hybridfree/eevblog-posts huggingface dataset:
Please review my PCB design - Page 1
Forum section: electronics / beginners

author: redgear
author_rank: Frequent Contributor
timestamp: September 30, 2020, 02:14:27 pm
content: The PCB is simple. Connects to the mains, steps down to 5v using a switch supply. There is a relay on-board that controls the load. Each load draw 0.33A nominal current with inrush current reaching as high as 7A.I have used 2mm track for the mains and the minimum clearance of 2.5mm. The pitch of connectors in is 7.92(actually 3.96 but I use a 3 pin for 2pin with a empty slot in-between).Questions:1) Does the mains side and LV need to be isolated like I have done it?2) Should I remove the ground pour below the relays?3) Any other suggestions or improvements?Thank You.

author: No.Mad
author_rank: Regular Contributor
timestamp: October 27, 2020, 02:53:50 pm
content: Hi Redgear,Quote from: redgear on September 30, 2020, 02:14:27 pmYes, it's good practice. I would go even further and made cut outs on PCB. For reference check how mains-to-DC PSU boards look like.Quote from: redgear on September 30, 2020, 02:14:27 pmIf you are concerned when and when not I recommend:https://electronics.stackexchange.com/questions/218676/how-about-ground-pouring-under-an-electromechanical-relayIn your case I don't see any noise-sensitive routing under relay so answer is No.Quote from: redgear on September 30, 2020, 02:14:27 pmYes, two:1) You have a lot of PCB real estate left. I would recommend making PCB smaller or rearrange components so you would be left with straight horizontal line between mains and +5VDC (instead of current "stepping" one)2) I would make bottom half of schematic in three parts: J3 connector, buzzer section and relay section (with Q1, D1, D2 and voltage divider included). Rotate J3 so you could read net names on pins. Keep it as signal goes: from left to right, top to bottom (I don't know if J3 is input or output). Oh, and C2 voltage rating is a bit overkill. Rule of thumb is 2.5 times larger than voltage on rail, so 5 x 2.5 = 12.5V. Closest rating is 16V, I would use that.Hope that helps.Regards,No.Mad
please suggest module to control a two-phase stepper mottor - Page 1
Forum section: electronics / beginners

author: exe
author_rank: Unknown
timestamp: July 19, 2019, 07:51:05 am
content: I bough small stepper motors for a project and just realized I don't know how to control them. They are very small, I thought can just hook it to my signal generator and play with it. Now I'm thinking that an inductive kick may kill the signal generator... So, I'd like to buy a dedicated driver for experiments, but I just realized I don't know what to buy. Do you have any suggestions?To my surprise there are different types of stepper motors, and they are driven differently. Mine seems the simplest type, it's just two coils without any taps. I did some research, it seems I need two H-bridges to control it because the control signal is bi-polar. Am I correct? If so, what IC or ready module would you suggest? Preferably a small module because the servo is very small and doesn't require much power.This is stepper motor I have:https://www.aliexpress.com/item/1523213660.html?spm=a2g0s.9042311.0.0.27424c4dQPazQFHere is the description from the seller:Quote

author: Nominal Animal
author_rank: Super Contributor
timestamp: July 19, 2019, 11:24:20 am
content: I like to use the DRV8834 for this kind of small stepper motors. It works with 2V to 10V motor voltages, has microstepping support, and is trivial to connect to a microcontroller: just two pins, STEP and DIR. The existing DRV8834 stepper driver boards have a small potentiometer for controlling the current. DIR controls the step/microstep direction, and rising/falling edge of STEP causes a step/microstep rotation.
Please tell us about the semiconductor of Raspberrypi 3 - Page 1
Forum section: electronics / beginners

author: Jeison.power
author_rank: Newbie
timestamp: August 30, 2019, 12:11:17 pm
content: HelloSee photo.Raspberrypi3 pcb board see red circle.Tell me semiconducter product name.Where do you sell them?Regard.JeisonI can’t speak english.Trancelate by google.

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 30, 2019, 12:31:08 pm
content: No Photo.

author: Jeison.power
author_rank: Newbie
timestamp: August 30, 2019, 01:09:26 pm
content: sorry

author: PA0PBZ
author_rank: Super Contributor
timestamp: August 30, 2019, 01:23:48 pm
content: It is a fuse.https://robu.in/wp-content/uploads/2016/03/robu-9-1.jpghttps://www.raspberrypi.org/documentation/hardware/raspberrypi/schematics/rpi_SCH_3b_1p2_reduced.pdfhttps://www.bourns.com/pdfs/mfmsmf.pdf

author: mikerj
author_rank: Super Contributor
timestamp: August 30, 2019, 01:24:52 pm
content: It is usualy called a "Polyfuse" or a "PTC fuse". These are self-reseting semiconductor fuses for overcurrent protection. The correct part number for the Raspberry Pi 3 seems to beMF-MSMF250/Xand should be available through the main distributors such as Mouser, Farnell and Digikey.

