hybridfree/eevblog-posts huggingface dataset:
Reverse Engineering a Chinese flashlight - Page 1
Forum section: electronics / beginners

author: Nexo
author_rank: Regular Contributor
timestamp: July 20, 2016, 12:01:54 am
content: Hello everyone!This is my first post and I'm a newbie in the ellectronic's world so please, go easy on me.I took apart a Chinese flashlight and started to Reverse Engineer its circuit in order to learn more about circuits.This part is the AC-DC converter of the flashlight and it looks like this:The red and black wires goes to the positive and negative of a battery that looks like this:And this is the schematics that I tried to make:I think there is something wrong with it because, as you can see, R2 and the led are connected to the point 1 which has AC current, ¿right? ¿Shouldn't it exploit or something like that?I'll add more questions in a few minutes.Thanks in advance!

author: Nexo
author_rank: Regular Contributor
timestamp: July 20, 2016, 05:51:14 am
content: Anyone?

author: MK14
author_rank: Super Contributor
timestamp: July 20, 2016, 06:07:47 am
content: Quote from: Nexo on July 20, 2016, 12:01:54 amWhat do you mean by "exploit" ?Do you mean explode ?If you do, it should be fine, because if you carefully analyse the circuit, you should be able to see that the rectifier diodes, only allow the current to get in one direction as regards that LED. In the other direction, both sides of the LED (marked as point 1 and + on your schematic sketch) will be approximately at the same positive potential (give or take a diode drop), so no problem.Only when point "1" becomes negative, will the LED get much current, and light (presumably it is an AC/Mains on LED, and is wired that way so it does not empty/drain the battery when not charging).I don't like the fact that the mains input (AC) does not appear to be isolated, and there is no transformer. Be careful.

author: imidis
author_rank: Frequent Contributor
timestamp: July 20, 2016, 07:14:49 am
content: I can't be of too much help, it's an interesting circuit and confuses me. See a lot of similar circuits on the cheap ebay stuff big clive does, with the bridge rectifier, capacitor, discharge resistor, and usually a couple other resisters in there as well and smoothing cap (for lights).Seems to be the cheapest way for them to convert ac/dc, although not the safest.My newb questions, whats R2 for? surge?And must be some circuitry in the battery?

author: Brumby
author_rank: Unknown
timestamp: July 20, 2016, 07:26:13 am
content: The capacitive dropper is not one that gets my vote of confidence - mainly because of safety.Sometimes it is easier to remove reverse biased diodes from the picture....Here are two versions of your diagram - one for each half cycle of the AC input:
Reverse engineering a Chip on board - Page 1
Forum section: electronics / beginners

author: miker7940
author_rank: Contributor
timestamp: March 31, 2016, 06:23:41 am
content: Hi everyone,So I have a chip on board I need to reverse engineer. I have done the rest of the circuit but now it is down to this one chip on board. I have extracted the die, however destroyed the connection wires in the process. I have access to items to view the die - but i'm not sure what to do from there.

author: Errmy
author_rank: Contributor
timestamp: March 31, 2016, 06:29:59 am
content: Well, it is possible to reverse engineer a Die, but it is combined with a lot of effort and expensive tools. The process in general is to picture the top layer, then remove this top layer, and picture the next layer till you are at the bottom of the Die (can be up to 16 metal layers + resistor layers + cap layers and finally the transistors on the substrate).In the end its a really pricey process.

author: miker7940
author_rank: Contributor
timestamp: March 31, 2016, 06:32:35 am
content: Quote from: Errmy on March 31, 2016, 06:29:59 amYou're right, that does sound expensiveDo you reckon a better way to do it would be to look at what it does, and then try and find a replacement IC/MCU that can do the job?Cheers.

author: krivx
author_rank: Frequent Contributor
timestamp: March 31, 2016, 07:18:27 am
content: If you have the die you might as well throw it under a microscope. It's very common to see a part number, manufacturer logo or other identifying mark on there and it's often the largest visible feature.i.e. this part is pretty easily identifiable as National Semi, fabbed or layed out in 1996, part number is LMC555http://s.zeptobars.com/National-LMC555-HD.jpg

author: danadak
author_rank: Super Contributor
timestamp: March 31, 2016, 11:20:55 am
content: If the OEM designer did his job correctly the CPU Flash holding the program isunreadable by external stimulus (you). The only way of hacking it is to use aSEM (Scanning Electron Microscope) and probe each Flash cell for its charge.The good news is this is how designers protect their intellectual property fromtheft.Regards, Dana.

author: poorchava
author_rank: Super Contributor
timestamp: March 31, 2016, 11:29:20 am
content: It's quite possible it will be a very proprietary / obscure device, quite possibly an ASIC. If they go to such measures as chip-on-board, it's quite possible that eventual program memory will not be flash but rather a mask ROM or OTP, which are easier to read out than flash.Sent from my HTC One M8s using Tapatalk.

