hybridfree/eevblog-posts huggingface dataset:
Why is my multitester beeping???! - Page 1
Forum section: electronics / beginners

author: Erwin Ried
author_rank: Regular Contributor
timestamp: March 28, 2014, 01:53:11 am
content: Why is this beeping when I measure something in parallel to a small running dc motor?Bug? Broken? Can anyone test their UNI-T?

author: pickle9000
author_rank: Super Contributor
timestamp: March 28, 2014, 02:20:25 am
content: I don't have one but some meters have a non contact voltage detector built in.

author: VK5RC
author_rank: Unknown
timestamp: March 28, 2014, 02:31:45 am
content: I am guessing but ? back EMF off the motor, it can sometimes be quite high voltage and high frequency so one lead will pick it up, do you have an oscilloscope to see if this is the case?

author: mariush
author_rank: Super Contributor
timestamp: March 28, 2014, 02:32:47 am
content: That motor has brushes which make and break contact lots of times each second. That connecting and disconnecting may cause sparks and high voltages for very small periods of time. That high voltage may be picked up by the non contact voltage detector if the meter has any.

author: Erwin Ried
author_rank: Regular Contributor
timestamp: March 28, 2014, 03:26:42 am
content: Quote from: VK5RC on March 28, 2014, 02:31:45 amYes I have one, but these high "voltages" will not damage it? how do I setup the connections to the scope? exactly as with the meter?

author: VK5RC
author_rank: Unknown
timestamp: March 28, 2014, 03:56:20 am
content: You could make a 'rough and ready' voltage divider with resistors say a 1K in series with 1M (roughly 1000 to 1 reduction) from the active to earth, put the motor across both resistors, the oscilloscope across the 1 K resistor (which should be on the earth side) and start with a 10x probe on the highest scale.Another experiment would be to put a capacitor across the motor and see if that suppresses the beep.
Why is my wein bridge gain setting supply voltage dependant - Page 1
Forum section: electronics / beginners

author: Dan Moos
author_rank: Frequent Contributor
timestamp: June 24, 2023, 10:11:37 pm
content: I have a wien bridge breadboarded with a split supply.My filter network is 10k resistors and 470 nf caps. I get ~36 hz (as expected)My gain is set with a 20k resistor from out to inverting in, and a 7371 lamp in series with my resistor subst. box to ground. I buffer the output withe the other half of the tl072 I'm using.I have the supply set at + and - 2.5vSo if i increment the supply by 100's of millivolts, I have to adjust the gain of the circuit with my resistor box. If I raise the supply. I have to lower the resistor (raise the gain) to maintain oscillation.Why? Shouldn't gain be independent of supply, at least at such low variation in supply? and shouldn't the lamp be dealing with this anyway?

author: Benta
author_rank: Super Contributor
timestamp: June 24, 2023, 10:25:50 pm
content: The 7371 is rated at 12 V, 40 mA. I doubt that a TL072 will drive that. Also, a TL072 will be unhappy operating at just +/- 2.5 V.

author: Dan Moos
author_rank: Frequent Contributor
timestamp: June 24, 2023, 10:33:50 pm
content: QuoteI can't find any detailed data on the lamp as to its low voltage characteristics. Certainly I shouldn't run it at its rated voltage, right?

author: Dan Moos
author_rank: Frequent Contributor
timestamp: June 24, 2023, 10:37:13 pm
content: ok, I just raised my supply to +- 5 volts. The thing is now way more stable withs adjusting the supply. Guess I was just running the opamp to low.

author: Benta
author_rank: Super Contributor
timestamp: June 24, 2023, 10:45:19 pm
content: Quote from: Dan Moos on June 24, 2023, 10:33:50 pmNo, but it should at least be heated. And incendescant lamps have a much lower resistance when cold (5...7 times lower), so it'll draw more current than you might think.
Why is not working with Pseudo GND? - Page 1
Forum section: electronics / beginners

author: SpoNNw
author_rank: Newbie
timestamp: September 30, 2024, 10:52:03 pm
content: Hi, I’m working on a small project to capture EMG signals, and I plan to read them using a microcontroller’s ADC. In a very general overview my setup includes an instrumentation amplifier (AD620ANZ), a second-order bandpass filter to capture frequencies from 20 Hz to 500 Hz, full wave rectifier amp op, and last a peak detector. However, I need a dual-rail power supply (+12V and -12V) to power my ampOps, the ideal solution would probably be using a dual power supply, which I don't have. After doing some quick research, I found that using a voltage divider and a buffer configuration might be sufficient to generate the dual-rail voltage. The issue I'm encountering is that my differential amplifier works perfectly fine with V+ and V- supplied from dual sources of -12V and +12V, along with their respective ground. However, when I apply a voltage divider and a buffer configuration and generate a PseudoGND, something strange occurs in my simulation circuit (LTspice); I might be doing something wrong! I expected to have +12V and -12V connected to the supply terminals, instead it, I'm having -24V at V+ and -48V at V- ! Can someone pls help?https://prnt.sc/i4rFAIj2ZGATDual Supply (Working fine)https://prnt.sc/loR_ikVnlpnkGND configuration

author: ledtester
author_rank: Super Contributor
timestamp: October 01, 2024, 12:39:42 am
content: It would help if you could post the .asc file and the relevant component models.What happens when you just use the UniversalOpAmp model instead of a LM741 for the rail splitter?I have a feeling that SPICE doesn't handle this case very well -- attaching GND to the output of the LM741. I would just attach ground to a more conventional location and subtract the value of PseudoGND from whatever voltage node you want to plot.

