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Messages - profdc9

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1
General Chat / Re: Eurasian blue tit in 1000 FPS slow motion
« on: June 13, 2020, 06:04:59 PM »
That's a beautiful film.  I would like to get slow motion video of hummingbirds myself, especially of one flying backwards.  Hummingbirds are the only kind of birds that can fly backwards.  What kind of camera did you use for this?

Dan
 

2
Electronic Circuits / Re: Electronics projects I have been working on
« on: April 16, 2020, 02:39:38 PM »
Yeah, I am trying to build up a library of simple projects with common parts to teach electronics and have fun as a hobbyist.  When I was growing up in the 1980s I benefited from home computers being very accessible devices.  I used to fix my Apple ][ by replacing TTL chips in it myself!  You can't really imagine doing that anymore.  But on the up side, there never has been such easy access to development software and hardware and a wide range of components so cheaply, so learning electronics for oneself has never been easier.  I just think projects that are somewhere between the low-level of lighting up a LED and the high level of writing javascript are needed.  Also, I can do surface mount, I am just not great at it, and it can make a big mess with the amount of flux required to get good solder joints and prevent solder bridges which can be difficult to clean even with alcohol (some use an ultrasonic bath).  When I do use surface mount in a project it tends to be 0805 and larger in size, and I try to minimize use of fine pitch packages.  It is often an impediment to beginners, so I try to use commonly available through-hole components which can just use a soldering iron and a roll of solder.  Anyways, I am hoping that Chinese vendors pick them up like some of the other kits they sell on aliexpress or ebay, so I use the kinds of parts you would readily find on lcsc or other Shenzhen vendor.

You definitely like to keep busy! The nixie clock looks awesome, especially with the blue light and the traces on the pcb board

3
The device could use an improvement from PFC, but I think the trip is primarily from overload and not from peak instantaneous current.   I can run briefly with high power before the breaker trips, for example, I can go as high as 30 A temporarily until the breaker trips or the fuse blows in the variac. 

One interesting thing I would like to try with the skip pulse circuit is to make a very high impedance primary like you would with a QCW DRSSTC, with may turns on the primary flat coil and less capacitance.  This would increase the number of cycles needed to reach peak voltage before the pulse skip kicks to be more like a QCW tesla coil.  Other aspects of the design would have to be more like a QCW tesla coil too, such as a high resonance frequency, so very small primary capacitance and a low inductance, short secondary coil.

Also another place I think the skip pulse behavior could be useful is for induction heating.   The tesla coil driver could be easily adapted for this purpose, even if it is overkill.  If there is a great dissipative load in a work coil (hunk of metal), the current through the work coil can potentially be quite high because the tank resonance is damped.  Skip pulse can prevent excess current from flowing in the primary circuit, feeding the power to the secondary at the rate at a rate limited by the overcurrent trip value.  Therefore it might serve as a simple way to regulate power to the inductive load.

In theory in NZ we are limited to 10A*230V=2300VA per device, but 16A or 20A circuit breakers are common, so you can push it to 4+kVA pretty easily, though I've certainly tripped breakers there.
The UK has even more headroom - the plug is fused internally at 13A max (giving ~3100VA at 240V), but would literally handle hundreds of amps given the huge pins, and the circuits can be up to 32A or so. Kettles etc certainly work better in the UK (at 3kW) than in the US!
The northern europeans probably all have 16A 230V circuits in addition to 3 phase 10kVA+ options even domestically, lucky bastards!

Regarding keeping a long pulse time coil happy on a limited mains circuit, I've plans on the back burner to build a software-controlled active PFC with input current limiting. As long as the voltage on the DC bus caps at the end of a pulse is above the peak mains voltage (easy at 120V) you'll always have control of power, and in addition you'll draw your current as real rather than reactive power, also maximising the use of a limited mains supply.

4
Electronic Circuits / Electronics projects I have been working on
« on: April 16, 2020, 03:50:40 AM »
I have built a standalone device for encryption called the ParanoiaBox.  You plug it into a TV and a keyboard, type messages, and you can encrypt them with AES 256 and EC25519 Diffie-Hellmann encryption.

https://github.com/profdc9/ParanoiaBox

There are literal screenshots of the television of the device at work.

