hybridfree/eevblog-posts huggingface dataset:
circuit grounding issues - Page 1
Forum section: electronics / beginners

author: stachu0
author_rank: Newbie
timestamp: February 02, 2025, 03:33:33 pm
content: hello everyone!!! i'm building a small vfd interface. the most suitable transformer i had was one with a 12V and ~35V secondary. i need 3.3v for the vfd filament (don't eat me for using DC) and for a future microcontroller. i stepped down the 12V to 3.3V with some common aliexpress step-down converter. everything got connected through darlington pairs like in the schematic i attached below. the display was flickering, so i was going to scope the rails to see if the voltages are stable. before that i decided to common the grounds, since that's what i thought you're supposed to do. the display stopped flickering and got brighter. amazed by the results, i didn't notice a bulging capacitor, which exploded and scared the shit out of me. it was the one that's connected before the step-down converter. both of the filtering caps are 10uF, 50V-rated (mistakingly marked 50u in the schematic, excuse my laziness) electrolytics. could someone please guide me towards what happened here? why did the display stop flickering, why did it get brighter, why did the cap explode (duh), should i even connect the grounds together, and am i stupid? anyhow, thanks for any help, schematic should be an image below \/excuse the lazy vfd too...

author: benj38
author_rank: Frequent Contributor
timestamp: February 02, 2025, 04:34:30 pm
content: Are you sure the two secondary transformer windings are isolated from each other?

author: Terry Bites
author_rank: Super Contributor
timestamp: February 04, 2025, 11:31:27 am
content: Ideally all grounds need to connect at a common point, usually near the psu.If your schematic is correct and the two rectified outputs are isolated from one another, then its a good idea to join them.Floating grounds are rarely advisable.

author: Fryguy
author_rank: Regular Contributor
timestamp: February 04, 2025, 12:08:11 pm
content: The fact that the vfd got brighter when you connected the grounds should have been an indicator for you to immediately re-check the power rails - the voltage should not jump up like that .benj38 is right - looks like something added up when you connected the ground rails . Did the 12v->3.3v regulator survive this ?

author: Peabody
author_rank: Super Contributor
timestamp: February 04, 2025, 03:33:31 pm
content: Quote from: benj38 on February 02, 2025, 04:34:30 pm+1. Separate windings, or just taps at different points in the secondary?I don't know if this is entirely valid, but when I face the issue of whether to connect grounds, I measure the voltage between the grounds with my meter. If it's zero, then either they are already connected, somewhere, or the two grounds are not galvanically connected at all, in which case I can connect them. But if it's a solid 4V, or whatever, then you know you've got a problem.
Circuit power sanity check - Page 1
Forum section: electronics / beginners

author: garethw
author_rank: Regular Contributor
timestamp: June 08, 2020, 07:19:05 pm
content: Quick overview, I have a project that has both 3.3V and 5V rails. 3.3V is supplied by a LDO from the 5V rail. I'm currently supplying the 5V rail from my bench PSU.Is it ok to supply the 5V rail directly from a 5V wall wart AC/DC adaptor? I'm thinking perhaps not, as I have 5V ICs connected and if the AC/DC adaptor has a 'moment' then who knows what voltage will be fed to my 5V side.Some advice would be wonderful!Many thanks in advance
Circuit power supply question - Page 1
Forum section: electronics / beginners

author: nemo000111
author_rank: Contributor
timestamp: April 25, 2013, 06:32:14 pm
content: Hi All,This is my first project, and I could use a little help/advise from those with some more knowledge and wisdom than I have. Here's what I came up with for a psu for it. Not sure if it's the most efficient want of doing it or not. It's a battery powered (2x AA batteries) circuit. In it will be an xbee, attiny 84, and a few switches and sensors. Then entire circuit is going to run at 3.3v. It will need to run several months (ideally 6-8) without a battery change. Meaning each component needs to have as little overhead as possible. Most of the components after the psu either have near 0 constant current draw or are toggled on and off as needed via software. The way the P-channel mosfet is hooked up should give me reverse voltage protection (with a drtop lower than that of a standalone diode if I looked at the right numbers) and the MCP1640 does the dc step-up conversion. I can't figure out a cheap (money and electrically) way of doing over-voltage protection on the battery side (nothing over 5v). Any advice would be helpful, espically if there's a better way to do the reverse voltage protection with less constant current loss. Thanks again.

author: user_ivo
author_rank: Contributor
timestamp: April 30, 2013, 05:09:07 pm
content: Have you tried connect the circuit with reverse polarity? Since the chip has a EN(enable) pin probably the chip will not operate and you will not need the Mosfet, if there isn´t any problem for you in burn the MCP1640, i would try to connect the chip with reverse voltage and see what would happen. Regarding the over voltage protection, make one without get a increase of consuption, nothing come to my mind, at the momentthe most problem is you have a tradeoff between protection and consuption.
Circuit Puzzle - Page 1
Forum section: electronics / beginners

