hybridfree/eevblog-posts huggingface dataset:
Question about heat index (perceived heat) and wind - Page 1
Forum section: electronics / projects

author: ivan747
author_rank: Super Contributor
timestamp: September 23, 2015, 04:06:39 pm
content: Hello, guysI have been assigned a small research project for college where I am required to measure the perceived heat at some metro stations. According to my research, factors that affect our sensation of heat include the actual temperature (which is hot in the Dominican Republic) and humidity (which is high in DR). That's what's called the heat index. On colder temperatures (around 15C), the perceived cold is indicated based on actual temperature and wind speed. 15C is extremely unusual in my city.One factor that I think affects metro stations a lot is wind. Being underground, some of our stations are naturally ventilated, because the metro entrance sort of works like an air scoop. On others, it doesn't happen that way and that's where it gets really hot (unacceptably hot, IMO). But I haven't figured out how to include this in the perceived heat calculations. I can't really quantify the contribution of wind in the heat index.Now, here comes my question. Why isn't wind speed included on the heat index calculations? Right now I'm typing under a ceiling fan, and trust me, if that thing wasn't on, I would be sweating all around. I have searched high and low for heat index tables and none of them consider wind a factor. Was it too much hassle for the researchers or wind/ventilation works in a different way? I would expect act like a heatsink fan if the wind temperature was lower than body temperature.Also, does anyone know of a more specialized forum for this? If Dave allows (I think he does).Thank you so much.

author: ajb
author_rank: Super Contributor
timestamp: September 23, 2015, 05:16:03 pm
content: From a quick googleing, it looks like you wantWet-bulb globe temperature. My guess is that wind isn't included in heat index because it's too variable and adding a third parameter means you can't have a simple two-dimensional chart to reference. Note that WBGT also incorporates radiation, which is another confounding factor in perceived temperature. So for a complete picture of perceived temperature at a metro station, you'd probably need to evaluate the overall temperature, humidity, generalized airflow conditions, and shading. The latter two will be particularly tricky to aggregate in a meaningful way over different weather and seasonal conditions.

author: ivan747
author_rank: Super Contributor
timestamp: September 23, 2015, 06:48:39 pm
content: In my subjective experience, the temperature down in the metro stations is pretty much constant, unless you're in the way of a wind current.I ordered a cheap-ish $35 device that measures temperature and relative humidity, according to a handful of reviews, it's spot on accurate.I won't include the effects of wind in the research, and I'll avoid the windy parts of the station (I'd love to map out the wind currents inside the stations and the railway some day, but good luck getting inside the tunnel itself...).
I2C logic-level voltage and how to implement it with Sparkfun Products - Page 1
Forum section: electronics / projects

author: LoveLaika
author_rank: Frequent Contributor
timestamp: September 23, 2021, 05:51:50 pm
content: --Rewording my old question, realizing a better way to ask questions.Ok, in a nutshell, I have two MCUs: theArduino Nano Every, and theArduino Portenta. Two totally different processors operating at different voltages (5V for Nano, 3.3V for Portenta). I'm reading a sensor via I2C,Adafruit's LIS3MDL. It's pretty straightforward to wire a single sensor on a breadboard, but I'm a bit lost when it comes to scaling it up over long distances in terms of the voltages.So, in my efforts to scale up, I'm using Sparkfun's Qwiic products: amultiplexer, adifferential endpoint, and adifferential midpoint. My goal is to have the MCU connect at one endpoint (call that EP1), connect to the midpoint (call that MP), and connect to another endpoint (call that EP2). The MUX will be connected at the midpoint along with 8 sensors, and EP2 will host one sensor itself. Thus, a total of 9 sensors. Pretty straightforward, but looking at the schematics of how it wires up, I'm lost when it comes to I2C voltages.Thesensoris straightforward. Following the guide, hook up 5V or 3.3V to VCC, hook up SCL/SDA lines, hook up ground, easy. Or, use a Qwiic cable, with V+ being the voltage that the MCU is based on.TheMUXis also straightforward being powered via Qwiic. Now, the schematic has it labeled as 3.3V, but the PCA9548A can take 5 volts. So, if one uses an appropriate cable, the MUX can take +5V and pass that along to other sensors via Qwiic.Theendpointalso seems simple. On the schematic, VCC and VCC1 are tied together via jumper, so the PCA9615 can see the same voltage on both sides. VCC1 can be passed to another endpoint via RJ-45 Blue wire. So, when using two endpoints, the voltages would be the same.Themidpointdoesn't seem as simple. Power comes in via RJ-45 Blue or Green. Focusing on Blue for now, the midpoint schematic has it labeled as VCC_1. The default option of the midpoint is to power it with 3.3V through its header, the RJ-45 Blue wire, or the Qwiic connectors. However, it appears that if you power it via RJ-45 blue (say in the instance you deliver 5-volts through it), if PSEL is left open, you still tie VCC_1 to the "3.3V" net with the short at the end of the buck regulator. In effect, you would be powering the PCA9615 on the midpoint with +5 volts on both sides.Now, the question is: when working with the two different MCU boards, will this set-up work with both voltages? With the way things are set up, it appears that through RJ-45 blue, you can hook up the appropriate pins and voltages on the MCU side (+5 with the Nano, +3.3 for the Portenta), and it should work with both systems (putting aside question whether or not the MCU board will be able to supply enough current for everything). Does this hookup seem correct in terms of making sure operates correctly with the appropriate MCU?
Question about impedance matching transformers - Page 1
Forum section: electronics / projects

author: Ben321
author_rank: Frequent Contributor
timestamp: October 12, 2022, 04:18:22 am
content: Using a circuit simulator program, I was experimenting with different turns ratios of a transformer (it uses an ideal transformer model, including having no resistance for the windings of the transformer), and noticed something interesting when using the transformer for impedance matching. In this experiment I was also just treating the source and load impedance as resistance (not taking into account reactive impedance that would exist in real life). It seems that when matching a source with a resistance that is 10 times the resistance of the load, a 3:1 turns ratio is what works best. That completely threw out what I had assumed would be the case. I had assumed that a 10:1 turns ratio would be needed to match a source to a load when the source had 10 times the resistance of the load.Why is it that the best turns ratio in this case is 3:1?

