hybridfree/eevblog-posts huggingface dataset:
Which wire for probes? - Page 1
Forum section: electronics / beginners

author: analogo
author_rank: Regular Contributor
timestamp: March 26, 2017, 03:31:25 pm
content: I would like to make my own probes for my multimeter. Where can I find these soft and flexible cables of which all the probes are made?If they are cheap enough, I could cut some ready-made probes and attach my own terminals. No need for professional stuff here, "not horrible" is good enough.Any recommended Aliexpress or ebay shops?

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: March 26, 2017, 03:35:27 pm
content: Try this:http://www.ebay.com/itm/311692117311?_trksid=p2057872.m2749.l2649&var=610598724718&ssPageName=STRK%3AMEBIDX%3AIT

author: alm
author_rank: Super Contributor
timestamp: March 26, 2017, 03:48:00 pm
content: Try ourresident Hong Kong test leads supplier:Franky's eBay store.
Whine from standing fan - Replacing the polypropylene film capacitor? - Page 1
Forum section: electronics / beginners

author: Zingiber
author_rank: Newbie
timestamp: June 04, 2021, 10:04:56 pm
content: Hi all. I've got a standing fan which for the most part works fine, has fanspin etc. However it has an awful whine to it, very noticeable when on standby and incredibly annoying. (Crappy phone recording attached below, you'll probably need to bump the volume up).I suspect it's the XRY Polypropylene film capacitor, as the tone is muffled when I cover only that capacitor.My question is, would replacing this capacitor solve the whine issue, and if so what should I replace it with?Would this be suitable?:https://uk.rs-online.com/web/p/polypropylene-film-capacitors/8712622/
white circuit traces on brown pcb? - Page 1
Forum section: electronics / beginners

author: breadbox
author_rank: Contributor
timestamp: May 03, 2020, 02:32:02 am
content: What are the traces on this board made of? I scraped at the edge of the damaged portion, and there seems to a very thin silvery layer under the white.

author: wraper
author_rank: Unknown
timestamp: May 03, 2020, 02:42:53 am
content: Probably silver. Though likely in form of something like conductive paint. Not silver foil.

author: breadbox
author_rank: Contributor
timestamp: May 03, 2020, 03:08:14 am
content: Thanks. I have seen silver traces on boards, but without the white coating. What is the reason for using silver on the keypad side of this board? The reverse has copper traces and green solder mask.I was planning to repair the break with a bit of wire-wrap wire, but I can't remove the coating mechanically without removing the silver paint. I thought about cutting a piece of wire, trimming it to fit the break and tinning the ends, then gluing it in place and heating the tinned tips, hoping that the solder finds the silver paint on either end. Alternatively, I could try running a wire from via to via. Is there a better way to go about doing this that doesn't involve silver paint?

author: wraper
author_rank: Unknown
timestamp: May 03, 2020, 03:18:30 am
content: Quote from: breadbox on May 03, 2020, 03:08:14 amProbably this was easier/cheaper. Also this looks like phenolic board, not FR-4, You cannot do copper plated vias on that. Nowadays you can see something like this in cheap PC DVD drives. Cheap phenolic PCB with proper copper traces on one side and carbon crap on another. Or copper on both sides, but carbon filling in vias instead of copper plating.
White line in Altium pcb - Page 1
Forum section: electronics / beginners

author: Eliza
author_rank: Contributor
timestamp: March 16, 2021, 12:48:29 pm
content: Hi,I don't know why in my pcb the white line that show which pins are connected together is hidden.Do you know how can I appear them?

author: tszaboo
author_rank: Super Contributor
timestamp: March 16, 2021, 01:00:25 pm
content: ratsnestPress L and enable "connection lines" in "system colors"

author: Eliza
author_rank: Contributor
timestamp: March 17, 2021, 05:22:52 am
content: Thanks guys, It solved
White material at base of capacitors - Page 1
Forum section: electronics / beginners

author: fixit7
author_rank: Regular Contributor
timestamp: May 29, 2019, 09:30:37 pm
content: These boards are from a junked Yamaha receiver I found.What is the white material at the base of the capacitors?I noticed it resists efforts to desolder it.https://www.dropbox.com/s/gjg2nscusaum0mn/CapsWithWhiteMaterial.jpg?dl=0I see copper coils around some resistors while some are free standing like the ones next to the relays.I thought maybe the coils are some kind of shielding?https://www.dropbox.com/s/x1jh6hhnfdqesp1/AudioBoard.jpg?dl=0

author: blackbrayn
author_rank: Contributor
timestamp: May 29, 2019, 09:37:57 pm
content: The white stuff it's glue , to hold down large components on the board so the solder joints will not get afected by things like shocks , general vibrations.As time pased a lot of glue types were used for the job , in recent yeas the white type it's the most common one.I'm sure it has a specific name , some forum member with more experience will know.

author: blackbrayn
author_rank: Contributor
timestamp: May 29, 2019, 09:42:36 pm
content: The coil and resistor construction is common in audio amplifers , you will see it in schematics on the output stage of the amps.Quick example i found on google : "R19" and "L" in the picture.

author: mariush
author_rank: Super Contributor
timestamp: May 29, 2019, 10:28:20 pm
content: Like another person said above, the white stuff is just a somewhat elastic material put there to prevent vibrations, solder cracking on the other side and so on ... it holds the big capacitors in place.As for resistor inside the coils ... my guess is simply because there is space within the coil for the resistor, I don't think it's any special reason.

