hybridfree/eevblog-posts huggingface dataset:
Unexpected behaviour from LM399 board when drawing it's schematic - Page 1
Forum section: electronics / beginners

author: systemCorrµPti0n
author_rank: Newbie
timestamp: October 26, 2023, 09:17:46 pm
content: HiI recently acquired a cheap LM399 board and when drawing it's schematic I don't understand why it is working correctly if the resistors markings are to be "followed"More specifically I don't understand why the resistor R2 says 18k. In the non inverting opamp configuration R2 and R7 would have a gain of `1.9` $$1 + \frac{18}{20} = 1.9$$If I were to short the first 3 switches, J1-J2, J3-J4 & J5-J6 I would get the 6.95v from the reference directly into the non inverting input of the opamp and the output should be $$6.95 * 1.9 = 13.205$$But it is in fact 10v, and when measuring R2 (in circuit tho) it reads 9k, which would make sense with the non inverting gain calculation, but the reading of the resistor still says `1802`$$1 + \frac{9}{20} = 1.45$$$$6.95 * 1.45 = 10.0775$$So I made a list of stuff it could be, but idk how I can tell for sure without applying heat to the board (from what I know that would mess the stability of the ref and the resistors)The marking is wrongI drawed something wrong from the board to the schematic. This and: knowing that when measuring in circuit the reading shall not be trusted as internally the opamps output "leaks" into other pins, hence puting the resistor in parallel with the rest of the circuit.(Although this doesn't explain why the gain is `1.45` and not `1.9`)Something else completely that has just gone past meThe board in question:The schematic I came up with:The jumpers table:Regards

author: Alex Nikitin
author_rank: Super Contributor
timestamp: October 26, 2023, 10:15:46 pm
content: The resistor is made out of two 18K resistors stacked in parallel one on the top of another, from the look of it …CheersAlex

author: systemCorrµPti0n
author_rank: Newbie
timestamp: October 26, 2023, 10:53:39 pm
content: Damn.I was so not expecting that. I thought I could be missing another resistor in parallel and even checked under the opamp with a thin wire!It was something so obvious and simple thoThank you, I was going nuts re-checking everything trying to find what was missing or wrong!Best regards
Unexpected bytes received by RN-131 - Page 1
Forum section: electronics / beginners

author: alfo48
author_rank: Newbie
timestamp: March 31, 2018, 02:51:09 pm
content: I'm trying to test a small HTTP server based on WIFLY module RN131 and an AVR micro in my wifi home local network.I know that this device is designed to work as a client, however in my case I find a strange behaviour that i cannot explain and don't know if related to the design of this module or if I am missing something in module setup.Here is my test:After power on the server correctly joins my home network and is listening on port 2000. His IP address is 192.168.1.2.From a browser (firefox on PC or on Android device connected to my wifi) i fill the following URL line:http://192.168.1.2:2000/LEDON.The browser sends the following HTTP requests:GET /LEDON HTTP/1.1Host: 192.168.1.2:2000User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:59.0) Gecko/20100101 Firefox/59.0Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8Accept-Language: en-US,en;q=0.5Accept-Encoding: gzip, deflateConnection: keep-aliveUpgrade-Insecure-Requests: 1Pragma: no-cacheCache-Control: no-cacheThis request is correctly received from the RN131 serial port, and is processed by the AVR program (led is turned on).After this, the server sends back the following HTTP response to the RN131 serial port:HTTP/1.1 200 OKContent-Length: 49Content-Type: text/html; charset=utf-8Connection: Closed<blank line><html><body><h1>Led turned on!</h1></body></html><blank line>Looking at the data received at the browser side, i see many bytes of garbage (mainly 0xFF's - ASCII ÿ ) around the HTTP response sent by the server like this:ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿHTTP/1.1 200 OKContent-Length: 49Content-Type: text/html; charset=utf-8Connection: Closed<html><body><h1>Led turned on!</h1></body></html>ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿThis doesn't allow the browser to format the HTML message in the <body...</body>.Has someone an idea why these bytes generated by the RN-131 serial port?Thanks and regards.
Unexpected offset in voltage follower circuit - Page 1
Forum section: electronics / beginners

author: brumbarchris
author_rank: Regular Contributor
timestamp: March 25, 2022, 04:06:51 pm
content: I am not a noob, but something eludes me at the moment and the question is a beginner one...I have the attached circuit on a board, and I have marked in the picture the DC voltage values I can measure on this circuit. There is an unexplained offset when comparing the input and the output of the opamp, about 25mV or so. Yet, the maximum offset voltage of the AD8544 is indicated in the datasheet at max 6mV at room temperature (and I measure at room temperature).Input voltage is DC, current from a adjustable bench power supply, though a switched high side transistor. Supply voltage of the opamp is (measured 3.1V).What is wrong with this measurement (or circuit)?Cristian

author: magic
author_rank: Super Contributor
timestamp: March 25, 2022, 04:29:06 pm
content: Input bias current could be a problem, but not in CMOS.Input voltage range could be a problem, but not with R2R input.Guaranteed to work from 2.7V up, no problem.Do you have 100nF across the supply pins?Any way means of checking if the output is stable and doesn't oscillate?Is the chip obtained from a legit source or evilBay?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 25, 2022, 04:56:57 pm
content: If the voltages are measured with a dmm with 10 M input impedance, this could be just the loading of the divider at the input. 195 K relative to 10 M is some 2% and 2 % of 1.4 V would be 28 mV.To avoid much of the loading one could measure between the OPs output (or behind the 100 Ohms) and the input. This will likely show closer to 0.