author: Jeison.power
author_rank: Newbie
timestamp: August 30, 2019, 02:34:51 pm
content: Hello,Buy digi-key or mouser.Please tell me again.Thank you very much.Thank you very much.Regard,JEISON

author: TimNJ
author_rank: Super Contributor
timestamp: August 31, 2019, 04:05:06 am
content: https://cn.mouser.com/ProductDetail/Bourns/MF-MSMF250-16X-2?qs=9fn1gpisni78zr7pGyDhCQ%3D%3Dhttps://www.digikey.cn/product-detail/zh/bourns-inc/MF-MSMF250-16X-2/MF-MSMF250-16X-2CT-ND/3437789?_ga=2.35181153.1759826097.1567133075-637692205.1533093672
PLL driven resonant converter - Page 1
Forum section: electronics / beginners

author: B7S1
author_rank: Newbie
timestamp: July 22, 2025, 07:54:51 pm
content: This may be more than I can chew but I'm looking for a way to keep a power converter switching at resonance by watching the phase difference between two signals and driving a VCO such that the said phase difference is maintained at the prescribed value.Resonant frequency is somewhere in the 15 - 25 kHz range and varies depending on load mainly.Do I need a PLL for this?Thanks,B7S1
PLL with a constant phase shift over frequency range? - Page 1
Forum section: electronics / beginners

author: David_
author_rank: Contributor
timestamp: August 28, 2017, 04:54:09 pm
content: Hello.I have been trying to make sense out of PLL's (Phase Locked Loop) but I am still unable to answer the question about how to make a PLL to be able to lock in the range of 10Hz - 1MHz while always providing a output which is phase shifted by 90 degrees related to the input no matter which frequency the input is at (within that previously stated range).Do you know how such a circuit could be realized?This will be incorporated within a dual channel Lock-In Amplifier used to measure complex impedance.Regards

author: BigBoss
author_rank: Regular Contributor
timestamp: August 28, 2017, 05:25:47 pm
content: Because VCO is an integrator and Transfer Function of an integrator is 1/s in s-domain.So, there is a 90 degree phase shift in time domain.

author: Kleinstein
author_rank: Super Contributor
timestamp: August 28, 2017, 06:38:13 pm
content: Most phase comparators produce an output proportional to the phase difference. If the loop filter behaves like an integrator for the low frequency part, if will lock at 0 output signal from the phase comparator. It depends on the type of phase comparator at which phase difference this will happen. For the XOR type phase comparator this would be at a 90 degree phase. By adding an offset / additional signal one can adjust the phase by a frequency independent offset if needed.However there might be some small additional phase shifts from the input stage and amplifiers. So one usually needs the adjustment for these errors.For an Lockin one will usually run the VCO at a higher frequency so that the coarse phase steps (like 90 degree and maybe 45 deg.) can be done digitally with high accuracy.For an impedance measurement, there usually is a single oscillator to generate for the driving signal and the reference signals. So no PLL is needed, just a divider. Small errors (e.g. due to the amplifiers) is usually better corrected numerical afterwards. In modern implementations the Lockin part can very well be in the numerical domain, so behind an ADC that samples the signal. Except for very high frequencies it is usually better to use the ADC on AC and avoid an DC signal.

author: Yansi
author_rank: Super Contributor
timestamp: August 28, 2017, 08:02:21 pm
content: Quote from: David_ on August 28, 2017, 04:54:09 pmYou better use a dual channel DDS for that purpose. At 1MHz top, that won't be much of a problem. Either find a suitable IC for that, or make one yourself. (dual channel DAC of your choice + SRAM + small CPLD otherwise). Making a PLL+VCO for that that will work over that range will be one pain in the butt, am telling you right!
PLL with output amplitude proportional or equal to input amplitude - Page 1
Forum section: electronics / beginners

author: ricko_uk
author_rank: Super Contributor
timestamp: January 04, 2020, 07:08:26 pm
content: Hi,just a curiosity,are there such thing as:1) a PLL or other device device that produces an output frequency (equal or different from the input one) whose amplitude is equal or proportional to the input signal amplitude?2) a device whose output frequency is proportional to the input signal amplitude?Thank you

author: MagicSmoker
author_rank: Super Contributor
timestamp: January 04, 2020, 11:10:42 pm
content: That sounds like a V/F converter, not a PLL. These were all the rage in analog design back in the 80's as a precursor (or substitute, really) for ADCs (Analog-to-Digital Converters), because real ADCs were very expensive.
Pls, Help me identify this chip - Page 1
Forum section: electronics / beginners

author: Azhar
author_rank: Regular Contributor
timestamp: July 11, 2015, 11:47:03 am
content: I couldn't find any datasheet for these chipsIs there a way or a method to test a chip in order to identify it or know what is job?