author: Zero999
author_rank: Super Contributor
timestamp: October 01, 2024, 12:28:39 pm
content: Yes. It's a problem with the models. The circuit will work.UniversalOpamp doesn't model the supply volage pins and currents. Use UniversalOpamp2, which does.To change it so it approximates the LM741, right click on the symbol and replace the default peramaters with the following:Avol=200k GBW=1Meg Slew=500kIlimit=25m Rail=2 Vos=0.8mEn=0 Enk=0 In=0 Ink=0 Rin=2Meg

author: SpoNNw
author_rank: Newbie
timestamp: October 01, 2024, 01:42:05 pm
content: Yup, I can confirm, it's definitely a problem with the models. It's working now, thanks!https://prnt.sc/lJ2ykn0gpF9RSimulation
Why is silver band in the middle of these 5 band resistors ? - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: April 22, 2018, 04:43:17 am
content: I'm looking at 2 low value resistors that look wire wound around a 2W pink ceramic-finish looking resistorColors to numbers are52silver41 or 14silver25 ?52silver21 or 12silver25 ?So why's silver in the middle ? All the other 5 band resistors I have aren't like that

author: Canis Dirus Leidy
author_rank: Regular Contributor
timestamp: April 22, 2018, 05:12:52 pm
content: Most likely this is not a silver, but a white. The values of 14.9 and 12.9 kOhm exactly meet the E192 series.

author: Twoflower
author_rank: Frequent Contributor
timestamp: April 22, 2018, 05:26:19 pm
content: My wild guess would be that's not the correct answer ans a 2W E192 series doesn't match. Maybe in metrology, but I doubt that this is here the case. Also as Lorvader88 claims to be low resistance.Can you take a decent picture of them and what device they came from?

author: bitwelder
author_rank: Super Contributor
timestamp: April 22, 2018, 08:29:17 pm
content: If the resistors are really low value as you guess, you should be able to measure them decently even if they connected to a circuit.Have you tried that?

author: glarsson
author_rank: Frequent Contributor
timestamp: April 22, 2018, 08:37:03 pm
content: Silver in a band used as multiplier indicates x0.01.Does 0.14 ohm +/-2% 20ppm/K and 0.12 ohm +/-2% 20ppm/K make sense?

author: Brumby
author_rank: Unknown
timestamp: April 23, 2018, 03:22:41 am
content: Quote from: glarsson on April 22, 2018, 08:37:03 pmThis was my first suspicion as well.QuoteI'll second this.Quote from: bitwelder on April 22, 2018, 08:29:17 pmPlease do this and let us know.Even in circuit, the answer will be helpful.

author: lordvader88
author_rank: Frequent Contributor
timestamp: April 23, 2018, 06:46:39 pm
content: Quote from: glarsson on April 22, 2018, 08:37:03 pmYeah silver for 0.01x for sure,The 52silv21 reads as 0.20 or 0.27, it moves a lot. There r 2 in parallel are between negative of a 4pin rectifier, and GND-ref of the tank cap, for almost everything else HS on a CX600W SMPS.the 52sil41 started at 0.60 and quickly dropped to 0.02 and shorting my BM869 gave 0.03 atm.Could they be inductors ? There are beefy NTC thermistors or something right before the main tank cap, IDK maybe it's more inrush current limiting ?
Why is stranded wire more flexible than solid? - Page 1
Forum section: electronics / beginners

author: piguy101
author_rank: Regular Contributor
timestamp: August 13, 2017, 01:57:55 pm
content: This is mostly a question out of curiosity. Stranded wire is more flexible than solid core for the same wire gauge. Since they have the same cross sectional area of copper, why is stranded easier to bend? I couldn't seem to find anything on the Internet that discusses why mechanically stranded is more flexible.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 13, 2017, 02:26:56 pm
content: Think about bending itself. If you have a rectangular cross-section, which direction is it easiest to bend in?Now consider: how many times easier is it to bend in that direction?If the rectangle is 1x2, say (like a 2x4, or 50x100 in the rest of the world), about how much easier is it to bend? Like, a lot, like four times, not just twice.And it's still harder to bend than two 2x4s stacked, i.e. a 4x4 without nails holding the 2x4s together.What is bending? It's compression on the inside and stretching on the outside. The outer curve physically stretches to a greater length. Two 2x4s nailed together, and deflected to the same angle as a single one, means the outer one is stretched as a whole -- because it's entirely along the outside -- while the inner one is all in compression, for the same reason! Just bending a single 2x4 only compresses and stretches half and half of the single 2x4. A pair laying together (but not bonded) both bend on their own, and there is sliding on their touching faces.So what's the deal? Thebending momentis proportional to distance from the centroid (the point were there is neither tension nor compression). The springiness of the material acts at this moment, too. That is: if a point on the beam is strained by so-and-so percent, it pulls proportionally. But that pull is already proportional to the moment, so the stiffness of the beam as a whole goes as widthsquared!TL,DR: solid wire has to bend a big fat hunk of metal, while strands can slide past each other.Tim

author: piguy101
author_rank: Regular Contributor
timestamp: August 13, 2017, 07:38:59 pm
content: T3sl4co1l, actually that makes a lot of sense. I forgot about the bending moment being proportional to the distance from the centroid and the possible sliding effects of the individual strands. Thanks for satisfying my curiosity.

author: Brumby
author_rank: Unknown
timestamp: August 14, 2017, 11:55:51 am
content: Quote from: T3sl4co1l on August 13, 2017, 02:26:56 pmI would have gone down that path.
Why is the advantage of using VRM doublers in PC motherboards ? - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: March 23, 2023, 02:45:55 pm
content: According thispage:QuoteIf I understand correctly : you need to double the number MOSFETs and chokes.If it's the case, why not use a "true" multi-phase system (eg: why 3*2 would be cheaper than 6 if you still need to double everything).There is probably something I am missing.EDIT : thispagealso give useful info.It looks like using doublers halves the frequency (so putting to 2 times less stress on each phase).

