hybridfree/eevblog-posts huggingface dataset:
Help to identify an odd shaped MAC CLASSIC resistor - Page 1
Forum section: electronics / beginners

author: gkmaia
author_rank: Frequent Contributor
timestamp: June 10, 2020, 12:26:51 am
content: Sorry for the silly question but I got this 20ohms resistor (RP2 in the schematics) in line on my primary circuit.I am struggling to identify it. It does not appear a regular resistor. It is a thermistor?

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2020, 02:53:35 am
content: Yes, an NTC thermistor. Note that the schematic indicates a “cold” value for RP2 resistance.

author: gkmaia
author_rank: Frequent Contributor
timestamp: June 10, 2020, 02:59:04 am
content: thanks for your answer.so if it is negative it as current flows through it will increase temperature and reduce resistance. I imagine to a point where it will just be a jumper.if that is correct i could replace it with a jumper temporarily for now just for testing purposes.Also what is the reason for such device right out of the mains?

author: bob91343
author_rank: Super Contributor
timestamp: June 10, 2020, 03:49:50 am
content: I believe it's to reduce the inrush current. When it gets hot, its resistance is low for normal operation.

author: gkmaia
author_rank: Frequent Contributor
timestamp: June 10, 2020, 04:18:03 am
content: So it starts smoothly. As i mentioned it is the fine to replace it with a jumper or maibe a fuse?

author: floobydust
author_rank: Super Contributor
timestamp: June 10, 2020, 05:16:23 am
content: No, the part burns due to a short/overload on the SMPS primary side. If you must jumper the NTC, add a lightbulb in series and it should not stay lit. It's rare these parts burn up due to their old age.First I would check the main switching transistor for shorts, bridge rectifier etc. Need to see more of the schematic/model number.

author: james_s
author_rank: Super Contributor
timestamp: June 10, 2020, 05:59:53 am
content: For temporary testing it should work to use a jumper, but if the NTC failed you'll want to make sure there isn't a short that fried it. It's there to reduce the inrush when switched on, that increases the life of the power switch and reduces the stress on the rectifier and bulk filter capacitor.

author: gkmaia
author_rank: Frequent Contributor
timestamp: June 10, 2020, 09:22:45 am
content: nice, thanks!!!! Will give it a go.
Help to identify component - Page 1
Forum section: electronics / beginners

author: gabrimor
author_rank: Newbie
timestamp: September 17, 2025, 05:16:37 pm
content: Hi, thank you for reading this topic.I know it's hard, but can you help me identify this little component in the attached picture?Thank you.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 17, 2025, 06:30:07 pm
content: Good Morning Gabrimor, A close up magnified photo would be ideal, but if you can't do that, give us any identifying lettering or numbering and any symbols. Also an accurate measurement of width and lengthof the component(s).

author: golden_labels
author_rank: Super Contributor
timestamp: September 17, 2025, 07:13:30 pm
content: This isn’t even your own photo. It’s a random image copied from another site.Take actual photos of the component in question, in decent light conditions. Show the surroundings too, as seen on the board you really have. Write down the markings and report them too,regardless of the photo.Provide information on what board is that, exactly —manufacturer,(1)model. No, it doesn’t matter that we can track back the source site and guess the model from there.For anybody inquiring: the original TechPowerUp’s photo, before OP degraded it, was also of inferior quality and not revealing much.(1)Manufacturer of the board. Not the brand licensing the chip.

author: gabrimor
author_rank: Newbie
timestamp: September 17, 2025, 08:50:37 pm
content: Hi, BILLPOD!No lettering or numbering.I tried to show the component in the linked pictures:https://ibb.co/album/JW56PqIn another forum, someone thinks that it's a zener diode SOD123 or SOD323, so I think the guy will find it for me.Anyway, thank you very much!

author: gabrimor
author_rank: Newbie
timestamp: September 17, 2025, 08:52:32 pm
content: Hello, golden_labels.It's a Radeon 9800 Pro AIW, made by ATI.No markings available.I tried to show the component in the linked pictures:https://ibb.co/album/JW56PqIn another forum, someone thinks that it's a zener diode SOD123 or SOD323, so I think the guy will find it for me.Anyway, thank you very much!

author: gabrimor
author_rank: Newbie
timestamp: September 18, 2025, 11:59:34 am
content: Now, we think it's an inductor. Looked like a diode cause it was physically broken.The rating is probably 3.3µH.Thank you.
Help to identify connector - Page 1
Forum section: electronics / beginners

author: tipo1000
author_rank: Newbie
timestamp: February 20, 2024, 08:27:36 am
content: Hi,I'd need help to identify this connector.Pitch is 2mm.It has locking tab on top.Thanks,Tipo

author: chrisjs
author_rank: Newbie
timestamp: February 20, 2024, 09:27:03 am
content: Maybe JST PH series -https://www.jst.co.uk/productSeries.php?pid=163

author: tipo1000
author_rank: Newbie
timestamp: February 20, 2024, 11:29:37 am
content: It is not JST PH-connector. JST PH-connector doesn't have locking tab which is visible here.

author: tooki
author_rank: Super Contributor
timestamp: February 21, 2024, 10:14:03 am
content: Looks like it could be JST PAseries, or the similar not-quite-clone of PA known as “HY 2.0mm”. The most common way to buy HY connectors and cables from western distributors is as “Grove” connectors. Otherwise you have to get them on Ali/ebay/LCSC/Amazon etc.Example HY connectors:https://www.hegxing.com.cn/product/smt-connector-hy-2-0mm-pitch/

author: sparkydog
author_rank: Regular Contributor
timestamp: February 21, 2024, 05:13:28 pm
content: Comparing to the exampleshere, yours looks quite similar to the 2.5mm JST PA, but there are at least a couple differences visible. Note how the 2mm version of the genuine JST header doesn't have slots in the top, while the header in your picture does. Nor do either of the genuine connectors have a groove on the bottom of the header, while yours does. This being the case, I'd guess that what you have is a clone of a PA, but it might be close enough to be physically compatible with a genuine JST PA. (Of course, it's also possible that JST just changed their molds at some point.)