author: abdullahseba
author_rank: Frequent Contributor
timestamp: April 22, 2014, 09:57:01 am
content: In the October 2011 issue of the epe magazine their was a project by John Clarke called Wideband Air-Fuel Mixture Display.But what puzzled me was that all the displays & bar array where connected together at the same output of the PIC without triggeringall the segments e.g seg B on DIS 1 was on but the same seg was off at DIS 2 & DIS 3 while connected to each other as shown in the picture.Does any one know how it works? I've seen other diagrams with the same configuration but only in EPE.if it is a code in the PIC please include it.The diagram is in Diptrace format free download fromhttp://www.diptrace.com/(.dip) & CAD (.dxf) formatpicture of diagram:https://onedrive.live.com/redir?resid=F0C48114460E32FD!110&authkey=!ACpm54rBoXeCZqU&v=3&ithint=photo%2c.PNGDiptrace & cad diagram:https://onedrive.live.com/redir?resid=F0C48114460E32FD!107&authkey=!AMUNx9c-bFob9NQ&ithint=file%2c.zip

author: GeoffS
author_rank: Unknown
timestamp: April 22, 2014, 10:18:26 am
content: Do a google search for 'multiplexing 7 segment displays'
Circuit response changes when I put my hand near it.  - Page 1
Forum section: electronics / beginners

author: captainscarlet
author_rank: Contributor
timestamp: June 28, 2013, 11:48:29 am
content: I don't know if this is a common occurrence, but I'm building an 8x8x8 LED cube at the moment and I'm in the process of debugging some problems.First off, there's 64 anode column pins and 8 cathode layer pins. Now, some of the LEDs light up even when the cathode pins are not connected to ground. I presume that indicates a short somewhere, maybe the current is sinking to a logic 0 pin on the latch.I'm also getting a substantial ghosting problem with nearly all the LEDs when I connect everything up.But I'm seeing that the LEDs flicker when I put my hand near to some of the ICs on my stripboard. I grounded myself, but I'm still seeing some response.Can anyone give me an explanation for this?

author: Skimask
author_rank: Super Contributor
timestamp: June 28, 2013, 12:14:31 pm
content: "Hand capacitance""Skin effect""Magic"Google

author: Paul Price
author_rank: Super Contributor
timestamp: June 28, 2013, 05:57:32 pm
content: The effect is caused by one or more pins on an ic on the circuit board that is an input pin and is not being pulled up or pulled down a connection to anything., it is.just floating and since it is a very high impedance it is able to be reacting to the electrostatic fields of your hand. Check you circuit carefully for floating inputs.

author: MacAttak
author_rank: Unknown
timestamp: June 28, 2013, 11:31:03 pm
content: It might be helpful if you have a schematic to share that shows the design. Might be a bug.

author: drew_the_mutant
author_rank: Newbie
timestamp: June 29, 2013, 04:04:56 am
content: Magic is bad.http://www.outpost9.com/reference/jargon/jargon_46.html"It was clear that this switch was someone's idea of a silly joke. Convinced by our reasoning that the switch was inoperative, we flipped it. The computer instantly crashed. "

author: KJDS
author_rank: Super Contributor
timestamp: June 29, 2013, 09:29:35 am
content: You either have something oscillating or an open gate input.
Circuit schematic for battery charge controller. - Page 1
Forum section: electronics / beginners

author: Siddhat
author_rank: Regular Contributor
timestamp: June 16, 2018, 04:54:58 am
content: Hello,Can anyone help me with the circuit diagram to make a 12V lead acid battery charger?What I need is it should cut off the the power when the battery attains fully charged voltage(which is the upper threshhold voltage)and it should also auto recharge the battery when the battery reaches a certain lower threshhold voltage.But the charging should not be done between the upper threshhold and the lower threshhold.i am planning to use a schmitt trigger as shown below but I cannot make a proper circuit diagram.I have searched the internet and tried on a bread board but none of the circuits seem to work.I have my presentation tomorrow and I dont have a circuit that works.So can somebody make a circuit diagram for the above explained works.Appreciate your help
Circuit Simulation SOftware "read-requirments' - Page 1
Forum section: electronics / beginners

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 15, 2017, 03:01:32 am
content: Looking for some suggestions for paid / free software. I am a audio nut and design small & larger schematic circuits. I want to be able to design a schematic and test it, ie load and input and output under load with a wave form.Would like to :Input signal 1khzRail voltages up to 60V 60-0-60 VoltsMeasure current draw or see it on the power-supply.Measure output on oscilloscope & use a load and see what its doing..Example like this, but in a simulation before it's built..

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 15, 2017, 03:22:27 am
content: Quote from: blueskull on October 15, 2017, 03:20:35 amWOuld you be able to provide a link to what you are suggesting( just so i have the right one )thanks sir !

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 15, 2017, 08:54:00 am
content: It sounds like you're describing Multisim. IIRC, full versions start around $500-2000, but they made a free web version now too, didn't they? Haven't touched it.The more intuitive and interactive instruments are fun, but keep in mind, you cannot escape the responsibilities of a numerical simulation environment. Among free and low-tier simulators, I don't know of any that use any improvements over the last free academic release (XSPICE), save for LTSpice (which offers multi-core support and an "improved" solver, except that the improvements are specific to LT models and detrimental to accuracy, so beware; you can select fall-back options in the config).The responsibilities have to do with numerical stability, building a system that is actually reasonable and representative of the thing you intend to build, and using models that are representative as well (many manufacturer's models miss important factors -- if in doubt, test -- test both the model and the physical part!).Tim

author: dashpuppy
author_rank: Regular Contributor
timestamp: October 15, 2017, 04:41:29 pm
content: Quote from: T3sl4co1l on October 15, 2017, 08:54:00 amThanks Tim ! Totally understand

