hybridfree/eevblog-posts huggingface dataset:
Questions about AC Coupling - Page 1
Forum section: electronics / beginners

author: slowaudio
author_rank: Contributor
timestamp: March 11, 2014, 01:33:38 am
content: In a lot of AC coupling applications, most notably some audio equipment I've been looking at, the inputs are AC coupled. Now, this is nothing out of the ordinary. However, I've noticed that a lot of the AC coupled inputs are a parallel combination of two capacitors, usually an electrolytic and a film/foil.I've posted an example. The added capacitor doesn't really add any appreciable significance to the corner point. Why are they doing this? I read/heard something about this once (maybe?) where one capacitor cancels out some non-linearities of the other capacitor. Is there any truth to this?

author: Andy Watson
author_rank: Super Contributor
timestamp: March 11, 2014, 01:43:51 am
content: It's Hi-Fi, oops, sorry, I'll take off my cynical hat.Bigger capacitors, were (probably still are) made by wrapping two conductive foil into a spiral. Thiscangive rise to appreciable series inductance, i.e. the capacitor no longer behaves as a capacitor at higher frequencies. The smaller capacitor is there to overcome the manufacturing artefact.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: March 11, 2014, 01:48:02 am
content: Keep in mind, by higher frequencies we're probably talking MHz.

author: slowaudio
author_rank: Contributor
timestamp: March 11, 2014, 01:54:45 am
content: Quote from: Andy Watson on March 11, 2014, 01:43:51 amIt's not audiophoolery. These are out of professional pieces (not that section of the industry isn't filled with black magic).FWIW, I've seen this in other circuits too, not just audio pieces.

author: Andy Watson
author_rank: Super Contributor
timestamp: March 11, 2014, 02:14:11 am
content: QuoteMay be not, but the reason I gave above still stands. You'll also see this trick applied, perhaps with more validity, across power supply rails.

author: SeanB
author_rank: Super Contributor
timestamp: March 11, 2014, 05:07:13 am
content: In the old days, when electrolytic capacitors were made by winding 2 multi meter long strips of kitchen foil into a cylinder, with the ends used as the tabs, you could have a very high inductance of the resulting capacitor. Not a problem at 100/120Hz for power supplies, but they could have an inductive reactance at audio frequencies, so the bypassing with film capacitors with lower inductance was common. Modern units use a higher gain foil which is shorter, and the tabs are often attached in the middle of the winding, so that they are only going to be inductive over 1MHz. Some have multiple tabs, and a corresponding lower self inductance.The old design habit of bypassing with a foil is still there, but with modern units it is a question of which capacitor is actually doing the bypass. The modern electrolytic is likely to have a higher self resonant frequency than the film unit.
Questions about charge protection. - Page 1
Forum section: electronics / beginners

author: GadgetBoy
author_rank: Regular Contributor
timestamp: April 17, 2019, 11:21:06 pm
content: Specifically the little boards in the photo.First question: can I harvest the board from a small lithium cell and pop it onto a larger lithium cell? (I'll be using it in a very low-current application, I just want a bigger cell)Second question: once the board is attached, can I charge the lithium cell directly from 5V relying on the overcharge protection, or should I still use a buck regulator?Thanks!Sent from my ONEPLUS A3000 using Tapatalk

author: Gyro
author_rank: Super Contributor
timestamp: April 18, 2019, 12:21:42 pm
content: First question: Yes you can. Even if the cell is bigger, the controller on the PCB is set to limit / cut-off at a safe current for its FETs.Second question: No you can't. It's a protection module only - designed to cut out if the battery voltage gets to an excessive (safety, not proper long life operation!) level. You still need a charger circuit. You can pick up little linear USB charger PCBs very cheaply though, they have charging status leds etc built in.E.g.https://www.ebay.co.uk/itm/10Pcs-1A-5V-TP4056-Lithium-Battery-Charging-Module-USB-Board-Electronic-Componen/273242540349Note, you still need to keep the protection PCB too.

author: tszaboo
author_rank: Super Contributor
timestamp: April 18, 2019, 12:29:34 pm
content: Imagine the charge protection as a fuse. It is there to make sure that your battery doesnt blow up, not for normal operation. If it does undervoltage or overvoltage cutoff, you are damaging the cell already.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: April 18, 2019, 07:07:56 pm
content: Quote from: Gyro on April 18, 2019, 12:21:42 pmThose were the answers I was expecting, I just wanted to make sure. I'm up to my eyeballs in 5V buck/boost regulators harvested from dollar store battery packs, so that's not an issue as far as the charging goes (was just hoping for a simpler solution).As far as the load goes (some LEDs and a motor), should I power them from the 5V rail with some kind of regulator (the circuit needs 3V), or can I draw directly from the cell (like the drone I got that cell out of)?Sent from my ONEPLUS A3000 using Tapatalk

author: kjr18
author_rank: Regular Contributor
timestamp: April 23, 2019, 05:00:24 am
content: Fully charged cell is about 4.2V so it a bit too much. If your circuit draws less than, let's say, 500mA you can use a linear LDO, 3.3V or even some 3V ones exist. Or use some small buck regulator module that works from single cell.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: April 23, 2019, 05:07:56 am
content: Quote from: kjr18 on April 23, 2019, 05:00:24 amI was going to use a 317.Sent from my ONEPLUS A3000 using Tapatalk