author: amyk
author_rank: Super Contributor
timestamp: March 24, 2023, 03:05:15 am
content: Doubling is used to get more phases than the PWM controller has. A 3*2 wouldn't make sense, because 3-phase controllers are common.

author: mariush
author_rank: Super Contributor
timestamp: March 24, 2023, 04:42:54 am
content: A lot of manufacturers these days stopped using doublers and just paralleled two power stages and their inductors and capacitors.A 8 phase controller + doublers can be cheaper than a 14-16 phase controller and also some smaller controllers could be more flexible ... for example that 8 phase controller could be run in 6+2 or 6+1+1 modes and save another vrm controllerIt may also be more advantageos for the manufacturer to stock on the 8 phase controller in huge volume and reuse it across a wide range of boards, while using a higher phase controller only on premium expensive models.

author: barshatriplee
author_rank: Regular Contributor
timestamp: April 03, 2023, 02:22:52 pm
content: This vid may interest you too:
Why is the LED lit with these transistor logic gates? - Page 1
Forum section: electronics / beginners

author: harnon
author_rank: Regular Contributor
timestamp: April 08, 2019, 04:06:39 am
content: I'm guessing this is a fairly obvious question... I've soldered together a simple AND logic gate circuit using two transistors, but when I open the first switch and close the second the LED unexpectedly comes on - see the first attachment. Transistors are BC547s. I can add a pull down resistor between the two transistors to prevent this, so I'm assuming its something to do with the voltage between the two transistors floating.Running a simulation shows that the voltage between the two transistors is 2.5V with both switches open (second diagram), which seems to show the transistors are acting as a voltage divider between +5V and GND. When I close the second switch only, the voltage drops to 1.55V (20mA above the LED voltage).It looks like current is flowing from base to emitter of the second transistor to power the LED, however from what I read the BE junction can be treated as a Zener, with a breakdown voltage of 6V (according to the datasheet). As my voltage is well below this breakdown, where does the current to supply the LED come from?

author: oPossum
author_rank: Super Contributor
timestamp: April 08, 2019, 04:10:17 am
content: The LED & resistor should be on the high side between the +5 supply and the top transistor. The emitter of the bottom transistor connected to ground.

author: vk6zgo
author_rank: Super Contributor
timestamp: April 08, 2019, 04:42:11 am
content: Quote from: harnon on April 08, 2019, 04:06:39 amA Zener has a reverse biased junction.The BE junction is forward biased, & will have a voltage drop of about 0.6v.

author: Nerull
author_rank: Frequent Contributor
timestamp: April 08, 2019, 05:30:46 am
content: You have about 270 microamps flowing through the base to emitter junction of the transistors when the switchers are closed. This is plenty to light a led.Moving the led to the high side would prevent the base current from lighting the led.Remember that the entire function of a transistor depends on the current flowing through the base to emitter junction. If the voltage you were using wasn't enough to conduct through this junction than your transistors would never work at all.

author: harnon
author_rank: Regular Contributor
timestamp: April 08, 2019, 05:34:00 am
content: Thanks for the replies.Quote from: vk6zgo on April 08, 2019, 04:42:11 amOh, I see - the diode is the opposite polarity to what I had in my head. That makes sense, thanks.

author: amyk
author_rank: Super Contributor
timestamp: April 09, 2019, 12:22:20 am
content: Hint: the arrows in transistor symbols point exactly the same way normal diodes do.Your simulation doesn't seem to make sense --- what type of (visible light) LED has <1.5v forward voltage?The others have pointed it out already, but in summary, the LED is being lit by the base current.
Why is the RSC resistor needed to sample the choke current in the system? - Page 1
Forum section: electronics / beginners

author: akea
author_rank: Newbie
timestamp: May 05, 2019, 09:12:03 am
content: Hello guys. Can u pls tell me Why is the Rsc resistor needed to sample the choke current in the system? Thank you

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 05, 2019, 09:32:20 am
content: Thesystem?Tim

author: akea
author_rank: Newbie
timestamp: May 05, 2019, 09:47:35 am
content: in converter

author: soldar
author_rank: Super Contributor
timestamp: May 05, 2019, 09:56:16 am
content: Quote from: T3sl4co1l on May 05, 2019, 09:32:20 amThe code.

author: akea
author_rank: Newbie
timestamp: May 05, 2019, 01:30:12 pm
content: Anyone knows Why?

author: mikerj
author_rank: Super Contributor
timestamp: May 05, 2019, 02:07:09 pm
content: No one has any idea what you are talking about, you haven't even described thesystemyou are referring to.

author: akea
author_rank: Newbie
timestamp: May 05, 2019, 03:25:15 pm
content: sorry about it. i have just uploaded the system

author: mikerj
author_rank: Super Contributor
timestamp: May 05, 2019, 05:23:04 pm
content: The circuit seem to be incomplete, there is no inductor (choke) shown.The device block diagram looks like an MC34063 switching regulator, is that correct? If so the resistor is used to provide current limiting, if the voltage drop across the resistor is greater than 300mV the duty cycle will be reduced to lower output voltage and hence lower the current. Without current limiting an accidental short on the output could destroy either the regulator or the load.