author: eblc1388
author_rank: Frequent Contributor
timestamp: March 26, 2022, 10:26:42 am
content: Assuming your R74 and R76 voltage divider is accurate, then voltage at TPV3 should be 2.929V/2 = 1.4645V. You have measured 1.4628V at the opamp output and this is only 1.7mV off from the expected value. Based on this I would say the voltage follower is working as it should.Follows Kleinstein's measurement method or checks to see if your DVM has a Hi-Z input mode at the lower DC voltage range. Mine does at 10Gohm.

author: brumbarchris
author_rank: Regular Contributor
timestamp: March 28, 2022, 06:54:46 am
content: QuoteThat was exactly it!I got two DMMs to simultaneously measure both the input and the output. And on the output it is clearly visible: when I place the probe on the input, the output voltage also decreases to 1.437V.Thanks a bunch!Cristian
Transformer current spike on flyback converter - Page 1
Forum section: electronics / beginners

author: Username1
author_rank: Newbie
timestamp: November 18, 2018, 09:30:52 am
content: I'm designing high voltage output flyback converter using the method in this websitehttp://www.simonbramble.co.uk/dc_dc_converter_design/flyback_converter/flyback_converter_design.htmbut when I simulated it on LTspice, it shows some unexpected behavior.High initial current flows on the transformer and when output voltage reaches setpoint, high current spike shows on the primary side of the transformer.Why this happens and how can I solve them?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 18, 2018, 05:21:40 pm
content: What transformer are you using?A real one won't be k=1.Likewise, you'll probably have to deal with the leakage inductance resonating with the transistor and diode capacitance. An R+C across one or both addresses this (use R = sqrt(LL / Cc) and C >= 2.5 * Cc, where Cc is Coss or Cjo as the case may be).The stray capacitance of the secondary may also be significant.Also, you should probably check the simulations. That jagged current doesn't make any damn sense, and I suspect it's because of LTSpice's "optimized" solver (which is notorious for sacrificing accuracy to gain that speed). GEAR 2 is usually best for switching circuits.Tim
Unexpected Results for the Simplest of Circuits - Page 1
Forum section: electronics / beginners

author: naragon1
author_rank: Contributor
timestamp: December 28, 2015, 05:35:32 pm
content: Hello,I'm trying to get a solid understanding of basic electronics. I got a hold of a used copy of the second edition of theThe Art of Electronicsand theStudent Manual for the Art of Electronics, and I'm planning to work my way through all the labs. As I set up the first lab, which is basically verifying Ohm's law, I got some strange results.The lab is basically to measure voltage vs. current for a 20k resistor. Not having a 20k resistor, I put two 10k resistors in series and constructed the circuit as shown in the first image - easy enough. I was also using an adjustable power supply and taking measurements at 0.5V intervals. As I noted the results, I got twice the value of the current I expected each time. For example, for 5V I expected to get 250 uA, but instead I got close to 50 uA. I've posted a plot of the values I was getting, and sure enough I confirmed the linear result for Ohm's law, but the values of current appeared to be always 2x the expected value. I measured the resistance of each of the resistors and I got ~9.9k.What gives? Maybe someone can point out something obvious I may be missing.

author: pmbrunelle
author_rank: Regular Contributor
timestamp: December 28, 2015, 05:53:15 pm
content: What kind of power supply do you have?Consider that your ammeter will have a certain resistance; it is not zero Ohms.

author: Simon
author_rank: Unknown
timestamp: December 28, 2015, 06:00:27 pm
content: are you sure they are 10K resistors ?, something does not add up. As per above reply there will be some voltage loss in the ameter and so effectively lower voltage on the resistors. the ameter also has a resistance.

author: Seekonk
author_rank: Super Contributor
timestamp: December 28, 2015, 06:12:00 pm
content: This is an important lesson, Never fully trust what instruments read. For a good explanation read Dave's explanation of uCURRENT operation. Using such low currents will induce a lot of errors. Read the voltage at the resistors.

author: naragon1
author_rank: Contributor
timestamp: December 28, 2015, 06:45:46 pm
content: Doh.It turns out I was not properly breaking the circuit when taking the current measurement!Thanks everyone for the replies. Everything works as it should, carry on ...

author: alsetalokin4017
author_rank: Super Contributor
timestamp: December 29, 2015, 12:58:04 am
content: For a crosscheck, and as an interesting exercise, you might try eliminating the ammeter and, instead, look at the voltage drop across the resistors using a voltmeter, and computing the current from that, using Ohm's Law.

author: babysitter
author_rank: Frequent Contributor
timestamp: December 29, 2015, 10:48:23 am
content: ... which might lead to errors due to the instrument impedance in parallel to one of the resistors if done right (big enough resistors). Predictable as your meter impedance is known at least as a ballpark figure (most times its 10 MOhm).Very educating, too
Unexpected waveform class D output - Page 1
Forum section: electronics / beginners

author: lutkeveld
author_rank: Regular Contributor
timestamp: August 28, 2018, 09:51:31 am
content: I wanted to verify the output power of a Texas Instrument class D EVM (TAS5754MDCAEVM)After hooking up a 4 ohm test load and a 24V 5A power supply I got the following waveform after the LC output filter (see attachment)If I reduce the output to <1V the output is what I expected (two out of phase sines)However, when increasing the volume the individual outputs starts to distort, but the differential signal (purple) seems okay.Is this a problem? Do I measure incorrectly? My speakers dont seem to clip audibly.