Also I built a temperature controller to make a dry heat disinfection unit using incandescent light bulbs as a heat source.

https://github.com/profdc9/SimpleTempController

Also I made a Nixie clock which can be built using common components and IN-14 Russian Nixie tubes. 

https://github.com/profdc9/NixieClock

It has time, date, temperature, and humidity.  You can see a video of it at work:

/>
These projects are all through-hole for those who want some neat simple projects to build.   The Nixie clock and temperature controller uses an Arduino Nano V3 as the microcontroller and the ParanoiaBox uses a bluepill.  Something to play with while you are confined.

Dan

5
Cool.  Let us know how it turns out.  I may try building another coil, especially if I can get access to more power than available in residential mains in the USA.  We have about a limit of 1800 W per circuit.  That is very easy to exhaust using skip pulse if you have long pulse times.  I have thrown the breaker many times and blown many fuses operating my coil. :)

Dan


Sooooo.

This is going to be my attempt at a pulse skip coil! I've wanted a pulse skip coil for a while now, and also *hopefully* after I finish building this coil the AUD would have recovered a little bit and I can continue in my drsstc 4.


6
General Chat / Personal Protective Equipment reuse / Covid-19
« on: March 28, 2020, 10:20:04 AM »
In the USA (and I would imagine elsewhere) physicians use N95 respirators and other similar worldwide standards (see attached document) to prevent being infected while treating the infected.  Under ordinary circumstances, these respirators are designed to be discarded after use.  Because there is not an adequate supply to treat all of the anticipated infections, there are many ideas on how to disinfect and reuse these masks.   For example, look at

http://ppereuse.com
http://n95reuse.com

Personally, I have been working on methods of UV germicidal sterilization of these masks.  I wrote a document of how to create an ad-hoc UVGI sterilizer:

https://drive.google.com/open?id=1wF4yYgSE1n0Jqewb8JdwosTRhx0X89wF

Please spread the word about these resources to physicians that might need them.

One potential method of disinfection is ozone treatment.  Ozone (as well as nitric oxide and other nitrogen oxides) can be generated using a corona discharge.   Many of the above methods require specialized equipment or chemicals.  Perhaps a simple ozone disinfection device can be built from commonly available electronic parts that minimizes the risk of electric shock during construction and use. 

Another possibility is a device that can be used to heat enclosures to low temperatures safety, these temperatures being less than 150 C.  Look at the "dry heating" portion of this document:

https://docs.google.com/document/d/193mt42jUR8PxuONUY4A6YZsyOOmy6Psg6BDme3rjai8/edit#heading=h.h1qjojk7297y

Something like this Arduino temperature controller could be used to maintain the temperature of an enclosure at 60 C for an extended period, which is hot enough to cause accelerated degradation of the virus but not significant damage to the mask.

https://circuits4you.com/2016/06/06/arduino-temperature-controller/

Anyways, perhaps you can think of ideas on how to disinfected masks.


7
General Chat / Re: Corona lockdown thread, tell about your situation
« on: March 26, 2020, 09:09:39 PM »
I can only imagine this...


8
General Chat / Re: Corona lockdown thread, tell about your situation
« on: March 14, 2020, 04:00:48 AM »
I am on a leave of absence from work for awhile anyways because of health problems and we are waiting for a government contract.

In the meantime, I have been still working on projects.  I made a Nixie clock:

https://github.com/profdc9/NixieClock

You can see the video here

/>
It uses IN-14 tubes and through-hole parts, as well as an Arduino Nano.  Now I am working on a hardware random number generator.  Someday I will get back and make a new Tesla coil.

9
Spark Gap Tesla Coils (SGTC) / Re: NST
« on: February 12, 2020, 05:56:29 PM »
I made an asynchronous spark gap using an angle grinder, stainless steel screws as spark gap points, and G10 laminate for the wheel holding the screws.  I used two microwave oven transformers in series with a voltage doubler to get 12 kV peak rather than a NST.  I will say it is very tricky to balance a wheel rotating at high speeds (10,000 RPM) and maintaining a small enough gap for reliable triggering  (1-2 mm) between the rotating wheel points and the stationary points.  Eliminating all of the imbalance is nearly impossible and you will have to secure it down so that the spark gap doesn't "walk." You definitely need to build a sturdy enclosure around it in case it flies apart, and you might destroy an angle grinder's bearings before you get one to work correctly.  But it can be done.  I would say that a DRSSTC in some ways is much easier to build for this reason.