author: fixit7
author_rank: Regular Contributor
timestamp: May 29, 2019, 11:39:38 pm
content: Quote from: blackbrayn on May 29, 2019, 09:42:36 pmThanks.The radio is 240 watts.I think the clicking I hear when turning on another radio (Denon) comes from a relay.

author: paul8f
author_rank: Regular Contributor
timestamp: May 30, 2019, 05:47:52 am
content: I just asked a similar question on EEVblog forum recently.Read here:https://www.eevblog.com/forum/repair/if-this-isnt-heatsink-paste-then-what-is-it/It's calledSilastic(well that's one of the brand names anyway...)It gives strength to components like tall standing electrolytic caps (also holds them in place during the manufacturing process), dampens noise like transformer whine, improves vibration and physical impact protection in portable devices. Also has some minimal thermal properties.
White on blue LCD display refresh rate - Page 1
Forum section: electronics / beginners

author: e100
author_rank: Frequent Contributor
timestamp: April 14, 2012, 03:50:43 pm
content: All the white on blue 1602 or 128x64 LCD displays I've purchased from Ebay have a draw/refresh rate about 3 times (or more) slower than the black on green LCDs with the same resolution and controller chip and similar price ($6-$20). Any kind of animation, or characters that change more than twice per second just appear as a blur in the transition from blue to white and back again.Is this just my bad luck, or is there something inherently slow with the white on blue type of display?Finding refresh specs for these 'no name' displays is near impossible because there are so many variations.Mike

author: FreeThinker
author_rank: Frequent Contributor
timestamp: April 14, 2012, 05:01:41 pm
content: I Don't know if the refresh rate is different but 2/3 a second is high for an Lcd display. Perhaps the white blue are more temperature sensitive but really you can't expect high refresh on them. Just look at your digital watch, seconds are ok but in stopwatch mode they can't resolve the higher digits in real time normally.

author: amyk
author_rank: Super Contributor
timestamp: April 15, 2012, 07:39:08 am
content: White on blue is Negative STN (>90 degrees twist), black on green may be STN or regular TN (90 degrees twist). TN has faster response time than STN (but better contrast) because the crystals don't have to twist as much.
Who knows this particular diode - Page 1
Forum section: electronics / beginners

author: whoKnows
author_rank: Newbie
timestamp: March 24, 2018, 08:54:35 pm
content: ... and knows where to get the datasheetthe diode is called DECIA7 it appears to have a forward voltage of about twice as much as a normal silicon-type diode has (~1300mV)i looked it up on bing, google, and some obsolete datasheet search sites and found nothing only a russian forum that mentions it.but not even by looking it up on yandex.ru (ie. the russian google equivalent) i found something.

author: MasterT
author_rank: Frequent Contributor
timestamp: March 24, 2018, 09:42:50 pm
content: http://forum.cxem.net/index.php?/topic/46690-%D1%80%D0%B0%D1%81%D0%BF%D0%BE%D0%B7%D0%BD%D0%B0%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5-%D1%80%D0%B0%D0%B4%D0%B8%D0%BE%D0%B4%D0%B5%D1%82%D0%B0%D0%BB%D0%B5%D0%B9/&page=104someone says diode same type as 1N4007. 1000V, 1A.

author: whoKnows
author_rank: Newbie
timestamp: March 26, 2018, 01:08:26 pm
content: Quote from: MasterT on March 24, 2018, 09:42:50 pmthis is the russian forum i mentioned and the 1n4007 is definitely not the same diode because decia7 comes in a way smaller formfactor than the 1n4001 and the 1n4007 is the bigger brother that is rated for higher power if i remember that righti should propably provide a comparison picture of the 1n4000 series diodes and my onegive me second to do this

author: whoKnows
author_rank: Newbie
timestamp: March 26, 2018, 01:25:22 pm
content: this is a comparison of 1n4001 vs 1n4002 vs 1n4148 vs decia4 vs decia7you see the decia diodes are ~½ the size of the 1n4000 series diodes so they cant be identicalcant compare to 1n4007 because i dont have one but they will be the same size as the 4001 anywayby the looks of it these decia diodes seem not to be able to dissipate the power at 1a or 1kv

author: Jwillis
author_rank: Super Contributor
timestamp: March 26, 2018, 07:56:44 pm
content: The form factor isn't usually an issue as long as the characteristics are the same or within an acceptable range.Many different components have been discontinued because more common ones fall within the same operating range.

author: floobydust
author_rank: Super Contributor
timestamp: March 27, 2018, 03:57:16 am
content: That half-size DO-41 package is from Japan; Sanyo and Toshiba make "DO-41SS" package, On-Semi got the Sanyo line.i.e. Toshiba S5688G 400V 1A rectifier
:: whoa ! interesting samsung project ~! - Page 1
Forum section: electronics / beginners

author: 3roomlab
author_rank: Frequent Contributor
timestamp: November 27, 2014, 01:02:37 pm
content: using eye movement and blinking = equiv of mouse controlhttp://www.eyecanproject.org/p/english.html

author: ttp
author_rank: Regular Contributor
timestamp: November 30, 2014, 11:53:10 am
content: Using eye movement is not so new, Canon EOS3 film camera would pick one of its auto focus sensors based on where you were looking in the viewfinder and focus on that area. EOS3 was released around 1998.

author: peter.mitchell
author_rank: Super Contributor
timestamp: November 30, 2014, 12:24:26 pm
content: Quote from: ttp on November 30, 2014, 11:53:10 amAnd it wasn't just a gimmick either, it did it WELL.