author: akea
author_rank: Newbie
timestamp: May 05, 2019, 05:51:33 pm
content: Yes its correct.Thank you very much
Why is the voltage across my load so far off from the 3V zener diode “regulation - Page 1
Forum section: electronics / beginners

author: renzoms
author_rank: Regular Contributor
timestamp: October 13, 2019, 02:44:36 am
content: I used a 3V .500W Zener diode 1N5225B for it's voltage regulating abilities. Here is a link to a 47s video including schematics, results, and explanations in voice.The circuit is Vin, a resistor in series with the Vin (330 ohm), and then the 3V Zener diode and a load (resistor) in parallel.The Vin ranges from 5V to 9.6V. The load ranges from 330 ohm to 3300 ohm to 33000 ohm. The maximum expected voltage "differentiation" (how far the measured results are from the expected results) is .39V.For the 3300 ohm and 33000 ohm load the expected result is 3V at 9.6V Vin and 2.61V at 5V Vin. The measured results are 3.01 V, 2.58 V, 2.99V, and 2.61V, respectively. Great!For the 330 ohm load, the results are 2.81 V and 2.16 V.Why are the measured results so far from the expected results for the 330 ohm load?https://youtu.be/f6LKJ-PjRwk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 13, 2019, 02:49:58 am
content: Low voltage zener diodes (under 5V) have a very soft characteristic. You need to run it at a lot of bias current to stay close to the rating (note it's measured at 20mA).Tim

author: Gyro
author_rank: Super Contributor
timestamp: October 13, 2019, 09:55:50 am
content: You might find that you get better regulation with a series chain of 4 forward biased silicon diodes instead.Alternatively, you could go the whole hog and use a 3V low-dropout linear regulator. It would be more power efficient than a zener shunt too.

author: w2aew
author_rank: Super Contributor
timestamp: October 14, 2019, 04:18:57 pm
content: As @blueskull and others have mentioned, low voltage zener diodes have a fairly soft knee in the IV characteristic due to the zener effect. Higher voltage zeners are actually much sharper due to the avalanche effect. I did a video on zeners that you might be interested in. In particular, check out the curve tracer results starting at about 11:45 in the video:

author: SeanB
author_rank: Super Contributor
timestamp: October 14, 2019, 05:59:41 pm
content: A cheap reasonably good 3V zener is a blue or white LED, though it has a rather soft knee it is a lot sharper than most zener diodes at low current, and also makes a handy power on indicator, though you are best keeping it shadowed from light, as it also can be a photoelectric generator as well.
Why is the voltage mode control Buck converter isotope triangle wave better for  - Page 1
Forum section: electronics / beginners

author: PCBindex88
author_rank: Newbie
timestamp: March 11, 2019, 07:51:15 am
content: The control circuit of the voltage mode control Buck converter adopts a PWM control mode, and the output voltage and the reference voltage Vref generate a control signal vcon via an error amplifier. Since the horizontal width and height of any point on the sawtooth wave are linear, when compared with the control voltage vcon, a pulse u having a width proportional to the amplitude of the control voltage can be obtained. When the input voltage fluctuates or the load changes, the closed-loop negative feedback maintains the stability of the output voltage by changing the duty ratio of the control signal u.Like the sawtooth wave, the isosceles triangle wave can also be used as the PWM control drive signal. Through simulation and experiment, I found that the converter system is more stable when the isosceles triangle wave is used for PWM control than the sawtooth signal.What is the reason for this?

author: David Hess
author_rank: Super Contributor
timestamp: March 11, 2019, 02:04:31 pm
content: In practice I have never noticed a difference but for the same frequency, the triangle wave has a slope twice as great so noise at the comparator input produces half of the timing variation per edge. However since there are two comparator edges instead of one and the noise is uncorrelated, the timing variation will be 1/Sqrt(2) instead of 0.5 (one half).I doubt the above difference caused what you found though.

author: adamcord
author_rank: Contributor
timestamp: March 11, 2019, 03:56:54 pm
content: That's an interesting observation, but what exactly do you mean when you say the system is "more stable"?

author: David Hess
author_rank: Super Contributor
timestamp: March 11, 2019, 04:44:00 pm
content: Quote from: adamcord on March 11, 2019, 03:56:54 pmI mean with the greater slope of the triangle wave, the PWM signal has less jitter even though two edges are contributing noise instead of just one with a saw-tooth. But like I said, this should be insignificant compared to other sources of noise.Switching power supply controllers typically use a saw-tooth for ease of implementation reasons and because the reset time of the saw-tooth is an easy way to generate fixed dead-time.

author: adamcord
author_rank: Contributor
timestamp: March 11, 2019, 07:40:19 pm
content: Thanks for the details, but my question was in response to the original post. I'm fairly new here, did I reply incorrectly?

author: David Hess
author_rank: Super Contributor
timestamp: March 12, 2019, 03:21:38 am
content: Quote from: adamcord on March 11, 2019, 07:40:19 pmYou did not quote what you were responding to so it was not clear.
Why is there a connection to ground in this RJ45 jack schematic ? - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: June 18, 2020, 05:42:02 pm
content: Why is the center tap of the transformer "connected" to ground with a capacitor in between ?Would the transmition of data still works without that connection (with some drawbacks) ?The capacitor is rated 2KV which is far more than voltage that what goes in a RJ45 cable.AFAIK the transformer is to provide some galvanic isolation between the two devices (eg: the RJ45 cable could connect two buildings with that have potential difference)