10
Hello folks,

After long last, a friend and I got together and we made music using a saxophone and a Tesla coil.  The saxophone has a piezo disc contact microphone which is connected to the interrupter I designed:

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/interrupter

which then is connected to the driver

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/ud29

The piezo disc is amplified by a JFET op-amp circuit powered by a 9 volt battery that connects to the interrupter sound input.   If anyone wants the details I can provide them.

Anyways, here's the videos of my friend playing the Tesla Sax:



/>
Enjoy!

Dan

11
I built a simple peak voltage meter this way.  Sorry, don't have schematic handy right now.

I used a 50 microamp analog DC current meter.  I made a full-wave-bridge of 4 1N4007 diodes into the DC current meter to rectify the AC to DC.   Then I made about a 600 megaohm resistor by putting 33 20 megaohm resistors in series and place this in series with the full wave bridge.  To prevent end-to-end arcing breakdown between the resistors, I laid them out in an undulating pattern and potted them all in epoxy.  This was able to read up to 30 kV peak, but you could add more resistance for a higher range.

12
So how much higher voltage rated MOSFETs could be used? Or have you tested?

The offline (230VAC~325VDC) fed ZVS drivers have always been a widely sought topology but it almost always ends up in flames :)

Yeah, the peak voltage on the transistors is very high.  Perhaps 1200 volt transistors would work for ZVS from mains, but half/full bridge can be run with ZVS easily with an inductive load in series with the primary coil.  For me the high-voltage ZVS is a dead end.  The one advantage of the low voltage ZVS is that it is somewhat safer for induction heaters if no isolation transformer is used to the work coil, but probably isolation is needed for any reasonable safety.


13
Spark Gap Tesla Coils (SGTC) / Re: SGTC MK1 - An Accomplishment in Progress
« on: November 12, 2019, 08:24:38 PM »
You seem to have solved many problems I had when trying to do this.

One problem I had when trying to use a TV flyback transformer is that the peak voltage can be very high and damage the capacitors.  The open circuit voltage of some flyback transformers can be 30-40 kV!  The other problem is that I destroyed many transformers because when the arc is quenched, it causes a brief burst of high voltage, MHz-frequency RF in the transformer that over the course of a few minutes arced through and destroyed the internal insulation of the flyback transformer.   Then I tried to construct my own beefier  transformer on some huge U-shaped ferrite pieces, and those worked better, but even those were destroyed after a short run. 
I also had problems and could not use a static spark gap, because even with a strong fan blowing on the spark gap it was too hot.  So eventually I had to make a rotary spark gap out of an angle grinder, which is very difficult because it spins very fast and has to be balanced perfectly or will shake itself and everything else to pieces.

Eventually I went to dual MOTs and used a Terry filter which removes the RF spikes, and it was reliable.  This is one reason why DRSSTC can be so much easier, because there is no spark gap to cause voltage spikes, and especially good rotary spark gaps are hard to reconstruct.

Anyways that is a great build and very impressive you got it to work that well.

14
Electronic Circuits / Talk on open source hardware in ham radio and KiCAD
« on: October 03, 2019, 03:52:54 PM »
I gave a talk on open source hardware in ham radio, and had a tutorial on using KiCAD to design PCBs as an example of open source hardware design.  You can download the talk from:

https://www.rars.org/documents/Open%20Source%20for%20Amateur%20Radio%20Projects_%202019_09.pdf

Enjoy!

Dan

15
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: UD2.7 Gate Signals
« on: September 14, 2019, 04:50:10 PM »
You might want to consider the UD2.9 version I posted earlier.  You can see the results here:

https://highvoltageforum.net/index.php?topic=346.0

It is a "skip pulse" version so that, unlike the UD2.7 where the spark stops growing when the overcurrent is tripped, the skip pulse will resume exciting the primary once the current falls below the threshold.  It will keep going on as long as you keep the interrupter pulse on.  It might be one way to grow the spark bigger.

16
Dual Resonant Solid State Tesla coils (DRSSTC) / Re: UD2.7 Gate Signals
« on: September 08, 2019, 07:20:04 PM »
I don't know if it would help but I made a through-hole version of UD2.7 that might be easier to work on...

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/ud27c%20thru%20hole

I also made a slightly more featureful one I call UD2.9

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/ud29

Dan

Hi

yesterday I viewed every thing twice because there has to be an error somewhere. And while grabbing around on the board I feel something warm on my finger but not the 5V V-reg or something like that it was the comparator it selfe  :o
Its not driving any load at all so I can´t imagine that this is its normaly state... It makes sense because the inverted output is doing this hook thing and it seems that the IC is switching, according to the feedback but not at the right time, maybe its because it can not detect the right voltage level any more, dont know.