author: Stonent
author_rank: Super Contributor
timestamp: November 30, 2014, 04:11:12 pm
content: I think they use something like this for Stephen Hawking to control his keyboard.
Why a Feedback Diode? - Page 1
Forum section: electronics / beginners

author: LoveLaika
author_rank: Frequent Contributor
timestamp: March 27, 2025, 10:38:24 pm
content: I'm looking at the design for theLT1765 switching regulator. I previously used it in an old project, but I wanted to make some improvements, specifically for the inverting-buck boost configuration. I was looking at the datasheet for it when something caught my eye. A diode (D3) in Figure 12 connects the feedback node to the negative output. Why is that there? If you look at the block diagram, it goes between the inputs of the error amplifier. The feedback node would be more positive than the GND terminal (which would be the negative output here), so that diode just ensures that the error amplifier difference is maintained? I don't see how the diode would ever conduct.For what it's worth, I tried to use the configuration previously to convert 13.8 V to -10 V. It worked, but it could not handle a 1-amp load despite using a 10 uF inductor. It could only handle a 0.5-amp max load while maintaining the correct output voltage. According to my calculation sheet, a 10 uF inductor should be able to handle that amount of current. Incorrectly following the design shown in Figure 12, I had the cathode of D3 connected to the common ground instead of the feedback node, so I'm wondering if this would have made all the difference.

author: David Hess
author_rank: Super Contributor
timestamp: March 27, 2025, 10:48:17 pm
content: If there are loads between -5 volts and a positive voltage, like +5 volts, diode D3 prevents those loads from pulling the output positive which could prevent the switching regulator from starting.

author: LoveLaika
author_rank: Frequent Contributor
timestamp: March 27, 2025, 10:49:54 pm
content: Thanks. I understood that explanation.
Why and when use round edges in SMD pads? - Page 1
Forum section: electronics / beginners

author: bittumbler
author_rank: Contributor
timestamp: January 20, 2025, 10:07:28 am
content: In the Kicad footprint libraries, a lot of SMD pads have round edges. But some of them have rectangular pads with "pointy" edges.Also many vendor data sheets show rectangular pads, without round edges.What are the advantages/disadvantages of round edges?When to use round, when to use pointy edges?TiA

author: eleguy
author_rank: Regular Contributor
timestamp: January 20, 2025, 10:52:04 am
content: In lower frequencies, if not considering the heat dissipation, the shape - instead it looks visually different - does not matter too much. But when working in higher frequencies the shape, size and transition from a trace to the pad do affect the impedance and has to be therefore treated more carefully.Here is some discussion about it

author: PGPG
author_rank: Frequent Contributor
timestamp: January 20, 2025, 11:45:58 am
content: The paste comes off more easily from rounded corners.

author: DutchGert
author_rank: Frequent Contributor
timestamp: January 21, 2025, 06:45:59 pm
content: Rounded edges should be the standard imo. Main reason being that this results in a rounded stencil opening that is much more reliable in terms of solder paste application.In my prev. company (automotive) rounded corners where mandatoryIn high speed designs you can add arcs to more gradually go from a thin trace to a thick pad and more gradually adjust the impedance that way.But 95% of the cases its just for DFM purposes.
Why are "30A" relays shaped so weirdly? (what do they look like on the inside?) - Page 1
Forum section: electronics / beginners

author: incf
author_rank: Frequent Contributor
timestamp: March 23, 2025, 08:30:14 pm
content: I've used a lot of these Asian "30 Amp" relays over the years.I've always wondered why are they the weird shape that they are?And: What do they look like on the inside? (I can guess, but still am curious)My best guess is that it is related to creepage and clearance requirements in 230V countries.Decades ago, were the original relays with that footprint completely rectangular? (Is this a modification of the terminal layout used by some ancient pluggable relay module?)I don't understand how they settled on that particular shape.edit: source  has a line drawing of an open frame modelhttps://www.citrelay.com/Catalog%20Pages/RelayCatalog/J115F1.pdf

author: golden_labels
author_rank: Super Contributor
timestamp: March 24, 2025, 02:30:02 am
content: Note that not all 30 A relays have that shape (most are cuboid), not all of that shape are 30 A, and they’re not Asian (see thisPolish 40 A relay).I don’t know, what’s the rationale behind so many manufacturers using this form. If they had spade connectors, it would be dictated by the socket shape. But it’s a PCB mount component. I’ll be happy to hear from anybody, who has authoritative or at least reliable information on that topic.I may make some guesses, though. The package follows the outline of its contents. See this image of a bare form (photo from Rayex, depicts the L90 series):It also uses less material and leaves more space on the PCB.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: March 25, 2025, 12:07:39 pm
content: The question never really popped up in my mind. I hope somebody related to relay manufacturing will answer this.

author: BradC
author_rank: Super Contributor
timestamp: March 25, 2025, 12:11:24 pm
content: Longer lever. More contact force and a faster action?

author: Gyro
author_rank: Super Contributor
timestamp: March 25, 2025, 01:51:36 pm
content: Quote from: BradC on March 25, 2025, 12:11:24 pm... and, importantly, larger contact and pin/spade clearances.Rectangular relays tend to have their coils oriented vertically and are taller. Those horizontal coil ones have a larger footprint but lower headroom (gross generalization!)As golden_labels says, it's not just Asian relays, all of the European and US manufacturers produce them in that form factor too (in fact, the Asian manufacturers try to match formats to occupy the lower cost second source market).
Why are AC/DC adapters for musical instruemnts tip negative? - Page 1
Forum section: electronics / beginners

author: Frankentronics
author_rank: Regular Contributor
timestamp: April 11, 2018, 01:09:35 pm
content: After many years of wondering about this, I finally decided to Google the question and was unable to find the answer.I see that all musical instrument accessories which use wall warts require the input for be tip negative and thus the coax cable to be shield positive. Why is that, please?Thanks...