author: KrudyZ
author_rank: Frequent Contributor
timestamp: October 12, 2022, 04:41:04 am
content: Because you are transforming voltages / currents by that ratio, so the perfect ratio is sqrt(10) to get the best power match.If you had 1 A going through a 10 Ohm load you would have 10 V across for 10 W of power.For the same power in a 1 Ohm load you need 3.16 V yielding 3.16 A...

author: Bud
author_rank: Super Contributor
timestamp: October 12, 2022, 04:46:55 am
content: Because impedance ratio is proportional to N^2, where N is winding turns ratio.

author: Ben321
author_rank: Frequent Contributor
timestamp: October 13, 2022, 07:59:53 am
content: Quote from: KrudyZ on October 12, 2022, 04:41:04 amThat makes sense.
Question about inductors, inductances, and 'bias currents' - Page 1
Forum section: electronics / projects

author: Etesla
author_rank: Regular Contributor
timestamp: April 14, 2020, 03:54:53 am
content: Hi all,Inductor datasheets like this one:https://www.digikey.com/product-detail/en/pulse-electronics-power/PG0077-202NLT/553-2034-6-ND/3179497usually state that the actual inductance changes with the 'bias' DC current going through it. For example, the inductor above is spec'd at 1.66uH at the rated current, and 2uH with no current.I want to know on what timescale the inductance actually changes. In other words, if I quickly changed the current through the inductor, how quickly would it's inductance react to that change in current?I'm asking because I'm messing around with discontinuous mode switching power supplies. I want to know if modeling the inductor in spice as a constant valued inductance at high (above maybe 20 Khz) switching frequencies is accurate. I would, in that case, use the average or maybe RMS current through the inductor as the 'bias current' that I would use to get the actual inductance.Thank you!

author: ejeffrey
author_rank: Super Contributor
timestamp: April 14, 2020, 04:21:52 am
content: Its essentially instantaneous. The small-signal inductance will vary throughout the switching cycle.
Question about IP2368 // specific request - Page 1
Forum section: electronics / projects

author: james21180
author_rank: Newbie
timestamp: December 09, 2023, 02:20:23 pm
content: I’m building a cellular mobility case for a client and they’ve made a specific request that I cannot seem to find an answer to…yet.They want a single USB port that they could use to power the mobility case, but also charge devices if the case is on mains, so basically one port that allows power in and power out both using PD for power negotiation.The only product I can find is the IP2368, but I’m not sure it will allow this sort of function without a battery attached.I’ve give my client the option of two ports, power in and power out but they want one or none..so here I am.
Question about LCD in hand held operator - Page 1
Forum section: electronics / projects

author: CalG
author_rank: Contributor
timestamp: May 06, 2016, 11:18:06 pm
content: I have an older VFD with an LCD operator MIO interface for monitor and programming.The LCD screen is less than brilliant in regards to it's ability to display information screens. Today, when the device was powered up, the LCD screen displayed the page as a mirror image.Am i correct not to consider the LCD module it's self as the bad component
Question about LCDs - Page 1
Forum section: electronics / projects

author: Miti
author_rank: Super Contributor
timestamp: December 02, 2019, 01:30:18 am
content: Hi,I have a question about 7 segment LCDs. I'm trying to improve a weighing scale and reuse the load cell, LCD and case. The initial device was supplied by two AAA batteries, I have a boost converter on my board and I boost the 3V to 5V. I'm using a PIC16F917 and a HX711 load cell ADC.The question is, are the LCDs built for a specific voltage? At this moment my code can display something on the LCD but depending on the supply voltage, I get lots of ghosting or not. AT 5V, the intended supply voltage, everything is turned on regardless of the LCD registers. At 3V, it works well. The ghosting starts after 3.1 - 3.2V.The LMUX is 1/4, the bias is 1/3.I wonder if a resistor between VDD and LCD Bias 3 to reduce the Bias 3 voltage to about 3V would help.Thanks,Miti

author: coppice
author_rank: Super Contributor
timestamp: December 02, 2019, 01:37:17 am
content: Most segmented LCDs only give optimum contrast over a narrow voltage, and the contrast degrades radidly as you move away from that. Narrow temperature range 4 mux panels are usually specified for somewhere in the 3V to 5V range. Wide temperature range 4 mux panels are usually in the 3.5V to 5V range. The bias resistor lets you tweak things for optimum contrast, but it can't usually overcome a big voltage error.