author: Dat Tran
author_rank: Contributor
timestamp: August 28, 2018, 10:32:08 am
content: Can you show me your circuit ?And which channel is output, input on your oscilloscope ?

author: lutkeveld
author_rank: Regular Contributor
timestamp: August 28, 2018, 10:37:39 am
content: The circuit is the TAS5754MDCAEVM, which is a 2x50W max class D amplifier.I am measuring one channel with a simple DSO. The output is differential, but the measurement is single ended.That is why I use the 'math function' on the scope to subtract the signals to get the differential output (purple).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 28, 2018, 11:25:30 am
content: Differential works, who cares?No idea why it's making unbalanced waveforms, you'd have to ask them (but I doubt they'll say why).Tim
Unexplaned voltage drop on the 12V wire from head unit ACC to reverse camera - Page 1
Forum section: electronics / beginners

author: Charlie Whiskey
author_rank: Newbie
timestamp: June 05, 2024, 05:28:30 pm
content: Some electrical gremlin must be having fun with the new head unit I'm trying to installThe problem is my new reverse camera not powering up and I traced the problem to the 12V wire that is supposed to supply the power.Both the camera and the RCA signal cable are fine - I know because I tested them with a separate power adaptor (i.e. from the wall socket) and the head unit displays the image from the camera just fine.I tested the 12V power cable however and it was only giving me 9 to 10 volts and strangely fluctuates a fair bit.That 12V power cable is connected to the head unit's ACC cable with a T-tap connector. I had another equally long cable T-tapped to the same ACC wire and that is giving me a steady 12V.Any obvious ideas I should check for before I pull the head unit and all of the trim panels apart again? I'll probably break a few more pieces of plastic doing that...My chief suspect right now seems to be that T-tap perhaps not done right.

author: IanB
author_rank: Super Contributor
timestamp: June 05, 2024, 06:19:17 pm
content: If you have two sides of a T-tap and one side is giving 12 V while the other side is not, then the signs would point to a fault inside the T-tap, or a fault in the wire leading from the T-tap. It is not likely the fault is upstream of the T-tap.

author: Charlie Whiskey
author_rank: Newbie
timestamp: June 06, 2024, 12:20:02 pm
content: Found the culprit!Turns out this connector wasn't quite done properly, and I know the wire was too thin for it. The insulation was holding it in place, but the conductor itself was basically floating in air.A drop of molten solder solved it. Gremlin terminated.

author: CaptDon
author_rank: Super Contributor
timestamp: June 06, 2024, 01:00:29 pm
content: I have run into that scenario several times on a boat that I operate. The boat had a fire many years back and the company who was working on the boat and caused the fire agreed to fix the damage at their cost / insurance. Apparently one of their numb nuts electricians thought that those spade lug connectors were designed to bite through insulation like a T-tap. I have had an endless group of failures. No power to bilge pumps, announciator lights not coming on to warn of certain conditions, intermittent power to other ship systems. What a nightmare!!
Unfamiliar D-FF construction? - Page 1
Forum section: electronics / beginners

author: BurnedResistor
author_rank: Regular Contributor
timestamp: June 13, 2020, 07:47:34 am
content: Hey Gang!I was looking at some of the different construction techniques for D-FlipFlops (Specifically with async set and reset) and came across the ones I have attached.They seem to consist of multiple NAND SR-Latches interleaved with each other?I was having a hard time figuring out if there is a name for them and an explanation of how they work.Could someone point me to some resources?Thanks!

author: ataradov
author_rank: Super Contributor
timestamp: June 13, 2020, 08:35:15 am
content: This is a regular schematic for SN7474 IC. This is a typical DFF schematic. The simplified version of this circuit (without set/reset part) is described in wikipedia under "Classical positive-edge-triggered D flip-flop".The goal of the first stage latches is to ensure that it only triggers on the clock edge, not the level.The more simplified schematic you typically see is actually a transparent latch, not a flip-flop.

author: Benta
author_rank: Super Contributor
timestamp: June 13, 2020, 06:28:29 pm
content: What atadarov said.In the old (70s...80s) TTL databook from TI this was particularly emphasized calling it a "master-slave flip-flop". This term has since disappeared, as edge-triggered FFs have become standard.

author: gcewing
author_rank: Regular Contributor
timestamp: June 14, 2020, 08:21:00 am
content: Quote from: Benta on June 13, 2020, 06:28:29 pmA master-slave flip flop is actually a slightly different circuit, with subtly different behaviour:The difference is that the master-slave FF will remember if J or K has been high (and the other low) at any time before the clock edge, whereas the edge-triggered FF only responds to the state of the input right when the clock edge occurs. But for most applications this doesn't matter.
ungrounded oscilliscope question - Page 1
Forum section: electronics / beginners