author: Ian.M
author_rank: Super Contributor
timestamp: April 11, 2018, 01:29:58 pm
content: My first guess would be its a legacy of early Germanium BJT effects boxes. Back in the early solid state era, as Germanium PNP devices were far more available and had better specs than NPN ones, circuits almost invariably had a positive ground. Knowing that roadies aren't particularity inclined to read the small print on equipment labels when setting up, It would take a brave manufacturer to change the convention once established.

author: drussell
author_rank: Super Contributor
timestamp: April 11, 2018, 02:41:48 pm
content: The usual answer goes something like this:QuoteSee EEVblog #1015

author: Ian.M
author_rank: Super Contributor
timestamp: April 11, 2018, 04:40:44 pm
content: The reason why common usage swapped over to center positive is NOT the battery switching. There is *NOTHING* to stop you switching the negative side of the battery using the sleeve shunt of a center positive power jack.If, however you have a PSU with a three pin grounded mains plug, and the output is grounded, then putting 0V/Ground on the center contact with the outside 'hot' at whatever the DC output voltage is would be F&*%ing *STUPID* - the first time its sleeve touches another ground (e.g. a grounded case), it would short out the PSU.As unwanted ground loops are a major problem for music kit, you pretty much never see a grounded PSU for an effects box or pedal so there has been no good reason to change over to center positive, and the vast number of center negative devices out there are an excellent reason *NOT* to change over.

author: darrellg
author_rank: Unknown
timestamp: April 11, 2018, 05:31:55 pm
content: Dave did a video about that:

author: Frankentronics
author_rank: Regular Contributor
timestamp: April 11, 2018, 06:02:42 pm
content: Quote from: drussell on April 11, 2018, 02:41:48 pmThanks for pointing me in that direction. I now watched that video and I also saw there was a forum link to a debatehttps://www.eevblog.com/forum/blog/eevblog-1015-beware-evil-(but-clever)-dc-jacks/?all. I can also see there's speculation and disagreements.In any case, I read through that other debate and it pretty much satisfies my curiosity.Thanks...
why are bad solder joints dim? - Page 1
Forum section: electronics / beginners

author: m4rtin
author_rank: Regular Contributor
timestamp: April 28, 2013, 06:29:02 pm
content: If I solder two wires together and during the few seconds, when the solder cools down, I move the wires, the solder joint remains dim. As I understand, dim solder joint is not as reliable and strong as a shiny one. Why is this so? Does solder crystallize in a different way when parts are moved during the solder cooling processes?

author: ddavidebor
author_rank: Super Contributor
timestamp: April 28, 2013, 06:53:11 pm
content: because the big mass of the wire and the high termal conductivity of the copper "suck out" the heat from your solder joint very fast.

author: mariush
author_rank: Super Contributor
timestamp: April 28, 2013, 06:54:05 pm
content: There's a chemical reaction between the metals, you're messing that up when you move the wires. If you want to reduce this problem, you can try switching to 63/37 solder, which goes transitions much faster to solid, at a fixed temperature. The 60/40 has a wider temperature range, so you have to keep the 2 parts fixed until the solder goes outside that transition temperature range and becomes solid.There's a very good series of soldering tutorials at Pace's youtube channel, here's the first part:The other parts are in the same channel, easy to find.The videos are a bit dated, but the information still applies to this day and the production quality is quite good.

author: Unknown
author_rank: Unknown
timestamp: April 28, 2013, 09:00:38 pm
content: Dry joints also depend on using tinned copper wire or components, of the same solder alloy metals, or type !... current pre-tinned wires or components are led-free, so if you wet a joint using the old 40/60 tin-led ratio resin flux, then the joint will look dull and even not flow.Disturbing a solder joint while it cools, will change the crystal structure of the joint particularly, if insufficient flux is present; a good solder joint is made by firstly pre-heating the clean junction area first, and then applying the solder; correct temperature is important too for good solder flow, leaving a joint with a concave shape around the component, to PCB surface.Personally, I still keep to 40/60 resin flux solder, due it's low temperature flow properties... since I also keep to through-hole designs, for personal use.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 29, 2013, 12:11:30 pm
content: Unfortunately you can't judge solder joints anymore by how shiny they are thanks to ROHS, some of the lead free solders are always dim no matter how good the joint .

author: marshallh
author_rank: Unknown
timestamp: April 29, 2013, 10:27:04 pm
content: If you want nice looking leadfree joints, look into nitrogen-assisted soldering stations. The resulting joints seem to be less prone to whiskering as well.
Why are ceramic disc capacitors sometimes coated in wax? - Page 1
Forum section: electronics / beginners

author: Ranayna
author_rank: Super Contributor
timestamp: April 17, 2017, 01:14:43 pm
content: The other day i soldered a cheap kit that contained a few small ceramic disk capacitors. When i populated them to the board, i did not really notice the wax coating, but after i soldered them, i immediated saw that they made a mess on my esd mat. I had one that was not yet soldered, and with taht one i could confirm that they were coated in some kind of wax. Not all of them were, just all of a certain value.Now in hindsight, i remember from the past, especially when i tore down electronics as a kid, that a lot of those disk capacitors were covered in wax. Sometimes whole boards were covered. For the whole boards i figured it was some kind of cheap conformal coating or vibration dampener, but what is the reason to coat only capacitors?