author: tooki
author_rank: Super Contributor
timestamp: February 21, 2024, 09:04:29 pm
content: Quote from: sparkydog on February 21, 2024, 05:13:28 pmJST PA is 2.0mm.You’re probably thinking of XA, which is 2.5mm.It really looks like the clone HY. The link I posted above also has their own PA clone linked at the bottom, making it easy to compare them.
Help to identify logo/chip [Solved] - Page 1
Forum section: electronics / beginners

author: ace1903
author_rank: Regular Contributor
timestamp: October 29, 2022, 06:44:47 pm
content: I am trying to find intermittent problem on Testo flue gas analyzer. I have two chips in signal chain that I can not identify.Most likely ESD protection or analog switches. 0501 is probably date code and SDA is chip marking.Logo is circle with P inside. Looked for logos on net and closest I can find is Plessey semiconductors but they seems do only LEDs and optoelectonics.If anyone have some info to share I will be grateful.

author: DavidAlfa
author_rank: Super Contributor
timestamp: October 29, 2022, 07:35:43 pm
content: This was a hard one. Protek devices:No idea about the part number, definitely not a HCPL-0501Check their catalogue:http://www.protekdevices.com/xyz/documents/kb/tech/gl1123.pdf

author: ace1903
author_rank: Regular Contributor
timestamp: October 29, 2022, 07:50:00 pm
content: @DavidAlfa - You nailed it. This part number SMDA05CN-5 looks like potential match.Will look more at the catalogue. I guessed ESD protection but this is like more TVS protection.Now I am unsure if TVS also covers ESD but for sure that is not the cause for the intermittent problem that I have.Those devices have electrochemical sensors that leaks and destroy the PCB but I did regular maintenance of mine device and I am sure that is not the cause.Thanks DavidAlfa.
Help to identify pins on PT204-6B - Page 1
Forum section: electronics / beginners

author: RobH
author_rank: Regular Contributor
timestamp: November 07, 2022, 05:00:06 pm
content: I have just bought x2 PT204-6B photo transistors, and see that 1 pin is longer than the other. But I can't find any information to say which pin is emitter and which pin is collector.Thanks

author: gamalot
author_rank: Super Contributor
timestamp: November 07, 2022, 06:07:23 pm
content: https://media.digikey.com/pdf/Data%20Sheets/Everlight%20PDFs/PT204-6B.pdf

author: RobH
author_rank: Regular Contributor
timestamp: November 07, 2022, 06:44:26 pm
content: It wasn't easily obvious when I looked before, but on close inspection, I can see which pin is which now.Thanks
Help to identify Programmable Timer IC - Page 1
Forum section: electronics / beginners

author: aju11
author_rank: Contributor
timestamp: March 04, 2019, 11:58:29 am
content: I am looking for a programmable timer/counter IC which will generate a digital output (high/low) after the programmed time has elapsed.Monostable Multivibrator.Programmable time range = 5 to 15 minutes.I do not want to use 555 because since the time is large, values of R and C will be large and value of C degrades over years.I am looking for a solution similar to TPL5xxx nano timer series by TI. (but without micro-controller). And with minimum component count.Any suggestions?

author: Moriambar
author_rank: Unknown
timestamp: March 04, 2019, 01:02:14 pm
content: Quote from: aju11 on March 04, 2019, 11:58:29 amIf you have a copy of the art of electronics at hand, they explain how to use anLTC6991oscillator, with a logic gate, in order to obtain 1 hour of power. The idea behind it is to cut the output after half the cycle is complete.Unfortunately I have not the copy right here, but it's in the monostable multivibrator chapter. It's called "one hour of power".Similar ideas are featured in theLTC6995datasheet. I think they're worth taking a look.Unfortunately I don't know any better and personally I've used the LTC6991 solution for a ~20 minutes solution in my design

author: Zero999
author_rank: Super Contributor
timestamp: March 04, 2019, 02:23:11 pm
content: The modern way to do this is to use an 8-bit micro-controller, such as the PIC12F508, PIC10F200, ATTINY9-TS8R etc.If you don't want a microcontroller then there are counter+oscillator ICs such as the CD4536, CD4541 and ICM7242.There might be a day when the above are no longer available so why not use a microcontroller? They're cheap, the programmers are widely available and using the built-in RC oscillator will give a better accuracy than an astable with an external resistor and capacitor. I could write an assembly program for a programmable delay of 5 minutes to 15 minutes using the PIC12F509, fairly quickly, even though I've not done it in years.

author: Benta
author_rank: Super Contributor
timestamp: March 04, 2019, 04:39:37 pm
content: MC14536/CD4536. Cheapest and easiest to find.
Help to identify SMD transistor and SMD diode - Page 1
Forum section: electronics / beginners

author: raffs
author_rank: Newbie
timestamp: September 20, 2017, 02:48:05 am
content: Hello there!These puppies are from Intel's DH77EB motherboard!I guess the transistor is a BFT92 and the diode a pdz3.9b... not sure!How to find these SMD components??The transistor code is W1A (24) and the diode code is T4 (Z5).By the way, what are supposed to mean these vertical codes?If someone happens to have the DH77EB service manual, I'll appreciate!