author: miker7940
author_rank: Contributor
timestamp: April 01, 2016, 05:24:49 am
content: Okay,So I have had a look at the die under a microscope.It looks quite simple -which worries me. No markings at all.Would it be possible to write a implementation of this Chip on board in AVR? (it is a memory bank controller) I will create a separate thread.New thread:https://www.eevblog.com/forum/beginners/possible-to-replace-a-chip-on-board-with-a-avr-microcontroller/
Reverse engineering a module based on a TDA8004T. - Page 1
Forum section: electronics / beginners

author: makerimages
author_rank: Regular Contributor
timestamp: July 16, 2014, 09:27:01 am
content: Well, long story short- I salvaged the Smart-card reader module from inside an old Thomson set-top box, this one to be exact. That was way before I got my soldering station, and my 80W(yup, I'm an idiot) iron made sure work of getting rid of most of the 10 pads that were on the module(ribbon cable broke, otherwise I hadn't gone near them with my iron). The module is numbered 3571777A, and has the NXP semiconductor TDA8004T Smart-card chip on it. I'd now like to reverse engineer the module and bring out the connections again. Any bright ideas on what 10 signals could've been there/anyone have that set-top box to beep out? Many things seem to be on one line there on the module... multiple power inputs to the chip.. I'm puzzled.
Reverse engineering and a logic analyzer - Page 1
Forum section: electronics / beginners

author: Jane
author_rank: Frequent Contributor
timestamp: August 22, 2015, 03:22:44 pm
content: I need to find out how a device read some data from its CPU.It uses a program that runs on PC and the PC ,via 4 lines( 3.3V, ground and 2 more lines), communicates to the device( uploads data to flash, reads registers from CPU etc). So, I used a logic analyzer but not sure how to start interpreting the output (waves) from the logic analyzer. It seems it could be SDA/SCL protocol but not sure for 100%.Can anyone provide a clue?Thanks

author: German_EE
author_rank: Super Contributor
timestamp: August 22, 2015, 03:49:15 pm
content: USB is two wire. One signal wire is the inverse of the other so in this case look for signals that are a complementary pair.I2C is two wire (plus Chip Select) and the signal and clock lines are normally high, pulled low by the sending device.SDI is two wire (plus Chip Select) and the signal lines are normally low.There is also a signaling format called 'One Wire' which is anything but, I have no experience of this signal format

author: Godzil
author_rank: Frequent Contributor
timestamp: August 22, 2015, 05:12:39 pm
content: German_EE: There is no ChipSelect for i2c, as there is no need for one, as device selection is part of the i2c protocol, so only two signals, SCL and SDAFor SPI it's 3 or 4 wires depending if the slave answer or nor, but it's generally 4: Clock, MISO, MOSI and CS (MISO : Master In Slave Out, MOSI is the reverse)And the 1-Wire you speak about is a really slow serial interface, that use only one wire (as it's name) do I doubt that it is used on a board like this, it's generally only used for some specific need when we have only one wire that could be used, it's often use for the gas gauge we find insides batteries.OP: If your logic analyser have i2c protocol decoding function, try it, it's should be fairly easy to find which one is the clock and which one is data.Apart from that, the protocol used on top of i2c (if it is i2c) could be anything.Could you explain more about the device you try to reverse?How the 4 lines are connected to your PC? how it is connected on the other side?etc.

author: mazurov
author_rank: Frequent Contributor
timestamp: August 22, 2015, 05:59:44 pm
content: Asynchronous serial also uses 2 wires. Any decent LA software can decode it and most even auto-detect the speed. Just poke around with several decoders until you start getting info that makes sense. Post a screenshot with a capture, some protocols are trivial to guess.
Reverse engineering and reimplementing a garden hose water timer - Page 1
Forum section: electronics / beginners

author: markitus
author_rank: Newbie
timestamp: August 13, 2019, 09:05:51 am
content: Hey, first post here.. Long time Youtube channel follower! I know I shouldn't use the first post to ask for help but ... I am having a hard time trying to understand how this water timer worksI bought a cheap chinesse water timer with the idea of reimplementing the electronics to add Lora Radio managment so I can turn or or off the valve from a large distance and all running on batteries.I want to reuse the mechanical design of the product and create my own Arduino based PCB that fits on the plastic enclosure and I want also reuse the latching solenoid inside the device to manipulate the water flow.While trying to reverse engineer the product I have seen that it's powered by 3xAAA batteries and uses 3.3v logic (I also want to use 3.3v to be as eficient as possible) , the solenoid needs at least 5v to turn or/off so it uses some kind of booster design to charge a 2200uf capacitor and then dump it's load with a very short pulse in one polarity or reversed polarity using a H-Bridge to open or close the valve.I came up with the following design while using my tester in continuity mode and following the traces on the original PCB but I can't really understand how it works (suposing I have done it right!)The product PCB'sHow I supose it should work:When the operation of the solenoid is required (it's very rare, maybe twice a day open/close cycle) the MCU operates a transistor to boost the voltage from the battries <5V to something between >7V and <10 and then charges the capacitor to this voltage for a few seconds then uses a second transistor to dump the capacitor load for a short period of time (150ms to 250ms) to a H-Bridge to operate the solenoid in one polarity or to the reversed polarity, then disconects the boster and the capacitor to preserve energy when no needed and sleeps till the next cycle is required.A few questions:1) Does the schematic makes any sense at all?2) For my understanding it's using the inductor to boost the voltage, it's conected to the battery and ground with C11 and R14, since it's only needed to charge the capacitor and it's only required maybe only once a day it's not wasting lots of energy from the batteries?3) What is R6 and D2 used for? to discharge the capacitor of residual energy? taking a look at the PCB D2 is a pin diode, why ?