author: Gyro
author_rank: Super Contributor
timestamp: April 17, 2017, 01:52:37 pm
content: The simplistic answer is, to keep moisture out. Ceramic disks are covered with some kind of cement rather than resin / epoxy, so impregnating it with wax achieves the moistureproofing function. I suspect that without it, there would be issues with the internal silver metalization degrading.

author: SeanB
author_rank: Super Contributor
timestamp: April 17, 2017, 02:00:36 pm
content: Ceramic disks are generally wax impregnated as the wax keeps the silver used to coat the plates from oxidising away very quickly. The ones that are dipped in epoxy ( the nice shiny hard ones) are not wax impregnated, as the epoxy does this job, and chip ceramics have a clear coating on them to do the same, keep water vapour out.Most capacitors need environmental protection, in many cases by dipping in epoxy, potting in resin or coating in wax, and electrolytics use a rubber bung so the liquid electrolyte does not evaporate.
Why are Darlington transistors used to drive the 28BYJ-48 - Page 1
Forum section: electronics / beginners

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: July 12, 2019, 09:43:55 am
content: Hi everyone!So I’ve been playing around with some cheap Chinese stepper motors (28BYJ-48) and I have no idea why they use a ULN2003 "stepper motor driver". It’s just a Darlington array.Why not used mosfets?Could someone shine a light on this?

author: capt bullshot
author_rank: Super Contributor
timestamp: July 12, 2019, 10:25:14 am
content: Because the ULN2003 is old, dead cheap and has free wheeling diodes built-in.

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: July 12, 2019, 10:27:24 am
content: Quote from: capt bullshot on July 12, 2019, 10:25:14 amIn addition to that, for those steppers even the faked, even more cheaper ULNxxxx knockoffs are absolutely fine.
Why are mains earth and ground connected together on osciloscopes? - Page 1
Forum section: electronics / beginners

author: little_carlos
author_rank: Regular Contributor
timestamp: March 29, 2016, 03:36:31 pm
content: Hi, why in scopes ( and maybe some other devices) ground and mains earth connected together? i make this question mainly because i saw dave jones video on how not to blow a scope, and i found that this is more like a risky thing than a safety thing, plus, i dont know the main reason of mains earth completely, can someone explain me?

author: Delta
author_rank: Super Contributor
timestamp: March 29, 2016, 03:39:46 pm
content: Because mains earth IS safety earth / ground!

author: nomadd
author_rank: Contributor
timestamp: March 29, 2016, 04:34:32 pm
content: Quote from: little_carlos on March 29, 2016, 03:36:31 pmThe "live" side of the mains supply is at a different electrical potential (think voltage) to the Earth (and that's Earth, the real Earth, and not simply some local "ground" inside a device.) So the mains electricity supply will readily flow to Earth, if given the chance.Now imagine a device malfunctions and becomes "live"... You, the operator, could easily form a conducting path back to Earth, which is not a good thing for your health.So, by actually "earthing" the device - that is, having a nice low resistance (pedantic: impedance) path back to earth through a separate run of cable - the "live" flow of electricity will take that route rather than you (and of course blow fuses, trip circuit-breakers, etc. along the way, hence shutting off the supply.)

author: zal42
author_rank: Contributor
timestamp: March 29, 2016, 04:42:08 pm
content: What nomadd said. I can only add the observation that I would much prefer to burn out my scope than my body.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: March 29, 2016, 04:53:20 pm
content: Suppose the common inside the scope is not grounded. You stick your scope probe "ground clip" on a 300V rail in the device you are testing. Now the scope common bus is 300V. So you then go to connect a probe cable to the other BNC jack on your scope, the outside of which is scope common - and now 300V. Your thumb brushes the jack as you connect the cable and a second later you are laying on the floor with the magic smoke escaping your ears.
Why are older LCD backlight so power hungry... - Page 1
Forum section: electronics / beginners

author: alank2
author_rank: Super Contributor
timestamp: January 08, 2015, 09:26:12 pm
content: Hi Everyone,I've got a 4x20 LCD display that is new off of eBay from China and it is hugely bright for 60mA or so. Then I've got some older displays - they run about 150mA and aren't nearly as bright. Is it just the efficiency of the LED's used for the backlight? Have they really gotten this much more efficient?Also, how can you date code something like this.20400S1MBLY306502020101.23/028967PHICO D0-0011694V-0P70-1Thanks,Alan

author: danadak
author_rank: Super Contributor
timestamp: November 26, 2016, 02:58:31 pm
content: 1994 was a turning point in LED development with InGAS process. It stilltook a few years before the high brightness led became mainstream. Thejump in brightness went from tens of candelas to thousands. As timeevolved the older processes disappeared as the new process volumesurpassed the older.Regards, Dana.