author: Miti
author_rank: Super Contributor
timestamp: December 02, 2019, 03:02:17 am
content: Quote from: coppice on December 02, 2019, 01:37:17 amThanks, good info!Aren’t those 3 bias resistors supposed to set exactly that, the voltages the mux swings between?Just look in the LCD section of PIC16F917/946. That should make it independent of the supply voltage.
Question about LED strip design - Page 1
Forum section: electronics / projects

author: lordrafa
author_rank: Newbie
timestamp: October 31, 2021, 12:05:17 am
content: Hello,I bought a couple of LED strips from Leroy Merlin and I discovered that they need to be connected to 220V CC. Since I was not that much comfortable to work with that voltage, I decided to chop strip in smaller sections and connect them in parallel to a much safer 12v CC PSU. It actually works perfectly however there is something that I don't understand from the strip schematic:As it can be seen on the schematic, the strip was made from 120 LEDs divided in 60 parallel pairs of 2 LEDs each. Also, in between, there were 24 resistors (12x82ohm and 12x68ohm) connected in series with the LED pairs adding 1,8KMy question is, why not to add a single 1.8K resistor? is this because dissipated power? if so why to choose two different values?Thanks everyone in advance...

author: John B
author_rank: Frequent Contributor
timestamp: October 31, 2021, 12:41:49 am
content: Having multiple resistors will help to balance each parallel bank of LEDs.edit: I misread that schematic. Probably not for balancing current, but to decrease the chance of the high voltage arcing over a single resistor.

author: lordrafa
author_rank: Newbie
timestamp: October 31, 2021, 09:18:55 am
content: Thanks for your reply, just I still don't understand why to use two different values (82 and 68 ohm) rather than use single one (75 ohm). On the other hand, is it important where do you put the resistors? I would say no but is there any logic to put them in between rather than all on the beginning?
Question about MLCC under DC bias... - Page 1
Forum section: electronics / projects

author: opa627bm
author_rank: Regular Contributor
timestamp: August 18, 2015, 05:56:59 am
content: Hi Guys,Long question short... Does a 22uf 6V X5R MLCC will have more capacitance than a 4V rated one when they are under 2V DC bias?I tried to use the simulator on Murata and NIC website and they seems to have the same capacitance...Regards,Li

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 18, 2015, 05:58:37 am
content: You're essentially buying the same chip under different part numbers (and possibly different pricing).Tim
Question about Modeling of RC BLDC Motor.. - Page 1
Forum section: electronics / projects

author: ammjy
author_rank: Regular Contributor
timestamp: May 13, 2019, 11:53:30 am
content: Hello, EEVBlog Users !Always Thanks you for your time and convenience.I am looking for information to modeling transfer function of RC BLDC motor.Actually, I found one paper in IEEE Xplore. but, transfer function and procedure was too simple.and I couldn't find more detail paper.If you don't mind, could you recommend to me good book or detail paper to modeling transfer function of RC type BLDC motor ?Please, let me know !

author: Benta
author_rank: Super Contributor
timestamp: May 13, 2019, 12:52:49 pm
content: Why do you think the model is too simple? DC and BLDC motors do not have a complex electrical model. The complexity lies in the drive system and your drive strategy.You say "RC" BLDC motors, so I suspect you are looking for sensorless drive. This needs a special controller with startup functionality, and you will only be able to start the motor with limited mechanical load (eg, a propeller).

author: ammjy
author_rank: Regular Contributor
timestamp: May 13, 2019, 01:26:28 pm
content: Hello, Mr. Benta !Thanks you for your time !I think, I thought more than necessary about BLDC. I mean, I guess My brain has filter that make simple things to difficult always. because, I already know structure of sensorless BLDC motor.Thanks you for your help Again, Mr. Benta. I appreciate it.
Question about one of the circuits in LM399 datasheet - Page 1
Forum section: electronics / projects

author: opa627bm
author_rank: Regular Contributor
timestamp: March 16, 2014, 04:00:50 am
content: Hello everyone,Can someone tell me what is the functionality of the 12k, 2k and 20k resistors in the circuit? They seems formed a voltage divider to prevent the output from the trimpot goes too low?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 16, 2014, 04:07:36 am
content: They control the output voltage. The trimpot is just that, a trimpot, not a wide range control.Tim

author: c4757p
author_rank: Super Contributor
timestamp: March 16, 2014, 04:16:27 am
content: Trimpots haveshittemperature coefficients. This arrangement allows good quality, fixed resistors to exert most of the control over the output voltage.

author: quantumvolt
author_rank: Frequent Contributor
timestamp: March 16, 2014, 11:26:36 pm
content: The left divider 12/2 gives an output (6.95*(2/(2+12)) which is a bit less than 1 volt and has internal resistance a bit less than 2k. Adding the 20k in series increases the source resistance to some small 22k. The 100k trim and the 2M makes a 6.95 volt source with resistance a bit more than 2M (a hundred times greater than 20k). So the trim will be able to alter the summed voltage with around 1 %. The right side 2k buffers the op amp and is small in order to not disturb the balance of the op amp bias (the two inputs should see appr. the same DC resistance, hence the left side arrangement so-so balances the 22k feedback resistor).
Question about Op-Amp MAX4238ASA - Page 1
Forum section: electronics / projects

author: m.abdelwanis
author_rank: Contributor
timestamp: September 04, 2024, 11:35:46 pm
content: Can I use this circuit designed to measure temperature from a thermocouple with a resistance of 1.2 ohms at 25°C to measure temperature from a PTC sensor with a resistance of 50 ohms at 25°C? If so, what adjustments need to be made to the resistor network?