author: radiolistener
author_rank: Super Contributor
timestamp: August 13, 2019, 11:00:05 am
content: it looks like Q3 make battery short circuit by MCU signal

author: ledtester
author_rank: Super Contributor
timestamp: August 14, 2019, 02:21:20 am
content: You may find this MOSFET bootstrapping design idea helpful:https://youtu.be/zcQV_ZpK1W8?t=2m35sThe link starts at 2:35 into the video where it explains hi-side switching using a P-channel MOSFET. It then goes on to how to replace the P-channel MOSFET with an N-channel MOSFET using a bootstrapping circuit.
reverse engineering my old piezo shock detector.  - Page 1
Forum section: electronics / beginners

author: spikey1973
author_rank: Regular Contributor
timestamp: November 05, 2024, 10:27:30 pm
content: Oke hello to all.I recently decided to pick back up a small project I started on a few years ago.While starting this, I decided I want to redo the electronics part of this prototype because it is not really usable they way I had it in mind.An important part of the project is a shock detector pased on a piezo disk.This is not only to determin if there is a shock but also to measure the intensity of the shock by measuring the voltage on the signal line to a wemos s2 mini board.To make sure I don't fry the S2 board/pin I (tried to) make a small tool to max the voltage to 3.3V and keep it positive.Since I have to re-make this too and I lost all my documentation and the original link to the forum thread (here / somewhere else?)So I started to reverse engineer my "own" work.I tried to make a schematic drawing of this but I have big doubts about it being correct. Either by my reversed-enginering or if I made it correctly originally.As said, unfortunately, I can't find the former forum thread back, or even find a similar "network" design.So I was wondering if someone here can help me out a little, with getting the diagram correct.In advance, thanks for any offered help.Kind greats. Matthieu
Reverse engineering pinout of 3 pin soldering iron handle - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: May 05, 2019, 08:16:30 pm
content: Hello everyone,the bakon 950d soldering iron has a 3 pin connector like this for the heater handle.What i don't know is, how can i find out what each pin does so i can make a new handle for it?Can i use a multimeter or oscilloscope to find out which pin does what? (I assume there's AC power, Ground and Temp Control?)Thank you so much in advance.... i have no idea where to start on reverse engineering this plug.

author: KL27x
author_rank: Super Contributor
timestamp: May 05, 2019, 09:31:29 pm
content: If you view the end of your T12 cartridge as a stereo plug, I believe it goes like so:;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;Sheath is earthring is negative terminaltip is positive terminal;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;The thermocouple is read between positive and negative. Power is also applied between these two terminals.If you buy a clone 951 handle for it, the ones that are like 10 bucks, the colors of the wires are all screwed up. I believe the Red is earth, green is positive, black is negative. But you can trace them all out yourself using the previous information. All you have to do is wire up the new handle connector like the last one, going by what wire contacts what part of the cartridge... not necessarily by the color of the wire. Hint: I imagine most people with experience in this sort of thing would partially disassemble the handpiece so they can get to the socket, then use a continuity tester to figure out which wire contacts which part of the connector (sheath/ring/tip).

author: Mp3
author_rank: Frequent Contributor
timestamp: May 06, 2019, 05:22:17 am
content: Thanks, that makes sense! By the way, is the plug on the unit i posted a mini XLR? It has a little bolt that screws in place to hold it in and a notch on the plug.

author: Shock
author_rank: Super Contributor
timestamp: May 06, 2019, 07:10:42 am
content: Looks like GX12-3-M12.

author: fkfaraz
author_rank: Regular Contributor
timestamp: May 06, 2019, 07:49:15 am
content: what handle are u going to use???i have changed handle of my bakon bk 950d with the aluminium handle one...working fine....
Reverse engineering where to start... - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: April 30, 2020, 05:54:49 am
content: Hi All,I'm new to RE, I have a discontinued proprietary PCB, it has a NXP T1024 (PowerPC e5500) on there and a 5-pin header, from the datasheet I assume this is JTAG (TCK TDI TDO TMS & TRST_B) I'm 100% this thing runs Linux, *all* I want to do is put my own Linux on it, with telnet for comms to start with, I can see an two RTL8211's/RJ45's so networking should be easy if I can get Linux on there, how do I get connected to the JTAG (I have a Xilinx/Altera USB Blaster thing, will that work?), should I probe the pins with an oscilloscope, can I figure out which pin is which function without a schematic. This thing has no serial port/USB so I'm guessing I have to "blind" flash it with Linux/DHCP/Telnet and hope I can get in, the thing was really cheap and I have more of them so I don't mind killing one or two in the quest...anyone feel like helping me?Why do I want to do this, well it's a closed-source network security device I would like to use the hardware (it's neat and I don't really know of any dual NIC w/PoE embedded systems that can be had for $10) for an open-source version.I think you need a valid support subscription to download the firmware for it, so that might be a dead end, from the look of it the storage is BGA so that would be a nightmare to remove and dump.Thanks for looking.CheersRichard

author: nfmax
author_rank: Super Contributor
timestamp: April 30, 2020, 06:54:29 am
content: Start at the end, go on until you reach the beginning, then stop.Sorry about that, couldn't resist!

author: MosherIV
author_rank: Super Contributor
timestamp: April 30, 2020, 07:33:51 am
content: HiStart by getting the data sheet and user guide for the NXP T1024.I doubt the jtag will allow you to just flash/program linux. Application microprocessors do not have on board flash memory for running the application program (that is an embedded micrcontroller).As you pointed out, there is a storage device. This most likely is some kind of solid state disk. Most versions of linux are disk based, so you need to figure out how to re-load a new build of linux with telnet, ftp, etc all turned on, onto that storage device. Check if NXP have any info about how to do this, they usually have reference design for processors and some info on how to get reference design working.So, you will need to cross compile linux for that processor. You will have to check if there is support in linux builds for that processor.
Reverse enginnering of multilayered PCB board to schematic? - Page 1
Forum section: electronics / beginners

author: dds
author_rank: Contributor
timestamp: September 16, 2013, 08:53:52 am
content: Is that possible? If yes, can somebody describe the process?Thanks!