author: Buriedcode
author_rank: Super Contributor
timestamp: November 26, 2016, 08:06:29 pm
content: Older backlights were arrays of LED's in epoxy, with a diffuser sheet over the top. This means they are a series/parallel grid, and as danadak pointed out, often low efficiency LED's (or rather the most efficient green at the time, which were yellow/green).Newer backlights are often just an edge lit light pipe. It doesn't need to be as bright for transmissive displays, as there is no partial reflector foil (that lets some light through, but reflects some, allowing for transflective displays). In the early 2000's newer software allowed for better lightpipe design, meaning that more of the light injected into the lightpipe could be ejects out the front, rather than just going out the back or sides where a reflector was place - these reflector sheets absorbed some light to.Polarisers have also got better, so when pixels are transparent, they absorb only slightly more than 50%, rather than the 60-70%.So I think its a combination of things, LED efficiency, better lightpipe design, better optical films (3M was the big player here) that all added up to the point where a 80mA backlight really can be as good as a 240mA. Also, a 20x4 display is obviously much larger than the standard 16x2 and so will draw more power. But 20mA seems to be standard for 16x2 these days.
Why are PCB guard traces bare copper? - Page 1
Forum section: electronics / beginners

author: Syntax Error
author_rank: Frequent Contributor
timestamp: July 27, 2020, 08:28:19 pm
content: Rookie question: Why are PCB guard traces bare copper on what is often a wide ground plane that's coated with solder mask? Is solder mask opaque to RF/EMC?Or does the studious EE intend to bond a tin can to the copper trace but the accountant always says no?

author: Gyro
author_rank: Super Contributor
timestamp: July 27, 2020, 08:33:16 pm
content: It depends. If it's low leakage circuitry then it's because otherwise, stray leakage currents would bypass them by going through surface contamination on the solder mask.I can't think of a particular reason for RF, other than the one you mentioned - allowing for a screening can to be fitted on top (if it fails emissions). Edit: That's the reason for the one in your image.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 27, 2020, 08:38:10 pm
content: Assume for example the PCB gets dirty after some years, and is coated with some slightly conductive dirt.If the guard traces are bare, then they connect locally with that dirt and null voltages.If the guard traces are covered with solder mask, then they are isolated from the dirt, and it can create a leakage path over the solder mask.The picture you show is not a guard trace though.It looks more like an area to solder some shielding metalbox to the PCB, and then someone decided it was not needed.

author: tszaboo
author_rank: Super Contributor
timestamp: July 27, 2020, 08:42:06 pm
content: That is not a guard trace. That is a place where you could place an RF shielding can, as you identified correctly.Sometimes you need the can, sometimes you dont. Depends on which RF standards you need to follow. If you learn anything as an engineer, is that your specification will always miss something. They typically come with the most crucial specification in the last minute.
Why are power supplies' PCBs always yellow? - Page 1
Forum section: electronics / beginners

author: anfang
author_rank: Regular Contributor
timestamp: October 13, 2016, 06:54:17 pm
content: How come the PCBs of power supplies are always yellow?There is always at least one side that is not coated with the usual (green) layer of soldermask. I suppose the yellow color comes from the exposed FR4 layer.Do they use a different coating? Are there safety reasons? Are they just being cheap?

author: Towger
author_rank: Super Contributor
timestamp: October 13, 2016, 06:56:46 pm
content: Cheap...

author: chris_leyson
author_rank: Super Contributor
timestamp: October 13, 2016, 07:13:11 pm
content: I can't say I've ever seen a yellow power supply PCB, do you mean light brown ? FR4 without the solder mask is light green and that is most likely due to the flame retardant chemicals in the resin for UL approval, they used to be clear back in the day before UL but only old timers on the forum would remember this. Paper reinforced phenolic resin PCBs are light brown and they are the cheapest to manufacture, the holes for through hole components are usually stamped out rather than drilled. Does that help or have missed the point ? RegardsChris

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 14, 2016, 06:44:04 am
content: And CEM1 tends to be white, and phenolic (designation??) tends to be light brown colored.The motivation is  only cost. The power supply in my desktop is black colored (on top), for cosmetic reasons alone I'm sure. It has no copper on top -- the black solder mask layer is purely cosmetic and added cost -- the bottom solder mask is conventionally green!Tim
Why are the LM358's the "standard" and not the LM258? - Page 1
Forum section: electronics / beginners

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: July 22, 2013, 05:27:09 pm
content: In posts likethis one, people discuss the opamps they keep on hand, and it generally seems to be the '3' in the series. Looking at the datasheets, it seems like the 2's have better specs so I figure I must be missing something.

author: SeanB
author_rank: Super Contributor
timestamp: July 22, 2013, 07:11:41 pm
content: 3 is the regular commercial spec device, with a rating from typically -40C to 70C operating temperature. 2 is the industrial rating, normally tested to a closer tolerance, and rated for typically -40 to 110C, and costing about 3 times the price typically per part and generally with a restricted range of package styles. 1 is the military/aerospace rated part. 100% tested for both functionality and tested for a long period typically 6 months at elevated temp to weed out the marginal devices. Rated from -55 to 125C and normally only available in a sealed hermetic glass sealed can or a ceramic package. Very restricted package styles, and typically 1000 times the cost of the commercial spec because of the long test times and each one having a serial number or lot number with a certificate of conformance associated with it.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: July 22, 2013, 07:25:40 pm
content: Ah, thanks! That extra background wasn't really in the datasheet. So it was probably a bigger deal when the x58 was newer. As it stands now, digikey has the 358 at $0.41 for one and the 258 at $0.43, so I really wasn't seeing a cost difference.

author: edavid
author_rank: Super Contributor
timestamp: July 22, 2013, 07:51:11 pm
content: Most people understand that LM358 implies LM258 or LM158 as well.When shopping for lab stock, it does pay to check prices on the better grades, especially for through hole parts that the distributors are trying to dump. For example, Arrow is currently selling LM358N for $0.1048 and LM258N for $0.0793.
Why are there covering caps on my DMM probes?  - Page 1
Forum section: electronics / beginners

author: jtruc34
author_rank: Regular Contributor
timestamp: April 17, 2019, 12:09:47 pm
content: There are covering caps which cover about 90% of the tip, and on which it is written 1kV Cat-IV. If I remove them, it is written 1KV CAT-II.If it is just a safety feature to prevent my fingers to touch the tips, I don't see how it is related to CAT rating which does not have to do with the probability of me touching something (or does it?).Or is it something that plays another role, like preventing arc formation or something like that?Thank you.