author: kjr18
author_rank: Regular Contributor
timestamp: April 23, 2019, 06:06:33 am
content: 317 needs about 3V difference between input and output, so even with 5V it might not work properly.
Questions about differential probe circuits - Page 1
Forum section: electronics / beginners

author: fw
author_rank: Newbie
timestamp: April 14, 2025, 09:04:45 am
content: Hi guys. I disassembled a high voltage differential probe, but I have a problem reversing the schematic diagram. Please refer to the attachment. I don't understand the purpose of connecting the varactor diode to the op amp like this. I hope you can help me. （Please refer to the following article, the errors in the schematic have been updated）

author: Terry Bites
author_rank: Super Contributor
timestamp: April 14, 2025, 05:29:23 pm
content: Attenuators need frequency compensation to null out the effects of parasitic elements. The compensation in this differential probe circuit is most likely used to maximise the CMRR.If you used a trimmer capacitor, the compensation would have to be set for the entire bandwidth. The trimmer value would be set for best overall performance.For maximum CMRR flatness across the band the trimmer capacitance value chosen will be a compromise.Instead of using trimmer capacitors that are fixed, you can use varicaps to adjust the compensation as required. "On the fly"This lets you use a smarter control system say, with a lookup table to optimally trim the circuit CMRR at the frequency of interest.You can use a combination of fixed and trimmer capacitors instead of the varicaps if you prefer.

author: fw
author_rank: Newbie
timestamp: April 15, 2025, 12:59:26 am
content: I think there might be some mistakes in my reverse-engineered schematic diagram, and some of the wiring is incorrect. Please wait for me to update it before I send it out again.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: April 15, 2025, 07:05:57 pm
content: What differential probe is this? Seems like a relatively-slow one, based on the choice of op-amp.

author: fw
author_rank: Newbie
timestamp: April 16, 2025, 12:56:09 am
content: Yes, this probe only operates at 100MHz with a voltage rating of 1500V. It is manufactured by a company in China.

author: fw
author_rank: Newbie
timestamp: April 16, 2025, 12:59:57 am
content: Hi everyone, I have corrected the error in my schematic diagram. Currently, the zeroing circuit should be located within the circuit, but I haven't been able to identify the corresponding circuit for the 5MHz bandwidth limit. Theoretically, the bandwidth limitation should be implemented as a low-pass filter, yet I haven't found it.

author: pigfun
author_rank: Newbie
timestamp: June 01, 2025, 01:09:26 pm
content: are you sure that the B of U3 doesn't connect to IN- ?

author: pigfun
author_rank: Newbie
timestamp: June 01, 2025, 01:30:29 pm
content: the V of BB640E6327HTSA1 is about 3.0V ,and the cap of BB640E6327HTSA1 is about 30pf,8 times is 240pf,plus 100 and 330 equals to 670pf

author: fw
author_rank: Newbie
timestamp: June 03, 2025, 02:03:59 am
content: yes

author: pigfun
author_rank: Newbie
timestamp: June 03, 2025, 03:12:31 pm
content: I think that the IN0 or IN1 should connect to a capacitor about 300PF to form a lowpass filter
Questions about ESD mats - Page 1
Forum section: electronics / beginners

author: openthomas
author_rank: Contributor
timestamp: October 07, 2012, 03:59:59 am
content: I have the 3m 8200 series esd mat. I plan on hooking it to a ground from my radiator and also ground from my socket. The monitor requires 2 grounds (3m 732).Is it unwise to use ground from the wall outlet ? Can I get shocked ?How can I test the radiator ground to see if it is really earth ? And also how can I test the quality of the ground connection ?Can a esd mat conduct and short pcbs laying on them ? Is it safe to power up pcbs resting on the surface ?The 3m 732 ESD workstation monitor applies a voltage of 9v or 16v with < 3ua to test the mat is continually grounded. Can this effect powered pcbs laying on the surface ?See page 4 herehttp://multimedia.3m.com/mws/mediawebserver?mwsId=66666UuZjcFSLXTtMxMaoxF6EVuQEcuZgVs6EVs6E666666--What is the better choice 9v or 16v ? And which is the safer option 10 megohms or 35 megohms ?Thanks !

author: notsob
author_rank: Frequent Contributor
timestamp: October 07, 2012, 05:51:30 am
content: some reading for youhttp://www.esdjournal.com/techpapr/eosesd/grounds/fsg.htmand some testershttp://www.transforming-technologies.com/constant-monitors.html
Questions about metal oxide recitifers - Page 1
Forum section: electronics / beginners

author: Algojervia
author_rank: Unknown
timestamp: November 24, 2016, 08:26:02 am
content: HiRecently got a few bags of assorted electronics and in them I found what I believe is a bunch of metal oxide rectifier. Using the diode tester I measured a drop of three volts over the outer and center plate. So I have some questions since I never seen this type before.First of all, are those the selenium or copper oxide type. If they are the selenium kind, how dangerous are they, I want to dismantle one just to have a look but I though I ought to wait until I heard what you have to say about it. As far as I understand there is only some risk if I would somehow vaporize the selenium.Secondly, could I have any use for them in some fun experiment or so? They seem to be enable to carry some current unless they are just inherently inefficient.And last, the person owning this before me was obviously a car audiophile (among all the other stuff I found over ten 400v 2.200µF caps) so what was his intended use for the rectifiers? Did he build his own rectifier circuits for the alternator or are there any other uses in car audio?