author: Bored@Work
author_rank: Super Contributor
timestamp: September 16, 2013, 09:17:42 am
content: You hire a shady company in eastern Europe or Asia, send them the board, pay the price and if you are lucky you get gerbers and schematic back. Google something like "pcb reverse engineering service china".

author: Bertho
author_rank: Regular Contributor
timestamp: September 16, 2013, 09:18:30 am
content: Quote from: dds on September 16, 2013, 08:53:52 amIf all components can be identified and all component pins are accessible, then use a multi-meter, do pin-pin measurements to see what is connected. And bring alotof patience.

author: Unknown
author_rank: Unknown
timestamp: September 16, 2013, 11:14:09 am
content: Or use JTAG boundary scanning if there are ICs with JTAG support on the board:

author: jeroen74
author_rank: Frequent Contributor
timestamp: September 16, 2013, 06:33:47 pm
content: What I've heard, they scan the PCB, mill away a layer so the next layer is exposed, then scanned... rinse and repeat until done. Some software to process the scans et voila.

author: dfmischler
author_rank: Frequent Contributor
timestamp: September 16, 2013, 08:08:33 pm
content: Quote from: jeroen74 on September 16, 2013, 06:33:47 pm'Cause that solves the problem of packages where you can't get at all the contacts (e.g. BGA).

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: September 16, 2013, 09:32:58 pm
content: If you don't want to remove components and go through sandpaper-wash-scan process using Cheap (~$500 off ebay), used dental x-ray machine with film pressed to the PCB (~$30 box of Fujifilm). Developed film should have low granularity and can be scanned and magnified to great extent later. Some people tried to use SLR cameras with these dental machines, but I think film gives better results especially with those cheap x-ray machines. I guess I don't have to mention that you should pint machine down and be like 5meters away in another room when you push the button (they usually come with remote).With sanding it is easy to go wrong and remove just a bit too much and it is very dusty and hard to remove layers of PCB evenly.
Reverse forward multicolor LED chaser circuit schematic - Page 1
Forum section: electronics / beginners

author: Shivram10
author_rank: Contributor
timestamp: June 29, 2014, 08:02:50 pm
content: Hello friends,I am a hobbyist in electronics, I wanted to design a multicolor festival lights with 5mm or 3mm LED lights in circle (blinking the same way as the Christmas star in the video below but in a circle).I don’t want to use arduino or any other programmable microcontroller (as I don’t have any knowledge of it), I just want to use basic IC’s such as 555 timer or some other. I will power it via wall-wart. I want to make 12inch Diameter circle using around 200 or more LEDs. I found a similar project herehttp://homemadecircuitsandschematics.blogspot.in/2012/10/200-led-reverse-forward-light-chaser.html.I just want to blink the LEDs in multiple colors in reverse and forward (center of the circle to edge and reverse) or any other pattern. Does anyone have any schematic for such projects, as I have Googled but found many articles such as thishttp://www.eleccircuit.com/led-chaser-by-ic-4017-ic-555/which only use less than 50 LEDs. Is it possible to build this circuit with 200 or more LED without using arduino or any other programmable microcontroller.Kindly let me know about any such schematic.Thanks in advance & Regards,Shivram10PS: - I can increase or decrese the number of LEDs as required, I don’t want to use SMD LED strip. This is a weekend project, just to keep me busy and brush up my electronics skill.

author: TheRuler8510
author_rank: Regular Contributor
timestamp: June 30, 2014, 03:12:43 am
content: Jeri has a really cool and simple solution for chaser lights.See this video:Good Luck!
Reverse polarity diode, Not stopping current. - Page 1
Forum section: electronics / beginners

author: Tomer
author_rank: Regular Contributor
timestamp: April 14, 2018, 07:45:05 pm
content: Hi AllThis is probably very basic but i am missing something, so your help is appreciated a lot!I am trying to use a 1N4001-G diode to act as a reverse polarity protection diode.Placing the Diode on the + rail have no affect, no matter the direction of the Diode. result is the same my led is ON.My understanding is that if i am placing the diode in reverse on the + rail, i should have no current flow.Why my Led is on ?Please see pictures in the link below:https://photos.app.goo.gl/PMFafxxXAEkuYWDs1Thank youTom

author: bd139
author_rank: Super Contributor
timestamp: April 14, 2018, 08:14:26 pm
content: The diode is shorted there. The breadboard rail isn’t broken between both legs of the diode.

author: Lee Leduc
author_rank: Regular Contributor
timestamp: April 14, 2018, 08:33:22 pm
content: Looks like you're trying to build a circuit on the power bus. The diode is shorted and not part of the circuit.Take a look at this short tutorial titled "How to Use a Breadboard and Build a LED Circuit"https://computers.tutsplus.com/tutorials/how-to-use-a-breadboard-and-build-a-led-circuit--mac-54746

author: Tomer
author_rank: Regular Contributor
timestamp: April 14, 2018, 09:18:20 pm
content: Ohh men, I feel so dumb now.Thanks guys for spotting the issue so quickly.Tom

author: Lee Leduc
author_rank: Regular Contributor
timestamp: April 14, 2018, 09:40:35 pm
content: Don't worry about it. We've all made mistakes like this when we were learning to use breadboards. Think of it as a rite of passage!You should see the burn marks on my breadboards when I've let the "magic smoke" out of a component!!

author: Tomer
author_rank: Regular Contributor
timestamp: April 14, 2018, 09:57:43 pm
content: Thank you for the encouragement!