author: Grayscale
author_rank: Newbie
timestamp: October 22, 2014, 01:25:11 pm
content: first of, i would like to say hello to everybody here, since this is my first post. been watching the videos, great stuff,i just recently started getting into electronics, cause i think it would help me in the long run in understanding certain devices or how they operate. i am an electrician, so i'm not new to this world. but i would like to expand my knowledge. maybe with your help....The subject of this post may have already caused some people to grind there teeth, i found out its kind of a touchy subject. its because of this problem i have, recently i bought a used scope. Its a Phillps PM3540. the guy i bought it from showed me that every thing worked. the knowledge is had of scopes was that they where al grounded to mains earth. but when i got home and wanted to plug it in i noticed it had a plug without an earth pin. when i started reading the manual it said " A double-insulated power supply allows the frame ground to be directly connected to a floating ground circuit provided this ground does not carry live potentials". it also said in a big warning box that the probes ground lead should not be connected to live potentials. this should mean that this scope is " floating" i think.my question is this. lets say i want to measure a 24Vac voltage. ground of this 24Vac is connected to mains earth. can i connect the probes ground lead to ground/earth and the probe to 24Vac. or should the mains earth be separated from the 24Vac ground.seeing as i'm probably only gonna measure voltages right now, can i "view" the scope as a multimeter and always put the probes ground lead on the earth? or on ground if earth is not available for instance in dc circuits?my confusion comes from the fact that if you measured with a grounded oscilliscope, the circuit your measuring on should be floating. but seeing as my scope is floating, does that mean i should be able to measured on circuits that have a common ground/earth?i hope this al makes sense. its been a long time that i had to type in english. and it proved a little harder then i remembered.anyways turned out to become quite a story. thanks for your help in advance.

author: Tandy
author_rank: Frequent Contributor
timestamp: October 22, 2014, 02:32:45 pm
content: Being an electrician you will be familiar with fitting an isolated shaver outlet in a bathroom, your oscilloscope will be similarly isolated.See this EEVblog post for useful information
Uni polar steeper motor drive  design doubt - Page 1
Forum section: electronics / beginners

author: NASK
author_rank: Contributor
timestamp: July 10, 2019, 06:15:16 am
content: I have a doubt about design stepper motor drive , therefore i refer this websitehttp://www.hteck.ca/electronics/stepper-motor-drv/sm-driver.htmlbut I cannot understand why use diodes series with Nchanal Mosfet

author: MosherIV
author_rank: Super Contributor
timestamp: July 10, 2019, 06:50:45 am
content: It is normal/standard to put 'flyback' (at least I think that is the technical term) diode to provide a path for current to flow when you turn off a coil.De energising a coil, the collapsing magnetic field will create a voltage oppisite to the one applied. In a circuit, the current will flow through any path available. In transistor switch circuits, the transistor needs to be capable of withstanding the high voltage.So it is normal to provide a path for the induced current to flow back.In the circuit shown, it is not well drawn for beginners to understand. There is a connection to positive voltage near the coils. The diode in series is the current return path only.

author: NASK
author_rank: Contributor
timestamp: July 10, 2019, 07:10:38 am
content: thank you for the support ! Is it same reason for this bipolar mode ?I think you telling about back emf current. Normally diode is used for protect transistor form the back emf .

author: pwlps
author_rank: Frequent Contributor
timestamp: July 10, 2019, 09:12:17 am
content: Quote from: NASK on July 10, 2019, 07:10:38 amBeware that in motors there are two phenomenons often both called "back EMF":https://en.wikipedia.org/wiki/Counter-electromotive_forcebut the naming is a bit misleading because they are actually of opposite polarities.The diode protection is for the EMF induced by a decreasing current in the motor inductance when the switch opens.Quote from: MosherIV on July 10, 2019, 06:50:45 amNot opposite (at least as far as the diode function is concerned). The voltage current relation for a coil is V=-LdI/dt so when the switch is opening there is a large negative dI/dt causing a large positive V, i.e. the induced voltage wants to sustain the current. A flyback diode will limit the induced voltage to the diode threshold voltage so that stopping the current will take more time. The energy of the stored magnetic field is then dumped into the diode.
Uni-T power supplies - Page 1
Forum section: electronics / beginners

author: grey_rabbit_25
author_rank: Newbie
timestamp: January 26, 2017, 06:36:33 am
content: Hi,I'm a beginner hobbyist with electronics, and i've been thinking about getting a desktop power supply.I've come across the following Uni-T power supplies, and wondering if anyone had any thoughts/commentshttp://www.mektronics.com.au/uni-t-utp3704-dc-power-supply.htmlhttp://www.mektronics.com.au/uni-t-utp3704-dc-power-supply-19396.htmlI've done a search and couldn't find much info (the one in the first link doesnt even appear on the company's website).It appears to me that the one in the second link is better specced, despite being cheaper.Thanks.

author: mmagin
author_rank: Frequent Contributor
timestamp: January 26, 2017, 05:30:33 pm
content: The first one is definitely a rebranded GW Instek

author: valentinc
author_rank: Regular Contributor
timestamp: January 28, 2017, 04:17:35 pm
content: From what I can see the second one has a better load regulation, but it's not very clear what is the spec for the first one (CV-20mV). They are good for the price. Also note there are others like them out there" GW Instek, like mmagin said, Siglent, you can search on ebay "0-30V power supply" and see what you find.http://www.siglent.eu/spd3303c-0-30v-0-3amp.htmlAlso this one is digitally controlled, for a similar price, but without that constant 5V output (if you don't need that, you can also consider this one)

author: Kleinstein
author_rank: Super Contributor
timestamp: January 28, 2017, 09:23:32 pm
content: The weight is suspicious: to heavy for a switched mode version and to light for a classical transformer. So maybe "Chinese" amps - a underrated transformer and thus the low MTBF.The Instek / Sigilent are nearly twice the weight.