author: beenai2018
author_rank: Contributor
timestamp: September 06, 2024, 06:59:42 pm
content: The gain of this circuit is R2/R1 +1 = 56000/100 = approximately 560You will have to adjust R1 ( make it higher to reduce the gain). The R13 could be changed also , but I show a method for calculating R1.Check how much the resistance varies in the new ptc ,from the datasheet , for your temperature range of interest.Using this ,calculate the maximum and minimum voltage at the positive node of opamp . (The ptc resistance and the 1M (R13) form a simple resistive divider) .Use the maximum and minimum voltages at the input to calculate the opamp gain . Remember the output should not go near the maximum supply voltage of 5 and minimum voltage of 0 .For ex . If maximum opamp input is 200mv and minimum is 10 mv ,your gain can be about 20 ( so the opamp maximum output voltage is 200mv * 20 = 4v ,and the minimum output is 10mV*20 = 200mV)Thus R1 = approx 2.5Khttps://www.electronics-tutorials.ws/opamp/opamp_3.html
Question about Philips PE1542 design - Page 1
Forum section: electronics / projects

author: mike_bravo
author_rank: Newbie
timestamp: August 28, 2022, 10:07:16 am
content: Hi folksI am currently repairing my PE1542 power supply. And while studying the schematics, I wonder what is the purpose of R30something, which is the 2.2Meg resistor in the lower left quadrant (see attached image).I dont see any purpose other than adding an error to current measurement & regulation.Any Idea?Best regards,Michael

author: srb1954
author_rank: Super Contributor
timestamp: August 28, 2022, 11:30:17 am
content: Quote from: mike_bravo on August 28, 2022, 10:07:16 amIt might compensate for the operating current of the regulator circuitry, that also flows through the current sense shunt resistor, so that the meter accurately indicates only the external current drawn from the PSU.
Question about PID controller for Quadcopter - Page 1
Forum section: electronics / projects

author: ammjy
author_rank: Regular Contributor
timestamp: September 17, 2019, 07:34:29 am
content: Hello.Thanks you for your time.Now, I'm studying one quadcopter simulation model that I found on Github.that name of simulation is "QuadSim Master" and link is as follows. (https://github.com/dch33/Quad-Sim)(Already I have sent question mail to publisher, but, it is already 5 years ago project so, I don't think that I can receive answer mail.)and I have few question about it.1st attached screenshot show us that PID controller block of Quadcopter.as you see, P and I controller connected with Phi command.but, D controller connected with Angular Velocity P.I don't understand why only D controller not connected with Euler Angles Phi.another, Theta and Psi controller also same. each D controller of Thea and Psi also connected with Q and R.I want know reason or clue.2nd attached screenshot show us that state-space model of BLDC motor.but, as you see,A = -1 / (Time Constant of Motor)B = 1C = 1 / (Time Constant of Motor)D = 0Initial conditions = Initial RPM * (Time Constant of Motor)//Time Constant of Motor is quadModel.T//Initial RPM is IC.w1I can't make any clue that why developer of this simulation made state-space model of Motor with this form.If anyone know about it, could you give me some clue or advise for these two questions ?please, let me know.

author: ammjy
author_rank: Regular Contributor
timestamp: September 17, 2019, 01:06:12 pm
content: Answer about second question :Simple RC BLDC motor can be simplified as a first-order low-pass filter and It can be expressed asw = 1 / (Ts + 1) * wsswhere, wss - desired steady-state speed; T - Time Constantif we express first-order low-pass filter transfer function "w" with state-space model.it looks same withA = -1 / (Time Constant of Motor)B = 1C = 1 / (Time Constant of Motor)D = 0namely,1 / (Ts + 1) is same withA = -1 / (Time Constant of Motor)B = 1C = 1 / (Time Constant of Motor)D = 0
Question about Quadcopter PID Control. - Page 1
Forum section: electronics / projects

author: ammjy
author_rank: Regular Contributor
timestamp: October 23, 2019, 06:38:29 pm
content: Hello, EEVBlog peoples.Thanks you for your time.Now, to design my own Quadcopter simulink model, I am studying one model that I have found in Github.About it I have a few questions.first, Please see the attached 1-st and 2-nd screenshot. The developer of this model have made PID controller as follows.Still I am not sure why developer have connect P(Angular Velocity) with "D" controller.and also at same time I don't understand why developer have used P signal for D controller.(I guess P should be needed connect with D controller to make connected result between each dynamics channels such as PQR PhiThetaPsi UVW XYZ 12 states.but, I am not sure about it...)and my second Curios is Correction circuit part. Please, see the 3-rd screenshot.PID controller of this model making 4 output signals, "Phi, Theta, Psi, Altitude" like this from the Inputs.and this model convert that 4 output signals to 4 RPM signal with this correction circuit after PID controller.I fully understand why this correction circuit is needed.but, I can't make definite mathematical base about it.I can just use this circuit and equation(right side) for my own model. but, minimum I want build some mathmatical clue in my brain.If you don't mind, Could you give some clues for it ?Please, let me know.Thanks you for reading it !

author: pwlps
author_rank: Frequent Contributor
timestamp: October 24, 2019, 12:28:52 pm
content: Quote from: ammjy on October 23, 2019, 06:38:29 pmThe angular velocity is the time derivative of the angle, so it is normal to use it as the derivative term of the PID.