author: fcb
author_rank: Super Contributor
timestamp: July 11, 2015, 12:00:34 pm
content: My guess is CLA means "configurable logic array" - probably a PAL/GAL.Would help to know what it is from?

author: SeanB
author_rank: Super Contributor
timestamp: July 11, 2015, 12:26:17 pm
content: Second one is probably a 65xx SIO chip, seeing as there are RS232 converter chips next to it, and you have baud rate setting links in the DIP arrays next to it.First looks like it is a 6522 PIA chip. Look at the datasheet athttp://archive.6502.org/datasheets/mos_6522.pdfand see if the pinout for supply and the data lines from the LS374 agree.

author: Azhar
author_rank: Regular Contributor
timestamp: July 11, 2015, 12:39:08 pm
content: Quote from: SeanB on July 11, 2015, 12:26:17 pmIt is from this telecommunications device, not sure what is its purpose

author: grumpydoc
author_rank: Super Contributor
timestamp: July 11, 2015, 01:05:03 pm
content: QuoteIt is an X.21 modem, says so on the front

author: SeanB
author_rank: Super Contributor
timestamp: July 11, 2015, 01:12:21 pm
content: Diginet NTU, used for a dedicated digital line of 56k or 64K, using a diginet link from point to point. Didn't think many are still around, i took one apart a while ago when we were force upgraded as Telkom SA no longer has any frame relay equipment left in exchanges, and is changing them out to something newer.What makes you think they are faulty, those things run essentially forever, only failing with lightning strikes. I still have the board somewhere in a box, though your one is a really aincent unit and probably not compatible with the newer( less than 15 years old) standards....https://en.wikipedia.org/wiki/X.21Basically it is a serial port that allows remote connections using a dedicated switched circuit through older ATM frame relay exchanges, so you can send digital serial data as if you had a direct wired connection between the 2 points instead of a packet switched network.http://www.arcelect.com/X21_interface.htmBasically a low speed means of sending data, though 20 years ago it was the gold standard for rock solid connectivity, on and up 24/7/365 and never dropping a packet unless the line was broken.
Plug ID - Page 1
Forum section: electronics / beginners

author: downhalo
author_rank: Contributor
timestamp: September 13, 2014, 05:50:48 am
content: Just wondering if anyone can ID this 3 pin plug..

author: miguelvp
author_rank: Super Contributor
timestamp: September 13, 2014, 06:24:03 am
content: Looks similar to an IP68 3 pin connector but the one you show has a key.What is it for? that will help narrow the search.

author: fcb
author_rank: Super Contributor
timestamp: September 13, 2014, 08:22:37 am
content: It could be (almost) anything, and as miguelvp suggests, posting what it connects to/does/brands will help.It does look a bit like a "TINY XLR", but could be a version of the "M8" industrial connector.

author: downhalo
author_rank: Contributor
timestamp: September 14, 2014, 05:11:55 am
content: found it, 709 series, IP40
Pluggable Terminal Coding Inserts - Page 1
Forum section: electronics / beginners

author: FrankT
author_rank: Regular Contributor
timestamp: July 14, 2017, 11:05:39 pm
content: How do these coding insertshttp://www.altronics.com.au/p/p2506-dinkle-coding-insert-to-suit-p-2512-p-2522-25pk/work with these plugs?http://www.altronics.com.au/p/p2512-dinkle-2-way-5.08mm-pluggable-terminal-plug/I have two connections with the same number of pins - one high voltage, the other not, so I'd like to ensure I don't connect them incorrectly.Do the inserts take up one of the circuits? I have the plug and socket in my hands (but no insert), I can't see how these work.
Plugged non-polarized IEC into polarized TV - Page 1
Forum section: electronics / beginners

author: azmi
author_rank: Newbie
timestamp: July 02, 2018, 02:13:08 pm
content: Hello everyone,I found a Vizio TV at an estate sale that didn't have a power cord. It had a slot for a polarized IEC 320 C7. I only had a non-polarized plug, so I used that. It worked, but eventually the unit would not turn on. Did I fry something?
Plz help me identify a router CPU frequency - Page 1
Forum section: electronics / beginners

author: sam1275
author_rank: Frequent Contributor
timestamp: May 07, 2015, 04:56:34 pm
content: Hi everyone.Could anyone tell me the CPU frequency of this device: Edimax BR-6228nS ?I searched a lot and just found it's a Realtek RTL8196C, but what's the speed?Thank you very much!

author: amyk
author_rank: Super Contributor
timestamp: May 07, 2015, 05:02:22 pm
content: ...Google "RTL8196C" and read the datasheet?

author: sam1275
author_rank: Frequent Contributor
timestamp: May 07, 2015, 05:28:30 pm
content: Quote from: amyk on May 07, 2015, 05:02:22 pmThank you, a 3rd-party firmware bootlog shows 390MHz, the highest frequency of this chip, however I don't the stock speed of it.