author: AndyC_772
author_rank: Super Contributor
timestamp: June 18, 2020, 07:28:37 pm
content: You're quite right that the transformer is there to provide isolation, which is a required part of the Ethernet spec.The capacitor to GND is there for EMC. Connecting it to a locally quiet ground means there is zero common mode component on each of the differential pairs, and if the differential components cancel (as they should, in theory), that results in minimal emissions from an unshielded cable.It's rated 2kV in order to match the dielectric strength of the transformer; this rating is chosen so as not to expose the user to a shock hazard if the cable is shorted to the mains supply.
Why is there a resistor across those bridge rectifiers ?  - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: November 06, 2023, 09:32:52 pm
content: I came across this schematic (power supply of a old Pinball). This is the secondary side of the main transformer :What is not clear to me :- Why do we have a resistor across some of bridge rectifiers ? Is it to protect them ? I would have say this to discharge some caps but that part is used to power the left and right flippers coils directly.- Additionally, one of there is (AFAIK) a variable resistor. Is it used for some kind of tuning (since it's not self regulated, unlike a SMPS)

author: Whales
author_rank: Super Contributor
timestamp: November 06, 2023, 09:44:25 pm
content: Best I can think of is that maybe the diodes were getting fried by inductive kickback from the flipper coils? Perhaps the few K resistance is much better than the many megaohms a backwards diode looks like. But there are better ways of doing this.No the diodes in their existing config will handle anything that arcs through the switch/contacts.

author: Floopy
author_rank: Regular Contributor
timestamp: November 06, 2023, 09:47:09 pm
content: My guess would be to provide a very crude way of regulating voltage. The variable resistor can adjust your peak output. Someone is bound to correct me though, just taking a guess. Is it just a coil connected to it? Or is there some switching occurring in between. Is it an analogue switch? Relay? Transistor?

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 06, 2023, 09:54:48 pm
content: It's just a minimal load to keep the output at a safe level.Transformers can reach way higher voltages than nominal in open circuit, a 12V secondary could easily output 18-24v.The varistor provides further protection, as it's resistance decreases with voltage, thus increasing the load as the voltage rises.

author: tigrou
author_rank: Regular Contributor
timestamp: November 06, 2023, 09:56:50 pm
content: Quote from: Floopy on November 06, 2023, 09:47:09 pmHere is the link to the fullschematic(page 49). That file is available publicly that is why I included it here.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 06, 2023, 09:57:44 pm
content: Why are there red boxes on your schematic?They obfuscate both the RefDes and the values of those resistors.Also, VR1 is not a resistor.

author: tigrou
author_rank: Regular Contributor
timestamp: November 06, 2023, 10:08:07 pm
content: Quote from: Doctorandus_P on November 06, 2023, 09:57:44 pmSorry about that. I have uploaded a new picture.

author: Veteran68
author_rank: Frequent Contributor
timestamp: November 06, 2023, 11:44:47 pm
content: Quote from: Doctorandus_P on November 06, 2023, 09:57:44 pmI was waiting for someone to call that out. I was about to.
Why is there no voltage at the drain of the mosfet when in DC mode - Page 1
Forum section: electronics / beginners

author: tastychickenwings69
author_rank: Newbie
timestamp: March 03, 2022, 07:12:25 am
content: Hi.I have a normal Mosfet Switch which is turned on by VDD with a resistor.Can someone explain why there practically no voltage present at drain of the mosfet if the gate is turned on with DC?If the switch turns on via pwm signal there is 12V but with DC its only 10mV.I get that there is still full current and power at RD but I dont get why theres no voltage.

author: ledtester
author_rank: Super Contributor
timestamp: March 03, 2022, 08:56:35 am
content: When the gate voltage is low, the MOSFET becomes a very high resistor. In the diagram below I made a 1 gigaohm resistor -- essentially it is an open circuit. The voltage at OUT is then +12V.When the gate voltage is high enough the resistance between the drain and gate will be very small (less than 1 ohm and usually a lot lower). This will pull the output voltage close to ground -- it's just voltage divider with a very small lower leg. You'll find a more in-depth explanation of how to analyze voltage dividers here:https://learn.sparkfun.com/tutorials/voltage-dividers/QuoteIf the gate is driven by a separate PWM signal then output will oscillate between +12V and 0V.
Why is there no voltage on this winding tap? - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: August 24, 2018, 03:01:25 am
content: I'm checking an unknown transformer from an old 1970s TV, about a 1kg / 2lb, ~3"x3"x1.5" coreThere's 3 windings total, and on the 3rd with 5 wires I measured these resistancesBlk-Blk/Grn 2.16RBlk-Grn 7.72RBlk-Grn/Wh 7.76RBlk-Grn/Red 45.7RThen with 120V on the primary something seems wrong on the 3rd windingBlk-Blk/Grn 19.8VBlk-Grn 17.3VBlk-Grn/Wh 22.4VBlk-Grn/Red only 0.026Vac ?? , no DC at allIt's not getting hot yet, no smoke or smell at all. So whats going on, also I'm curious why the 1st pair is so close to the 2nd/3rd pair. Do they use different wire gauge between the taps ?I measured inductances too, they seemed normal enougheditok the Blk-Grn/red was only 1.1mH whereas the others were 94mH, 71mH, 121mH

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: August 24, 2018, 04:12:22 am
content: My guess: Shield winding to block electrostatic coupling between primary/secondary.