author: Fraser
author_rank: Super Contributor
timestamp: January 28, 2017, 09:49:10 pm
content: UNI-T Power Supply units are made by a third party who also makes their Function Generators.Having owned one of the function generators and spoken to a UK retailer of them, I would not touch the PSU's or Function Generators. The retailer ceased selling them due to very high failure rates and customer dissatisfaction with performance. That is what he told me anyway. The retailer claimed that the build quality was very poor when compared to the UNI-T portable multimeters and DSO's. He continued to sell those as they offered good value fro money with low failure rates. The bench multimeters are also suspected of being built by a third party. I had a couple of those as well.....junk.This is indirect feedback from a retailer so consider it unconfirmed. I can state that the UNI-T Function Generator was a turd though. Very poor build and performance. Nothing like the quality of the handheld multimeters that I have.Be aware that many pieces of equipment mimic the competitions cases so just because the case looks the same, it does not men the contents are the same or good quality.Fraser
UNI-T Thermal Cameras - any good? - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: March 05, 2024, 07:51:59 pm
content: I came across these UNI-T Thermal Cameras, I wanted to know if someone has experience using them, I want to use them mostly for electronics repair workUTi120UTi256MUTi260M

author: sairfan1
author_rank: Frequent Contributor
timestamp: March 18, 2024, 07:00:03 pm
content: looks like they are quite new to market, there are no reviews on youtube.

author: Veteran68
author_rank: Frequent Contributor
timestamp: March 18, 2024, 07:27:40 pm
content: The Uni-T UTi260B/690B are quite good. The 690B is a Banggood exclusive whitelabel of the 260B, same device.The cheaper Uni-T models I'm not as familiar with.

author: PartialDischarge
author_rank: Super Contributor
timestamp: March 18, 2024, 07:39:46 pm
content: I have the 260 with the close up lens which is very important for PCBs. Works well, except you have to remove the battery otherwise it will drain quickly, I use it only from time to time.
UNI-T UT181A charging issue - Page 1
Forum section: electronics / beginners

author: kakci
author_rank: Newbie
timestamp: March 20, 2023, 09:55:40 pm
content: Hello,I've just received my UT181A and I am experiencing a strange charging behaviour, I have uploaded a video on youtube.https://youtube.com/shorts/cZ3PvdBTmr8Anyone else experiencing the same or similar issue while charging? Is this normal for this meter?

author: kakci
author_rank: Newbie
timestamp: March 20, 2023, 10:38:35 pm
content: Ok looks like the charging adapter supplied for the unit is too weak (9V DC 1A output), using a 9.5V DC or rather a 10V DC 1A power supply will solve this issue. The original charger cannot overcome the battery power source.

author: sstenks
author_rank: Newbie
timestamp: August 29, 2024, 04:46:54 am
content: This is how the original 9V charger that comes in the kit behaves.Try to use 10V 0.7 -1A and everything will be fine, otherwise the user manual says that a 10V 1A charger is supplied.Hope you is help.

author: wolfy007
author_rank: Frequent Contributor
timestamp: May 15, 2025, 03:16:02 pm
content: Sorry for this late reply (might be useful for someone), as I was just looking at why mine wasnt charging and saw a few of these charging issues comments. Mine wasnt charging because the 800mA fuse was blown, replaced fuse and it charges.But for OP, I suspect you are correct and that the supplied 9V @500mA adapter is not quite enough.Need a better adapter, the supplied 9V 500mA adapter is marginal. If you charge from a power supply at 9V you will see it draws a bit more than 500mA (mine draws 520mA at 9V). If your adapter can supply 9V and more than 500mA it will charge properly. 9.5V adapter @ 500mA should work also I think (mine draws 500mA @ 9.4V). Or at least thats what I have seen with mine.Also you can set the meter to charge and then connect banana connectors to the meter directly from your power supply to charge it. +9V to mA socket and negative to COM, just like the Agilent U1253B does (but dont use the Agilent adapter on the UT181A as the Agilent adapter is 24V).

author: joeqsmith
author_rank: Super Contributor
timestamp: May 15, 2025, 03:22:43 pm
content: Mine behaves like their video but I just let it go. It will eventually reach full charge. Normally long after the job I needed it for is done.....
UNI-T UT210E CLAMP METER PROBLEM ISSUE - NOT READ - Page 1
Forum section: electronics / beginners

author: matalcacer
author_rank: Newbie
timestamp: September 13, 2021, 04:33:57 pm
content: Hello:Please sorry but I don´t speak english very well. I live in Argentina (Spanish)I have a UNI-T UT210E clamp meter and this do not read measures in any mode, or shown heretical numbers.In buzzer continuity mode the buzzer is beeping continuously with or without leads connected.No AC or DC amperage meter, no resistance meter, no capacity meter..... it's like the test leads are shorted...No signs of burns or exploded components inside the clamp meter.More details on this video:TRIED TO MAKE CALIBRATION MODE (HOLD DOWN BUTTONS BLUE+YELLOW AND TURN IT ON). CALIBRATION DONE AND NO ERRORS FOUND...Thanks a lot and please sorry for my English.Have a nice week !!!Matias.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 14, 2021, 05:30:55 pm
content: Good Morning Matalcacer, I recommend returning the meter from wherever you purchased it, and asking for a new one.