author: cpt.charlie
author_rank: Contributor
timestamp: May 08, 2015, 11:14:05 pm
content: Try to locate a serial interface on the board and connect an adapter to it, while booting it's common to read in the console the status, frequency, memory and other interesting info.
PMBS3904 or MMBT3904 - Page 1
Forum section: electronics / beginners

author: Jwillis
author_rank: Super Contributor
timestamp: July 04, 2021, 03:57:06 am
content: I've been given a Lenovo G710 to repair. The power plug had been broken and was an easy fix . But still no power or charge.I found a transistor with a a short between base and emitter which would cause something not to turn on. Very difficult to track those tiny traces and vias .I can replace it but I only have the MMBT3904 in stock . Both the PMBS3904 and the MMBT3904 are virtually identical except the MMBT3904 has a collector current of 200mA where the PMBS3904 is only 100mA . Problem is the PMBS3904 has a Max base current of 200mA and the MMBT3904 is only 100mA.The gain for both is identical at 100mA and no mention of any thing higher than that .Can they be interchangeable as is or should I order the PMBS3904 ?

author: gcewing
author_rank: Regular Contributor
timestamp: July 04, 2021, 04:19:50 am
content: That depends on what it's being used for. Is it switching a load of over 100mA? If not, the MMBT should be fine.

author: Jwillis
author_rank: Super Contributor
timestamp: July 04, 2021, 05:33:06 am
content: Quote from: gcewing on July 04, 2021, 04:19:50 amIt's the base current I'm concerned about . The MMBT has a higher Collector current than the PMBS . The PMBS is the one in the computer .MMBT3904PMBS3904

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 04, 2021, 06:55:30 am
content: I would assume that's just the Philips (now NXP now Nexperia, or whatever other fragment now owns that product line) designation for an MMBT3904. Apparently with somewhat different specs as I don't think *3904 ever had noise spec for instance.I would be shocked if the peak base current figure is used in your application.Tim

author: magic
author_rank: Super Contributor
timestamp: July 04, 2021, 09:16:55 am
content: That's more base current than the absolute maximum Ic rating. No one in his right mind would do that

author: Jwillis
author_rank: Super Contributor
timestamp: July 04, 2021, 02:58:34 pm
content: Quote from: T3sl4co1l on July 04, 2021, 06:55:30 amQuote from: magic on July 04, 2021, 09:16:55 amThat makes sense now . So what is most likely is just a mistake on the data sheet ? Wouldn't be the first time I suppose .

author: magic
author_rank: Super Contributor
timestamp: July 04, 2021, 03:12:28 pm
content: I just commented on what T3sl4co1l said before: it seems highly unlikely that you really need a transistor capable of 200mA base current in this circuit. The datasheet may or may not be correct but it doesn't matter.But you may be right - perhaps the PMBS is also supposed to be Ib<100mA, Ic<200mA. Typically 3904 types are indeed rated for 200mA Ic.editI downloaded the DS and it doesn't seem to be a typo. The 100mA limit is repeated twice, and there is also a peak 200mA limit. Base current limit is peak 200mA, no continuous rating on this one.
PMIC question - Page 1
Forum section: electronics / beginners

author: roogadget
author_rank: Contributor
timestamp: September 28, 2018, 12:25:46 pm
content: I am designing the power management section for my project and I'd like some feedback on my design choices.I am wondering about a PMIC chip (Boost/Buck Converter) that I've picked.http://www.ti.com/product/TPS55165-Q1There is a pin that requires an external 5V input when a 12V output in desired. (Power Good Pin - PG)My input varies between 9V and 18V. So I would need to step it down to achieve the 5V required.I also need a 5V output because my STM32 requires 3.6V (Which I'll likely use a linear voltage regulator to achieve).I would like to know if this is the appropriate method to handle various inputs and stepping down voltages.

author: stmdude
author_rank: Frequent Contributor
timestamp: September 28, 2018, 01:01:53 pm
content: From the datasheet:The power-good (PG) pin is a low-side FET open-drain output which is released as soon as the output voltage isgreater than the PG undervoltage threshold ....It's an output, but you can't really put any load on it.Which means, you'll need to convert your 12V output into 3.3V for the STM32. Plenty of DC/DC bucks does this for very little money.

author: roogadget
author_rank: Contributor
timestamp: September 28, 2018, 01:34:10 pm
content: Wow! Thanks! I just avoided a big problem.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 28, 2018, 08:58:26 pm
content: So you need what voltages? Just 5V, with an LDO to make 3.6V? (3.3V is more traditional, do you have a reason for going on the high side of that?)That reg has a 5V output option, but it looks like a much cheaper buck regulator will meet your requirements in that case.Tim
PMK Oscilloscope Probes - Page 1
Forum section: electronics / beginners

author: flano
author_rank: Contributor
timestamp: December 20, 2011, 10:29:59 pm
content: Hi,Does anyone have any experience with PMK Oscilloscope Probes?I have just purchased a Tek 2235 and would like to get some decent probes for it. These seem to be reasonably priced.http://australia.rs-online.com/web/p/oscilloscope-probes/6784029Thanks Mike