author: SeanB
author_rank: Super Contributor
timestamp: November 27, 2016, 01:20:39 pm
content: Don't think those are selenium, they never had a shiny anodised aluminium plate, more a lot of steel plates for cooling with a paint on them.mor clearer pictures of the sides and all angles will help, that might be a split charge controller for a car, or some other device. In any case 400V 2200uF capacitors are more commonly used in high power inverters, a 2200uF capacitor in a car is typically only rated for 25V, and is quite small. Those 400V ones will be as large as your hand each, with screw terminals on the top.
Questions about motor current consumption - Page 1
Forum section: electronics / beginners

author: little_carlos
author_rank: Regular Contributor
timestamp: September 27, 2014, 05:32:25 pm
content: Hey guysIve been wondering, how or why the current that a motor takes increases with the amount of load taken by the motor?i mean, is there a magnetic consumption or something? how do this works?

author: Kremmen
author_rank: Super Contributor
timestamp: September 27, 2014, 06:23:51 pm
content: Basically a motor turns electrical energy into mechanical energy.Or where did you think the mechanical energy came from?

author: SeanB
author_rank: Super Contributor
timestamp: September 27, 2014, 06:37:45 pm
content: Spinning motor generates a back EMF from the coil moving in a magnetic field ( basic electromagnetism) and as you load it the speed drops, so the back EMF drops and the opposing voltage drops so more current can flow in the motor, limited by the resistance. This increased current provides the force turning the coil so it provides more torque till the torque into the load equals the power applied.
Questions about parts selection and things I don't understand - Page 1
Forum section: electronics / beginners

author: AvariCe
author_rank: Newbie
timestamp: September 15, 2019, 09:45:48 am
content: Hello!I have an idea for a project that will hopefully lead me to design my first pcb. It will be an attiny13a which will send a pwm signal toa 4 to 16 demultiplexerwhich will then fade in/fade out an LED out of 16 at random. All of this will be powered by a 3v coin cell battery. The whole idea is to make self contained christmas ornaments.And I've hit a wall due to not understanding a few things:From what I understand (which, again, is not very much), I will actually be able to feed a pwm signal to the demultiplexer and have it work as intended. Is that correct?On thedatasheetof the demultiplexer, there isn't a figure for power consumption(unless I missed it), only a figure for total power dissipation of 300 mW. Does that mean it will continuously draw 300 mW? As you might have guessed by this question, I can't understand power dissipation.I can't decide about what leds I shoud use. As this will powered by a meek battery, I don't want the leds to draw a lot of power (hence the fade in/out shenanigans) but I want them to be fairly to somewhat bright as well. From your experience, what mcd's should I be looking at and at what is the point I should compromise?Lastly, I don't have much experience designing stuff like this or choosing parts, so any help or suggestion is welcome.Thanks for your time.

author: ledtester
author_rank: Super Contributor
timestamp: September 15, 2019, 10:47:04 am
content: 1. It should work. If you look at the rise and fall times (t_r and t_f) you'll see they are in the nanosecond range. All of the digital ICs are designed to be used in circuits which operate in the megahertz and faster range.2. The 300mw is a limit - that's the maximum power the chip can safely dissipate without being damaged. At 3V 300mw is 100mA which is a lot of current for a CMOS logic chip.Power consumption of CMOS logic chips (4000-series, 74HC/HCT) is very, very low - in the micro-watt range.3. Generally a higher mcd means a brighter and more efficient led which is desirable if you want to conserve power. You also want to choose an LED for its appearance which includes how it's encased - clear vs. diffused. You might just have buy a bunch of different ones and try them out.You should consider using a micro with a few more IO pins and using charlieplexing:https://www.reddit.com/r/explainlikeimfive/comments/47097a/eli5_what_is_charlieplexing_and_how_does_it_work/If you have 5 free IO pins you can charlieplex 20 leds.Update: Realized you might even be able to use the attiny13a. If only one LED will be illuminated at a time, just write a custom routine for each LED which will fade it in and out via charlieplexing.

author: AvariCe
author_rank: Newbie
timestamp: September 15, 2019, 10:56:56 am
content: Thanks a lot! Also appropriate username. I had no idea about charlieplexing, will look into it now!
Questions about PCB layout and Circuit Design for Analog Audio - Page 1
Forum section: electronics / beginners

author: warpigs330
author_rank: Contributor
timestamp: June 20, 2022, 10:40:28 pm
content: I have been working on some designs for analog synth parts, and have a few PCBs ordered, and am trying to figure out exactly what is important and what isn't when designing a schematic and PCB for analog audio. I am trying to learn what causes interference, both external RF interference, and also potential power supply ripple induced in the circuit. I guess my question is what causes certain elements of an analog circuit to be more or less sensitive to interference? For instance I have a Voltage Controlled Filter, based on a diode ladder filter design, that has a resonance pot that will occasionally pick up some radio signals. At the moment, the signal flowing through the pot (set up as a simple voltage divider) is only roughly 60mv peak to peak, and the mounting points are floating. Is this susceptible because the peak to peak voltage is so low, and will grounding the mounting holes help? I know a bit about designing PCBs for signal integrity for fast digital systems, but I don't know as well the analog side of things. What are good rules to go by and things to avoid? Thanks for all the help.