author: b_force
author_rank: Super Contributor
timestamp: October 15, 2017, 04:52:38 pm
content: I would also (highly) suggest Multisim, very nice program to use. (in fact, I think it's one of the best user interfaces that can be completely customized)Actually the combination with LTSPice is really nice.Multisim can just do a lot more things easier, better and quicker.Enough ways to look at transients, freq response, distortion etc.But like said before, don't blindly trust ANY simulator.It's very hard to simulate oscillation and temperature runaway etc.
circuit solving - problem - Page 1
Forum section: electronics / beginners

author: noname!
author_rank: Newbie
timestamp: March 31, 2020, 10:05:18 am
content: delete

author: aneevuser
author_rank: Frequent Contributor
timestamp: March 31, 2020, 11:04:29 am
content: I guess you want to model the diode as either fully off or fully on with a 0.6 V diode drop across it?If so, then I would draw a "diode on" and "diode off" equivalent circuit, and analyse those separately.Note that you can just add the the DC and AC signals to compute the voltage that the diode feels at any time, and from that you'll be able to see when the diode is forward or reverse biased. There is no current flow until the diode is forward biased by 0.6 V, so no voltage drop across the 100R until then. When the diode is on, the current through it does not affect the voltage drop across it (it's always 0.6 V in our assumption) so you can apply KVL in the usual way to find i(t), and hence V_R(t) and U_D(t).

author: noname!
author_rank: Newbie
timestamp: March 31, 2020, 12:54:50 pm
content: I think I have to assume that diode break down voltage is Ut, so it's 0V in this case. In order to compute the voltage i compute the rms so its 10sin(wt) => 10/sqrt(2) = 7,07V. After that i add this voltage to DC, 7,07 + 5 = 12,07V. Right now i have total voltage AC + DC. If diode's break down is 0 V so Ud is always same as voltage drop on R, right? But i dont have idea how to compute current with KVL in order to compute max voltage drop and draw the diode's model.

author: SG-1
author_rank: Regular Contributor
timestamp: March 31, 2020, 02:47:58 pm
content: When adding AC + DC to get the RMS value.Square each value, add together & take the square root of the sum.Square root of (7.072+52)=8.66I do not know if you are interested in the RMS value.

author: rstofer
author_rank: Super Contributor
timestamp: March 31, 2020, 08:37:55 pm
content: LTspice - just to see what is happening.

author: Zero999
author_rank: Super Contributor
timestamp: March 31, 2020, 10:13:14 pm
content: Quote from: noname! on March 31, 2020, 10:05:18 amNo don't do that. It seriously pisses people off. Don't waste people's time.

author: Simon
author_rank: Unknown
timestamp: April 01, 2020, 08:52:24 am
content: Quote from: Zero999 on March 31, 2020, 10:13:14 pmYes and doing that will get one banned.
Circuit stopped working when transferred to breadboard - Page 1
Forum section: electronics / beginners

author: fixit7
author_rank: Regular Contributor
timestamp: June 08, 2019, 10:41:44 pm
content: I transfered my components to my breadboard.The circuit stopped working.This is a detector for a laser alarm.With low light or no laser beam striking the cadium photo cell, the alarm sounds.To work on my porch, I will place a 3 inch piece of pvc over the photo cell to prevent ambient light from setting the alarm.The only change I made is use a 3A spdt switch instead of the board mounted type spdt switch.

author: KL27x
author_rank: Super Contributor
timestamp: June 08, 2019, 11:24:48 pm
content: The breadboard you are using is not the solderless kind. You usually put the components and jumpers into the other side, then solder the leads that poke through to the copper.And what in the hell are you reading?

author: ogden
author_rank: Super Contributor
timestamp: June 08, 2019, 11:54:59 pm
content: This could be trolling about misinformation in thewikipedia page.If not, then I am sorry.Breadboard:Not breadboard but pegboard:

author: fixit7
author_rank: Regular Contributor
timestamp: June 08, 2019, 11:57:39 pm
content: Thanks pegboard it is.

author: fixit7
author_rank: Regular Contributor
timestamp: June 08, 2019, 11:59:24 pm
content: Quote from: KL27x on June 08, 2019, 11:24:48 pm

author: sibeen
author_rank: Frequent Contributor
timestamp: June 09, 2019, 12:15:51 am
content: Put the components through the other side, so that the component is on the side of the board thatdoes nothave any copper. You then solder the copper side.

author: fixit7
author_rank: Regular Contributor
timestamp: June 09, 2019, 12:17:58 am
content: Ok. Thanks sibeen.This is my 2nd circuit.I did my first the same way and no one told I was doing it wrong. ??Do you think my method would affect the working of the circuit?I would like to know that the circuit works first before doing it the right way.

author: sambonator
author_rank: Regular Contributor
timestamp: June 09, 2019, 02:37:32 am
content: Quote from: fixit7 on June 09, 2019, 12:17:58 amyou could be causing unintended shorts.

author: mariush
author_rank: Super Contributor
timestamp: June 09, 2019, 02:42:13 am
content: redo the circuit with the components on other side.double check connections between partstake advantage of the strips on your board to join leads of two components. solder leads to pads not leads to leads.the copper pads seem a bit oxidized. maybe rub them before soldering with a hard eraser or some abrasive materialif still not working test your transistor and other components that may be heat (from soldering) sensitive, like the led for exampleoh and btw hope you noticed the red wire broke off from the battery holder in your picture.