author: ocw
author_rank: Regular Contributor
timestamp: September 20, 2017, 03:05:24 am
content: Hit the W1 and T4 icons athttp://www.s-manuals.com/smd

author: raffs
author_rank: Newbie
timestamp: September 20, 2017, 01:14:46 pm
content: Thanks ocw!But I have one more question.If you hit the T4 as you mentioned, you'll see that T4 may refer a 1N4148W which is a normal diode and also a BZX384-C2V7 which is a zener diode.Any idea?

author: ocw
author_rank: Regular Contributor
timestamp: September 20, 2017, 01:26:15 pm
content: QuoteThat's the obvious problem with space for just a few characters but a large number of components. The 1N4148 is more likely but the only way to be sure (short of having a schematic diagram) is to trace out enough of that circuit to see if it supports a regular diode rather than a zener.

author: raffs
author_rank: Newbie
timestamp: September 20, 2017, 02:18:50 pm
content: trace the circuit on a multi-layer board?hehe that's a long way full of "trap for young playas"! (like Dave Jones says)ok, I'll give a try! Should I begin looking if the diode is reversed biased? (this eliminate the zener hypothesis, right?)

author: ocw
author_rank: Regular Contributor
timestamp: September 20, 2017, 05:44:05 pm
content: Measuring the voltage across agooddiode will tell you if it is a zener or not. If the diode is shorted, that's generally easy to detect. Open, depends on how it is connected.
help to identify some components - Page 1
Forum section: electronics / beginners

author: raffs
author_rank: Newbie
timestamp: October 13, 2015, 03:24:31 pm
content: Hello Masters!Could you please, help me to identify these little components (marked in red)?This is the D-Link DSC-930L Ip camera's back view. I believe this is the power rectification portion.I Googled for the labels but google brings me nonsense results (maybe custom?).The labels are:10 leads IC => "A E-DH S13"5 lead (SOT-23?) => "DS-P0R"regards,

author: ion
author_rank: Regular Contributor
timestamp: October 13, 2015, 04:17:03 pm
content: The SOT-23 package seems to be a 1.5V LDO.Datasheet:http://www.s-manuals.com/pdf/datasheet/r/t/rt9193_richtek.pdfCan't find anything on the larger chip, but I would guess it's some sort of DC-DC converter IC.

author: Josh
author_rank: Contributor
timestamp: October 13, 2015, 05:32:27 pm
content: Maybe you could probe the pins to get an idea? Just be careful not to short anything.

author: raffs
author_rank: Newbie
timestamp: October 14, 2015, 01:14:33 am
content: ion, thanks for the datasheet.This camera do not work anymore.I'm learning electronics yet and unfortunately I don't know from where to start troubleshooting this camera.Taking into account where this camera was installed (the mains voltage varied widely), I think some part of the power circuit burned.This camera uses the IChttp://www.ipassion.com.tw/pdf/DSH_iP2970_1.2.pdfwhich runs at 3.3v.I tested the 38th pin (iP2970), it should be at 3.3v but it was at 0v.Indication that the dc-dc converter is probably fried?

author: AMS
author_rank: Contributor
timestamp: October 14, 2015, 02:16:58 pm
content: Quote from: raffs on October 14, 2015, 01:14:33 amThats a possibility, Have you checked the output of the power supply without connecting it to the board ?(if mains had issues I expect that to go first).
Help to identify unknown connector - Page 1
Forum section: electronics / beginners

author: Martin781
author_rank: Newbie
timestamp: April 15, 2025, 02:56:23 pm
content: Hi all,I am trying to identify a particular female panel mount triax connector. On the outside the outer diameter is 18mm, the inner one 6.5mm. The diameter of the central insulation part is 2mm. On the inside he thread is M12 and 17mm long.The only sign on the connector is a red capital "V" on the side of the outer part (see last photo).I do not have the matching male connector, just a vague photo of it (see attached photo).Has anyone seen this connector before?Thanks!

author: timeandfrequency
author_rank: Frequent Contributor
timestamp: April 15, 2025, 04:48:54 pm
content: Hello Martin781,Couldthis onemate with your chassis connector ?Datasheethere.UK reseller.

author: Martin781
author_rank: Newbie
timestamp: April 15, 2025, 06:51:00 pm
content: Thank you timeandfrequency, nice find. I am not sure it fits. I do not know if my connector is standard or not.I am also wondering if the "V" letter on the side isn't an identifier for the manufacturer. Or something else.

author: tooki
author_rank: Super Contributor
timestamp: May 13, 2025, 11:48:23 am
content: I very strongly suspect you have a LEMO S series, size zero, in the vacuum-tight version (hence the V). Most likely, it’s aHGP-0S-CTLSVor similar*. (Note that the image is generic for the HGP series, so does not reflect the contact insert used!)The inner diameter of the 0S (S-series, size 0) is 7mm, I think you just have a bit of measurement error. The length matches up perfectly (21.5mm-4mm flange=17.5mm)Here’s the main catalog:https://web.lemo.com/img/resources/catalog/ROW/UK_English/unipole_multipole.pdf(see page 91)This is the catalog of coaxial inserts, like the style 650 for 50-ohm triax:https://web.lemo.com/img/resources/catalog/ROW/UK_English/Coax_triax_mixed_en.pdf(see page 19)Concentric contact insert ID guide:https://web.lemo.com/img/resources/faqs/Quick_Reference/concentric_contacts_id_guide.pdfReceptacle ID guide:https://web.lemo.com/img/resources/faqs/Quick_Reference/receptacle_id_guide.pdfGuide to finding a mating plug for a receptacle:https://web.lemo.com/img/resources/faqs/Quick_Reference/plug_id_for_given_recep.pdfPlug ID guide:https://web.lemo.com/img/resources/faqs/Quick_Reference/plug_id_guide.pdfRecommended triax cables:https://web.lemo.com/img/resources/faqs/recommended_triaxial_cables.pdf*for the life of me, I can’t figure out what the “SV” option suffix stands for. The catalogs list “PV” as the code for vacuum-tight, but the -SV part number is what the website’s connector finder outputs. “P” means watertight, “PV” means water- and vacuum-tight. Neither the catalog nor their part number decoder list the “SV” option, though it’s fair to assume the V still means vacuum-tight.
Help to translate jitter design constraint in a frequency synthesizer design - Page 1
Forum section: electronics / beginners