author: bd139
author_rank: Super Contributor
timestamp: April 14, 2018, 10:34:05 pm
content: Yeah don't sweat it - it happensOnly last week, after 30 years of doing this stuff, I burned my fingers on a diode because I accidentally connected it across the supply instead of in series with it
Reverse polarity protection using mosfets - Page 1
Forum section: electronics / beginners

author: derGoldstein
author_rank: Regular Contributor
timestamp: March 22, 2017, 07:45:43 am
content: I have a circuit with an input voltage of between 5V to 20V, which I want to add reverse-polarity protection to. Attached is the circuit that I'm going to try.If the power is connected correctly the mosfet allows the current through and the led on the right (which is green) turns on. If it's connected in reverse then the current is blocked and the led on the left (which is red) turns on.Firstly -- will this work the way I described above?Second, I want to make sure that I'm using the right mosfet. What I'm looking for is a logic-level mosfet (turns completely on by the time Vgs reaches 5V) which can also tolerate Vgs going up to 20V+. Here are some that I've found:http://www.mouser.co.il/ProductDetail/Diodes-Incorporated/DMG7430LFG-7/?qs=sGAEpiMZZMshyDBzk1%2fWi4P4wC6csLMYIC%252bvOe09BV0%3dhttp://www.mouser.co.il/ProductDetail/Diodes-Incorporated/DMN3018SSS-13/?qs=sGAEpiMZZMshyDBzk1%2fWi4P4wC6csLMY9iJ21xVc378%3dhttp://www.mouser.co.il/Search/ProductDetail.aspx?R=BSC100N06LS3_Gvirtualkey63830000virtualkey726-BSC100N06LS3Ghttp://www.mouser.co.il/ProductDetail/ROHM-Semiconductor/RQ3E100BNTB/?qs=sGAEpiMZZMshyDBzk1%2fWi5brl1xcCtmLSztafmJM%252bzn0STSOkcaEpQ%3d%3dThe maximum current that will flow into the circuit is around 5A, but I want to avoid heat buildup so I looked for mosfets that can handle over 10A, though I understand that some of those are going to be overkill.Lastly, is there a reason to use a p-channel mosfet instead? Many example circuits opt for a p-channel mosfet connected to the positive input rather than an n-channel mosfet connected to the negative input. But n-channel mosfets are a lot cheaper and there's a much wider range of them. Is using a p-channel mosfet more efficient in some way?Thanks in advance.
PFET Reverse Polarity Protection - Page 1
Forum section: electronics / beginners

author: hgg
author_rank: Frequent Contributor
timestamp: March 08, 2014, 11:16:12 am
content: Hi,I am trying a simple but very effective little circuit for reverse polarity protection whichyou may have seen.Same circuit with a small modification:I have just added a little diode and an LED so that when the polarity is reversed the LEDwill light up and give you a warning. The diode is to protect the LED from reverse voltageunder normal operation and its the BAT45S. It works great.My question is that when the polarity is correct I can measure 456mV across the LED.(2.5mV across the diode). Do you know why is that?Thank you.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 08, 2014, 01:06:18 pm
content: Hmm, bet the voltage drop across the LED is even higher. You could test with a JFET source follower, or JFET opamp follower, to see about what voltage it's at.You would expect with, say, 8.2V in as shown, that "no" current flows, so R1 has 0V across it and the voltage between the diodes is undefined (anywhere between 0 and 8.2V). In reality, BAT45 is a very leaky diode, and will drop very little voltage relative to the LED, which might be a very good diode (i.e., low reverse leakage). Depending on ambient light level, that is.Worth asking... did you measure this with real instruments (and if so, which), or in the simulation (that looks like... Multisim?)?Tim

author: hgg
author_rank: Frequent Contributor
timestamp: March 08, 2014, 01:24:33 pm
content: QuoteYou found it! I forgot that LEDs become voltage sources under a light source.When I cover the LED, the voltage drop goes from 456mV to 10mV and whenI shine a very strong light on it, the voltage drop goes up to 1.3V !!! It actedlike a solar panel. That is a nice way to burn any sensitive components.Mystery solved. Thanks!p.s. No simulations.With an even stronger flashlight, 2.1V...

author: hgg
author_rank: Frequent Contributor
timestamp: March 08, 2014, 03:51:22 pm
content: Correction for those who want to try it.If I leave the resistor as is, then when polarity is reversed I get a -3.0V across the load...It should be connected from the anode of the warning LED to ground and the MOSFET gatetied directly to ground. Not sure why it works like that. I guess Vgs becomes lower than itshould be, because of the voltage drop caused from the diode and the LED.Corrected
Reverse schottky diode voltage in a USB hub... - Page 1
Forum section: electronics / beginners