author: Nerull
author_rank: Frequent Contributor
timestamp: April 17, 2019, 02:24:44 pm
content: The ratings specify a minimum distance between you and exposed conductors.

author: jtruc34
author_rank: Regular Contributor
timestamp: April 17, 2019, 02:51:25 pm
content: What surprises me is that they are only CAT-II without those caps while I saw Fluke CAT-IV test leads of which the metal tips were not particularly further from the fingers than with mine (Brymen BL21S2-T4SC).

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 17, 2019, 03:43:01 pm
content: Those probe condoms are for compliance to some kind of law, but are a nuicanse to use.That is why they are on the probes when you buy them, but can be easily removed and thrown away.A small minority of people seem to think they are usefull for preventing accidental shorts, and I have to admit, a few months ago I accidentaly shorted an 100V 17mF elco and that was pretty scary. It also burned a hole in the side of the probe of almost half it's diameter.

author: SG-1
author_rank: Regular Contributor
timestamp: April 17, 2019, 04:23:05 pm
content: They are there to prevent arc formation between the two probes exposed metal or a single probe & earth or another energized conductor, which in a cat 4 environment would be a life altering event if you survive the blast & fire. It is uncomfortable in a cat 2 environment & generally discolours what ever you are probing.I agree they do get in the way from time to time. I try to work with them on & only remove one of them when needed. I saw a guy take his own picture yesterday. Fortunately his head blocked my view of the arc. The temporary blind spot in his vision eventually went away.

author: ejeffrey
author_rank: Super Contributor
timestamp: April 17, 2019, 04:49:09 pm
content: Quote from: jtruc34 on April 17, 2019, 02:51:25 pmThat requirement is fairly new (5-10 years? I don't remember). Older equipment rated for CAT-IV at the time of manufacture doesn't require those covers. Probably those fluke test leads just predate the updated standard.I usually take them off because I almost never work in anything but a CAT-II environment. If I went probing around in distribution panels or high power circuits I would put them back on.
Why are there no 12 pole ribbon cables ? - Page 1
Forum section: electronics / beginners

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 20, 2017, 01:12:51 pm
content: Hi, i need a 12 pin ribbon cable (1.27 mm) with connectors, only i found out on wikipedia that it dont exists :https://en.wikipedia.org/wiki/Ribbon_cableBased on availability of standard connectors, the number of conductors is usually restricted to a few values, These include 4, 6, 8, 9, 10, 14, 15, 16, 18, 20, 24, 25, 26, 34, 37, 40, 50, 60, 64 and 80.Why ?

author: amyk
author_rank: Super Contributor
timestamp: August 20, 2017, 02:59:12 pm
content: Counterexample:http://www.mouser.com/ProductDetail/HARTING/33152430500006/?qs=sGAEpiMZZMsgIz308WEU0%252bv%2fKA8EWsjTuGvo9T3HiHw%3dI wouldn't trust the wiki too much.

author: technogeeky
author_rank: Frequent Contributor
timestamp: August 20, 2017, 03:33:56 pm
content: It's also worth noting that it's nearly trivial to strip ribbon cable wires from one another (assuming you are terminating them yourself).So, for instance, it would be economical to buy 24 pin cables and split them in half. Or buy 14 pin cables and pull two wires off.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 20, 2017, 04:19:24 pm
content: If they don't make 12 wire cables, chances are you won't find a 12 pin connector.So the obvious way would be to use a 14 wire cable and connector and have 2 extra ground lines.

author: JanJansen
author_rank: Frequent Contributor
timestamp: August 20, 2017, 04:21:54 pm
content: Quote from: amyk on August 20, 2017, 02:59:12 pmYes nice at mouser, only i wanto make them myself, cut cable on a certain length, then attatch the connectors.Quote from: technogeeky on August 20, 2017, 03:33:56 pmAre you sure that they still fit exact, its millimeter work with these things.Do you ever cut a ribbon-cable wires off yourself ?Quote from: Kleinstein on August 20, 2017, 04:19:24 pmindeed

author: Yansi
author_rank: Super Contributor
timestamp: August 20, 2017, 04:26:26 pm
content: They fit exactly, the wire pitch is always 0.635mm (or 0.025").And yea, I always cut and crimp them myself. Using either a generic smaller vice, or the nice crimp tool for these I have recently found at work.