author: Albs
author_rank: Newbie
timestamp: April 13, 2016, 05:00:56 pm
content: Hello to all,I'm trying to design a frequency synthesizer with the old-school 4046 and 4017 ICs, with a scaling factor N = 1,5,7,10.The input signal is a square wave with adjustable frequency from 1 kHz to 10 kHz.I want to get a time jitter < 1% of the period.I'm a newbie in PLL design, so I've done the only possible thing: study. I already knew control theory, filters, loop gain, stabilty and so on but I still can't understand where to start in the design to achieve the desired performance. Many books state that the design should start from the closed-loop bandwidth, but how do I relate this to jitter? I've read about calculating RMS time jitter from phase noise, but the datasheet of the 4046 has no data about VCO phase noise (for example) and I have zero infos about the source phase noise (the project is for college and the professor didn't give me any other information).Please if you could help me, I literally have zero ideas on how to go on.Thank you in advance.
Help, Transistor VS. DS1102e rigol DSO - Page 1
Forum section: electronics / beginners

author: IonizedGears
author_rank: Regular Contributor
timestamp: June 06, 2013, 07:33:38 pm
content: I recently got a ds1102e. When i connect it across a powered pnp or npn transistor (Between the base and emitter) I get an extremely weird waveform that is extremely unstable but semi trigger-able and view-able if you use the stop button. After this when i disconnect everything, my oscilloscope gets all wonky and if i cycle the power, it starts up with a blue flash and some noise then the splash screen for rigol. I hope i am not harming my oscilloscope? Can you tell me if it is bad for the scope or my scope is bad, etc.

author: c4757p
author_rank: Super Contributor
timestamp: June 06, 2013, 07:37:40 pm
content: What does the waveform look like? Can you take a screenshot? And what is "wonky"?

author: daveshah
author_rank: Unknown
timestamp: June 06, 2013, 07:46:23 pm
content: Is the transistor being powered from a mains earth referenced source (i.e. a device connected to a USB port)?

author: w2aew
author_rank: Super Contributor
timestamp: June 07, 2013, 01:59:04 am
content: Quote from: IonizedGears on June 06, 2013, 07:33:38 pmA 10x scope probe is NOT the same as the probes on a DMM. The DMM inputs are floating, the scope input is not. The "clip" on the scope probe is electrically connected to the mains ground. It sounds as if you are connecting the scope probe's ground lead to a part of the circuit which ISN'T ground. Dave did a good video on this, entitled something like "how not to blow up your scope".

author: IonizedGears
author_rank: Regular Contributor
timestamp: June 07, 2013, 05:59:53 pm
content: I know, the circuit was battery operated. I can't post any pictures right now since my main computer needs a new motherboard and it has the pictures. But when i am measuring across the transistor it looks like a sinusoid but getting progressively smaller in amplitude. When i disconnect the scope, the scope starts to measure an insanely high amount of noise that is unreadable. Also, sometimes when i turn the scope off then on. A blue screen shows up for a second right before the rigol logo screen.

author: smashedProton
author_rank: Frequent Contributor
timestamp: June 07, 2013, 09:30:44 pm
content: That is normal. The rigol display module has a shitty power sippky

author: IonizedGears
author_rank: Regular Contributor
timestamp: June 07, 2013, 11:20:40 pm
content: Quote from: smashedProton on June 07, 2013, 09:30:44 pmWhy would this be a power supply problem? It looks as if the display driver is to blame as it only happens if i cycle the power in a relatively short period of time. Maybe it takes a lot of time for the power from the power supply to bleed so the scope goes into a "hibernate" mode but not enough to resume? Hmm
Help Troubleshooting COSMAC 1802 Membership Card? - Page 1
Forum section: electronics / beginners

author: tcv
author_rank: Contributor
timestamp: January 24, 2014, 12:39:03 am
content: Hi,I recently put together a COSMAC 1802 Membership Card and, well, it's not quite working. It's probably more accurate to say that it's broken.If possible, I'd like help troubleshooting the problems. I have been in touch with the kit's author, Lee Hart, and he's been very gracious and has pointed out a lot of helpful information. Regrettably, he's not been available to help for a few weeks and I'd like to get going on it a bit more.I'm very new so I'll be slow!First, here are some relevant links:1. Schematics:http://www.retrotechnology.com/memship/mem_revfsch1.pdf2. The Kit page:http://www.retrotechnology.com/memship/memship.html3. Troubleshooting page:http://www.retrotechnology.com/memship/mship_broken.htmlThe main symptom right now is: I can input data, but I have not been able to read anything back.I am going over the board looking for bad solder joints. I've been through the bottom board and I think things are OKAY there, but this is my first larger project and I can't swear to everything. I have yet to go over the top board. Going through the bottom board made things a little more stable, it seems. The lights generally respond as they should.Here's my first question:On the troubleshooting page, Lee says, "Check to see if the oscillator is running. U4D pin 12 should be high, and U1 pin 39 should be an AC voltage (as indicated on your multimeter)."I know I have AC voltage on pin 39 (I'll have to go back and check what the reading is). My logic probe on a BK Precision 2707b Multimeter which says, "Connect the red test lead to the test point and the black lead to the common buss of the logic circuit."What is the "common buss" in this case?
Help troubleshooting Mosfets in Switching Circuit  - Page 1
Forum section: electronics / beginners