author: joedevola
author_rank: Contributor
timestamp: December 21, 2011, 12:08:52 am
content: I have a 2225 and a Rigol and use these from ebayhttp://www.ebay.com.au/itm/New-2-Two-100MHz-Oscilloscope-Probes-Probe-Tektronix-HP-/130554595161?pt=AU_B_I_Electrical_Test_Equipment&hash=item1e65a90759#ht_3069wt_1165about $15 shipped and they work fine. They take about 2 weeks to arrive from Hong Kong, but then again the ones you picked from RS are not next day delivered, they are shipped in from OS too.Cheers

author: Unknown
author_rank: Unknown
timestamp: December 21, 2011, 01:22:20 am
content: PMK probes are fairly decent. The high voltage isolated probes sold by Fluke and Tek are PMK probes. In quality they are between the expensive Agilent/Lecroy/Tek probes and the cheap brands like ProbeMaster or the even worse no-name brands ('For HP-Agilent-Tektronix').
PMOS switching with MCU and additional mechanical switch override-any idea how? - Page 1
Forum section: electronics / beginners

author: Cvijo
author_rank: Contributor
timestamp: March 18, 2025, 07:55:07 pm
content: Hi all,I have PCB with multiple mosfets (16) outputs that are switching DC loads on the boat. It is controlled by touch display and esp32. I would like to implement backup option if for example display stop working, or some other failure to be able to switch loads with mechanical switch (rocker switch for example). All the switching is done on high side and all the positive wires are routed to the console for each load.Installation is already connected to control panel with mechanical switches and now i just remove from mechanical ones and connected to my PCB.Is there any elegant way to have those 2 options available without rewiring and changing current installations.I was thinking to add additional input connection for each load to my PCB that will be connected to mechanical switch on the other side and using it will override my MCU controller and turn on/off the mosfet, or somehow directly close the load circuit but i am not sure how or is it possible.I know that the downside would be that the mechanical switch will take priority over the display and display switching will not work while the mechanical one is ON, and if there is a better solution I would be glad to listen to some suggestions or ideas.All loads are using 12V battery supply that previously was controlled by mechanical switches.Thank you all for helping.

author: ahsrabrifat
author_rank: Regular Contributor
timestamp: March 19, 2025, 08:01:25 am
content: You can connect the mechanical switch in parallel with the MOSFET but add a diode (Schottky recommended for low voltage drop) in series with each control line. This way, if the ESP32 is OFF or faulty, flipping the mechanical switch will still complete the circuit and turn on the load.
Pn junction diode theory help! - Page 1
Forum section: electronics / beginners

author: khatus
author_rank: Regular Contributor
timestamp: February 13, 2021, 03:58:06 pm
content: I can not understand the meaning of the sentence underlined above. Can anyone explain?

author: Terry Bites
author_rank: Super Contributor
timestamp: February 13, 2021, 04:11:28 pm
content: Yeah that's academic gobbledygook for you.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 13, 2021, 07:13:23 pm
content: Can you explain what issue you are having with the sentence?It looks clear to me. But if you lack definitions, or an understanding of the physics involved, it won't be very meaningful, no. Perhaps that is the place to start?Tim
PNP differential pair in ltspice - Page 1
Forum section: electronics / beginners

author: vixo
author_rank: Regular Contributor
timestamp: May 17, 2022, 09:43:04 am
content: I am trying to understand this circuit (below) as I'm trying to fix a piece of equipment. I tried to simulate it but the simulation (ltspice) is giving me strange results. I would have expected to get a high gain circuit, as the top resistor is 470 and the bottom is 30K. If I look on R5 to ground I get a signal which is only a few micro-volts around 15V.I'm not sure if I need to be driving this circuit differently. I haven't simulated the whole thing because the schematic is quite big. I included a second picture that shows more of the circuit (this doesn't work either, so I tried to start with a smaller chunk and work upwards) but I would rather not simulate more of it.Can anyone help me understand what I should do to see the normal circuit behaviour? I also included the ltspice fileany help much appreciated!

author: mikerj
author_rank: Super Contributor
timestamp: May 17, 2022, 01:24:14 pm
content: In the simplified top diagram the constant current source Q3 is not biased into conduction, which in turn means Q1 and Q2 are also not being biased into conduction. The lower diagram has additional components R3,R4 and V6 to bias Q3, but from inspection it looks like this would be turning on Q3 far too hard and likely saturating Q1 and Q2. However the node "VM" may play a role in this and I don't see any other matching net names.

author: vixo
author_rank: Regular Contributor
timestamp: May 17, 2022, 03:56:00 pm
content: ahhh, thankyou so much. I biased it correctly and everything works as expected
PNP equivalent of ULN2803? - Page 1
Forum section: electronics / beginners

author: dog80
author_rank: Regular Contributor
timestamp: October 30, 2013, 09:28:04 am
content: I'm trying to drive a common anode 7-seg display with an Arduino and use a ULN2803 to drive the cathodes.Is there a PNP equivalent to the ULN2803 to drive the anodes instead of using individual transistors?

author: David_AVD
author_rank: Super Contributor
timestamp: October 30, 2013, 09:39:43 am
content: What you need to search for is "octal high side driver".They are not as common or cheap as the low side (NPN) ones though.