author: Terry Bites
author_rank: Super Contributor
timestamp: June 21, 2022, 02:31:31 pm
content: In essence, a radio receiver is a filter and a rectifier. Any trace or wire can act as an antenna. A good ground will help you recieve a stonger signal. So you have to track down where the RF gets in.Long lines on the control pots?You need a number of strategies to deal with unwanted signals. You need to understand the source of the problem and its remedy.How does the interference get into your system. Electromagnetic, Electrostatic, Grounding errors, poor insulation, optical, vibration, proximity?It’s hard to say if particular elements are more sensitive because it depends on the topology of the circuit. In general you need to keep the big signal stuff away from the small signal stuff. This is requires a combination of physical and electrical isolation.Avoid long loops for both signals and grounds. Use local decoupling. Don't connect opamp summing nodes to long lines. Current doesn't take the shortest path to ground, it takes all paths.The lower the impedance the more preferential the path.How to fix it. Shielding, Filtering, correct grounding, layout ,mounting.

author: Grandchuck
author_rank: Super Contributor
timestamp: June 21, 2022, 04:34:27 pm
content: https://resources.altium.com/p/removing-noise-analog-signals-your-pcb
questions about ppm's - Page 1
Forum section: electronics / beginners

author: tron9000
author_rank: Frequent Contributor
timestamp: September 15, 2015, 01:41:19 pm
content: I have an AD680JN voltage reference, 2.5V, typically drift of 10ppm/oC + 24ppm/1000hrs longterm stability with an initial accuracy of +/-10mV. (spare you scrolling through thedatasheet)First off: date code on it appears to be 0609 - 6th week 2009? so does the longterm stability only apply to how long the device has been powered or does it affect it if it's been sat in a box?secondly: I plan to use it as a reference for a potentiometer that has a ppm of about 50ppm/oC, so at the wiper of my pot: do I have an affective drift of 60ppm/oC?

author: bitshift
author_rank: Regular Contributor
timestamp: September 15, 2015, 01:54:12 pm
content: Quote from: tron9000 on September 15, 2015, 01:41:19 pmI would imagine that long term stability will apply irrespective of if the device is powered on on off. This is why you would cal instruments each year and not after XXX hours of operation. Don't quote me on this thoughQuote from: tron9000 on September 15, 2015, 01:41:19 pmAs far as I understand, yes.

author: tron9000
author_rank: Frequent Contributor
timestamp: September 16, 2015, 08:12:28 am
content: Cheers bitshift,so weeks past between date of manufacture and now (week 38 of this year) =344ok so after 344 weeks in a box @ a drift of +/-24ppm/1000hrs =1387.008ppm total driftassuming room temp (output ideally = 2.5V) and taking into account the initial accuracy I should expect the output of this reference to be between:2.4855V & 2.5134Vso approximately+/-0.6% of stated outputthat sound right?
Questions about software used in the industry - Page 1
Forum section: electronics / beginners

author: Sypher
author_rank: Contributor
timestamp: April 29, 2012, 01:57:05 pm
content: I was wondering what actual software is used by professionals? For example, in my Computer Engineering lab we are using Quartus software to simulate our designs. Is this software actually used (I don't like it very much)? Other software we use: Altium PCB designer and Candace PSpice.Is this software actually used by professionals? I'm guessing MatLab is used a lot? What else?

author: olsenn
author_rank: Frequent Contributor
timestamp: April 29, 2012, 02:40:04 pm
content: Quartus would be for Alterra FPGA's I would imagine. To be honest there really isn't so much of a standard practice amongst companies for which software they choose; both as an individual and when working with a company, the software you use should be chosen to match the specific task you are working on. For PCB design, Altium is quite feature rich (and expensive) and can be found at a lot of places. MATLAB, Mathematica, LabView, Eclipse, Multisim, PSPICE, AIR Workstation... are all popular pieces of software.Undoubtably, the only pice of software that darned near ALL companies buy is Microsoft Office. Everything else is decided by you and your team mates and relayed off to your purchasing department for approval.

author: T4P
author_rank: Super Contributor
timestamp: April 29, 2012, 07:54:12 pm
content: Some *cough* companies use Mentor Graphics and it's the worst CAD package designer i have used .It's so expensive and yet so much bovine byproduct .Stay away from Mentor as much as you can !

author: EEVblog
author_rank: Unknown
timestamp: April 29, 2012, 10:14:17 pm
content: Yes, all of those packages are used by professionals.But there is no standard, everyone uses what they like and are used too, or what the company standard is etc.Dave.