author: Sultanpepper123
author_rank: Regular Contributor
timestamp: February 13, 2024, 10:38:06 pm
content: Hello,I've been trying to design a simple circuit to switch between two Supply rails (3.3V_SW & Vbat) while giving one of them a higher priority (3.3V_SW). The circuit in simulation is showing to be not working well as shown below.As shown above the toggling between VBAT (3.6V) & 3.3V_SW (3.3V) is unsuccessful , the transition from 3.6V goes down to 2.4V instead of 3.3V.And I've built the circuit in person and the operation goes as follow, When the VBAT is activated the output is 3.6V (good) , when the 3.3V_SW is activated the output is 3.3V (good) . Now the problem starts when 3.3V_SW is deactivated the output is 3.3V instead of 3.6V coming from VBAT.Would definitely appreciate it if anyone would share their insights on what might be the solution to make this circuit work as intended.

author: Benta
author_rank: Super Contributor
timestamp: February 13, 2024, 11:07:10 pm
content: Your MOSFETs are upside down. And 470k is waaay too high for pull downs. the 2N7002 will supply more current due to leakage than those.

author: TheoB
author_rank: Regular Contributor
timestamp: February 13, 2024, 11:29:12 pm
content: Q5 source is tied to the internal bulk and needs to be connected to the highest voltage. Indeed source drain need to be swapped. Once switched on, you cannot switch off as vdd and 3.3V_SW are connected together by Q6. You have to short 3.3V_SW to ground to overcome this latched state. It does not work if you only leave it floating.With no connection to 3.3V_SW, your circuit has two solutions, Q6 is on or off. That's not what you intended.
help tuning this relaxation oscillator  - Page 1
Forum section: electronics / beginners

author: amateur_25
author_rank: Regular Contributor
timestamp: August 16, 2012, 10:38:41 pm
content: HII want to know how do I tune the frequency of the following circuit up to 100KHZ as accurately as possible?Would appreciate it if you could explain how you arrived to the solution

author: 6502nop
author_rank: Regular Contributor
timestamp: August 17, 2012, 01:57:58 pm
content: This looks suspiciously like a homework problem. Most forums don't particularly cater to doing someone else's work, just to give you a "head's up".However, the manner in which this was asked makes me think it's legit, so...I've attached the way I go through and read schematics, showing the simple steps involved. Start with the upper left corner and work your way across and down. I didn't outright solve your problem, but I do provide a (hopefully) clearer picture of how to solve it on your own, to suit your particular needs.nop
Help umderstanding this rising/falling edge - Page 1
Forum section: electronics / beginners

author: AlfBaz
author_rank: Super Contributor
timestamp: June 27, 2013, 01:22:12 pm
content: Messing around with the PWM module on a PIC18F4550, I decided to up the frequency to just under 50kHz and all of a sudden I noticed the pulses aren't looking very square anymore.Looking a little closer I realised the lower frequency waves looked squarer because the scopes time base was increased to fit a couple of cycles. Expanding the edge at these frequencies yielded the same edge.Thinking it may be the PWM module I simply toggled an output... same thingThe 18f4550 supply is rated from 4.2 to 5.5V, yet it seems the output drives to 3.3V then just "coasts" to VDDThe images bellow are of the edge at 50us and 1us time baseIn the 1us image the sharp rise has 2 slopes if you expand even more. The first slope takes 6ns to get to about 2.16V the second is an additional 20ns to reach 3.3V. The total time for the initial edge is 26ns to 3.3V shown in the image. Its then another 7.8us to reach VDDIs this normal?

author: AlfBaz
author_rank: Super Contributor
timestamp: June 27, 2013, 01:25:11 pm
content: Oh I forgot to mention, the outputs look similar regardless of wether they are loaded or open cct

author: MikeK
author_rank: Super Contributor
timestamp: June 27, 2013, 02:07:19 pm
content: Have you adjusted probe compensation?

author: AlfBaz
author_rank: Super Contributor
timestamp: June 27, 2013, 02:10:08 pm
content: Quote from: MikeK on June 27, 2013, 02:07:19 pmYes

author: AlfBaz
author_rank: Super Contributor
timestamp: June 27, 2013, 02:36:41 pm
content: Hey Mike just tried another probe, problem solved... Thank you very much

author: marshallh
author_rank: Unknown
timestamp: June 27, 2013, 06:49:52 pm
content: Watch w2aew's video about ground leads.Also, the rounded leading edge like that smacks of capacitive loading. I had a similar phenomenon with a pcb failure causing that kind of issue.You can also see these kinds of waveforms on weak outputs driving long cables (also capacitive loads)
Help understand the workings of the signal detector opamp circuitry. - Page 1
Forum section: electronics / beginners

author: Yamin
author_rank: Frequent Contributor
timestamp: March 01, 2021, 11:52:52 am
content: Hi guys,I am working on restoring a bass amplifier. I am trying to figure out how the circuitry which detects the signal and which detects clip circuitry works. Its working fine but would like to know how it works. It looks like an inverting amplifier but I am not sure whether I am right and also what is the purpose of D29?I would greatly appreciate if you could help me understand how these two circuitry work and also advise on further reference would be appreciated too.Thanks in advance.

author: Kibabalu
author_rank: Regular Contributor
timestamp: March 01, 2021, 12:45:22 pm
content: Are the opamps supplied single or dual?In this case the two opamps are pursued as comparators with hysteresis resp. as Schmitt triggers. The function of the diode in the positive feedback path is unclear to me. I guess it gives non-symmetrical hysteresis points. Maybe somebody else knows more!