author: fixit7
author_rank: Regular Contributor
timestamp: June 09, 2019, 02:54:49 am
content: Thanks.I will redo it using a new board after I clean it first.The red wire was not broken.I tested the circuit by touching the red wire to my batteries.
circuit switching - Page 1
Forum section: electronics / beginners

author: terryBW
author_rank: Newbie
timestamp: September 12, 2019, 04:51:44 pm
content: I am wiring up my granny flat and shed with 15 Amp sockets 1) for oven in granny flat and 2)socket in shed for plasma cutter/welder and compressor, can I get a switch that will switch one circuit off and the other on?

author: jpyeron
author_rank: Regular Contributor
timestamp: September 14, 2019, 03:25:33 pm
content: What region of the world?

author: Gyro
author_rank: Super Contributor
timestamp: September 14, 2019, 05:59:11 pm
content: Welcome to the forum terryBW,Sorry to say it, but it sounds like you're bodging it.- UK sockets are 13A, not 15A.- Cooker circuits are normally 30A, wired as a 6mm2radial circuit.- You would normally (always) run a separate circuit from the consumer unit to an outbuilding.I don't know of any standard changeover switches capable of handling a cooker circuit - double pole isolators, sure (also used for electric showers) but not changeover.You need to provide more information on what you are trying to do to get meaningful answers.... Location of the granny flat, shed relative to the house etc. A diagram would help.Needless to say safety and adhering to wiring regs is the utmost priority, especially if you have a Granny in the granny flat.

author: themadhippy
author_rank: Super Contributor
timestamp: September 14, 2019, 06:21:36 pm
content: QuoteThere pretty common in the world of back up supply's,for examplehttps://www.tlc-direct.co.uk/Main_Index/Distribution_and_Switchgear_Index/Change_Over_Switches/index.html#Change_Over_Switches_CGCS1004Phowever for the cost you could do the job properly
circuit that can turn a capacitor into a super high inductance value inductor - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: January 19, 2021, 12:45:17 pm
content: I remember seeing a circuit that can make a capacitor behave like a high inductance inductor, but I forgot what it was called. maybe someone knows what I'm talking about and knows the name of the circuit?

author: ledtester
author_rank: Super Contributor
timestamp: January 19, 2021, 12:48:10 pm
content: A gyrator:https://en.wikipedia.org/wiki/Gyrator#Simulated_inductor
circuit to automatically power-on laptop - Page 1
Forum section: electronics / beginners

author: batou
author_rank: Contributor
timestamp: February 05, 2016, 02:29:42 am
content: Hi, first time poster and electronics noob so please be nice!I want to build this circuit that I found on stackexchange (see picture). It is to power-on a laptop automatically after a power failure. Its for an old laptop that i'm using as a router and it doesnt have the BIOS feature to do this by itself.I understand that when the circuit recieves power, it waits for a short time then shorts the power button, until it sees voltage at the LED, then opens the switch again. I'm trying to figure out exactly how this circuit works, and this is what I have so far. I would appreciate if someone could tell me if i'm on the right track:1) When there is power at S1, the 22uF capacitor starts charging, via the the 57k resistor.2) When the capacitor is charged, transistor Q1 is activated (this bit I don't understand - can someone help?), which shorts the switch and powers on the laptop.3) Once the power LED comes on, there is a voltage at L1 which activates transistor Q2. Now the capacitor is bypassed, and there is a shorter path to ground (through Q2) so Q1 is deactivated, opening the power switch again.I'm assuming 22uF was chosen for timing, but I'm not sure about the choice of 1k and 57k resistors. Can anyone explain this for me?I hope someone can take the time to educate me here, I find electronics so facinating! And thanks Dave for all the great videos.

author: jeroen79
author_rank: Frequent Contributor
timestamp: February 05, 2016, 09:37:44 am
content: Q1 is an NPN transistor.It will turn on when current flows from the base to the emitter.Therefore the base must be .6V above the emitter.C1 determines how much charge is needed to reach the required voltage.R1 restricts the flow of charge into C1.Together they determine the time needed to reach the required voltage to pass current through Q1's base.R2 restricts the current into the base of Q2 so you don't blow it up.

author: batou
author_rank: Contributor
timestamp: February 06, 2016, 04:56:37 am
content: Hi, thanks for that info! Please excuse my ignorance.So does the cap actually discharge when Q1 switches on, or does it stay charged?
Circuit transformation - Page 1
Forum section: electronics / beginners

author: promach
author_rank: Frequent Contributor
timestamp: April 15, 2025, 08:06:35 pm
content: Could anyone help to come up with transformation mechanism maths from Figure (a) to Figure (b) below.Note: I am a beginner, so be a bit patient with this question.

author: SteveThackery
author_rank: Super Contributor
timestamp: April 16, 2025, 04:43:18 pm
content: Homework question?

author: jwet
author_rank: Frequent Contributor
timestamp: April 16, 2025, 04:47:08 pm
content: I saw you got no responses so I'll try. These types of circuits can be transformed using "Millers" theorem or some derivative.The idea is that when you have feedbacks and gain, miller's theory can be used to split things up and move impedance. The famous example is the common emitter amplifier with a gain of A and an impedance of Z from collector to base. The impedance looking into the base is dominated by the gain and the Z. Miller let's you transform the CB load to input Z from base to ground- here the input Z would be Z/A.I won't solve your particular problem because it looks hard and might be homework ;-) but Miller is the key to the transform as you asked.