author: ammjy
author_rank: Regular Contributor
timestamp: October 24, 2019, 01:58:48 pm
content: Thanks you for your time, Mr. Pwlps !oh yes.. I missed that point during looking up clue of it.Thanks you !
Question about resistor networks/arrays - Page 1
Forum section: electronics / projects

author: MaximRecoil
author_rank: Regular Contributor
timestamp: December 18, 2016, 07:05:40 pm
content: That's the original part, along with what the silkscreening for the part looks like with it removed from the board. 5.1K, 6-resistor, 7-pin SIPs seem to be hard to find. Does anyone know of a source for them? Mouser and Digi-Key both list exactly one:Bourns Inc. 4607X-101-512LF, and neither site has them in stock. Mouser has a 10-week factory lead time on it and Digi-Key has an unknown factory lead time.If I can't find one, is there something I could substitute? For example, versions with7 resistors and 8 pinsare readily available. Could I just cut off the extra leg (not the common leg of course) and use one of those?

author: ataradov
author_rank: Super Contributor
timestamp: December 18, 2016, 07:25:04 pm
content: Quote from: MaximRecoil on December 18, 2016, 07:05:40 pmYes, absolutely. I'd do exactly that. Or just assemble 6 resistors, if you don't want to wait and have resistors readily available.

author: MaximRecoil
author_rank: Regular Contributor
timestamp: December 18, 2016, 07:42:12 pm
content: Quote from: ataradov on December 18, 2016, 07:25:04 pmThanks. I don't have any 5.1Kohm resistors onhand, though it does look easy to make one of these from 6 resistors:
Question about RTV-Silcone-? used for strain relief for securing small wires - Page 1
Forum section: electronics / projects

author: M_i_c_k
author_rank: Newbie
timestamp: February 16, 2018, 07:56:53 am
content: I am aware that you need to use a neutral cure adhesive for wire to PCB strain relief. My question, is there some commonly used special brew out there? I am talking about the yellow/orange stuff that you normally see securing wires on joysticks and gimbals or larger caps on circuit boards.Plenty of neutral cure adhesive in clear, white out there I just have not been able to locate a source for the high visibility colors that I see used by many manufactures.Thanks in advance...
Question about Samsung's MLCC , is it good or at least decent ? - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: March 07, 2016, 12:24:33 pm
content: I mean compared to others established brands like Murata, Panasonic, AVX, Kemet and etc. Of course with the same or on par at it's specifications like capacitance, volt rating, dielectric type, size, tolerance grade and etc.Reason is, I keep seeing Samsung's MLCCs are much-much cheaper, isn't it ?Please share some insight or your experiences especially at multiple brands of MLCC. TIA

author: BravoV
author_rank: Super Contributor
timestamp: March 10, 2016, 03:23:46 am
content: Quote from: blueskull on March 07, 2016, 01:11:59 pmI had the same thought too, its just I'm hoping there are members here that had in hand experiences dealing with multiple brands mlcc, especially in high volume production could have few words here.Googled return nothing significant, guess I will be using Samsung then, thanks.

author: nctnico
author_rank: Super Contributor
timestamp: March 10, 2016, 10:05:16 am
content: MLCC capacitors can vary widely between different manufacturers and you can buy different kinds of (for example) X5R capacitors from the same brand. I strongly recommend to stick with the same brand and part number in a production design and check the datasheet for the MLCC to see whether it fits your circuit. I have seen cases where the same part (brand/part number) got a lot worse in the next production batch but it was still within specs.

author: tszaboo
author_rank: Super Contributor
timestamp: March 10, 2016, 10:14:38 am
content: Yes, they are very cheap, probably because the billons of stuff that samsung sells. MLCC is very unlikely to fail anyways, cracking seem to be a handling issue anyways, leakage should be solved on design level, so to be honest I never see a reason why not use use it.Or their resistors for that matter.

author: tszaboo
author_rank: Super Contributor
timestamp: March 10, 2016, 10:37:35 am
content: Quote from: blueskull on March 10, 2016, 10:26:10 amMost of the time it is not even specified, or poorly. I usually dont even bother looking up. Again, most of the time, it doesnt even matter what capacitor I place there, just make sure there is something between 100-1000nF on that power supply pin, and it will be OK. I know, it is probably ignorance on my part, but I dont have the luxury of time.

author: BravoV
author_rank: Super Contributor
timestamp: March 10, 2016, 11:46:24 am
content: Quote from: blueskull on March 10, 2016, 10:26:10 amEven though I didn't mention it at the 1st post, imho, actually Samsung does provide quite details on their MLCC's spec. on it's dynamic specification.For example, just purchased few hours agothis 1210 sized, 10 uF 16V X7R 10% for bulk power coupling caps, here the provided datasheet from Samsung web site below, looking the details provided, its not that bad right ?See attachment below.
Question about semiconductor materials in LEDs - Page 1
Forum section: electronics / projects

author: Ben321
author_rank: Frequent Contributor
timestamp: January 09, 2023, 09:23:06 pm
content: I know for example that gallium nitride is used for blue LEDs, but what portion of the LED chip has the gallium nitride? Is it the p-type side or the n-type side of the chip? Like is it GaN p-type with Si n-type? Or GaN n-type with Si p-type? Or are both halves using the same semiconductor material just with opposite doping (GaN n-type with GaN p-type)?

author: moffy
author_rank: Super Contributor
timestamp: January 09, 2023, 09:44:01 pm
content: Google is your friend e.g. type "gan blue led" and you'll get all the answers you need. To summarize, GaN is the base semiconductor which is doped both P and N to create the diode structure.

