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Projects, Designs, and Technical Stuff / Re: HV transformer isolation
« Last post by jmelson on Today at 07:25:10 am »
The transformer died almost instantly with a visible arc inside the epoxy  :'(

I have to find a better insulator. I got that epoxy from RS Components, so it is supposed to be high quality, but it was very difficult to apply it to a ETD59 coil former, it had lots of bubbles.

Notice the core I'm using: ETD59.
Did you have layers of insulating material between winding layers?  This is standard practice.  You wind a layer on the coil form, then lay down a layer of insulating paper.  Then, wind the next layer of windings, and repeat.  This creates an additional amount of insulation between each winding layer.  The insulating paper is longer that the circumference around the winding, so the ends of the paper overlap.

Jon
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Projects, Designs, and Technical Stuff / Re: Tektronix 475A restoration
« Last post by oldway on Today at 07:22:45 am »
I guess it depends on which specific blue phosphor it is, there are several. I looked it up and here's a list:

http://w140.com/tekwiki/wiki/Phosphor
Yes, you are right.....I looked at the technical specifications of the 475 and optional phosphor is P11, not the long decay P7. (standart P31)
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Somebody has been smoking too much <something>.  That circuit is INSANE!  two op-amps, a switching power supply controller, several assorted transistors, 4 voltage sources, and on and on, for 6 W?

There are single chips that will do this very nicely, possibly with an additional resistor or two to set the parameters.

Jon
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Projects, Designs, and Technical Stuff / Re: Battery balancing - big cells
« Last post by C on Today at 07:19:04 am »

I think that some are missing that battery voltage is not equal to charge.

A battery is not a simple thing.
There is a internal series resistance that must be taken into account.

Any current in or out of battery changes voltage you can monitor.

You have a choice of allowing for Max-Min resistance change in measured voltage
Or
Measuring internal resistance.

To compute internal resistance requires measuring Current & Voltage over a short time with different current load.
The internal battery charge will change little over short time, so internal voltage will change little.

But note that many things can change internal resistance.

c
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Well, if the "not reliable" comment was simply about the fact that the sun doesn't shine 24 hrs a day, then I find the use of the term "unreliable" to be very poorly applied.  If it was used in the proper sense that the solar tracking panels fail even when the sun is shining is a problem of maintenance or perhaps design.  I agree tracking is a failure in general but perhaps it was an experimental design to see how well tracking did. 

Also, you use the phrase "I was told" or similar in several places to report what some unqualified stranger told you about the design/usage. Personally, I would take that with a large grain of salt and do a little additional research before condemning the whole thing to complete stupidity, mismanagement or worse.

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Beginners / Driving LCD backlight and contrast ping by Arduino
« Last post by VEGETA on Today at 07:10:22 am »
Dear Friends,

I have a finished project with Arduino that contains LCD 16x2, I just need the Arduino to control the contrast and brightness to allow user to adjust brightness the way needed.

I thought of outputting PWM then filtered by 330 ohm + 330uF capacitor but it didn't work as I expected. Although I am outputting (PWM = 255) the output of the RC filter is about 3~3.5v while at the Arduino pin itself is 5v. So I thought perhaps current is not enough or so because a drop voltage happened.

I am powering my circuit by USBtinyISP programmer right now, so could it be the case? that it does not give enough power to circuit?

best regards,
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EEVblog Specific / Re: EEVblog #611 - Electret Microphone Design
« Last post by Richard Crowley on Today at 07:06:26 am »
No transistor (inclucing the one inside the electret capsule) is perfect.  They all have some absolute limit of how much current they will pass, AND they all have an intrinsic series resistance which limits how much current we can see externally.

But then the capsule isn't supposed to be a power or current device.  It is supposed to be a signal or voltage device.  If you need more current use a buffer stage. That is how most electret condenser mics are designed.  For example here is a circuit using a typical electret capsule, and then a pair of resistors as an impedance buffer to drive the low-impedance balanced typical microphone circuit:

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I posted this in the youtube comments but figured I'd have a better chance here:

for the life of me I dont understand why gain goes down as the external resistor goes down which has the effect of increasing Vds, correct?

I've simulated as much and can see that the amplitude of the output wave does in fact go down as the external resistor gets smaller (1k vs 5k for example) but I don't understand why.

anyone?

researching my own question, common source amplifier configuration (https://en.wikipedia.org/wiki/Common_source) we see from the voltage gain equations, Rd being in the numerator now makes sense mathematically as to why as Rd gets small gain goes down.  However, it still doesn't make sense intuitively, to me yet, why when Ids is fixed and Vds is increasing due to Rds decreasing gain goes down?
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Sidenote: Texas Instruments has a whole range of cell monitoring / balancing chips which do all the work for you based on field proven algorithms. There is not much sense in trying to roll your own balancing system. TI is putting a lot of research into these chips but you have to configure them properly to match the cell specs ofcourse.
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Test Equipment / Re: DPO3000 Hacks
« Last post by darkstar49 on Today at 06:58:39 am »


also for those who think that a frequency upgrade means their model ID changes:

The official Tektronix bandwidth upgrade does NOT modify the model ID !!!!!!!!!!!!!!!!! So this doesn't have any effect, other than showing the world that it's been hacked !!  ::)
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