author: promach
author_rank: Frequent Contributor
timestamp: April 16, 2025, 05:16:20 pm
content: no, it is not homework problem.By the way, this is a pierce oscillator. Miller theorem will increase the input gate capacitance by gm , but Figure (b) is not showing such.
circuit voltage drop simulator - Page 1
Forum section: electronics / beginners

author: Jbates58
author_rank: Regular Contributor
timestamp: November 16, 2016, 09:11:49 am
content: hi alli am wanting to design a power cuircit and am needing to factor the voltage drop into it for multiple tap out points for multiple loads, the loads and tap out points are at varying distances from eachother, and are all fed from the same supply.i am wanting to know i there is a program that allows me to design the circuit, and then enter the cable properties and the power draws and it will tell me the drops at various tap out points.i have tried to google for something, but all i can find is drop calculators and general design software.any suggestions?Jason

author: Rerouter
author_rank: Super Contributor
timestamp: November 16, 2016, 09:17:36 am
content: I dont believe it exists exactly in the flavour your hoping for,Software like kicad can give you trace length between 2 segments, which you can then throw into a normal calc, or you could even use excel if your only using a few trace widths,Pretty much you would use a normal trace calculator to find the resistance for the length, and then figure out your drop based on that.I do agree functions like this would be nice, however i have yet to see them first hand

author: Ian.M
author_rank: Super Contributor
timestamp: November 16, 2016, 09:27:36 am
content: It would be possible to model the circuit in LTSPICE, entering each wire of each cable as a resistor, with a value given by a user defined function of the wire size and length that calculated the resistance of that wire.

author: Jbates58
author_rank: Regular Contributor
timestamp: November 16, 2016, 09:48:45 am
content: hmmm, i guess i will break out the calculator and do it manually. was just hoping to be able to adjust the parameters more on-the-fly to minimize the calcs.oh well.cheersJason
Circuit works fine attached to power supply, but not battery - Page 1
Forum section: electronics / beginners

author: FIFO
author_rank: Newbie
timestamp: June 08, 2012, 08:20:16 pm
content: I'm running power and serial communication through a really long cat6 cable. When powered using my bench power supply, everything works great, but when I switch to a 12v battery, communication(over serial) starts erroring out pretty badly. I'm just looking for general advice on what to look for, or ways to increase the signal quality.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: June 08, 2012, 09:16:44 pm
content: Do you have a ground connection through the CAT-5 cable? If not, the ground connection may be being made via the power supply.

author: FIFO
author_rank: Newbie
timestamp: June 08, 2012, 09:46:14 pm
content: Originally, I did not use the ground pin on the serial connection. This was no problem with the bench top supply, but as soon as I moved to a battery, communication broke down. I then tried shorting the ground pin to the negative side of the battery, and this did not work either. Then, I connected one of the wires in the cat6 from the circuit to the ground pin, and all was well again.Now, keep in mind, 1 wire is positive, one wire is negative, and now a third wire is from the negative side of the far end of the circuit. Why this works, I didn't understand.So now I switched to battery, and things are still working, great. THEN I connected the actual pc to the battery, and everything broke down. ALSO, I connected the device to another pc and the serial communication would not work either. So the real problem comes from connecting that original pc to the battery. I'm assuming it 'dirties up' the power or ground somehow? How can I test for the problem, protect from it, etc?
Circuitboard printing and designing - Page 1
Forum section: electronics / beginners

author: Undweeber
author_rank: Regular Contributor
timestamp: February 04, 2015, 04:42:22 am
content: hello, I have found some schematics online on various circuit-boards, but problem comes when it comes to executing them, I've seen people on youtube use this waffle board with holes and then just connect the leads under and over, but it seems crude. I found some online services that provided software and what not, but when I came to try it, it would normally be missing resistors, transistors, antennaes... my electronics knowledge is terrible at the moment, but the field is exciting and hope it becomes a hobby.Anyway, does anyone know some simple software where i could design and later a service that could print the board for me? I am talking about simple stuff, nothing major.

author: MrZwing
author_rank: Regular Contributor
timestamp: February 04, 2015, 07:17:03 am
content: Designspark, Eagle CAD are directly hooked up to manufacturer. though you can export and sent to someone who is cheaper in china.then there is Kicad and many other free PCB Cad's out there.both Eagle and designspark has basic components pre-installed and you can import catalogues of components, you can download them at supplies like Farnell, Digikey ect.but look through the tutorials or instructions how to do that since the process is varied depending on witch software.Google is your best friend to find a suitable program to design in.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 04, 2015, 11:50:49 am
content: If it is for simple stuff & learning, the board with holes is pretty much time-tested and recommended

author: Undweeber
author_rank: Regular Contributor
timestamp: February 04, 2015, 06:26:54 pm
content: Thanks MrZwing!@Ice-Tea, that i would rather use for testing, but when i want to actually use it id like it printed
Circuitlab help (transistor Vf changes not applying) - Page 1
Forum section: electronics / beginners

author: antenna
author_rank: Frequent Contributor
timestamp: September 25, 2025, 03:15:47 am
content: I have added a transistor to my circuit and wish to change the Vf of the transistor. When I double click the part and scroll down to V_JE (base-emitter junction built-in potential) and change it to something else, the circuit simulation still shows .7v across the junciton. How can I change this parameter?Thanks!