author: Jwillis
author_rank: Super Contributor
timestamp: August 25, 2018, 09:39:58 pm
content: I'm not understanding what your trying to do.Why are your taking measurements of a transformer with a DC setting on your multi meter.Transformers alone CANNOT convert AC to DC or DC to AC; they cannot change the voltage or current of DC; they cannot change the AC supply frequency. An alternating current (AC) in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings.Do your voltage measurements of a transformer in AC setting only Never in DC .It just leads to confusion .Taking inductance measures is pointless on a transformer.Taking resistance measurements is only relevant to check continuity of the coils.The values are mostly meaningless.Every transformer will have an inherent capacitance..Unless you plan on calculating the total losses of the transformer taking these measurements gives no meaningful values.If your looking at a Line Output Transformer (LOPT) / Flyback (FBT) here's a typical schematic
Why is this buck converter frying? - Page 1
Forum section: electronics / beginners

author: publicBETA
author_rank: Newbie
timestamp: September 28, 2021, 04:00:06 pm
content: I am trying to implement a 5V fixed buck converter, the XL1509-5.0E1, running off an appliance that has a 24VAC (500ma fused) transformer output.I've laid the circuit out according to the data sheet as far as I can tell, but the IC fails after applying power.It is failing by shorting the input to ground, blowing the fuse on the AC side.First attempt it failed immediately, second attempt it failed after 3 power cycles.Inductor :https://www.lcsc.com/product-detail/Power-Inductors_YJYCOIN-YNR6045-680M_C341069.htmlSchottky D1 :https://www.lcsc.com/product-detail/Schottky-Barrier-Diodes-SBD_Guangdong-Hottech-SS34A_C183891.htmlC1 and C2 :https://www.lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_ROQANG-RVT1H470M0607_C72523.htmlXL1509 Datasheet :http://www.xlsemi.com/datasheet/XL1509%20datasheet.pdfI've attached the schematic and board layout.What might be causing this?

author: thinkfat
author_rank: Unknown
timestamp: September 28, 2021, 04:22:39 pm
content: Diode on the wrong side of the inductor. Also, no bulk capacitor at the input. That will not work.EDIT: page 3 of the XL1509 datasheet has a sample schematic. I suggest you stick to it.

author: tunk
author_rank: Super Contributor
timestamp: September 28, 2021, 04:27:44 pm
content: Wouldn't really know, but the output from the MB6S is rectified but not smoothed.You could try a ~680uF capacitor after the MB6S.

author: publicBETA
author_rank: Newbie
timestamp: September 28, 2021, 10:47:04 pm
content: Ugh, thank you. Wiring the diode properly has fixed it. Smooth brain moment.
why is this error in this arduino program? - Page 1
Forum section: electronics / beginners

author: rizlesz2000
author_rank: Contributor
timestamp: October 18, 2023, 10:30:13 am
content: So in this program It actually uses a SSD1306 oled library. But when i change it to the sh1106 library, it shows me this errorC:\Users\sonid\OneDrive\Documents\Arduino\libraries\Adafruit_SH1106-master\Adafruit_SH1106.cpp:29:10: fatal error: avr/pgmspace.h: No such file or directory#include <avr/pgmspace.h>^~~~~~~~~~~~~~~~compilation terminated.exit status 1Compilation error: exit status 1and in this program if we enable bluetooth library and its functions, The bluetooth option appear on the project. but when i did that it showed me other errorsyes, im using ESP32C3 xiao

author: Ian.M
author_rank: Super Contributor
timestamp: October 18, 2023, 11:02:04 am
content: Seems like that library is AVR specific. Are you up for porting it to ESP32? (not an easy task for anyone who hasn't taken a deep dive into cross-compiling low level embedded applications with GCC, and isn't very familiar with the AVR and ESP32 documentation)

author: Shonky
author_rank: Frequent Contributor
timestamp: October 18, 2023, 11:07:31 am
content: Maybe something like this:https://github.com/SodaqMoja/Sodaq_DS3231/issues/5

author: rizlesz2000
author_rank: Contributor
timestamp: October 18, 2023, 11:15:46 am
content: i found a sh1106 library which can make compatable with esp32 chips but still gives me the errors. what should i need to change in the program?

author: tunk
author_rank: Super Contributor
timestamp: October 18, 2023, 11:50:23 am
content: What errors? And what library and what program?

author: rizlesz2000
author_rank: Contributor
timestamp: October 18, 2023, 02:02:20 pm
content: i used this library (https://github.com/koogar/Adafruit_SH1106_ESP32). but gave me other errors such as: did you mean this or that

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 18, 2023, 07:21:19 pm
content: Try changing the angle brackets to quotes

author: Manul
author_rank: Super Contributor
timestamp: October 18, 2023, 08:49:11 pm
content: Of course it can't find path <avr/pgmspace.h> if you are compiling for ESP32 (which is not AVR).Code:#ifdef __AVR__#include <avr/pgmspace.h>#elif defined(ESP8266) || defined(ESP32)#include <pgmspace.h>#else#define pgm_read_byte(addr) (*(const unsigned char *)(addr))#endifAbove are the first lines of Adafruit_SH1106_ESP32.cpp you linked. Have you even read it? You need to define ESP32 in your compiler, then it will include the correct header <pgmspace.h> and not <avr/pgmspace.h>.

author: rizlesz2000
author_rank: Contributor
timestamp: October 19, 2023, 01:39:53 am
content: So, I should add it to the first lines of the code. Right?

author: Helicoidee
author_rank: Newbie
timestamp: July 11, 2025, 10:27:16 pm
content: I had a similar error message on MacOs 15.5 - Arduino 2.3.6 - Esp32s3 - WaveShare LCD Screen.The solution that worked for me was to replace #include <avr/pgmspace.h> with #include <pgmspace.h>
Delete Delete Delete - Page 1
Forum section: electronics / beginners

author: The_Almighty_Bacon_Lord
author_rank: Contributor
timestamp: July 16, 2016, 01:27:21 pm
content: Delete Delete Delete

author: Andy Watson
author_rank: Super Contributor
timestamp: July 16, 2016, 01:42:53 pm
content: The limitation is probably due to the choice of the value of the inductor. Higher voltage means that the current in the inductor will rise quicker - the regulator IC must be able to react fast enough to control that current, i.e. turn-off. The value of the inductor has probably been chosen to optimise other operating parameters - allowing for a high voltage input would be a compromise too far. You would have to reverse-engineer the schematic know for sure.

