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Beginners / Re: Building an inventory
« Last post by watchmaker on Today at 01:23:55 am »
Provided below are lots of name brand NOS parts (in their retail packages) I purchased on eBay.  Bourne 20 turn trimmers, Cemert 28 turns, philmore trimmers, NTE ceramic capacitors, and unused inventory of electrolytic and trimmers from a manufacturer or distributor.
When you received the packages (from an eBay seller in China), did you notice the customs form (CN22) was marked as having originated from an obscure 3rd party country ? The last couple of orders I did like this, that was the case.

No,  I have not noticed that.  What I think the Chinese are doing is shipping orders in bulk containers to a center where it then gets sorted and sent USPS.  SOme comes DHL, but a lot of the "free" shipping seems to come repackaged for USPS.
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Microcontrollers / Re: How do you search for a microcontroller ?
« Last post by TimCambridge on Today at 01:21:03 am »
I'd just go to a supplier like DigiKey and do a parametric search using those parameters.

I agree. But the search options are very limited and there's no query system to formulate your own search. e.g. How do I find all the "STM32 with USB HS PHY and N channel ADC...."? And that's a pretty constrained query. Answer: try Goog.
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Beginners / Re: Simple Solar Power Bank Chargnig
« Last post by msuffidy on Today at 01:14:35 am »
Or you can just buy one. I did a little research and it has been a very covered topic out there. I stumbled across a find.

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Turns out the issue is not sdcard related, but memory depth. If my acquisition is on 8M it locks up on any save of any format both internal and external. Every other depth saves fine, is this user error, a known bug or just good luck?
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@Aramp
Agreed, 10T pots are worth installing. When I was fiddling with my kit I tried an open-circuit pot wiper to U1B and the supply shut down. Good to know that the 1M resistor from pin 5 to ground works.

I have ordered a fan as I am using a small heatsink.
enut11
Because of the way wire-wound multi-turn Pots can fail, the PSU's output can go high, regardless of how it's wired. This is due to the wire breaking rather than loss of wiper contact.
I have found the  cheap 3590S style Pots on ebay and Aliexpress to be very unreliable.
In 3 years, I have not had any WXD3-13-2W style Pots fail. But they are huge.
There is a shorter 5 turn variant.
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Beginners / Re: Understanding High Voltage and Creepage Clearances
« Last post by T3sl4co1l on Today at 01:06:53 am »
Solid board has tons of insulation, more or less the raw dielectric strength of the material.

You might not care about ground plane as the impedance is so high (100s V, ~mA peak?), and bandwidth not extraordinary (10s, 100s MHz?).

Tim
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Test Equipment / Re: Oscilloscope Music on DSOs- Post your Results
« Last post by KungFuJosh on Today at 01:02:40 am »
PC sound card to scope good enough?  Wouldn't think with audio, we need much?   Seems I tried it before with miserable results.   PC scope software out performed it by a mile.

Probably fine, assuming it has good volume level and sample rate. Not sure how much the latter matters, but some files are specified.
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Beginners / defective supercap?
« Last post by BrainyCapacitance on Today at 01:01:51 am »
err... I need help. I bought these 10F 3V supercaps made by Cornell Dubilier off Mouser. on my first time testing one, my circuit shorted out. I checked the circuit, but nothing was wrong. the circuit is supplying 2.3v, at 1.5a max. and the supercap polarity was correct. so I checked that supercap with my meter on a 2v conductivity test. it gave me the "short circuit" signal. and then, I ran it through resistance mode, and it shows the resistance between the supercap's + and - is 10Ω. yep. 10Ω. so I thought maybe that specific capacitor was faulty. I grabbed another supercap and conductivity then resistance. same thing. but I think, since these are all-new and haven't been used before, maybe it's just a "sleepy dielectric" :=\. what do you think? if it is a "sleepy dielectric", how can I "wake up" the dielectric without frying my MOSFET or voltage reg? plz be gentle :-\
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General Technical Chat / Re: Migrating as a PHD student to US
« Last post by LaserSteve on Today at 12:57:01 am »

I'm in the Central US...

Due to low birth rates 18 years ago, many small US Universities and Colleges are hitting severe funding shortages now.  Make sure where you go can cover you if your PI ends up short funded for any length of time.  Most schools have rules to protect you if this occurs, but a few are always shady or understaffed.   Better schools have large endowments.

  I was just downsized from what was once a 44,000 student school ten years ago.   Currently less then  25,000 total students, and only met this years minimum enrollment goal for continued government  funding by 4 students.  Many of that number are part time or commuter students.  They sold the food concession, are looking at selling the public/private partnership  new dorms, and the dorms go unoccupied because investors built nice new structures next to campus with lower costs, when they noticed the new dorms on campus.  Partnership dorms are not making a profit, yet the University has to pay due to the contract.  Tuition is capped by the state, and the faculty-staff layoffs were Legion during Covid. 

     I'm told yearly parking permits will hit 700$ this year for faculty and staff, the parking lots, once ran by the University and heavily subsidized, are now ran by a contractor and owned by the County Port Authority.  I used to pay 200$ a year total, and that was pre-tax payroll deduction, it isn't deductible now, due to the privatization.

If a PI has current students, he/she/it can probably generate these numbers for you.  Be aware, research groups at declining schools face a difficult time getting further grants.  Once the word gets out, and the teaching staff that can migrate do so, the reputation can take a severe hit.  This means in any given group, you may have to work longer, faster, and harder for an upset, depressed Professor.

Choose Wisely.  Without knowing you well, I will not say Go or No Go, but having worked with several hundred grads in my career, its not for everyone, and yet experiences can be fantastic. There is a bit of a lottery to it. Some change groups, some quit, some become world class.  It depends on YOUR attitude.  The great majority of the students I have worked with never write, never call, and never want to come back for a visit.  If I had Ten Dollars for every abandoned desk, issued laptop, and hundreds of unmarked sample bottles I have had to dispose of, because newly hooded Graduates RUN for the door, unless they are Post-Docs or part of a Start-up .  Simply because Grad School is TOUGH! 
 
Many US States are in severe post Covid Cutbacks. Funding is TIGHT outside Biomedical fields.  Consider Canada. Their funding is always tight, so they have a habit of choosing only the best for Grad School.
If you speak Arabic,  Spanish or German, you may have better options elsewhere.

No matter what, if you are not proficient at Math,  Extreme Patience, Spoken and Written English, Teaching Undergrads, Doing your own Equipment  Repairs, Living on Five Hours Sleep, and Teaching Yourself Everything! Think Twice.

Steve
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General Technical Chat / Re: Good soldering flux?
« Last post by T3sl4co1l on Today at 12:56:25 am »
A friend said a -- drat, now I forget which brand exactly, but probably any will do? -- window cleaner is effective on flux residues.

Seems like it would be slow, to me, but maybe a solvent-rich variety, or boosted with a little alcohol or ethyl acetate, would cover that.

There are a few different flux chemistries and it stands to reason flux cleaners need similar variation; alcohol works fine for your basic rosin based ones, but other solvents, surfactants, chelators, and acids or bases may prove more helpful for some.  Which is basically to say... try a lot of things and see what works best, but also, just buy the stuff that's recommended and be done with it? :-DD

Tim
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