author: bidrohini
author_rank: Regular Contributor
timestamp: January 10, 2023, 03:32:33 am
content: You may find these helpful:https://ieeexplore.ieee.org/document/9761770https://www.nature.com/articles/s41598-019-40095-7

author: Berni
author_rank: Super Contributor
timestamp: January 10, 2023, 07:07:33 am
content: Problem is that silicon creates too low of a bandgap voltage as a diode, so it can only produce low energy photons, making it only usable in the IR range.So for visible light LEDs they use entirely different semiconductor materials with no silicon involved (tho are sometimes grown on a silicon substrate, but none of its electrical properties are used). There are plenty of other semiconductor materials. A lot of them are actually special mixes of metals rather than pure elements like silicon or germanium. So GaN is a kind of semiconductor with a particularly high bandgap, making it suitable for blue LEDs. A diode can be made from most of these by doping it P and NSome of these more obscure semiconductor materials are also used to make light dependent resistors or resistive temperature sensors, rather than the diodes and transistors you first think of as semiconductors.
Question about swapping components - Page 1
Forum section: electronics / projects

author: tyguy2
author_rank: Unknown
timestamp: February 26, 2017, 11:47:09 pm
content: Hello all!I'm trying to assemble a custom PCB for a wireless charger circuit I've been working on (http://www.idt.com/products/power-management/wireless-power/wireless-power-receivers/p9025ac-r-evk-wireless-power-receiver-reference-solution)The coil that they have in the BOM is not available at any of the US manufactures:http://www.mouser.com/ProductDetail/Wurth-Electronics/760308103202/?qs=%2fha2pyFaduiEGTG6P8JInn6gBEfN9MbB0vGI6LOEl5KE%252bB5%2fdjOa%2fA%3d%3d&utm_source=octopart&utm_medium=aggregator&utm_campaign=710-760308103202&utm_content=Wurth%20ElectronicsI looked on Digikey, and found this coil:https://www.digikey.com/product-detail/en/wurth-electronics-inc/760308103203/732-5256-ND/4725720Could I use this to replace the other coil, or will it not work properly? The inductance value is the same, but not the resonant frequency or Q Miniumum. I'm not sure if I should change the oscillator circuit or the coil, any suggestions? Thanks!
Question about transformer with multiple primary windings - Page 1
Forum section: electronics / projects

author: aiq25
author_rank: Regular Contributor
timestamp: April 21, 2017, 01:45:42 am
content: Hello. I have a transformer that has three primary windings: 120V, 208V, 240V. The secondary output is 24V. The rating is 40VA. I live in the USA, so with a 120V output I get a 24V, but I was interested in a 12V output, so I hooked up the 120V input to the 240V line and sure enough I get about 12V out.I'm new to transformers and I'm not sure how the VA rating works. At 24V, you can get about 1.6A out... So does that mean at 12V I should be able to get 3A out? Or am I still limited to 1.6A.I don't really need 1.6A but it would be nice to have.

author: SouthPark
author_rank: Contributor
timestamp: April 21, 2017, 01:55:51 am
content: The VA rating is one where they want the product of magnitude of voltage and magnitude of current doesn't exceed this particular value during normal operation conditions. Or at least don't exceed it for any relatively long time, even though the factory guys often give plenty of head-room - just in case. But, one more thing.... condition becomes important when the voltage and current are mostly in-phase. So if the voltage and current happen to be like 90 degrees out of phase, then it doesn't matter too much - since real power dissipation is maximum when the voltage and current are in-phase..... or when the load appears to be fairly resistive.

author: Ian.M
author_rank: Super Contributor
timestamp: April 21, 2017, 02:11:03 am
content: Quote from: aiq25 on April 21, 2017, 01:45:42 amI hope you meant240V winding to the 120V lineas the other way would would almost invariably cause the core to saturate and the transformer to draw grossly excessive current, blowing the fuse or tripping the breaker or even damaging the primary winding. There's enough core area to 'stand off' the nominal supply voltage + typically 10% for normal line variations, + a small safety margin, but there is a limit past which it *WILL* saturate.Unfortunately the VA rating assumes nominal input voltage, and is the result of a careful compromise between core area and winding wire size to optimise efficiency to get the most out of the copper and iron used. If you decrease the primary voltage, it doesn't do anything for the wire size, so its current capability remains the same.TLDR: Use the nominal secondary voltage and VA rating to calculate the current. You get 1.66A RMS MAX. No free lunch.

author: aiq25
author_rank: Regular Contributor
timestamp: April 21, 2017, 02:23:30 am
content: Quote from: Ian.M on April 21, 2017, 02:11:03 amWhat I meant was, I hooked up the 120VAC mains to the 240V winding. So I think you are correct.Yeah I thought I wouldn't be able to get more than 1.6A out of it. That's fine with me.Thank you for the reply.
Question about USB Isolation - Page 1
Forum section: electronics / projects