author: Yamin
author_rank: Frequent Contributor
timestamp: March 01, 2021, 05:06:41 pm
content: Quote from: Kibabalu on March 01, 2021, 12:45:22 pmThanks, the op amps are supplied from +/-16V. Can I please ask what you meant by "hysteresis resp."?Thanks again

author: Kibabalu
author_rank: Regular Contributor
timestamp: March 01, 2021, 06:11:10 pm
content: Quote from: Yamin on March 01, 2021, 05:06:41 pmresp. is the abbreviation of respectively.What I meant was that "Schmitt trigger" is just another description for "comparator with hysteresis".Sorry for writing not clear enough!
Help understanding a crowbar circuit, magic smoke released. - Page 1
Forum section: electronics / beginners

author: pitpat
author_rank: Contributor
timestamp: March 02, 2021, 01:23:28 pm
content: Hi strangers!, I'm trying to repare this old scope and while trubleshooting i managed to set it on fire lolNow the point is to find the culprit.I've fed the inverter whit 43v 1A isolating the pre regulator, the reistor r934 (in the blue square) decided to lit as a lightbulb.Now the question is: assuming that all the inverter section is fine (as i tested) could a short in the secondaries get the SCR runnig and shorting that resistor?

author: mvs
author_rank: Frequent Contributor
timestamp: March 02, 2021, 02:42:32 pm
content: This crowbar circuit will be triggered in two conditions:- input voltage to high (controlled by zener diode VR039)- transformer current is to high (controlled by shunt resistor R949)So the answer to your question is yes.51V zener diode can conduct some current at 43V. Perhaps you had also some voltage spike on power rail.Try to power this circuit from a lower voltage.

author: pitpat
author_rank: Contributor
timestamp: March 02, 2021, 04:02:10 pm
content: Thanks, i did try lower voltage and it did fine until 14.5v. It was limited to 0.5A, i ramped up the current to 1.5A but it still was going so i stopped it.I did also tried to isolate the output with no succes.I'm starting to grow the feeling that the transformer windings might be busted, also with the voltage increase also an HF hiss.
Help understanding a simple datasheet - Page 1
Forum section: electronics / beginners

author: Moriambar
author_rank: Unknown
timestamp: October 18, 2018, 06:20:17 am
content: Hi.I'm planning to use thePCA2129in a battery powered circuit, since it's basically perfect for what I need.What I do not understand is this: can I power it from 3 AA batteries? The "absolute maximum ratings" seem to agree with it, but the normal electrical characteristics make me doubt it since rate the component to a maximum of 4.2VAm I hopeless?Thanks

author: capt bullshot
author_rank: Super Contributor
timestamp: October 18, 2018, 06:30:27 am
content: Quote from: Moriambar on October 18, 2018, 06:20:17 amRunning any device at its absolute maximum ratings isn't recommended. It may work, but may lead to lifetime shortening or other premature damage of the device. This is what nearly every datasheet says regarding the abs max ratings. Above the abs max ratings, instant damage may occur.So if you want to build a reliable product, you better not exceed the recommended operating range.Since the chip has a operating range from 1.8V ... 4.2V, one could run it from three batteries using a series diode to drop the voltage somewhat below 4.2V (the diode drop will be rather small because of the low operating current), and still have enough reserve for depleted batteries.IMO the specified operating range implies one shall be able to run this chip off a single cell Li-Ion battery.

author: Moriambar
author_rank: Unknown
timestamp: October 18, 2018, 06:32:38 am
content: Quote from: capt bullshot on October 18, 2018, 06:30:27 amThank you. I'll check the diode idea: unfortunately the Li-Ion battery cell is not an option at the moment!Nice answer
Help, understanding adjustable HALL Sensor from Aliexpress - Page 1
Forum section: electronics / beginners

author: Lenny
author_rank: Contributor
timestamp: March 23, 2020, 10:38:24 am
content: Can someone explain how this adjustable Hall switch should work?https://de.aliexpress.com/item/1997096887.html?spm=a2g0s.9042311.0.0.79ab4c4dhvrgbOThese switches are sold by various suppliers.I bought one, and after I couldn't deal with it, I did some research.In principle, the A3144 used is already a digital switch. In my opinion, a linear Hall switch would have to be used for the circuit to work?!With the A3144, the entire comparator circuit is useless. The analog output can also only take 5V or 0V.Or did I miss something?

author: mikerj
author_rank: Super Contributor
timestamp: March 23, 2020, 10:58:43 am
content: Don't think you have missed anything, the external comparator is useless if the intention is to change the operating distance.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: March 24, 2020, 12:28:40 am
content: There are different kinds of hall switches.Some of them output an analog voltage depending on the strength of the magnetic field. This is the only kind that makes sense with a comparator.Hall sensors often are also unipolar, they only generate generate a usable output with one polarity of the magnetic field, an they also have a limited detection range. If you use Nibidibibibium magnets, they may be too strong and seem to generate only an on/off because the linear range is small.You can try soldering a wire directly to the output pin of the sensor, and measure the output voltage that goes to the comparator. This gives you a much better understanding than just seeing the output of the comparator turn on or off.If you want to experiment on this level, I also recommend to buy a few loose Hall sensors, they are quite cheap.Fans in PC's usually also have Hall sensors in them, but they are the switching kind with built in comparator.

author: Mechatrommer
author_rank: Super Contributor
timestamp: March 24, 2020, 01:12:02 am
content: i suggest next time please provide link to english site. not everybody can read germany..