author: erakan
author_rank: Newbie
timestamp: December 28, 2017, 11:50:36 pm
content: Hello,I've a cheap usb hub with dc input jack that has no protection for current flowing from dc input jack to the usb connector, so I've tried to fix this with adding a schottky diode. I cut the power trace from dc input jack to usb connector, reverse soldered a SCD34 SURFACE MOUNT SCHOTTKY BARRIER RECTIFIER salvaged from a broken Apple charger, then I've connected a 5V power supply and test the voltage with my multimeter. On the dc input jack side, I've readed 5.18Volts, on the usb connector side I've readed 4.85Volts, while I was expecting to read 0 or leakage millivolts. So I think, I was damaged the SCD34 while soldering (when I was testing this on my multimeter it was working normally). Then I desolder SCD34, test it with my multimeter and the diode was working normally.Then I've tried two more schottky diodes, SS24F (which was salvaged from a Wun Hung-Lo brand charger) and SS14 (that I bought today). I got the same readings on both of the sides, and both diodes passed multimeter test (before and after soldering - desoldering).Then I've connected 2 led's to the both sides for testing purposes and tried all schottky diodes (SCD34, SS24F, SS14). The diode on the jack side lights up when I connect dc power, but the led on the usb side did not. When I connect usb, both leds lights up (with or without dc jack plugged in). So I think there is no current flowing from dc jack to the usb connector. But why do I get 4.85 Volts reading form the usb connector side?That made me curious and I've opened and tested the schottky diode in a decent usb hub that I own, and I've measured the expected 0 Volts on the usb connector side, and 5.18 Volts on the dc input jack. (By the way the schottky diode was SS14 on that hub)So does anybody have any idea what is the reason that I read that high voltage from reverse soldered schottky diode? Did I really fixed the cheap hub?

author: kkessler
author_rank: Regular Contributor
timestamp: December 29, 2017, 04:37:25 am
content: I'm having a bit of problem trying to picture what you are doing here. Maybe a quick schematic showing where you put the diode with respect to the other parts, and where you are measuring the voltages. The .33 V difference between the readings is a reasonable forward biased schottky diode voltage drop.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: December 29, 2017, 06:25:41 am
content: I think I understand. The diode is right on the 5v coming from the USB jack (which could power the hub if the barrel jack was not connected)?I suspect you're measuring the diode's reverse leakage current. If you look at the datasheets for these diodes, you'll see that these schottky diodes can leak quite a lot (100s of uA), but not enough to power a LED. Assuming your multimeter has a 10M input, 4.2v represents only 4-5uA leakage. You could try loading the meter with a resistor to see what happens.
Reverse standoff voltage vs breakdown voltage in bidirectional TVS - Page 1
Forum section: electronics / beginners

author: Jim from Chicago
author_rank: Regular Contributor
timestamp: September 14, 2023, 06:21:36 pm
content: I am comparing two bidirectional TVS diodes, the part we are currently using is this:https://assets.nexperia.com/documents/data-sheet/PESD5V0C1BSF.pdfThe part we potentially want to use as a substitute is this:https://www.onsemi.com/download/data-sheet/pdf/esd5481-d.pdfNexperia part lists reverse standoff voltage as max of 5V. But then it also lists the breakdown voltage as typically 10V. I don't understand. Isn't reverse standoff voltage and breakdown voltage the same thing?The OnSemi part lists "maximum working voltage" as 5V which I assume means the same thing as "Reverse standoff voltage". But then the OnSemi part lists its breakdown voltage as possibly as low as 4.5V for low current (5uA).I am very confused what the difference is between reverse standoff voltage/maximum working voltage and the breakdown voltage. Can someone please enlighten me? I need to understand this to determine if we can sub in the OnSemi part in the same circuit...

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 14, 2023, 06:31:46 pm
content: My understanding is that reverse standoff and maximum working voltages are the same, which means that this is the voltage that can be applied continuously with a minimum amount self heating and current leakage. The keyword is continuously.On the other hand, clamping voltage is the voltage drop at the maximum rated current, specified for a very short period of time. The reason this voltage is significantly higher, is that all diodes have a dynamic series resistance which adds its I*R drop to the zener voltage itself.That is my understanding. Somebody may not agree with me.

author: brumbarchris
author_rank: Regular Contributor
timestamp: September 14, 2023, 08:06:28 pm
content: Actually, the onsemi datasheet is confusing for me too. Outright conflicting, I would say.On one hand, the IR parameter indicates the maximum current through the diode when 5V are applied to it is 1uA. Otoh, the VBR parameter indicates you could have the possibility of having 5uA through the diode at a 4.5V drop on it.To me, this is a contradiction, and the minimum VBr at 5uA should be above 5V.Cristian

author: coppercone2
author_rank: Super Contributor
timestamp: September 14, 2023, 08:13:00 pm
content: sounds like you should just test it, you can do it with a momentary contact switch and a power supply
Reversing a DC motor using H bridge - Page 1
Forum section: electronics / beginners

author: engineheat
author_rank: Frequent Contributor
timestamp: July 11, 2019, 08:11:14 pm
content: Hi,I'd like to control a hobby DC motor with an Arduino (PWM) with a H-bridge. I'd like to have the motor spin in one direction for a few seconds (up to a max speed), and then reverse direction (up to a max speed), and so on...Would it damage anything if the current is reversed while the motor is at a high RPM? I heard this causes a back voltage spike which can cause damage to the power supply, and so forth...If so, how does a driver like L298N work? For size considerations I'd rather use a single H bridge IC rather than a complete driver like the L298N.Thanks

author: MosherIV
author_rank: Super Contributor
timestamp: July 12, 2019, 06:56:22 am
content: If the circuit is correct, reversing motor direction should not harm the circuit. The motor on the other hand is a different matter. Suddenly changing direction is not going to be good on the mechanics.Why can you not stop the motor first before changing direction?Stopping is acutually easy with a H bridge, just turn off any transistors in the upper part of the H and tur on both transistor in the bottom of the H. This is shorting the motor to 0V.You are partially correct about back emf. Inductors, like the coils in the motor, will cause a back voltage when the current flow through them stops. In a motor, this happens when the comutator switches to the next coil in the motor. Any switching circuit for coils should always have fly back diodes to protect the transistor.If the PSU cannot handle the voltage spikes, you need a better psu. The regulator on the Arduino may not have a diode across the Voltage regulator, a diode across the Vreg input to output protects the Vreg output from injecting a voltage to the output. The diode must be in the right direction, blocks voltage from the Vreg input to output.Do not kniw about L298N.