author: free_electron
author_rank: Super Contributor
timestamp: April 29, 2012, 11:33:54 pm
content: It depends what you do and at what scale.'Hardcore' software :Mentor DxDesigner/ Boardstation , Cadence Allegro ( PCB design )Agilent ADS , Eldo , Analog Artist ( spice simulation )Hyperlinx, AST studio ( field solvers for EMC )Flomerics ( Thermal modeling )Synopsys , SpecMan , Modelsim ( HDL synthesis / verification )High end software :Zuken CB5000 , Altium (PCb Design ) , OrCad, Mentor PADSQuartus (paying version), ISE (paying version), Modelsim Lite , Veritak, Aldec ( HDL synthesis )the difference between modelsim and modelsim lite is that they artificially slow down the simulator and things like compute farm runs are disabled. you can do the same thing but just much much slower. things that take the paid version 1 second to run take half an hour on the free version ... then again... by the time you need half an hour runs you're playing with thousand $ FPGA's.... or trying to do timing closure on an asic ... and then you have money to spend on tools anyway.Hard-core is not bought but leased. every year you need to fork over more money or it stops running.... My division of the company i work for spends a couple million $ every year on Cadence licences...
Questions about SPD modules - Page 1
Forum section: electronics / beginners

author: evin
author_rank: Newbie
timestamp: September 01, 2018, 12:43:50 pm
content: Hello,I have questions about installation of surge protective device (SPD) modules on a single phase 230V TNC mains line (EU).The engineer, who build the lightning protection system of my house, recommended to use Type 1 + Type 2 combined MOV protection device with Iimp=15kA (T1) and Imax=70kA (T2) and 50A back-up fuse (the main fuse to the house is 63A).I found SPD devices at good price with Iimp=7kA (T1) and Imax=70kA (T2) and recommended <=50A back-up fuse. Everything is clearly described in the SPD datasheet, but my specific question #1 is can I use 2 identical 7kA SPD modules in parallel via a common 50A back-up fuse? Will they work as a single device with Iimp=14kA for 10/350 us impulses?My question #2: If I buy SPD with recommended back-up gG fuse of <=160А (withstanding 10kA short circuit current), can I use this SPD via 50A back-up fuse? Will I limit the surge charasteristics of the device using a lower value fuse - and if so, what would be the limitation?Thank you in advance!
Questions about steel square tube as power supply housing - Page 1
Forum section: electronics / beginners

author: Barny
author_rank: Frequent Contributor
timestamp: March 20, 2019, 11:19:09 am
content: I want to use a square tube as housing.Is there a problem when a toroidal transformer is surrounded with thick steel in short distance?The square tube:Dimensions:160mm x 80mm x 4mm / 300mm longMaterial:Steel (S235)The toroidal transformer:Dimensions:ø142mm / 55mm highPrim:230VACSec:24VACThe fastener is a self-made bolt made of POM.Are there some potential problems which I have to look for?Are there traps for young-player?Is there a reason to not use a steel square tube as housing except the weight?

author: Brumby
author_rank: Unknown
timestamp: March 20, 2019, 11:28:38 am
content: The trick with toroidal transformers is to NOT have an electrically conductive path that passes through the centre of the toroid and forms a closed loop around the toroid core. This is a shorted turn and will cause major overload.

author: Barny
author_rank: Frequent Contributor
timestamp: March 20, 2019, 11:54:39 am
content: The center-clamping bolt will be made of POM.Its a plastic similar to PA, but with less water absorption and its better to be cut on a lathe.POM its not as waxy and translucent as PA.So you are saying that there is no problem with magnetic field through the air when there is steel close on the outside?

author: Gyro
author_rank: Super Contributor
timestamp: March 20, 2019, 12:08:33 pm
content: No, in that case it will just improve magnetic shielding.

author: digsys
author_rank: Unknown
timestamp: March 20, 2019, 12:09:53 pm
content: We've mounted literally 1,000s torroids on steel bases, steel caps and steel bolts clamping them in (hard rubber under the caps), no issues at all, of any kind.Like Brumby says, as long as you don'tcompletethe circuit, it's all good. I don't think we've ever had to use Nylon / POM etc to clamp.

author: Barny
author_rank: Frequent Contributor
timestamp: March 20, 2019, 12:22:26 pm
content: Thanks for your information.But I think I'll stick to the POM-Bolt version, because its easier to machine and I've more of it sitting in the shelves.

author: Benta
author_rank: Super Contributor
timestamp: March 20, 2019, 05:03:26 pm
content: Only thing I've experienced as an issue is mechanical 50/60 Hz hum from the enclosure. With proper rubber pads it should be avoidable.

author: Barny
author_rank: Frequent Contributor
timestamp: March 21, 2019, 11:04:05 am
content: Quote from: Benta on March 20, 2019, 05:03:26 pmNormally I'm using felt-pads (the kind which normally get stuck below chairs) or small slices of glue sticks as housing feets to avoid scratches.I think this will be enough to decouple the housing mechanical from the desk.Thanks to you all for your help.
Questions about the BQ27427 Fuel Gauge Schematic. - Page 1
Forum section: electronics / beginners