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: September 25, 2025, 03:30:44 pm
content: You’re talking about trying to change the base-emitter forward voltage (Vf ≈ 0.7 V) of a BJT in a SPICE-based simulator (e.g., LTspice, PSpice, Multisim, etc.) by editing the VJE parameter. VJE (junction built-in potential) is not the forward drop you see when the device conducts in normal operation.That ~0.7 V you’re observing comes from the saturation current (IS) and the exponential diode law in the BJT model: VBE≈nVT/ln(Ic/Is)VJE sets the built-in junction potential for depletion capacitance models, not the forward conduction drop.If you want to change the forward VBE, you need to adjust IS (saturation current) and possibly NE. Open the BJT’s model parameters and look for these parameters like IS, change it to shift the base-emitter forward drop.You can see thishttps://help.simetrix.co.uk/8.0/simetrix/mergedProjects/simulator_reference/topics/simref_analogdevicereference_bipolarjunctiontransistor_spicegummelpoon.htmYou can also explore some other online PCB design services.https://www.theengineeringprojects.com/2020/12/pcb-design-online-services-for-engineering-students.html​
Circuits with certain parts - Page 1
Forum section: electronics / beginners

author: josip.budimir
author_rank: Newbie
timestamp: March 18, 2014, 02:48:19 pm
content: So i have:-potentiometers, range of resistors-0,7V drop diodes-low voltage PNP and NPN transistors-Wide range of electrolytic and ceramic capacitors-Wide range of LED's-7 ohm speakers and an old phone 200 ohm speaker-"budget" inductors-DC power supply for up to 12V-NOchips/microcontrollers-NOAC power supply-Multimeters and sottering eqptThe farthest i've got is a buzzer oscilator, i was wondering if i could do something a bit more complex than that, thx for all the suggestions

author: desai_amogh
author_rank: Contributor
timestamp: March 18, 2014, 03:19:30 pm
content: You can do an Audio amplifier with LEDs as a bar graph display for beats, etc ..

author: mariush
author_rank: Super Contributor
timestamp: March 18, 2014, 03:31:29 pm
content: You can use a couple of npn transistors and a bunch of leds to make the leds flicker/light up on music beatWith a bit of effort you can make some AM (or even FM) radios using those transistors, just google for "transistor am radio" and you'll find various schematics, or look up youtube for the same phrase. You'll need some adjustable capacitors for them but they aren't hard to find (or make)
[SOLVED] CircuitWorks No-Clean Flux Dispensing Pen not working but liquid inside - Page 1
Forum section: electronics / beginners

author: FearTec
author_rank: Regular Contributor
timestamp: November 04, 2020, 09:17:18 am
content: I bought a CircuitWorks No-Clean Flux Dispensing Pen but it is not working, the tip is dry but when I shake the pen there is liquid inside.How can I get this pen working?SOLVED, I just had to push hard on the tip 10x times

author: Electro Fan
author_rank: Super Contributor
timestamp: November 04, 2020, 06:01:19 pm
content: Yes, first time might require more press down; after that depending on how recently you used it the flow might require less press but still some press. There is another current soldering thread in which people are interested in pens vs other flux dispensing methods - so maybe post further about your impressions of pros and cons on flow controllability, convenience, effectiveness, etc.
CircuitWriter Conductive Pen, Heat treatment????? - Page 1
Forum section: electronics / beginners

author: romantronixlab
author_rank: Regular Contributor
timestamp: February 16, 2015, 12:39:05 pm
content: Hi EEV Members,This might be a silly question but have found no answer for it and this might help others.I bought a Silver based CircuitWriter conductive Pen (CAIG) to fix a trace on soon to be lab power supply, that broke because of capacitor fluid leakage (corroded).Now, I have seen how to apply it but the instructions indicates that if it will be soldered on it needs to be heat cured.Well that is the first time I've read something like that. How it is performed? Hot Air Gun, Soldering Iron? What Temperature?The package only indicates to use low heat solder but it does not help.
CISPR standard? - Page 1
Forum section: electronics / beginners

author: generic_username
author_rank: Regular Contributor
timestamp: April 17, 2015, 07:18:49 am
content: Hi, I have a somewhat odd question, maybe someone can help me out.I have a measurement result from an EMC Lab, I wasn't present when the test was made and I wanted to know what kind of Step Size they used for their Measurement, my colleague asked the test engineer the same question and got "according to standard" as a answer (Note that my colleague and I are new to that kind of testing, so naturally I have a lot of questions, as some things confuse me)From what I could find on the net he probably meant the CISPR standard (could't find any free versions of that standard so probably have to buy them to get that information)All I could find on the net that there's a rule of thumb that says bandwidth / 2.Actually looking at the data it seems they used that bandwidth.Also that step size is to low for us to see all harmonics of our signal so is it valid to test with a better step size(I know that sounds like a stupid question, but it seriously confuses me)Hope someone can bring light to my question.cheers.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 17, 2015, 07:53:27 am
content: Around 1%, for the last susceptibility test I sat in on.CISPR 24 is probably the most likely,http://www.yme.gr/getfile.php?id=3028(wonder how long that link will last) but it merely refers to IEC 61000-4 series tests.Tim

author: generic_username
author_rank: Regular Contributor
timestamp: April 17, 2015, 08:19:32 am
content: Thank you for your answer,As we were doing radio interference measurement I think he was referring to the CISPR 16???(my bad didn't think before posting)QuoteSo to get you correctly: if the Bandwidth is 1MHz then the best I could do is 10kHz?cheers.