author: retrolefty
author_rank: Super Contributor
timestamp: August 20, 2017, 08:53:53 pm
content: Quote from: technogeeky on August 20, 2017, 03:33:56 pmAt work we always ordered 50 pin ribbon cable by the reel and then just strip off what was needed for any specific cable required. I think it was Jameco that we got the ribbon and assortment of IDE DB-xx connectors and we had a manual ribbon connector press for making up the cable assemblies.LOL that is where I once learned one could pump RS-232 9600 baud through 100 ft. unshielded ribbon cable.
Why are these mosfets passing large current, below turn on voltage ? - Page 1
Forum section: electronics / beginners

author: MathWizard
author_rank: Super Contributor
timestamp: August 19, 2022, 09:54:45 am
content: I was using LTspice to check some DC answers for a project and I never noticed this before, but 3 out of 3 mosfets I tried, all pass currents, even large currents, with their Vgs less than their turn on voltage.So what DC model or equations are they using ?I wanted to pass 80mA through a IRFZ44N, which has Vt=2.13V, but even with Vgs=2.12V, it's still maxing out and passing 304mA, which about max for 12.2V and a 40R resistorAn IRF510 did a lot better and only passed 2mA with it's Vgs a few dozen mV under it's Vth

author: jpanhalt
author_rank: Super Contributor
timestamp: August 19, 2022, 10:29:50 am
content: It appears you are simulating an IRLZ44, not an IRFZ44. Note the lowest Vth can be 1V for the IRLZ44.Datasheet snippet for IRLZ44 attached.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 19, 2022, 10:46:49 am
content: The Vth prameter in the MOSFET model can be a bit different from the Vth used to characterize MOSFETs.In the data-sheets Vth is given as the point where a small current, like 100 µA flows. The limit is set relatively arbitrary.For the model chances are the Vth is more like the cross over from square root law for higher gate voltage to the exponential sub-threshold behavior. Especially for rather large FETs this may be at a not so small current, where one does not consider the FET as off.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 19, 2022, 10:59:29 am
content: Also note Vgs_th is a poorly controlled parameter with a lot of unit-to-unit variation.In switching application, you want to stay far from the uncertain region.In linear application, you use feedback.

author: MathWizard
author_rank: Super Contributor
timestamp: August 19, 2022, 11:35:37 am
content: Ok I was just using LTSpice's Vt and Kp values, I know real-life values can vary a lot from the datasheet values.Ok so something else to watch out for in sim's.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 19, 2022, 12:14:20 pm
content: There needs to be a high value resistor between gate and ground so the mosfet will properly turn off. Either side of the power-gate resistor. One side forms a voltage divider, but offers an layout advantage. If the turn off resistor is high enough, the voltage divider can be ignored.
Why are we mixing data connections in SDRAM? - Page 1
Forum section: electronics / beginners

author: Bat91
author_rank: Newbie
timestamp: August 24, 2023, 06:51:23 am
content: Hello,Recently, looking through the schematics of finished modules from ST, I noticed an interesting connection of data signals (DQx) between the microprocessor (STM32MP135) and SDRAM (MT41K512M16VRP-107 IT). I would like to find out why this was mixed up like this and how it affects the operation or configuration of the RAM.

author: calmtron
author_rank: Regular Contributor
timestamp: August 24, 2023, 07:06:23 am
content: Probably done to simplify routing of the PCB. The SDRAM does not care about the order of the bits during normal use, it is possible one has to consider it during setup.

author: ataradov
author_rank: Super Contributor
timestamp: August 24, 2023, 07:27:35 am
content: It is absolutely for routing reasons. Just keep in mind that you can only mix them within the same byte (DQ0-DQ7 and DQ8-DQ15).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 24, 2023, 09:48:54 am
content: Quote from: calmtron on August 24, 2023, 07:06:23 amFrom memory, SDRAM only cares about some of the address lines during setup

author: Bat91
author_rank: Newbie
timestamp: August 24, 2023, 10:11:38 am
content: Thank you for all your responses. I couldn't find information anywhere regarding whether the order of the bits is important and whether this is configured in some way in STM32 (this is where I will have to read up)

author: BrianHG
author_rank: Super Contributor
timestamp: August 24, 2023, 11:33:51 am
content: Careful: The first 8 bits, bits 0-7 can have swaps within themselves. Same for the second 8 bits 8 through 15. You cannot swap bits between the first and second 8 bit banks as there is a write mask for selectively writing individual bytes at each memory address.
Why aren't my counters counting? - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: January 21, 2023, 12:56:35 am
content: I want to use my counters to count the output from my OCXO/10MHz/CMOS/Square/5Vpp. I can see the signal plainly with my scope and my scope will give the frequency. However, the counter functions on my Rigol function generator and my Siglent DMM aren't giving me a count. What might be wrong? Please and thank you.

author: xrunner
author_rank: Super Contributor
timestamp: January 21, 2023, 01:11:55 am
content: Quote from: t1d on January 21, 2023, 12:56:35 amI have a Rigol DG1032Z. Do you have that model? If so I can try it here. I have rarely ever used the counter function on that device so there may be a quirk to getting it to work.

author: t1d
author_rank: Super Contributor
timestamp: January 21, 2023, 01:36:45 am
content: Thanks for the help!Rigol DG822Siglent SDM3065X

author: xrunner
author_rank: Super Contributor
timestamp: January 21, 2023, 01:48:08 am
content: Quote from: t1d on January 21, 2023, 01:36:45 amFrom the manual for the SDM3065X -Frequency (Period) Range: From 3 Hz to 1MHz (from 0.33s to 1μs)

author: t1d
author_rank: Super Contributor
timestamp: January 21, 2023, 02:00:56 am
content: Quote from: xrunner link=topic=360991.msg4651657#msg4651657 date=167426568From the manual for the SDM3065X -[bDoh!!! My apologies!From the Rigol ManualNote: Enable the high frequency rejection when low-frequency signal with lessthan 200 kHz frequency is measured to filter out the high-frequency noiseinterference. Disable the high frequency rejection when high-frequency signalwith greater than 200 kHz frequency is measured. At this time, the maximuminput frequency can be 240 MHzI checked that the high frequency rejection was off. It was. I saw the sensitivity setting. I changed it to low and the count came through. So, all's good, now.Thanks to everyone, for your help!