author: 5af734377e
author_rank: Newbie
timestamp: March 26, 2020, 03:33:49 pm
content: Try Octave first and see if it has what you need. There is a bit of awkwardness getting it to load the toolboxes (Google for this) whereas MATLAB seems to do it by automagic. There is no Simulink equivalent if that becomes necessary butTutuapp9appsShowboxGoogle for 'octave simulink equivalent' and see if it gets you anywhere.

author: mikerj
author_rank: Super Contributor
timestamp: March 26, 2020, 04:53:51 pm
content: Quote from: Doctorandus_P on March 24, 2020, 12:28:40 amThe A3144 fitted to this board has a digital output, so the comparator is useless.Quote from: Mechatrommer on March 24, 2020, 01:12:02 amYou could just select English from the menu at the top of the website...
Help understanding circuit from a salvaged oven - Page 1
Forum section: electronics / beginners

author: redgear
author_rank: Frequent Contributor
timestamp: September 06, 2020, 07:10:26 am
content: I took this little board from a salvaged microwave oven.https://ibb.co/M1DkzkZThe top side has only THT components while the bottom has only SMD. The layer on the front is also different from regular PCBs. What are these types of PCB called?https://ibb.co/3rj0sbJWhat is the component identified as SG 941, it connects to a buzzer. Is it BC941 transistor?https://ibb.co/rMbcdfpIs the component identified as L50R1 a voltage regulator? The circled pads connect to two 47uf electrolytic caps.https://ibb.co/g4HmJySThe transformer steps down mains to 12v which then powers the relay. The output is unregulated. Considering that the voltage from transormer's secondary may vary upto 20% on load and no load conditions, would the relay be able to withstand those voltages?
Help understanding Diagram - Page 1
Forum section: electronics / beginners

author: mentaldemise
author_rank: Regular Contributor
timestamp: March 07, 2015, 01:47:27 am
content: Hi guys! Thanks for all the help already. Can someone point me in the right direction to figure out what's different between what I have attached and the diagram for CMOS Crystal Oscillator here:http://www.electronics-tutorials.ws/oscillator/crystal.htmlThe chip is an LM74LS14N, Hex Schmitt Trigger

author: codeboy2k
author_rank: Super Contributor
timestamp: March 07, 2015, 02:34:11 am
content: It's hard to tell exactly where everything goes, but if you're having trouble getting it to oscillate, then it might be a couple things1) it needs to be said... double check all your connections carefully. I've been known to find something on the 3rd or 4th check.2) check the crystal is really seated tightly, some of those little crystals have small leads that might not press all the way down into the breadboard.3) switch to another chip, or another invertor in the same chip if you only have 1. Maybe the chip is damaged.4) those extra long leads might have too much inductance, that will load the crystal too much and it won't oscillate.5) you might try it without the 2 capacitors to ground. The breadboard has a lot of excess capacitance already, and putting the 2 caps on the crystal might cause it to not oscillate. So take them off and see what happens.

author: Sirius631
author_rank: Contributor
timestamp: March 07, 2015, 02:46:58 am
content: If you are following the component values faithfully then it should be noted that the circuit you've built is using a true TTL gate, so the biasing will be different. It should work if you were using a 40106 IC.The following should give you an idea for TTL IC use:http://www.z80.info/uexosc.htm

author: tggzzz
author_rank: Super Contributor
timestamp: March 07, 2015, 09:59:31 am
content: You need PSU decoupling capacitors, properly located.The jumper leads aren't wires: they are inductors with a value ~1nH per mm of length. The mutual inductance between wires is variable.Breadboards have, reportedly, ~2pF capacitance between adjacent tracks.You shold consider using "dead bug" construction techniques for high frequency (i.e. >audio) circuits. Use google images to see what that means.
Help Understanding IC (UPC1237) - Page 1
Forum section: electronics / beginners

author: AngraMelo
author_rank: Regular Contributor
timestamp: September 16, 2019, 12:49:21 am
content: Hey guys,I got an old Sony Stereo (LBTn355) for cheap and the speaker relay is not activating.So it is controlled by the IC UPC1237. It appears to detect DC voltage and breaks off the relay to avoid damaging the speakers.Now, I think this IC is bad, because if I understood it correctly (datasheet below) if pins 1 or 2 are greater than the threshold voltage (set by pin "8") then it wont activate the relay.Now, this is the voltages I measured on the IC:1 - 0.004V2 - 0.011V3 - 0V4 - 2.52V (actually, I get a kind of a sawtooth wave that actually goes to positive and negative on respect to ground)5 - 0V6 - 36V7 - 0.007V8 - 3.49VAm I understanding the IC correctly? Or those voltages represent something Im not understanding?Here is the IC datasheethttps://pdf1.alldatasheet.com/datasheet-pdf/view/6669/NEC/UPC1237HA.html(Schematic of the Stereo)https://www.electronica-pt.com/esquema/audio/sony-audio/sony-lbt-n355-1318/Thank you guys!

author: floobydust
author_rank: Super Contributor
timestamp: September 16, 2019, 02:43:56 am
content: The IC is probably OK. I see a problem with pin 7 (Power-on delay timer input) if it goes above +2V, the relay is enabled (if no DC or overcurrent detected). You have nothing at pin 7, so something else is holding it down.Sony has the MCU pin 67 controlling that POWER_ON signal as the STANDBY switch. So the MCU thinks power is off and keeps Q1205 turned on.If pin 2 (DC Detect input) goes over +/-0.6V, the IC goes into protect mode.If pin 1 (Overcurrent Detect input) go over +0.7V, the IC goes into protect mode.If pin 4 (AC mains Detect input) go under +3.5V, the IC goes into protect mode.