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2013, 09:40:59 am
content: also, if you can handle SMT chips it will be much easier to find one.DIP pnp transistors arrays are much less common than SMT

author: mariush
author_rank: Super Contributor
timestamp: October 30, 2013, 09:43:32 am
content: UDN2981 may be a suitable part.See this thread where several ICs were suggested :https://www.eevblog.com/forum/projects/micro-controller-controlled-led-matrix-design-question/ps. In another thread, MAX7219/MAX7221 were mentioned by someone. But they're more complex:http://datasheets.maximintegrated.com/en/ds/MAX7219-MAX7221.pdf

author: ivan747
author_rank: Super Contributor
timestamp: October 30, 2013, 05:11:56 pm
content: Another solution is getting a common cathode display instead.
PNP High Side Switch? - Page 1
Forum section: electronics / beginners

author: Falcon69
author_rank: Super Contributor
timestamp: August 24, 2014, 09:30:44 pm
content: So, I'm trying to understand a circuit i have drawn up (only partial of the circuit for viewing). And Also trying to select the correct transistor.Now, I understand that in many applications that a Low Side Switch using an NPN transistor is better then a High Side Switch using a PNP, However, for my application, I must tie multiple LED grounds together and control them from the positive side of each of them. (no way around this, as the LED assemblies I have bought are wired this way).So, I'm trying to understand why, in simulation, that the voltage and the current going through this PNP transistor is negative voltage/current?I'm just having trouble understanding how the high side switch PNP transistor is taking the positive voltage and current, and changing it to a negative, then back into a positive to light the led.When choosing a PNP transistor, do I have to choose one with negative current/voltage? I ask this, because I'd like to have both an NPN and a PNP in one chip.Would this chip work okay?http://www.mouser.com/ds/2/302/PBSS4230PANP-354962.pdf

author: Dave
author_rank: Super Contributor
timestamp: August 25, 2014, 12:00:43 am
content: It's not turning any voltage or current into negative, or vice versa. You are looking at it the wrong way.In order to "open" a PNP transistor, you need to apply a negative voltage to the BE junction (as opposed to NPN transistors, where UBEneeds to be positive). That's all there is to it.When you are speaking of voltages, you are just talking about the differences of potentials. So if you are looking at UCE, it will actually be negative in your circuit. Write it down as UECand it becomes positive.It's all relative!The chip you picked looks alright to me.

author: Falcon69
author_rank: Super Contributor
timestamp: August 25, 2014, 12:10:27 am
content: Alright, thank you Dave.
PNP Transistor Circuit - Switch or Amplifier? - Page 1
Forum section: electronics / beginners

author: sunny1
author_rank: Newbie
timestamp: February 17, 2013, 02:34:58 pm
content: I am unable to figure out here if the the PNP transistor in this circuit acts as switch or amplifier? Can anyone please help me figure out how the output voltage Vout looks like in this circuit? Thanks!

author: mark-r
author_rank: Contributor
timestamp: February 17, 2013, 03:16:20 pm
content: Looks a bit like an integrator, although there is some detail missing from the circuit. If the base is held 10V below the +10V rail, then the emitter will be held at ~9.4V below the 10V rail (provided enough current can flow out of the base from the 10V source). So, there will be a constant ~9.6mA current flowing into the emitter, and so about the same from the collector. Assuming the capacitor is discharged, the voltage will rise linearly from -10V towards 0V.

author: jeroen74
author_rank: Frequent Contributor
timestamp: February 17, 2013, 03:34:25 pm
content: Get LTSpice and simulate it. Be sure to turn on the'skip initial operation point solution'option. The result is as mark-r says.
Pocket multimeters - Page 1
Forum section: electronics / beginners

author: pmrlondon
author_rank: Contributor
timestamp: May 08, 2011, 08:05:30 am
content: I am thinking of getting a pocket multimeter - maybe not quickly, but if the need for a multimeter starts arising in odd places frequently I might change my mind over this.I would be looking at one with frequency and capacitance functions, as well as voltage and resistance. Are there any particular models to look towards or to avoid? The Amprobe PM51A is not a bad price here.

author: EEVblog
author_rank: Unknown
timestamp: May 08, 2011, 11:36:02 am
content: Those Amprobe meters looks pretty decent, worth a try at the price.Dave.

author: Zero999
author_rank: Super Contributor
timestamp: May 08, 2011, 01:52:25 pm
content: I use a cheap Chinese Mastech meter for that but wouldn't use it for high energy circuits or mains.