author: matalcacer
author_rank: Newbie
timestamp: September 14, 2021, 05:57:14 pm
content: Quote from: BILLPOD on September 14, 2021, 05:30:55 pmThanks but no way... I bought it few years ago in USA no warranty at this time.Thanks.Matias.
UNI-T UT612 LCR meter and testing ESR in circuit?  - Page 1
Forum section: electronics / beginners

author: Stoempie
author_rank: Newbie
timestamp: July 07, 2020, 10:29:09 am
content: Hey guy's,I'm new to the hobby and i'm looking for an ESR meter for measuring in circuit, i had contact with my local shop and the say that the UNI-T UT612 LCR meter cannot read a ESR in circuit.The peak ESR meter can do that but is there a video or explanation or someone that can confirm that because i seen a lot of movies on testing ESR but cannot find a reason why that cannot be don by the uni-T it can test the ESR at 100khz just like the peak does ?Thank for the forum i learn a lot here.

author: mortrek
author_rank: Contributor
timestamp: July 07, 2020, 01:30:58 pm
content: Not an expert. You can sometimes test caps (I assume that's your main goal) in-circuit, but depending on the circuit and how they are connected within it, you can't really rely on the result. I think that false-negatives (where ESR looks good, but isn't) are less common than false-positives (where it looks bad, but isn't), so you can kind of get an idea of whether or not a cap is bad. The only surefire way to know is to desolder at least one leg before testing it. Also most ESR meters require discharging the cap first.It also helps if the meter is low-voltage, as it keeps from interfering with a lot of components like diodes. You also don't need a full brand-name LCR meter to just test ESR. One good design is the one by Bob Parker, but it's usually pretty pricey still at ~$80 US. Also those cheap ($10-15 bare) Chinese-made open source "component testers" can be found for very little and do a passable job. Some have sockets and some have clip leads. You'd need the ones with leads to even try using them in-circuit.

author: mortrek
author_rank: Contributor
timestamp: July 07, 2020, 01:33:49 pm
content: Also looking at the specs for the UNI-T UT612, I think it uses 0.6V for testing which is probably why it can't test in-circuit. Bob Parker's design uses something like 0.2V for testing, IIRC. Not sure about the component testers.

author: Stoempie
author_rank: Newbie
timestamp: July 07, 2020, 03:01:17 pm
content: ok thx, i will take a look if i can find what voltage the peak use to measure.ESR test voltage (into 40 Ohms): 40mV (typical) for the peak so ok now i can understand why the uni-t will not work.

author: Phoyle
author_rank: Newbie
timestamp: June 28, 2021, 03:02:06 am
content: Hi,Quote from: mortrek on July 07, 2020, 01:33:49 pmThere is also the UT622c. The Technical Specifications tab shows it has test V of 0.1 Vrms, 0.3 Vrms and 1 Vrms.https://www.uni-trend.com/meters/html/product/tyyq/ComponentTesting/UT622%20Series/UT622C.html
UNI-T UT61D or Uni-t Ut139C  - Page 1
Forum section: electronics / beginners

author: haralambosx
author_rank: Newbie
timestamp: August 29, 2016, 11:02:17 am
content: Hello all.I am new to electronics and this will be my first semester attending an electronics school, so I was looking to buy a multimeter. I often tinker with computer equipment and built some as a hobby. I know UNI-T is not the best brand out there but I am also not a professional I am a beginner and hobbyist. I was having a look at the two meters at the title but I would like some further opinions. I have found both on amazon.com for 40 and 35 $ respectively.Thank you!

author: Refrigerator
author_rank: Super Contributor
timestamp: August 29, 2016, 11:54:44 am
content: I'm leaning towards the UT-61D, since it has PC interface.But how about something like this ?http://www.banggood.com/Mustool-MT826-Ture-Rms-Professional-Digital-Multimeter-p-1058791.html?p=U627203391019201512Z&utm_campaign=electronicsNmoreBGDIY&utm_content=huangwenjieIt has data PC interface as well as a few more useful functions ( eg. temp ).Here's a review for it.

author: haralambosx
author_rank: Newbie
timestamp: August 29, 2016, 12:52:27 pm
content: Hey there I checked the meter though I believe they have trouble with their computer software not receiving proper support.
UNI-T UT61E Mods - Page 1
Forum section: electronics / beginners

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: October 28, 2012, 07:12:27 pm
content: I see that alot of people like the UNI-T UT61E meter but I want know if you guys could do any mods to the unit what would you do ... Also how the mod is done right in detail please and what you would need to do the mod ....ThanksJason

author: mariush
author_rank: Super Contributor
timestamp: October 28, 2012, 07:57:22 pm
content: There are several mods for this meter shown and explained in this forum, with pictures and notes.Don't be a lazy boy and do a search before asking.Basically the chip used in the meter is well documented so if you bother to read the datasheet then it's possible to solder thin wires to the pins of the IC and extend the functionality of the meter the way you want.