author: Dicko
author_rank: Contributor
timestamp: April 14, 2025, 09:13:54 am
content: Hello there,I have been looking at the BQ27427 fuel gauge by Texas Instruments and I want to replicate the design and add a small adjustment. However, when copying the design in KiCad I noticed a few points that I didn't understand and wondered if anybody is able to help. I contacted TI but they replied that this is outwith their scope.I've attached the datasheet, their schematic (from page 13/24) and my schematic with a small modification to the original.My questions are:1) On the J2 header, pin 2. What is expected to be connected here? Is this ground to pull-down R1? or something else.2) On the J3 header, pin 2. What is expected to be connected here? Is this ground to pull-down the 10K resistor ?3) Page 16 (section 9.2) of the datasheet says "If battery pack’s thermistor will not be connected to BIN pin, a 20 kohmpull-down resister should be connected to the BIN pin." Is this instead of R2 (the 10 kohm resistor) ? Or does the 10k represent the thermistor?4) On headers J8 and J9, pin 2. What do they connect to?5) I would like the option to be able to choose between using a thermistor in the design, and not using one. In the schematic I have added in a 3-pin header so that I can jump between the default setting using the 10k resistor, or a 2-pin terminal block for a thermistor. Does this look ok?6) Following on from 5) and related to question 2) these connect to J3, pin 2, but the schematic doesn't show what should be connected here, I'm assuming ground, is this correct? If it is, why wasn't it tied to ground on the PCB? Or was this in-case we connected to another device with a different ground?7) J10, pin 4, is this is meant to be unconnected ? Just using the VSS, SCL and SDA.As per the guidance in the datasheet, I have connected a 1.8M ohm resistor (R5) between BIN and VDD. Does this look ok?9) Do you see any issues with my design that I would need to correct before getting the board manufactured?Thank you very much.
Questions about the Elenco XP-581 power supply and MC1723 regulator - Page 1
Forum section: electronics / beginners

author: ledtester
author_rank: Super Contributor
timestamp: January 31, 2018, 12:54:50 am
content: I have an Elenco XP-581 power supply. It has supplies of +5V @ 3A, +/- 12V @ 1A and a variable 2-20V @ 2A.The problem is that the +5 output is a little low - it's more like 4.8V.Looking at the board it appears that a 604R resistor in the schematic has been fitted with a 560R resistor instead (see R107 in the attached photo.)You can find the schematic for the XP-581 here:https://www.csulb.edu/sites/default/files/groups/college-of-engineering/About/elenco-xp-581power-supply-manual.pdfAnd the datasheet for the MC1723 may be found here:http://pdf.datasheetcatalog.com/datasheet/motorola/MC1723.pdfThe configuration used in the XP581 most closely resembles Fig. 17 - Foldback Connection. Unfortunately the datasheet doesn't give a direct formula for how the output voltage is related to the program resistors, and I'm not sure how to make sense of the formulas there.My questions are:1. To trim the +5 output it seems I would want to increase R107 a bit to around 600R per the schematic. Correct?2. What is the formula for the output voltage in terms of the program resistors in this case?3. Is there an equivalent op-amp formulation of the MC1723? That would help me a lot in understanding what's going on.

author: ledtester
author_rank: Super Contributor
timestamp: February 06, 2018, 07:29:43 pm
content: Turns out the MC1723 is equivalent to the LM723, and TI's datasheet had the information I needed:http://www.ti.com/lit/ds/symlink/lm723.pdfReplacing the resistor with a 680R boosted the 5V rail from 4.8V to 5.1V which is more to my liking.
Questions about this schematic and my understanding. - Page 1
Forum section: electronics / beginners

author: Hextejas
author_rank: Frequent Contributor
timestamp: January 15, 2018, 07:45:02 pm
content: I am building this kit from Elenco and just soldered in the IC socket for the LM386.My soldering techniques are at best, intermediate, and the pins of the IC socket are tiny and close.I inspected the soldering with a good 10x loupe and some of the pins are suspicious. Paticularily 3&4, and 5&6 and 6&7.I have tried solder wick and re soldering 3 times now so want to avoid it if possible.I put my ohm meter on the points to see if there was continuity and it says yes.Reading the schematic, it seems to me that pins 3 to 4 would have continuity anyway since they go directly to ground. The other pin pairs I think could go either way, either a short between the pins or they get to ground through the other pathways.Is that an accurate reading of the schematic re pins 3 and 4 ?Thanks

author: tautech
author_rank: Super Contributor
timestamp: January 15, 2018, 07:50:12 pm
content: Quote from: Hextejas on January 15, 2018, 07:45:02 pmYep.When you have solder bridging probs hit the job with more flux, even if it means more solder....yeah I know it sounds wrong but it works. Also get a solder sucker. Ineveruse solder wick, ever.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: March 04, 2018, 08:42:25 am
content: Quote from: tautech on January 15, 2018, 07:50:12 pmAlso, make sure NOT to use the lead free stuff. 60/40 or better yet 63/ 37 tin lead stuff is far less troublesome to use. A good brand like Kester or the Ersin multicore stuff is a good bet. It is all technique. Make sure the iron is well tinned, apply it to the joint and add just enough solder. The tip size and even the solder gauge should be appropriate for the pads or terminals you are soldering. In close quarters, a fine tip and thin solder helps.Sent from my SM-G900V using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: March 04, 2018, 09:22:31 am
content: HexWatch this vid and the following a couple posts below, not so much for the SMD but the technique used.https://www.eevblog.com/forum/beginners/so-surface-mount-it-is/msg1442590/#msg1442590BTW, and get yourself a cheap jewelers magnifying visor for soldering and inspection.
Questions about using Sds 1204 X-E (50 ohm terminiators) - Page 1
Forum section: electronics / beginners

author: watchmaker
author_rank: Unknown
timestamp: October 26, 2023, 03:22:29 pm
content: When it is useful to use 50 ohm terminators at the end of coax when not using the probes? My generator does output at 50 ohms, but what is the application for these terminators?Regards,Dewey

author: abeyer
author_rank: Frequent Contributor
timestamp: October 26, 2023, 06:28:55 pm
content: Dave's demo & explanation was here

author: watchmaker
author_rank: Unknown
timestamp: October 26, 2023, 08:41:33 pm
content: Whoa. Very helpful. Did not know about the channel. I have added it to my learning resources. THANKS!Dewey

author: TimFox
author_rank: Super Contributor
timestamp: October 26, 2023, 08:45:38 pm
content: Also, note that many (if not most) 50-ohm output generators (function, audio, RF, pulse, arbitrary-waveform, etc.) are calibrated for the voltage across the 50 ohm external load.With a high-impedance load (such as 1 megohm 'scope input), the voltage will be twice that.