author: pwlps
author_rank: Frequent Contributor
timestamp: July 12, 2019, 10:42:13 am
content: Quote from: blueskull on July 12, 2019, 07:03:43 amIf the PWM is fast enough there is no need even to add an inductor (the motor inductance may be enough). The general condition for efficient regenerative braking is to keep the PWM period much smaller than the L/R time constant. There is a nice explanation here:https://electronics.stackexchange.com/questions/56186/how-can-i-implement-regenerative-braking-of-a-dc-motor

author: Zero999
author_rank: Super Contributor
timestamp: July 12, 2019, 09:27:27 pm
content: The problem is what to do with the energy when the motor is reversing?If the motor is powered from a rechargeable battery, then it's fairly straightforward to simply use the motor as a dynamo and charge the battery.If the motor is powered from a non-rechargeable battery or the mains, then it's a bit more tricky. The energy could be stored in a capacitor, then used later to accelerate the motor, but the capacitor will have to be huge, if the motor's load has a lot of inertial Alternatively the energy could be dissipated in a resistor.
"reversing" reverse LEDS? - Page 1
Forum section: electronics / beginners

author: TT_Vert
author_rank: Regular Contributor
timestamp: May 19, 2020, 04:30:32 pm
content: I am looking to replace some 1206 ( actually think they are 3014's but those are harder to find) red LEDs in a radar detector I own and am looking to keep the height of the LED down as these sit under a light pipe. I am also considering going w/ a 70-90 deg. beam LED since I'd rather not have the LED that is illuminating light up the other pipes and bleed over to the adjoining pipes.. Looking on mouser and digikey the only narrower beam angle LEDS are all fairly tall (1.5mm+) except the reverse LEDS which I can find in 1.1mm. Am I correct in thinking a tighter beam will help prevent bleeding of a color into another light pipe? All of the LEDS on this detector are red normally so I don't know that light bleed was an issue w before but I am going to make the KA band blue, K green and KA yellow. Looking at these image on mouser it seems the pad is on both sides and I could actually mount these so the led doesn't go through the PCB and faces up, do any of you see a problem with this? Am I barking up the wrong tree thinking a narrow beam will help with this? Unfortunately all the light pipes are molded together so I cannot just fabricate something to block the light between each of them. I've included a pic of the detector and the LED.I am also going to be doing something similar w/ the bottom 8 strength indicator ledsThanksDave
Review my schematic? - Page 1
Forum section: electronics / beginners

author: cryptyk
author_rank: Contributor
timestamp: May 14, 2015, 11:19:58 pm
content: [Edit: Actually attached the file]I'm new to this, and I'm trying my hand at Eagle to create a custom PCB. Can I get some feedback on the schematic before I create a board file?The board on the left is an mfrc522 RFID breakout board that I'll connect with a breakaway header connecter. The center board is the spark core (2x header connectors). The board on the right is a VS1053 mp3 breakout board (2x header connectors). I'm using breakaway headers so I can remove the daughter boards easily, and because they all already have pins on them from my breadboarding.There is also one other "satellite" board that I'll place elsewhere using the jumper headers at the bottom. It's a small hall switch.I don't really know what to ask for help on, specifically, so I'm open to any kind of feedback.Thanks!Ryan

author: RJFreeman
author_rank: Regular Contributor
timestamp: May 14, 2015, 11:26:53 pm
content: you don't appear to have uploaded the boards....

author: cryptyk
author_rank: Contributor
timestamp: May 14, 2015, 11:28:09 pm
content: Quote from: RJFreeman on May 14, 2015, 11:26:53 pmOops. Attached now.

author: charlespax
author_rank: Regular Contributor
timestamp: May 15, 2015, 05:01:00 am
content: Glad to hear you're making a custom board. This must be wildly excitingNothing pops out as being wrong. Can you link to the actual board you're using?On the mfrc522 there is IRQ and NSS. I'm not sure if NSS or IRQ is the SPI chip select pin. Probably NSS (SS = slave select).I assume the 3V3 and 3V3A on the spark core our outputs and don't need to be powered. Same for 3V3 and 3V32 on the VS1053.All your ground and power pins look connected.It looks like you're running two SPI busses on this device. If they are two hardware SPI busses, your good. If they're two software SPI busses, you're probably still good if speed isn't an issue. If there is only one hardware SPI bus the two devices should share MOSI, MISO, and SCK (SCLK is the same thing). Each one would need a unique chip select pin, which you already have.Do you have your designs up on github? I'd love to follow what you do.
Revision B PSU advice - Page 1
Forum section: electronics / beginners

author: steve632717
author_rank: Newbie
timestamp: April 21, 2014, 07:47:12 pm
content: Hello, I am after a bit of help. I am trying to build the Bench power supply unit (Version B) that Dave showed a few years ago. The question that I have is on Version `A` Dave shows that pin 21 labelled AREF on the microcontroller have a 3.3 Volt supply to it, however, when I looked on the plans for version B, the 3.3 v supply has been removed. It still is labelled as AREF and links into C23 but I cannot see where it goes to. I have watched the videos showing Dave placing the traces for Version B, here it stops at C23 and Dave does not have a trace from where C23 and Pin 21 meet.I have looked through the datasheet for the microcontroller and it says that Pin 21 AREF should go to the DAC.I have checked the plans for Version C and it shows Pin 21 AREF has been renamed as VREF and is connected to the 2.048 V ref.My question is should pin 21 (AREF) on the Atmel microcontroller be connected to reference voltage of 2.048v.Sorry if I have not put this in the wrong place on this forum.Thanks for any help.Steve

author: marabut
author_rank: Contributor
timestamp: April 23, 2014, 08:25:41 am
content: Best place for such questions is under proper Dave's blog entry, IMO.Looking at schematic, in revisions other than "C", ATMEGA's internal ADC is not used (port C pins are in digital mode), so both ways (of connecting AREF pin )are correct. Check ADC section in ATMEGA's datasheet (internal connections diagram and ADMUX register).