author: Audioguru
author_rank: Super Contributor
timestamp: July 16, 2016, 01:46:30 pm
content: It is Chinese and it is cheap. Then maybe its parts are poor copies of the real ones. Maybe its parts are rejected real ones that fail at more than 30V.Maybe its heatsink is big enough to cool its hot parts at 10A only if the voltage is at 30V or less. Try 38V input but a load current of no more than 7.9A.

author: Brumby
author_rank: Unknown
timestamp: July 16, 2016, 03:15:41 pm
content: It could be because of circuit design where the choice of components means something would exceed some parameter in it's SAO ... or it could be something as stupidly simple as the manufacturer having a bucket load of 35V caps and they limited the circuit to 30V so they could use them.The bottom line is - just because a componentcanhandle a range of parameters doesn't mean it will always be used to those limits.I'll go for a thermal limitation. (Cheap heatsink with questionable mounting.)
Why is this PCB wifi antenna shorted to the ground? - Page 1
Forum section: electronics / beginners

author: dusan
author_rank: Regular Contributor
timestamp: January 03, 2023, 07:54:54 am
content: In this image on the right the wifi pcb trace antenna is connected to the ground. That makes no sense.How does it supposed to work. If I want to extend the range can I connect wire to that squiggly part? Should I cut the ground short then?

author: Psi
author_rank: Super Contributor
timestamp: January 03, 2023, 08:05:55 am
content: No don't cut it, that is correct for that type of antenna.It's kinda like a termination resistor at the end of a transmission line. It's a short for DC but not for AC at 2.4Ghz.There's a reason people say RF is black magichttps://electronics.stackexchange.com/questions/365512/why-do-some-pcb-antennas-have-a-return-path-to-ground

author: ataradov
author_rank: Super Contributor
timestamp: January 03, 2023, 08:28:56 am
content: This is called Inverted-F antenna. Here is some basic description -https://en.wikipedia.org/wiki/Inverted-F_antennaThere is no good way to connect external antenna directly without modifying the matching network. And that is not easy to do without measurements. Your best bet is to find a module with a connector for an external antenna, they are readily available.

author: Terry Bites
author_rank: Super Contributor
timestamp: January 04, 2023, 06:08:32 pm
content: Its a short at DC but in the GHz its part of the antenna tuning.

author: golden_labels
author_rank: Super Contributor
timestamp: January 05, 2023, 01:31:21 am
content: I’m not the right person to explain this in detail: high frequency is something I do not know well enough. But the general idea here is that every conductor and groups of conductors have non-zeroreactance. Because it is minuscule and at low frequencies its effects are negligible, in such circumstances it is being ignored. But at higher frequencies the effects can no longer be ignored. Instead, they are used as a part of the circuit. At high frequencies electromagnetic coupling can’t be ignored either. That gives rise to thedistributed-element model.In other words, what seems to you as a short, at high frequency is probably an inductor used for impedance matching.

author: coromonadalix
author_rank: Super Contributor
timestamp: January 05, 2023, 06:30:46 am
content: Same herei work with rf stuff, at dc you have an short equivalent, but at 1Mhz it's another thing ...i use an ohm meter to check continuity and 0 Ohms for me tells the circuit is okay loll

author: Faranight
author_rank: Unknown
timestamp: January 05, 2023, 06:42:47 am
content: Jesus came to me in revelation when I figured out that resistance and impedance are two different things.Now that I have reached enlightenment, I have become proficient in using black magic! I understand RF!
Why is this PFET behaving like this? (conducting continuously >6-7v) - Page 1
Forum section: electronics / beginners

author: Odd
author_rank: Regular Contributor
timestamp: September 26, 2024, 09:58:07 am
content: Vin is +5...30v (relative to GND)Vout is the output of this voltageCTRL is pulled to GND when "on"if Vin is about 5v, it works as expected. if Vin is 8v or higher, the PFET remains on all the time.Also: at 5V 5A the voltage drop between D and S is 240mV at 10v 5A it is 210mV I do not see an easy way to improve on thatFET datasheet:https://www.lcsc.com/datasheet/lcsc_datasheet_2208260930_Vishay-Intertech-SQA405EJ-T1-GE3_C5143597.pdfWhat is going on here? (with the FET conducting at >5v)

author: newbrain
author_rank: Super Contributor
timestamp: September 26, 2024, 11:55:40 am
content: Quote from: Odd on September 26, 2024, 09:58:07 amHow much is Vcc and where does CTRL comes from?If CTRL is a GPIO pin from a microcontroller, it'll have a clamping diode with the cathode towards Vcc (or 3.3 to 5 V, in any case).So, when Vin is greater than Vcc, the clamping diode, fed by R66, start conducting and Vg becomes Vcc + Vdiode, so (for Vcc = 5 V), ≈5.7 V (probably even less, given the very low current).Vgs = Vg - Vs = 5.7 - 8 = -2.3 VThe negative polarization of the gate will strart bringing the PFET in conduction, deeper and deeper as Vin raises.To drive it from a 0-5 V (or 0-3.3 V) logic level, you need to interpose an NFET, and invert the CTRL signal.