author: tautech
author_rank: Super Contributor
timestamp: October 27, 2023, 03:16:40 am
content: Quote from: TimFox on October 26, 2023, 08:45:38 pmYes when the AWG is set for 50 Ohm loads.Not so when its output is set to HiZ, as then the amplitude value the generator displays will match that on the scope display.
Questions about Velleman VTSS4 - Page 1
Forum section: electronics / beginners

author: picofarad
author_rank: Regular Contributor
timestamp: January 26, 2014, 08:51:40 am
content: I need a cheap backup soldering station, just for emergencies.I have some questions to ask to the owners of Velleman VTSS4 or any chinese soldering station that looks like this:First question: Is the tip well insulated? Can someone check with a multimeter how many AC volts there are between mains ground and tip? This because sadly I had a badly insulated soldering iron with 12v AC on the tip!Second question: On the internet comments about this type of soldering station are various. Some says that it's a very great product, some says that it's a piece of garbage. Which is the truth?Third question: Is this soldering station grounded? I mean, there is the ground pole on the mains connector?Thanks!

author: mmilejski
author_rank: Contributor
timestamp: January 26, 2014, 10:19:05 am
content: I can't answer most of your questions, as I am not at home right now, but I certainly can say that this station is a waste of money. I've had it for about a year, and one day it just stopped working. Apart from that... Handpiece cable isn't flexible at all, and although the station has a bag of sandin it, it slides on the bench as you use the handpiece.It has earthed plug, but I'l have to check if the tip is actually earthed - later today.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 26, 2014, 10:41:55 am
content: The tip is properly earthed. The station is made in China, but under Velleman's supervision. I couldn't find anything dodgy inside. Works fine as an emergency soldering station. Mine has been gathering dust, since I got the Hakko FX888 though.There is a slab of chunky metal inside to weight the station down.Nothing fancy, but for the price, a safe and usable soldering station.

author: G7PSK
author_rank: Super Contributor
timestamp: January 26, 2014, 03:21:02 pm
content: Tryhttp://www.circuitspecialists.eu/soldering/desoldering-hot-air-rework?gclid=CKuqlJORnLwCFUj4wgoddU4A1Qthey have some reasonable soldering stations at quite good prices I got one a couple of years ago and it still works fine and the tip is earthed.

author: picofarad
author_rank: Regular Contributor
timestamp: January 26, 2014, 04:26:16 pm
content: Yep, prices are good, but I just need a backup soldering station for emergencies and I don't want to spend so much. The Velleman station goes for 15-20€, that's good.But now I'm also looking to those soldering irons that you plug directly to the mains. Maybe one of these will work fine for emergencies.

author: Polossatik
author_rank: Frequent Contributor
timestamp: January 27, 2014, 10:05:36 am
content: maybe more than you want to spend , but i have (for years) a Portasol P-1Kit not that i use it very often, but it has been a few times very handy to have, especially when repairing stuffBut you're not going to solder a production run with it.
questions of uni-t ut216c - Page 1
Forum section: electronics / beginners

author: Adrian_Arg.
author_rank: Frequent Contributor
timestamp: June 09, 2021, 10:47:59 pm
content: Hello, I have a question to ask you, I am going to buy an ampirometric clamp, the model is uni-t ut216c I think it is a very good option, what do you think?

author: Adrian_Arg.
author_rank: Frequent Contributor
timestamp: June 14, 2021, 01:51:14 am
content: From what I observe, nobody uses it, why is it?

author: Adrian_Arg.
author_rank: Frequent Contributor
timestamp: June 23, 2021, 08:02:51 pm
content: because:-High price?-Error of measurements?-Poor quality?-In that price range are there better and more complete?-Others?

author: firas
author_rank: Contributor
timestamp: June 12, 2024, 05:37:13 pm
content: It is a good device that I have owned for more than 10 years and it works
Questions on capacitors - Page 1
Forum section: electronics / beginners

author: giosif
author_rank: Frequent Contributor
timestamp: September 06, 2020, 09:42:22 pm
content: Hi,I have two questions with regards to some electrolytic capacitors I found while troubleshooting a power supply (please see attached photos):1. A 1000uF cap whose "skirt" got lifted.I am guessing this might be due to proximity to something getting hot.But the interesting part is both Cs and Rs/ESR are very close to those of a brand new cap with the same specs.At the same time, if I look at the bottom of the cap with the light shining at an angle, there seems to be a substance present there (could be electrolyte, but could just as well be flux from when it was soldered initially).I am replacing this cap anyway, but I was wondering if you would consider this cap as good (based on measurements) or bad (based on exterior details).2. A 220uF cap (light blue one) which I would like to replace.However, I'm slightly puzzled by the replacement cap I found in my stash, as the physical dimensions are quite different.Are these two caps really equivalent, or am I missing some parameter here (other than capacity, working voltage and ESR, which are the same between the two)?Thanks!