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: October 28, 2012, 10:56:34 pm
content: It's not a matter of being lazy it's just I have to read through hundreds of pages in order to find a single post that show me what I need to know... I have basic knowledge of electronics and I need help trying to figure out how to do the mods ...I was trying get all the info in one thread instead of being spread all over .....

author: mariush
author_rank: Super Contributor
timestamp: October 29, 2012, 12:20:48 am
content: It took me 2 minutes to find a thread, simply by entering "UT61E" in the search box and selecting "search in thread titles only". After all, you only get 9-10 results.Here's a page:https://www.eevblog.com/forum/general-chat/ut61e-auto-power-off-modification/There's a couple of other hacks in the long discussion thread :https://www.eevblog.com/forum/product-reviews-photos-and-discussion/uni-t-ut61e-multimeter-teardown-photos/Just press "/" in Firefox then press Ctrl+F and type a word like "hack" or "modification" and go from page to page clicking on the "Next" button on that search box at the bottom and it takes you a few minutes to find the pages showing up those links to mods or whatever.There's also a discussion somewhere in the thread about how to implement such hacks, and links to the datasheet of the chip inside the meter.You won't learn anything just by reading "solder wire here and you're done", put some effort into it.
UNI-T UT61E RS232 to USB converter - Page 1
Forum section: electronics / beginners

author: gigabyte091
author_rank: Contributor
timestamp: April 12, 2016, 01:10:58 pm
content: Hi guys,I bought UNI-T UT61E multimeter, and recieved a RS232 cable with DMM.My laptop is 7 months old and of course doesn´t have RS232 interface, only USB3.0 and 2×USB2.0I bought from ebay el cheapo RS232 to USB for 3 USD and adapter is recognized in windows but does not work with multimeter.I built +/-12V power supply and power DTS and RTS from it so adapter gets required voltage, and again, nothing... LED on DMM is transmitting data.What to do ? I have several arduino mini, and uno, or it is better to buy another converter ?

author: thisguy
author_rank: Contributor
timestamp: April 12, 2016, 07:20:58 pm
content: What is your adapter? The one I picked up was listed as rs232 but came with a 6 pin header instead of DB9, and uses ttl level signaling. The UT61E cable doesn't require +/-12V to function unless it's plugged into a port that requires it. (It will also function on 3.3v or 5v.) It puts out a positive polarity signal which I needed to invert to work with my USB serial adapter.If you gave more details on exactly what serial adapter you have, how you connected it, and how you tried to read your serial port on the PC, someone might be able to better help you.

author: Fortran
author_rank: Regular Contributor
timestamp: April 12, 2016, 07:36:33 pm
content: I have a UNI-T USB cable that I'm never going to use.If you want it, it's yours.

author: gigabyte091
author_rank: Contributor
timestamp: April 13, 2016, 04:49:27 am
content: I bought this one:http://www.ebay.com/itm/381494148148?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITWhen i plug it into laptop driver are installed immediately but when i connect multimeter nothing happened. I found out there is no voltage on DTR pin or DTS pin... I applied +5V to DTR pin and i hooked up osciloscope to rx pin and i can se waveform, but again data is not reaching laptop. Instead there is continous sound of USB device being unplugged from PC until windows display message that USB device is not working.(Pin DTR is not connected to converter)

author: gigabyte091
author_rank: Contributor
timestamp: April 14, 2016, 11:02:12 am
content: Problem is solved, i use another RS-232 converter, this one have MAX232 in and TTL to USB converter and is working
UNI-T UT81B Oscilloscope - Page 1
Forum section: electronics / beginners

author: cs.dk
author_rank: Unknown
timestamp: December 24, 2010, 11:43:58 am
content: Hi, new in here, and I have a question.(Sorry for my english, i'm from Denmark)I'm looking for an oscilloscope for automotive use. And i've been looking at Uni-T UT81B, which is very fair priced. Any clues about it?I know it's not a high-end thing, but i really don't think i need more than the 8 MHz.The things i will need to measure.Topdeadcenter (rpm-signal), ABS-sensors, and other sensors on the vehicle for fault-finding. The sensors will feed out a sinewave, or a squarewave. But at really low frequency? (Ie. Topdeadcentre @ 3000 rpm would not be much, or am I wrong?)The Uni-T seems to be better build that the DSO-Nano.Hope that someone can push me in the right direction. I have been looking at Instek 1000A-series, but as my first oscilloscope, i guess it will be overkill - I can allways upgrade, if i find a oscilloscope usefull.Thanks in advance

author: saturation
author_rank: Super Contributor
timestamp: December 24, 2010, 12:50:45 pm
content: Have you looked at the Velleman HPS 40? Its on liquidation sale in many places and it has a following for automotive use.

author: cs.dk
author_rank: Unknown
timestamp: December 24, 2010, 12:55:04 pm
content: Thanks,The Velleman looks great to, and it is still very fair priced imo. I can get one from Ebay Germany for ~€200.Am i right about the frequencies i will need to measure, never will reach the scopes limits?EDIT: Sure it would not push the scope.. Ie. TDC @ 3000 rpm.. 3000/60=50 Hz. Am i right?

author: Chasm
author_rank: Regular Contributor
timestamp: December 24, 2010, 02:21:11 pm
content: That is correct, but there is also the possibility that cars use a different encoding scheme. IIRC there were some attempts to change them over the time to make tacho hacks more complicated.Don't forget that virtually all modern cars use the CAN Bus to connect the various systems. But then CAN is not too fast either.I would think hard if I really need a hand held oscilloscope.Their memory depth is tiny unless you buy a high end version. Modern bench DSO have a really small depth and also much more bang for almost the same price.