author: AngraMelo
author_rank: Regular Contributor
timestamp: September 16, 2019, 03:29:25 am
content: Thank you so much!It is a pretty weird issue because the system is not reporting any errors, for example PROTECT or something alike.It plays music but the relay wont engage.Now pin "4" of the IC is fed by the taps on the transformer, the signal leaves the transformer goes to a resistor (R1303 and R1304), a diode (D1309 and D1310) and directly to pin 4.That tap on the transformer reads 23Vac, but the anodes of the diodes read 2.5Vdc. I already changed the diodes and the resistor dont seem to be an issue. I have no idea how those 23Vac are becoming 2.5Vdc

author: floobydust
author_rank: Super Contributor
timestamp: September 16, 2019, 05:02:18 am
content: uPC1237 pin 4 has a zener inside, so it clamps to around 4V. Resistors R1303, R1304 4k7 drop the 12VAC down.I would check base voltage on Q1205, +5V during standy/power off and goes to 0V when power is on (POWER-ON).This (Q1205 base 0V) allows the relay to pull in. Or capacitor C1221 on pin 7 might be shorted, or Q1206 or IC504 shorted on the panel board which turns the LED's on.Otherwise the MCU is thinking power is off and it is staying in standby.
Help understanding part of a circuit - Page 1
Forum section: electronics / beginners

author: uk.casmith
author_rank: Contributor
timestamp: September 08, 2018, 08:36:46 am
content: Hi,I'm following a book of electronics and I don't really understand what the author means:"This arrangement works because I have used a capacitor, C4, to connect the output of IC7 to the reset of IC6. The capacitor communicates the sudden change from positive to negative, but the reset of the time it blocks the steady voltage from IC7 so that it won't interfere with IC6"Can someone explain this further to me please.FYI:C4 = 0.1uF,R10 = 1kIC7 = 555 timerIC6 = 555 timer.Thanks

author: xavier60
author_rank: Super Contributor
timestamp: September 08, 2018, 01:45:26 pm
content: Quote from: uk.casmith on September 08, 2018, 08:36:46 amThe words " but the reset of the time it blocks the steady voltage from IC7" are difficult to understand. I think that he is trying to tell us that the steady state on IC7 pin 3 is not continuously applied to IC6 pin4. When IC7 pin 3 goes low, this transition is coupled by C4 to IC6 pin4 causing it to pulse low. R10 then charges the bottom end of C4 back up to + rail voltage.

author: rstofer
author_rank: Super Contributor
timestamp: September 08, 2018, 01:48:24 pm
content: Looking at the pinout for a 555, we see that pin 4 (of the lower IC) is Reset.The capacitor/resistor forms a differentiator circuit which puts out a pulse (not a level) when the input is changed. The pulse will go high on the rising edge of a signal and low on a falling edge. This is what we want, a brief low going pulse to reset the lower 555. You can see that pin 4 is held high through the resistor so the only thing the capacitor can do is pull is low. And that is exactly what it takes to reset the timer!https://en.wikipedia.org/wiki/555_timer_ICYou can see waveforms for various ratios of R to C about half way down this page. We're looking for the 0.1 RC or less (I'm guessing, without doing the math)https://www.electronics-tutorials.ws/rc/rc-differentiator.html

author: rstofer
author_rank: Super Contributor
timestamp: September 08, 2018, 01:51:50 pm
content: Quote from: uk.casmith on September 08, 2018, 08:36:46 amI fixed a typo in the quoted text. "...but the REST of the time..."

author: uk.casmith
author_rank: Contributor
timestamp: September 09, 2018, 09:38:22 am
content: Thanks for everyone's help with this. I'm going to read the link that was provided it's a little over my head but i'll try reading from the beginning.Cheers,

author: rstofer
author_rank: Super Contributor
timestamp: September 09, 2018, 05:24:24 pm
content: The short answer: When the upper timer output drops to 0V, the differentiator generates a very brief low going pulse to reset the lower timer. It's the fallingedgethat causes the pulse.All you need to know is that the lower timer reset pin is held high by the resistor and pulled low by the pulse from the capacitor.
Help understanding PTC specs - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: August 09, 2010, 11:59:22 am
content: Hi guys, I'm trying to select a PTC resistor for an application, I need a slight variation in value for temperature changes. I've looked yp parts on Farnell but none of them have a specific R/C value. How are PTC's characterized then ? how to i understand wehat they will do so that in my circuit I can predict the result ?

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2010, 12:20:11 pm
content: I'm not sure what you're asking.Most of the PTC thermistors have a clear temperature vs resistance graph on the datasheet.http://uk.farnell.com/epcos/b59701a70a62/thermistor-ptc-smc/dp/3876690http://www.farnell.com/datasheets/7181.pdfwhy does it need to be PTC? The most accurate temperature sensors are NTC and it's pretty easy to make the output voltage positive with a positive coefficient by exchanging the places in the potential divider.

author: Simon
author_rank: Unknown
timestamp: August 09, 2010, 06:23:26 pm
content: it needs to be positive because I want to use it to bias the output of a current sensing circuit, the current sensor is the MAX4172 which outputs a certain current for a certain voltage in (sensed from a series resistor), so normally the current output is just one resistor with a current through it proportional to the current under examination, you choose the resistor value to get the output voltage range you want it. I was thinking of putting something in series with the output resistor so that temperature would alter the reading and allow more current when cold and less when hot. I was going to use a diode but tests on a 1N4001 showed that the coefficient is negative

author: Simon
author_rank: Unknown
timestamp: August 09, 2010, 06:36:12 pm
content: and this is a very iluminating spec sheet:http://www.farnell.com/datasheets/357013.pdfI'm after through hole stuff as the SMD ones are too tricky for me at the moment