author: Ronnie
author_rank: Regular Contributor
timestamp: June 22, 2011, 05:13:22 am
content: You can consider the BK Precision 2700 3-1/2 digit with bargraph though without a capacitance meterhttp://www.mouser.com/ProductDetail/BK-Precision/2700/?qs=OfNnNsH3l7uJZoPcymEwIQ%3d%3d
Pocket oscilloscope? - Page 1
Forum section: electronics / beginners

author: Wartex
author_rank: Frequent Contributor
timestamp: December 17, 2009, 03:25:16 am
content: Dave what do you think about thishttp://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=130345369974&_trksid=p2761.l1259disclaimer: i'm not selling anything, I'm just asking if anyone tried this?I'm planning to get fluke 123 or something.

author: dmlandrum
author_rank: Regular Contributor
timestamp: December 17, 2009, 04:13:29 am
content: It's basically this:http://www.seeedstudio.com/depot/micro-digital-storage-oscilloscopedso-nano-p-512.htmlAnd you can buy it from the designer for cheaper. I have to wonder where those units on eBay are coming from, as the buttons are a different color, but otherwise I can see no difference.Dave gave his thoughts in this thread:https://www.eevblog.com/forum/index.php?topic=33.0I was looking at getting one, but decided not to bother. Though I do wish someone would make a good pocket oscilloscope like this that is actually adequate for serious use. Maybe in a few years.

author: qno
author_rank: Frequent Contributor
timestamp: December 17, 2009, 10:24:52 pm
content: This device somehow seems to lack the ruggedness of a device that needs to be used every day in many situations.I wonder how the performance would be checking you car battery at -10 deg C in winter and your solar panel at 35 deg C in the summer.And that is the not so professional work.

author: Wartex
author_rank: Frequent Contributor
timestamp: December 18, 2009, 01:44:23 am
content: thanks guys. What about fluke 123? I need a cheap one for RS485 debugging (< 19200 kbps)

author: Unknown
author_rank: Unknown
timestamp: December 23, 2009, 04:45:22 am
content: awesome...

author: michael18
author_rank: Newbie
timestamp: October 13, 2013, 06:26:01 am
content: Great i did try thr link however it was not good.
PoE Minimum Circuit - Page 1
Forum section: electronics / beginners

author: Signal32
author_rank: Frequent Contributor
timestamp: August 10, 2022, 04:55:18 am
content: Hello,I'm looking for a minimum circuit to request 48v power from a PoE switch (not based on a dedicated PoE IC).I built the below circuit fromthis articlebut it doesn't work. I both bread-boraded it and prototype boarded it and same result - the PoE switch seems to be sending an initial test voltage and then ... nothing.Any tips / does anyone have an example of a minimum PoE circuit ?Thanks

author: cortex_m0
author_rank: Regular Contributor
timestamp: August 11, 2022, 04:09:12 am
content: I do not have a complete circuit to share, but I do understand the problem.PoE switches periodically present a test voltage, and expect to see a 24.9k signature resistor. So you're good on that front.Then the switch will to see the PD present a low resistance to set the class (maximum power). I think the lowest possible class is approx 1800 ohms.What that means is you need some sort of state machine to present the right resistance at the right time. The switch is prohibited from powering a purely passive load, so putting 1800 || 24.9k won't work.I think the PoE PD chips are worth the cost. There are quite a few ways to mess up standards-compliant PoE, but the chips protect you from many of them.

author: kripton2035
author_rank: Super Contributor
timestamp: August 11, 2022, 06:54:04 am
content: with this, you have a cheap complete POE compliant supply for your device.https://www.aliexpress.com/item/32957907478.htmlor this cheaper one:https://fr.aliexpress.com/item/32956458370.html

author: Signal32
author_rank: Frequent Contributor
timestamp: August 25, 2022, 07:51:18 am
content: Found the issue. Just needed a diode bridge on the input and it works ... even the polarity is not flipped by the bridge.I guess the circuit is calculated to work only if having the voltage drop across the diode. If no diode, then the signature fails.

author: mclute0
author_rank: Regular Contributor
timestamp: August 25, 2022, 06:45:27 pm
content: IMHO ... I would suggest adding appropriate fuses to both sides. A dedicated PoE Ic has some short protection that you would be missing. Better safe than sorry. Maybe set an appropriate max current on the switch as an alternative, but that is hardly a replacement for fusing long utp runs.
Pogo Pins??? What are they? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: May 09, 2013, 11:32:18 am
content: I have seen mention, on another forum, of "Pogo Pins" being used for PCB test points. Can anyone tell me just what pogo pins are please? Thanks.

