JOOP's build picture shows C19 fitted to his Rev B board, (he was having noise issues at TP3 also....)
Hope that helps.
Cheers
John

[johnandles]

Ok, I made a new coil,300 uh,but still the same issue.
BUT...I did find something that's been causing a very noisy TP3, with a coil plugged in.
When I started my build I printed out both Rev B and Rev C build documents.
I must have got some of the printed sheets mixed up as I fitted C19 to my Rev B board..(as per Rev C document for rev C board.)
The C19 should not be fitted to the early board, as noted in the "B" build document.
This caused TP3 to show crazy patterns and noise. But dissapeared once the cap was removed.
So maybe other builders out there may have done the same.
I noticed JOOP's build picture shows C19 fitted to his Rev B board, (he was having noise issues at TP3 also....)
Hope that helps.
Cheers
John

[johnandles]

I will make a new coil and give it a try.
Cheers
John

[Chet]

Low flyback voltage.??
coil 398 uh
1.1 ohms
scope shots with coil and without. (10nf cap)
[ATTACH]31183[/ATTACH] [ATTACH]31181[/ATTACH] [ATTACH]31182[/ATTACH]

johnandles, your scope is correct as indicated by the -12v charge waveform preceding the flyback waveform in the flyback.jpg. I believe you problem may be that the 398 uh coil is not being fully charged by the narrow 58 us drive pulse. Can you remove some of the turns to bring it down to 300 uh or do you have another coil that is close to 300 uh? Other choice would be to adjust the resistors on the 555 chip to produce a wider pulse perhaps 100 us would work.