author: ion54
author_rank: Contributor
timestamp: April 17, 2015, 12:27:25 pm
content: What type of test are you doing? Emissions or Immunity?What type of product are you testing? What is the application? Is it automotive, consumer electronics, communications, medical?Step depends on the frequency range you are investigating.
/CK differential clock?  - Page 1
Forum section: electronics / beginners

author: u666sa
author_rank: Frequent Contributor
timestamp: December 11, 2023, 07:33:46 pm
content: One of the chips requires both CK, clock and /CK differential clock. How to get /CK if I only have a CK signal? Any easy way?https://www.eevblog.com/forum/chat/replace-54-pin-memory-with-66-pin-memory-will-this-possibly-work/
ckt protection if voltage cross +5V - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: May 29, 2015, 10:54:16 am
content: 1. My circuit is powered by +5V. It then runs a MCU with 3.3V (LDO used) & then lcd powered by +5V.2. Now if any case user coonects higher voltage than +5V then it will damage the lcd.3. Is there any way to protect it.4. One way is to place a zener of 5.1V. But usually zener conducts a lower voltage than rated & second its series resistor will limit the current.

author: Ian.M
author_rank: Super Contributor
timestamp: May 29, 2015, 11:01:40 am
content: Google: crowbar circuitN.B. it *MUST* have a fuse, polyfuse or other effective fault current limiter upstream of it.

author: Rerouter
author_rank: Super Contributor
timestamp: May 29, 2015, 11:03:21 am
content: ... if its very low current, you can use a buck/boost capacitor regulator or sepic switcher module, so that it can take in less than or greater than 5V, while still outputting 5V,Or if you want a crude solution, crowbar circuit set to trip on 5.1V, i promise you just about any 5V rail you use would trip it,

author: tron9000
author_rank: Frequent Contributor
timestamp: May 29, 2015, 11:58:20 am
content: yep crowbar circuit with a polyfuse. make sure you select the right working a trip currents for your polyfuse.Do 5V MOV's exist?

author: macboy
author_rank: Super Contributor
timestamp: May 29, 2015, 01:09:13 pm
content: You can use a low dropout 5 V regulator. A quick search found the LP2954 from TI. The voltage drop is only 60 mV at "light loads", which is what the LCD is. So if you put 5V in, you get 4.94 V out, perfectly acceptable. If you put 10 V in, you get 5 V out.
Clamp Meter Auto Ranging OL - Page 1
Forum section: electronics / beginners

author: potatotime
author_rank: Newbie
timestamp: May 15, 2022, 04:48:04 pm
content: I have a cheaper clamp meter and when I'm measuring inrush amperage, when it goes above 50 or 60 A with auto ranging, it will display OL and so I have to redo the measurement by manually setting the range.Do the more expensive clamps like Fluke's have this issue as well or will it adjust the range on the fly and display the measurement?

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 15, 2022, 07:48:10 pm
content: I don't know about other Fluke but I have used Fluke 374, 375, 376 also 381 all of them don't have the problem but that is not because they are better. These models although quite expensive only have 1 single 600A range. So they are not auto ranging at all. They don't have good resolution when I measure something that's only a few Amps.
Clamp meter uni-t 204A doesn't sleep after wake first time - Page 1
Forum section: electronics / beginners

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: November 06, 2018, 12:04:39 am
content: i found a feature or bug in one of my meters, it is the clamp meter uni-t 204A.. the one that is not true RMS... if it enters sleep mode and you wake up with any button it doesn't sleep anymore.... The other meters like bm235, ut139A they enter sleep mode ever ,and after awaken by buttons.It is still on for hours doing the job of discharging the rechargeable NIMH 9V battery... in volts range of course...My question if is this a really a feature or really a bug.This was the original post where i start this subject :https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1943203/#msg1943203

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: November 12, 2018, 11:59:38 am
content: The clamp meter still on during these days... this will allow to test the capacity of the poor rechargeable battery.Does anybody has this model with this feature? I've tried contact uni-t before and got no answer so maybe should i consider the waranty ?Should i post pictures with timestamps?
Clamping a negative voltage supply rail? - Page 1
Forum section: electronics / beginners

author: humidbeing
author_rank: Regular Contributor
timestamp: November 02, 2023, 05:57:40 am
content: I'm designing a low power -5V supply circuit. How do I go about protecting voltage from going too negative? Like if the 7905 failed and decided to let -12V through to the output?Normally, for a positive supply, I would use a polyfuse then a varistor across + and GND. Do varistors work on a negative supply? I googled but couldn't find the answer.Here's an example of what I have so far. (Capacitance not shown).

author: Zero999
author_rank: Super Contributor
timestamp: November 02, 2023, 11:23:06 am
content: Yes, varistors work with either polarity, but a crowbar circuit would be better.