author: Odd
author_rank: Regular Contributor
timestamp: September 26, 2024, 12:52:12 pm
content: Thank you, you did understood it right away- yes, it is a STM32 MCU. driving using 0-3.3v.changing the polarity of "on" signal is no problem.I wish to switch the positive side.Would you by any chance know where i can find a example of how to efficiently switch high-side(up to 30v) using an NFET, , where the control signal is 0-3.3v ?

author: newbrain
author_rank: Super Contributor
timestamp: September 26, 2024, 01:03:26 pm
content: You need both an NMOS (or an NPN BJT!) and a PMOS, unless you resort to gate driver ICs - sorry if I wasn't clear!See, for example, the discussion here:https://www.eevblog.com/forum/projects/p-channel-mosfet-as-a-gpio-controlled-high-side-switch/
can I convert this unusual tube output stage more suitable to a guitar amp - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: February 05, 2020, 11:06:49 pm
content: can I convert it to a guitar preamp by connecting r14 to ground not the feedback loop, removing c10 and c11, swapping 6n1n-EB tubes for a bit more output, changing R6 to a 47k pot with a 10k in series, swapping C3 for a 20uF and putting a 22k pot in series, swapping the coupling caps for something with less value and putting 1 or 2 gain stages in front of the amp?the output transformer is drawn weird but I found a website that listed the turns of wire for the taps and it seems it's symmetrical between the 2 sides.http://www.chipinfo.ru/literature/radio/197107/p31-34.htmlalso, I thought about connecting 5 (on the PSU) to the end of the bridge not after a dropping resistor. this would source about 340V (with load) + the 240 line voltage not 220. so basically it will source about 360v on the plates. but EL90's OR EL84's can only hold 250 volts. I don't think even new ones can hold about 110volts more.so I'll probably not do that.also, I think removing C6 would not hurt, it's basically useless AFAIK.and disconnecting U3, U1, U2 boards. since I won't ever be using it originally again and it's too far destroyed to try to fix those boards.pretty much I'm only after the output stage.and I'll disconnect 1 of the heaters from the ground and put a 300 Ohm pot between the heater to ground.maybe I'll even connect it to another heater lift divider but that, probably later.also probably gonna remove everything for L1 tube also cause that's useless for me even if I use it as a volume indicator.[ Attachment Invalid Or Does Not Exist ]

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 05, 2020, 11:09:42 pm
content: I'm not in lamp schematics just want to say that it will be easier to somebody to help you if you place a schematics you ask about right here.
Why isn't this circuit working? - Page 1
Forum section: electronics / beginners

author: rexxar
author_rank: Frequent Contributor
timestamp: June 16, 2014, 04:50:34 am
content: So I tried to build a little constant current/constant voltage supply to charge a lithium battery. Individually, the CC and CV sections work as expected. Originally I used an Arduino to read the voltage and switch to CC or CV, but I wanted to try to do the same thing with a voltage comparator.So I'm using one comparator to switch the CC section in, and another set up as inverting to switch CV mode. For some reason the comparators both output the same voltage, and never go above 0V.I've got diodes in there because I got negative voltage leaking from collector to base, and because sometimes the opamp would output negative voltages while the transistor was on. I'm using an LM358 opamp and an LM339 comparator.I'm sure I've done something terribly wrong, but please don't throw things, I just came up with this off the top of my head!

author: edavid
author_rank: Super Contributor
timestamp: June 16, 2014, 05:21:17 am
content: Your first problem is that the LM339 has an open collector output.

author: w2aew
author_rank: Super Contributor
timestamp: June 16, 2014, 01:56:52 pm
content: Quote from: edavid on June 16, 2014, 05:21:17 amIn other words, you need pull-up resistors on the LM339 outputs.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 16, 2014, 02:08:11 pm
content: Quote from: edavid on June 16, 2014, 05:21:17 amAnd your next problem will be the operation of the PNP transistors - they turn on with current leaving the base - which is at odds with the diodes. But, with a little thought it should be possible to make use of the open collector output of the LM339 to remove the PNP transistors and four diodes.

author: rexxar
author_rank: Frequent Contributor
timestamp: June 16, 2014, 02:47:18 pm
content: Quote from: Andy Watson on June 16, 2014, 02:08:11 pmOops, those are supposed to be NPN transistors, I used the wrong symbol.Quote from: edavid on June 16, 2014, 05:21:17 amThat would explain it then. I dunno why I just assumed it'd operate like an opamp. I'll try again when I get home from work. Thanks, guys.
Why it works - External PSU with ground unattached? - Page 1
Forum section: electronics / beginners

author: Robert M
author_rank: Newbie
timestamp: October 22, 2024, 04:40:15 am
content: Hi Guys,I am working on a preamp based on many OPA1688IDR and I wanted to test if I can connect external power supply. So I run the Entire preamp with one a standard power supplu that it has (+-12V)Then I bent the + and - Power supply pins (4 andon the opamp so that they do not have connection to the main power supply. I connected them to the second +- 15 V power supply and since the opamp itself does not have the ground pin itself I did not connect the external PSU ground to the preamp ground.I though it would not work correctly, but it did without any hum or issues. So my question is with +- 15V stabilised power supply with LM7815 and LM7915 i read that you have to connect the ground for proper operation.So does the opamp + - Pins only requere the + and - difference form the PSU and basically work like the Vaccum Tubes heaters where all they need is the power ?thank you for your insight since it's really intriguing to me

author: magic
author_rank: Super Contributor
timestamp: October 22, 2024, 05:22:11 am
content: I doubt this could work. Current runs in closed loops, so how could the chip drive its output load?Are you sure the ±15V PSU doesn't have a hidden connection with preamp ground, perhaps through mains?What are the voltages on those supply pins with respect to preamp ground?