author: gasmanpopey
author_rank: Newbie
timestamp: July 04, 2018, 08:35:52 am
content: Hi All,Just looking for a bit of advice. I’m planning a little project to add a couple of temperature controlled fans to my home network rack as it’s getting a bit toasty inside after adding some new equipment.I’ve been looking at PC case fans, and some of the fan controllers that are available. I’ve found a controller and a couple of fans that look like they fit my requirements, but the controller is designed to live in a standard PC case, so the USB connection (for management/programming) needs an internal USB header and the controller needs a SATA power connector.Where it gets more complicated however, is that there is no ATX style PC in my network cab - I do however have a little MSI Cubi that I use for management of a few things, so I need to convert the USB cable from a header connection to a type ‘A’ and I need to find a SATA power brick. The USB connection is easy, and I’ve found a good little triple rail power brick for the SATA power so that should be okay too.This leads us to my question – as the Cubi AND the fan controller are powered by separate switch mode, floating power supplies, do I need to isolate the USB cable to avoid cooking something?I’ve been pondering this for a week now and not come up with an answer I’m confident enough in to chance cooking my Cubi, so was hoping someone might be able to tell me i'm either right or wrong. In my mind, the USB ground would tie the two 0Vs together and thus it would be fine. But then i'm not sure how USB ports are wired up. My thinking is its no different to having a USB hub connected to a laptop.Would appreciate any insight you could offer.Cheers,James

author: ConKbot
author_rank: Super Contributor
timestamp: July 04, 2018, 03:11:57 pm
content: Nope, no problems with both supplies being isolated. Its like plugging the SATA power adapter into a drive that gets hooked up to a USB adapter and plugged into a laptop, where both the laptop brick and SATA power brick use 2-prong plugs.
Question about using ATTINY to drive a BH2220 D/A Converter - Page 1
Forum section: electronics / projects

author: optoisolated
author_rank: Unknown
timestamp: April 27, 2017, 09:21:00 am
content: Hi all, I am trying to get my head around using an ATTINY to drive a BH2220 DAC, and based on what I am reading in the datasheet (http://rohmfs.rohm.com/en/products/databook/datasheet/ic/data_converter/dac/bh2219fvm-e.pdf) am concerned that the ATTINY simply doesn't have the capability to drive this at the speeds required. I thought about using the SPI interface, even though it used an 11-bit register, I assumed there would be capability to use that, (serves me right for not checking) but if I'm reading the ROHM datasheet right, it suggests the high-load, rising edge clock set requires MODE 3 SPI which the ATTINY 44 can't do. I thought about bit-banging it, but i'm not sure I can get it to output fast enough on the GPIO pins of the ATTINY to get it to work and wanted to know if anyone had attempted something similiar, or could advise if I am approaching the problem incorrectly.Any feedback would be appreciated

author: Ian.M
author_rank: Super Contributor
timestamp: April 27, 2017, 09:48:38 am
content: I don't see any requirement for either a minimum CLK frequency or for CLK to idle high in that datasheet (even though the timing diagrams show it idling high).Try sending 16 bits of data in SPI mode 1 and see what happens.I would expect the high nibble of the first byte to be ignored and the low nibble taken as channel select, with the next byte used for data.
question about using pid to control atx smps over optocoupler feedback   side - Page 1
Forum section: electronics / projects

author: vortex
author_rank: Contributor
timestamp: March 24, 2025, 01:11:53 pm
content: hi friends . i have this idea that consist of controlling atx smps that use uc3843 over optocoupler feedback side using pid with stm32 pwm signal of 100khz plus low pass filter and iam wendring if this can work or not. i do have an ather project with moded atx smps but using op amp as comparator to control th cv an cc and mcu to read volte and amps value it work very well . and i kow that pid is not for non linear systemsdigital or analog aproch? wishe is betteri do my pcb using toner transfer simple design is better for me
Question about video signal... - Page 1
Forum section: electronics / projects

author: sam1275
author_rank: Frequent Contributor
timestamp: September 26, 2016, 01:29:50 pm
content: Hi everyone.I had a Armasight digital night vision monocular and then the eye piece optics brokes, I can still see the output from the very tiny LCD, but I decided just to reuse the sensor part.I took it apart, and found the "main" board is very simple, just some regulators and capacitors to distribute the power to the sensor board and the LCD board. The main video processors are all on the sensor board, and there are only 3 lines connect to sensor board: 2 are powers, another must be video signal, which goes through a potentiometer and then to the LCD board.But now the problem:1. It's only one line for the signal, so I think it must be composite signal, but is it possible to adjust the brightness just by a potentiometer on the signal line? I mean, from complete dark to a extremely sensitive(much more sensitive than human eye, with lots noise), I think that should be some settings to do with the sensor and DSP, not the output signal...2. The factory voltage on the sensor board is 7.86v, but I connected a 9.3v adapter to the board and hook a monitor to it, nothing output, did I burn it up or it's just not a composite video?I took pictures of the board:Thank you!

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 26, 2016, 01:55:01 pm
content: Pin 75 on the CXD3142R switches between PAL and NTSC, HIGH = PAL, LOW = NTSC. Looking at the pcb I think the pin is HIGH.Maybe your monitor doesn't like PAL?

author: bktemp
author_rank: Super Contributor
timestamp: September 26, 2016, 01:56:13 pm
content: The board looks like a ordinary camera module and the CXD3142R outputs a composite video signal. Therefore it is most likely a composite video output.Maybe it needs AC coupling or a termination resistor to GND or a high impedance buffer.

author: technotronix
author_rank: Regular Contributor
timestamp: September 29, 2016, 06:47:15 am
content: No, It doesn't look like burned. I think it is a composite video only.

author: sam1275
author_rank: Frequent Contributor
timestamp: January 10, 2017, 02:05:55 pm
content: Thank you everyone, I just confirmed that my monitor do support PAL, I also tried another device with AV in, still no signal.I think maybe it have some special design that not compatible with a normal composite monitor?
Question about Wifi RF section without metal shield box - Page 1
Forum section: electronics / projects

author: BravoV
author_rank: Super Contributor
timestamp: October 26, 2012, 07:31:33 pm
content: Opened my cheap wifi 3G router recently for hunting bad caps, and spotted the rf section is not covered with the metal box as usual. Apparently someone decided to save few pennies.Although its working fine, just curious what are the disadvantages without that piece metal shield/box ?The close up shot and added 4 arrows to show the exposed rectangle shaped copper traces that supposed to be installed with the metal shield.

