Replies to Minipulse Plus

[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

[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

[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.

[Chet]

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

[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.

[CAS]

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

[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]

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.

[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/showt...ght=Mini+pulse

[Qiaozhi]

Maybe you should take a look at Hammerhead II for some ideas.

[CAS]

Yes I was looking at optos to connect to the existing MPP circuit for test purposes but will probably redesign power supply and use 4016/4066 for shield version. I want to make sure all my timings work first and try to get optimum settings before I commit to final version. MPP is a great circuit to play with as all the test points are easily accessible and the circuit is pretty basic.

[Davor]

Remember that the optos are generally quite slow, with fall time being shorter than rise. There is a way of making them faster by using two optos as a push-pull driver.

[6666]

Davor, searching on opto push-pull drive etc, gives a whole swag of responses, what is your circuit ??? thanks.

[CAS]

The trick may be to use digital isolators or digital optos. They arent that expensive and have fast rise and fall times.

[Davor]

Davor, searching on opto push-pull drive etc, gives a whole swag of responses, what is your circuit ??? thanks.