author: Bored@Work
author_rank: Super Contributor
timestamp: April 23, 2014, 10:32:00 am
content: There is a reason Dave never finished that series of videos. Whatever version you try to build, the LT3080 tends to blow up because of a design flaw it has. The difference between the set pin and the output must not exceed 0.3V - something rather unlikely to always be ensured in a programmable power supply.

author: steve632717
author_rank: Newbie
timestamp: April 23, 2014, 12:25:10 pm
content: Thanks for the advice. Does anyone no of a good bench power supply diagram that can be used for a newbie to try?

author: Rerouter
author_rank: Super Contributor
timestamp: April 23, 2014, 12:27:45 pm
content: If your willing to use decent sized heat-sinks look into a basic LM317 supply, plenty of schmatics out there for a LM317/LM337 split supply with ajdustable current limits (it needs a -1.25V rail for the LM317 output to truly drop to 0V)

author: han
author_rank: Frequent Contributor
timestamp: April 23, 2014, 12:39:45 pm
content: Quote from: steve632717 on April 23, 2014, 12:25:10 pmis switching P/S suit for your need?

author: steve632717
author_rank: Newbie
timestamp: April 23, 2014, 04:58:54 pm
content: Not sure if I would need a switching P/S. All I want is a bench power unit to run small electronics. Would like to be-able to adjustable the voltage.
Design Revision / Version  numbering - Page 1
Forum section: electronics / beginners

author: Teti
author_rank: Regular Contributor
timestamp: August 12, 2021, 09:18:03 pm
content: Hi guys,I'm a little bit confused about numbering / lettering revisions. Would my first PCB be rev.0 (A) and consequential rev.1 rev.2 and so on, or do I start with number 1 (ei. rev.1)?So far I have come across both situations, but would like to do it right.Thanks for all constructive answers.Mart

author: ataradov
author_rank: Super Contributor
timestamp: August 12, 2021, 09:34:24 pm
content: There is no right, it makes no difference as long as you know what your numbering scheme was and it lets you differentiate designs.

author: floobydust
author_rank: Super Contributor
timestamp: August 12, 2021, 10:41:30 pm
content: It's what makes sense to you - I use prototypes as Rev 0 and numbers or letters in production like Rev. A or Rev. 1 but lately I prefer using letters.What gets confusing is your PCB has a part number and rev # and so doesn the entire build, the final populated board. It's possible to change traces or components or both.So think ahead a bit.
Reviving a multi cell lipo - Page 1
Forum section: electronics / beginners

author: SunBakedMike
author_rank: Newbie
timestamp: September 12, 2023, 06:27:21 am
content: I'm trying to get back into EE after a long time away so I will use the wrong terminology and I fogotten a lot of the basics. This is not only about the task but also about procedure. I'm going to treat this like a black box since I don't have a data sheet. Try and be kind, but absolutely tell me what I'm doing wrong. If I have to choose, I'd rather you be mean and teach me something.I need to "try" and revive a 3 cell lipo that I think was discharged lower than the cut off. Up 'till now I've let plenty of magic smoke out relearning. But this lipo (https://traxxas.com/products/parts/batteries/idpowercellbatteries/lipo/2872X-5000mah-111v-3S-25C) is not going to just let a little smoke. I know how to recharge a single cell with a bench power supply but not a multicell that I can't take apart.Grammer warning, I'm not going to bother with complete sentences.I'm going to measure the voltage of the battery. Current limit my supply to 1 amp (arbitrary, supply limited to 3A per channel) and set the voltage to measure voltage +100mV.Hook up battery and increase voltage in 100mV increments until I get current flow. Monitor for heat.Increase voltage as necessary to keep heat under control and current flowing. Above 3.7v I have to worry about 2 dead cells causing a fire, above 6.4V 1 dead cell, at 9V I've reached cutoff.Increase V until 10V is reached and wait for current flow to stopDisconnect battery and measure with MM. Record voltage. Wait 48 hrs and measure voltage.If voltage has not significantly dropped then batterys are good. Charge normally on appropriate charger.Is my procedure ok?What is a significant voltage drop after 48hrs?Sometimes I think that I should do normal old-guy hobbies and just fish. Maybe have a midlife crisis and buy a sports car I can't handle.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 12, 2023, 07:49:59 am
content: From what I know about Lipo, there is only one decent solution: Take the battery pack apart, dispose of the cells which are discharged to below 2.8V (I think that is the accepted standard) and then do whatever you like with the remaining cells.

author: wraper
author_rank: Unknown
timestamp: September 12, 2023, 08:03:45 am
content: There are balancing terminals, so you should have direct access to the individual cells. If some cell is discharged down to zero, throw it out. This battery won't be safe even if it doesn't burst in flames during charging.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 12, 2023, 01:28:12 pm
content: Is your battery pack Li-po, (Lithium Polymer), or Lithium Ion.....similar voltages, but other differences.