author: cs.dk
author_rank: Unknown
timestamp: December 24, 2010, 02:35:26 pm
content: Thanks,I won't need CAN-bus, i don't even know how to read/understand the signals. It is primary for older cars, from mid 1990's to ~2000I think the handheld could be good for troubleshooting. Many sensors sort of disconnect at a given temperature. I know some put them i the oven, and measure resistance, while they are heating up, to see if something is wrong.If i (a helper) drive, and i watch the scope, i guess i would be able to see the traces of a bad sensor, while the engine cuts out at a certain temperatur.?

author: saturation
author_rank: Super Contributor
timestamp: January 03, 2011, 09:26:32 pm
content: You can download self-tutorials on various waveforms found in modern automobile electronics. They are most, if not all, far below 10kHz.
Uni tutorial schematic - Page 1
Forum section: electronics / beginners

author: BlinkY
author_rank: Contributor
timestamp: March 01, 2014, 11:34:42 am
content: Hi guys,I'm a few weeks into electronics and I'd like to recreate the below schematic into Multisim. Unfortunately I'm stuck on the part circled.Is it a 5V source? But neither terminals are connected?http://oi59.tinypic.com/jjqtmd.jpg(image button isn't working, sorry for raw link)Many thanks

author: cyr
author_rank: Frequent Contributor
timestamp: March 01, 2014, 12:00:03 pm
content: It's not a part really, it's just a node marked as being a 5V supply line. In a simulator you probably want to connect a 5V source to that node (and to ground).

author: mariush
author_rank: Super Contributor
timestamp: March 01, 2014, 12:01:00 pm
content: It's just a 5v dc source (+5v) the other is connected to ground.Basically, the idea of the circuit is that a smaller voltage (Vin) turns on the transistor which then allows a particular amount of energy flow from collector to emitter ( if it opens fully or it's in linear region, depends on current going into the base through that resistor)

author: BlinkY
author_rank: Contributor
timestamp: March 01, 2014, 06:01:23 pm
content: Thank you both. Much appreciated.
Unidentified 4-pin DIP L 9922 [SOLVED] - Page 1
Forum section: electronics / beginners

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 21, 2014, 11:42:20 pm
content: I've had no luck, maybe you know?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 21, 2014, 11:48:35 pm
content: optoisolator or possibly MOSFET

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 22, 2014, 12:10:48 am
content: Any ideas what company the stylized "L" represents?I'll try searching some more against mosfet and optoisolator.

author: krish2487
author_rank: Frequent Contributor
timestamp: February 22, 2014, 03:02:07 am
content: It is a PC817 optocoupler.The second line is a dead giveaway

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 22, 2014, 03:15:46 am
content: That's why I never found anything, I know now to use any and all numbers to search.digi-key confirms what you say. Although they're called optoisolators so @mikeselectricstuff was correct as well. A collaborative effort!Now I have to read the datasheet.

author: amyk
author_rank: Super Contributor
timestamp: February 22, 2014, 08:16:03 am
content: Quote from: GiskardReventlov on February 22, 2014, 12:10:48 amLiteOn, the manufacturer. It's an LTV-817.http://www.us.liteon.com/downloads/LTV-817-827-847.PDF

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: February 22, 2014, 08:18:05 pm
content: LiteOn, if I recall they make good cd/dvd reader/writers. I think this part is from a Coby dvd player.

author: GiskardReventlov
author_rank: Frequent Contributor
timestamp: March 01, 2014, 04:20:02 am
content: Maybe the 9922 is a date code 22nd week of 1999.
Unidentified chip from cheap phone amplifier - Page 1
Forum section: electronics / beginners

author: botcrusher
author_rank: Regular Contributor
timestamp: March 05, 2016, 06:34:06 pm
content: I've got this battery powered amplifier that sounds surprisingly fine and is rather loud when hooked up to a 6 Ohm HK195 driver salvaged from pc speakers, but the only visible chip on the thing aside from some 1AM transistors is a TA8803N - HT110609The closest thing i can find is this:TA8800NSeems like a rather odd chip to use?attached is a pic of the board in question:The only component on the reverse side is a 220uf 6V capacitor connected directly to the power in, which used to be 3xAAA but i've since attached a usb lead to it. If anyone wants a pic of the reverse side to see all the traces, by all means i'll post it.Edit: oh, right. Power button is middle, volume up is left, volume down is right (board is upside-down so chip is readable)

author: Andy Watson
author_rank: Super Contributor
timestamp: March 05, 2016, 06:41:32 pm
content: Would this fit the bill?http://www.szczkjgs.com/UploadFiles/fujian/3572/TA8803.pdf

author: botcrusher
author_rank: Regular Contributor
timestamp: March 05, 2016, 06:50:24 pm
content: Perfect!that makes a heck of a lot more sense than the other chip, thanks!Now, i don't have an oscilloscope to get the full picture, but the "positive" lead for the speaker hits a max of -200mV on the loudest setting... it doesn't go positive at all.

author: Andy Watson
author_rank: Super Contributor
timestamp: March 06, 2016, 12:15:17 am
content: It claims to be a class-D amplifier, and it looks like it has a differential output too - without adding an appropriate filter the output signal will, more than likely, confuse a DVM. An analogue meter might show something sensible.