author: humidbeing
author_rank: Regular Contributor
timestamp: November 03, 2023, 04:08:56 am
content: Seems impossible to find crowbar examples for negative supplies.

author: Kim Christensen
author_rank: Super Contributor
timestamp: November 03, 2023, 04:52:23 am
content: Just move the 0V, or ground reference point "to the top":

author: pqass
author_rank: Super Contributor
timestamp: November 03, 2023, 06:30:57 am
content: Or use a TL431 (vs zener) for better control (see attached screenshot andsimulation).To trigger, adjust the pots until 2.5V appears between TL431 ref and anode. The simulator seems to have a problem (keeps tripping after backing-off the pots and clicking RUN/Stop then Reset buttons) so just reload the page for a fresh start.Circuit taken fromhere.You can adapt this to your specific need by placing the triac+fuse before your regulator and the rest (pot+resistor divider, TL431) after your regulator. Maybe even drop the pot for a fixed 1.1k; together with the 1k, the crowbar would trip at about +/-5.4V.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 03, 2023, 01:13:33 pm
content: There is no real difference between a "positive" and a "negative" voltage. It is only a matter of taking some arbitrary point and defining that as a zero or "GND" reference. Often a "logical" zero / gnd reference is chosen, but this is only a convention to make schematics easier to read.
Clamping digital signal for noise protection - Page 1
Forum section: electronics / beginners

author: sean87
author_rank: Regular Contributor
timestamp: September 03, 2018, 04:54:49 pm
content: I have a 5V signal which gets some noise because of a nearby coupling (it is hall sensor signal from a motor and the noise is I beleive the PWM switching into the motor for speed control).These spikes cause unwanted triggering of commutation. I have an RC filter in place but it does not help. The question is...clamping this using a zener diode would help or not? How can I effectively remove the noise you see in the picture?

author: Wimberleytech
author_rank: Super Contributor
timestamp: September 03, 2018, 09:07:49 pm
content: A schematic would certainly help in understanding the fundamental problem here.

author: David Hess
author_rank: Super Contributor
timestamp: September 04, 2018, 01:07:18 am
content: Is it an analog or digital signal?I do not see how simple clamping will be helpful at all. Some advanced analog techniques where fast settling is desired use adaptive clamping for lack of a better term.If the RC filter did not work on your example, then either there is not enough or the noise is actually present somewhere else like the ground.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 04, 2018, 01:17:29 am
content: Don't clamp it, clip it, removing the noise.You then amplify it to the original level.This was how it was done in the old days.
Clamping diodes on passive device? - Page 1
Forum section: electronics / beginners

author: joshuabas
author_rank: Newbie
timestamp: February 05, 2023, 05:27:15 pm
content: Hello!I'm wanting to use theSparkfun Weather Meter Kit, and out of curiosity I was looking at theirArduino Weather Shieldthat can interface with the kit's RJ11 connectors.The Weather Meter is a passive device, and its anemometer and rain gauge are basically just reed switches. By inspecting the associatedArduino code, the reed switch output is pulled up by with the internal resistors; however, I'm wondering what the purpose of the clamping diodes D5 and D6, for example, is? How could the RAIN output ever go below 0V or above 5V?Thank you for your help! I'm wanting to learn why pcbs might be laid out in some ways rather than others.

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2023, 05:38:20 pm
content: Quote from: joshuabas on February 05, 2023, 05:27:15 pmLightning or general EMI on the long wires can generate really high voltages. Diodes and current limiting resistors will protect against that to an extent. They will not be able to help against direct lightning hit, but they will help against induced currents.

author: joshuabas
author_rank: Newbie
timestamp: February 05, 2023, 05:42:04 pm
content: Oooh, that makes sense, given the application. Thanks for responding to my noobie question!

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2023, 05:46:44 pm
content: Note that their schematic is not ideal. It is better to have a resistor right on the input before the diodes, so that the current though the diodes themselves would be limited. I'd just split this 1K resistor into two 51 Ohm resistors one before the diodes and one after.

author: joshuabas
author_rank: Newbie
timestamp: February 05, 2023, 05:52:48 pm
content: And suppose I performed reed switch debouncing in hardware, with a capacitor as shown.Am I right in thinking the the 51Ohm resistor, in addition to limiting current through the diodes as you said, would also limit current going into the reed switch when the capacitor discharges?[ Attachment Invalid Or Does Not Exist ]

author: ataradov
author_rank: Super Contributor
timestamp: February 05, 2023, 06:02:45 pm
content: There are no capacitors here. The reference schematic has one, but not the actual one. And even then it is a 10 pF capacitor, it is basically nothing.You would need debouncing in the firmware for sure, but usually reed switches are better than manually operated mechanical ones. They still bounce though.
clap circuit - Page 1
Forum section: electronics / beginners

author: electronics technician
author_rank: Regular Contributor
timestamp: March 11, 2014, 05:23:39 pm
content: i said i was going to give an up date on this frustrating circuit but i fought with it and won its working and q4 was the problem swapped it out and it s working like a charmfinally

author: sachleen
author_rank: Contributor
timestamp: March 11, 2014, 05:50:57 pm
content: Probably a better idea to keep the updates in theoriginal thread. I had no idea what you were referring to until I looked in your profile for that link.

author: electronics technician
author_rank: Regular Contributor
timestamp: March 12, 2014, 12:12:11 am
content: thanks i will do that next time