author: PA0PBZ
author_rank: Super Contributor
timestamp: October 26, 2012, 07:39:57 pm
content: It's probably not going to degrade the working of your router, the shielding is there (or isn't in this case) to keep RF inside.Most likely it depends on the EMI regulations where it is going to be sold, they will put it in for countries with tighter regulations.
Question, Bourns CD-HD2xL bridge flip-mounting? - Page 1
Forum section: electronics / projects

author: k4rlhp
author_rank: Unknown
timestamp: May 27, 2017, 05:40:05 pm
content: Hi!I need a versatile solution to optimise clean routing flexibility around a low VF bridge rectifier.Bourns offers chip diode bridge rectifier CD-HD 20x(L) series. the CD-HD201L suits my other design characteristics.Datasheet:Bourns CD-HD2x(L) DatasheetI seek the flexibility to mount a rectifier either normal way (markings on top and visible) or flipped up-side down (top markings towards board).I'd like to avoid moving the part to the opposite side (bottom <-> top) to achieve this.Datasheet does not state this capability and for automated production it's probably not a good idea anyway but that's irrelevant at the moment.From data sheet drawing it seems to be doable without building large solder-blobs to achieve this.Does anybody have a sample to (visually)check or by experience if it would be okay for reflowing this way?I will need a run of maybe 100 boards with that setup if it works fine.And I will try it out before committingThanks!
Question: LEDs - Page 1
Forum section: electronics / projects

author: TheRevva
author_rank: Regular Contributor
timestamp: May 01, 2017, 06:42:30 am
content: Hi guys'n'gals,I'm toying around with some RGB LED Matrix panels and I've noticed that the use the terms DIP146, DIP346 and DIP546 for the individual LEDs.(They're always using the 'oval' type LEDs that have a wider horizontal viewing angle than the vertical viewing angle)Initially, I thought it might be the dimensions of the LED encapsulation (measured as mm), but then I started hearing about DIP146 LEDs and I;m fairly certain they're well above 1mm!Anybody go any ideas?
Question of clearance form SOIC-8 current sensor chips - Page 1
Forum section: electronics / projects

author: mike buba
author_rank: Contributor
timestamp: February 17, 2025, 04:47:00 pm
content: Hi all,In my project I am thinking of using 8-SOIC current sensor chips, e.g., LEM's GO 10-SME (datasheet) or Allegro Microsystems' CT416 (datasheet). Both are SOIC-8 packages with a pin distance of 1.27 mm.I am thinking of measuring current at high voltage (at 230 Vrms and 800 Vdc). From the IEC 62368-1 (link) the creepage distance at 800 Vdc, it is 4 mm for PD2.However, when looking at the recommended PCB layout for both chips, it looks like the clearance is less.In the previous project I used LA 25-P, and there was no problem with creepage and clearance, but now I am trying new sensors and am not sure how to achieve clearance since the pins are below the recommended distance.

author: Konkedout
author_rank: Frequent Contributor
timestamp: February 17, 2025, 05:10:37 pm
content: Are you able to put a slot in the board as recommended in the LEM datasheet?

author: mike buba
author_rank: Contributor
timestamp: February 17, 2025, 05:20:34 pm
content: I can do that. Thanks.What about between pins 1 and 2 (IP+) and 3 and 4 (IP-)? Do I need a slot between them?

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 17, 2025, 05:42:59 pm
content: The resistance between the two groups of pins (1+2 and 3+4) is only around 0.9 mOhms, so you won't have an arcing problem unless something isreallywrong as the voltage drop will be negligible across the gap of pins 2 and 3. At full rated operating specs, you'll see about 0.09V (say 0.1V) drop.
Question on 90V DC motors - Page 1
Forum section: electronics / projects

author: XaviPacheco
author_rank: Regular Contributor
timestamp: July 21, 2018, 05:11:03 pm
content: Back then, 90V dc motors were controlled by SCRs. Nowadays, some of them are PWM-controlled. Basically my question is:120VAC rectified and filtered are about 170VDC. For a 90VDC motor, this is too much. The idea on this is controlling the duty cycle under 50%?

author: james_s
author_rank: Super Contributor
timestamp: July 21, 2018, 05:14:10 pm
content: Aren't they typically powered by half wave rectified AC using a single diode? I remember seeing that arrangement in electric weed trimmers.

author: XaviPacheco
author_rank: Regular Contributor
timestamp: July 21, 2018, 05:28:19 pm
content: In treadmills, they're powered by full wave rectifiers, and the output is filtered with a bulk capacitor.

author: Seekonk
author_rank: Super Contributor
timestamp: July 21, 2018, 06:51:32 pm
content: Just because it is full wave doesn't require using the full waveform. 120 partial pulses gives better control than just 60.
Question on "studfinder" Possible to build one yourself/get quantitative output? - Page 1
Forum section: electronics / projects

author: cdev
author_rank: Super Contributor
timestamp: December 05, 2017, 04:08:40 am
content: I'm interested in how a studfinder works, does it measure capacitance, ability to modify a tuned circuit- magnetic properties or what?Is it possible to do something similar for imaging?