So to be on the save side, a couple of new TL3116 are on the way- also run out of other ideas  ::)

If the comparator do not thinks right, i´ll ending up having the phase lead induktor´s ferritcore drilled out because it´s doing nothing when turning it  ;D

I also come up with a new GDT drive stage ! There for I also bought some FDD8424H smd drivers which originaly build in, in Loneocean´s UD2.7  Because they contain a pair of good matched P and N fets, the problems about crossconductions should be eliminated.

The new comparator is now the more significant part so the "ringing end of burst" thing has to wait meanwhile.

I´ll give you a update such as the parts arrives ^.^


reguards, Andi

17
Electronic Circuits / Re: Version 2 of power supply
« on: September 02, 2019, 12:32:52 AM »
So I built up my power supply board.  So far so good.  I need to get a bigger heatsink, fan, and enclosure.  The next version has a few changes not on this version, including bigger pads for single diodes for the full wave bridge, capacitors, and TO-247 as well as TO-220 transistors.

If there are any other suggestions, let me know.



Dan

18
Electronic Circuits / Re: Version 2 of power supply
« on: August 28, 2019, 04:17:21 AM »
Ok, I changed it so there is space for four bigger diodes (P600 type) and bigger capacitors, with bigger holes to solder pads for external capacitors.

I also changed the footprints of the transistors to allow for TO-220 or TO-247 type pass transistors which has a higher power dissipation package.

I thought TO-220 was good up to 50 watts, but I suppose even with a good fan it will still get too hot, perhaps even to do 30 watts per device.  If so, then I had better go with the TIP3055 (TO-247 package).   I don't want to use the 2N3055 as the TO-3 package is expensive and rare, and is relatively hard to mount.


19
Electronic Circuits / Re: Version 2 of power supply
« on: August 27, 2019, 08:30:37 PM »
I am aware of the current sharing issue with diodes.  If I could find a TO-220 or some similar case power diode (especially cheap) it would be better.   But I was thinking that I could use some heatsink compound and use the copper layer on top of the board to equalize the temperature, or the same fan used to blow on the transistor heatsinks could also help cool the diodes.  Otherwise I could use one of the "brick" full-wave rectifiers.  I'm just trying to keep the costs down, anticipating that most of the components used to assemble this in practice are cheap fleabay/Shenzhen generic components.

For the capacitors, I was thinking that the large capacitor bank would be connected off-board, and a smaller capacitor on the PCB which a smaller inductance for surge currents.  So I just put locations for three capacitors, thinking that one or two might be used to place capacitors off-board.

The TIP41C goes up to 6A, but mostly the four are there so that if you drop a high voltage to a low one with high current, there are many transistors to share the heat load with.  Also, a TIP3055 can go up to 10 A, but I think the heat load will be a problem before the current is maxxed out.

I haven't put relays in this design but I will consider it for a future design.  However, I am trying to make the simplest, more adaptable design I can.  It's not elegant, given that a lot of power could be dissipated in the transistors, so if a high voltage is used, a large heatsink and fan is likely required.

Thanks for any feedback you can provide,

Dan

I have not looked through it fully, but there are a couple of areas that I'd think about:
- Diodes in parallel - they don't look like they will be heatsunk together, so equal current sharing may be an issue
- Tap switching relays may be useful to limit dissipation; these are common in the linear supplies that you're looking to upgrade (though I do not know what downsides they have, as I haven't designed one myself).

20
Electronic Circuits / Version 2 of power supply
« on: August 27, 2019, 04:39:47 AM »
I am working on my version 2 of a linear power supply.  The first one worked fine, but I think I can do better.  The idea of it is to make it so that when you tear down and recycle the bits of old linear power supplies (the transformers and capacitors for example) you can reuse them with this new power supply PCB.  This design is a constant voltage (up to 30 volts) and/or constant current (perhaps up to 20 amps, depending on dissipated power).   This design uses very common op-amps (LM358) and up to four pass transistors in parallel (TO-220 TIP41C or 3055-type).

The new design has a few improvements, including a connection for analog or digital meter voltage and current outputs on the PCB, and provides 5 volts low current (< 50 mA) output for digital panel meters.  Also, a connection for an external analog control of the voltage and current if you want to use an Arduino to control the power supply. 


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