author: Labrat101
author_rank: Unknown
timestamp: September 06, 2020, 10:11:21 pm
content: replace it . that discolouring looks like that it has been tracking overthe base .If the cap is getting hot maybe due to over voltage or high ripple duetoAnother Fault. As its on a power supply check the bridge rectifier itcould be failing . There are many reason a cap fails and the ESR canshow good but if leaky it will fail as the cap is loaded .Cap's in short can show good have a fairly close Uf rating but it willdepend on the Manufacturing quality .If you have removed a cap from a board and its a few years old replace it.Depending on the age of these I would also check for a reason and other components that are loading the cap.The Blue cap as you say looks like a high ripple capYXF for secondary filtration in power circuit, aiming at small size, high ripple-resistance, low impedance .You should also check the big 400v caps these are more likely to be your problem .RNS

author: giosif
author_rank: Frequent Contributor
timestamp: September 07, 2020, 07:23:44 am
content: Thank you for the good advice!I will replace the bigger cap and look for other faulty components.I will also check to find a more suitable replacement for the blue cap.(The 400V cap has already been replaced, BTW).

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 07, 2020, 07:45:48 am
content: The blue cap is probably just fine.The physical size of electrolytic caps has been shrinking ever since they first started manurefacturing them a long time ago. The big one is probably just 10+ years older then the black replacement.If you can find the exact datasheet of the series of both capacitors, then you can do a comparison of their spec's.
questions on dave's psu design  - Page 1
Forum section: electronics / beginners

author: amateur_25
author_rank: Regular Contributor
timestamp: April 07, 2012, 01:10:01 pm
content: The U3A opamp controlling the voltage is an noninverting amplifier. However am unsure what the opamp at the bottom is. I understand it there for the current limiting but it doesn't have any resistors so it can't be an noninverting/inverting amplifier. Is it a comparator?

author: amspire
author_rank: Super Contributor
timestamp: April 07, 2012, 01:35:59 pm
content: It is an opamp - basically a LM324 opamp IC in a 2 opamp package instead of a 4 opamp package.It is running in linear mode - it is not running as a comparator even though it is functionally described as a comparator. Dave is just using the word "Comparator" in the sense that it is comparing the actual current to the set current. It only really gets out of saturation when the current out reaches the current limit.Its feedback path includes at the current sense input, then there is the opamp U3B, then through Q2 that can reduce the voltage on the LT3080 regulator that lowers the output current - which of course lowers the current sense voltage completing the loop. An opamp does not necessarily need feedback directly across the opamp - it just need some feedback path from the output back to the input. U3B has such a path.Richard.
questions on PIC18F2550's USB device - Page 1
Forum section: electronics / beginners

author: iamericmin
author_rank: Contributor
timestamp: September 23, 2019, 03:40:36 pm
content: Hi,I'm a noob just getting started with PIC microcontrollers. After lots of research and googling I discovered the PIC18f2550. The fact that it comes in a DIP package with full-speed USB seems too good to be true, so I have some clarifying questions. Sorry if I sound confusing, english is not my first language.1) Is the USB just like a serial port? Can I upload programs directly through the USB port? Can I interface it through a serial terminal and send it serial commands? How does it compare to the Atmega32u4?2) I looked up some USB connection circuits and none of them have any passive components. Is it really that simple? The Atmega32u4 requires a resistor for both D+ and D-, so I just want to make sure. Do I have to set pull-up resistors through software?3) I found out that I need a USB bootloader to actually use the uC's USB device. However, every website I visit has their own version of the bootloader or simply doesn't give me one. Where can I find a reliable USB bootloader to use in all my projects? I assume you just burn it through a Pickit 3, just like with an AVR-ISP programmer?I know some of these questions might seem obvious, but as a complete beginner I just want to clear any misunderstandings before I buy a dev kit, such as this one:https://www.mikroe.com/startusb-pic.Thanks!

author: rstofer
author_rank: Super Contributor
timestamp: September 23, 2019, 04:04:20 pm
content: When an MCU has a USB device peripheral, it is just hardware. The MCU code sets up the USB device configuration and the host queries the setup. You could implement a serial port, a mass storage device, a HID device (my favorite) or some brand new device for which you write a PC USB driver. The peripheral itself has nothing whatsoever to do with chip programming (usually). You need a USB protocol stack and a deep understanding of the configuration tables.When you think about USB on the Arduino, you should be thinking about the ATmega16U2 that handles the USB connection. It has the USB peripheral, implements the protocol stack and talks to the PC. There are some output pins on the 16U2 chip that look like a serial port and they are used for programming the ATmega328P and as a serial port.The ATmega328P never deals with the USB connection itself.https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdfThere are variations in Arduino boards, not all use the 16U2, some use a different USB chip.

author: george4657
author_rank: Contributor
timestamp: September 23, 2019, 06:59:09 pm
content: Microchip no longer sells their PICDEM Full Speed USB demo board but you can still get their user guides and firmware.These guides will answer your questions.The 18f4550 is 40 pin version of same chip."https://www.microchip.com/Developmenttools/ProductDetails/DM163025"