author: GeoffS
author_rank: Unknown
timestamp: May 09, 2013, 11:35:36 am
content: "A Pogo pin is a device used in electronics to establish a (usually temporary) connection between two printed circuit boards."http://en.wikipedia.org/wiki/Pogo_pin

author: c4757p
author_rank: Super Contributor
timestamp: May 09, 2013, 11:36:12 am
content: Dude.http://en.wikipedia.org/wiki/Pogo_pinhttps://www.sparkfun.com/products/8870(for a better picture)Your Google-fu is weak this morning.

author: Unknown
author_rank: Unknown
timestamp: May 09, 2013, 11:37:40 am
content: http://www.adafruit.com/products/394Spring-loaded pins that you can solder in a fixture (eg. other PCB) and press on test points on the DUT. Sparkfun has atutorialabout pogo pin test fixtures.

author: Chris Wilson
author_rank: Super Contributor
timestamp: May 09, 2013, 11:46:48 am
content: Ahh, right. I should have Googled it, I was expecting something very obscure, and probably a colloquialismThanks very much, will watch the tutorial after, appreciated.
Points in PCB Layout - Page 1
Forum section: electronics / beginners

author: Kaio Macedo
author_rank: Contributor
timestamp: November 01, 2016, 06:58:23 am
content: Hello guys,I have a question about these points in IC PCB Layout, I believe that should mean pin 1, would it?Could show me some study material on this subject?

author: tautech
author_rank: Super Contributor
timestamp: November 01, 2016, 07:11:49 am
content: 7. Square pad pin 1 DIP

author: tautech
author_rank: Super Contributor
timestamp: November 01, 2016, 07:47:38 am
content: Dave's got some good and handy docs under PCB layout and CAD in his Wiki:http://www.eevblog.com/wiki/index.php?title=Online_Electronics_Tutorials_and_Books
PoKeys57E - Page 1
Forum section: electronics / beginners

author: deadshort
author_rank: Newbie
timestamp: May 24, 2014, 07:33:43 pm
content: I have just watched EEVblog #377 - Mailbag Monday and was very interested in the poKeys57E. I am interested in this this connected to a weather station. Dose anyone have experience connecting a pokeys to a weather station?
Pokit Meter anyone used one? is it any good? or is it more bullshit? - Page 1
Forum section: electronics / beginners

author: IVLRNR
author_rank: Contributor
timestamp: March 21, 2021, 01:34:56 am
content: Hi Team,Just got an ad for this thing, seems way to good to be true? anyone have any experience?https://shop.pokitmeter.com/collections/home-page-showcase-products/products/pokitmeter?utm_source=facebook&utm_medium=cpc&utm_campaign=PokitMeter%20-%20Top%20Geos_Pokit_Shopify_Pixel_1%25&utm_content=Pokit_meter_dymanic&utm_term=Top%20Geos_Pokit_Shopify_Pixel_1%25&fbclid=IwAR1BTD8CRbcebiCYRYS7wUSSmWMp46aS-aQlme3igXqmYjYsIpqOZyEz9gI
polar to bi-polar caps - Page 1
Forum section: electronics / beginners

author: nemo000111
author_rank: Contributor
timestamp: April 16, 2014, 03:15:08 am
content: What's the term for joining two polar caps in series (neg to neg or pos to pos) to create a bipolar cap? Also, why does this work and what are the trade offs of doing this? Decent quality links would be appreciated as well if possible. Thanks much.
Polarity Indicators on Current Source Symbol - Page 1
Forum section: electronics / beginners

author: eev_carl
author_rank: Regular Contributor
timestamp: November 20, 2017, 12:35:14 pm
content: Hi,Is it common to list a polarity on current sources as in this photo from my workbook? I searched through a few hundred images and didn't see any other examples of this online.Thanks,Carl

author: Ian.M
author_rank: Super Contributor
timestamp: November 20, 2017, 12:45:43 pm
content: IMHO No. The symbol should of course have an arrow to indicate the direction of positive conventional current flow, but as the polarity of the voltage across its terminals will depend on the circuit it is connected to, adding + and - there as part of the symbol is just misleading.
Polarity of MJ2955 transistor - Page 1
Forum section: electronics / beginners

author: naujoks
author_rank: Regular Contributor
timestamp: December 18, 2022, 07:23:36 am
content: I'm replacing a MJ2955 power transistor in a power supply.It's a NPN bipolar.The replacement has no indication which terminal is emitter and which is base (the old one has it printed on the back). How can I find out which terminal is which?

author: Ian.M
author_rank: Super Contributor
timestamp: December 18, 2022, 07:30:12 am
content: Pinout is in the datasheet . . .

author: srb1954
author_rank: Super Contributor
timestamp: December 18, 2022, 07:44:29 am
content: Quote from: naujoks on December 18, 2022, 07:23:36 amMJ2955 is aPNPbipolar transistor.The datasheet is available on the Onsemi web site listed under MJ3055, which is the complementary NPN transistor.

author: naujoks
author_rank: Regular Contributor
timestamp: December 18, 2022, 07:57:15 am
content: I found this data sheet:https://www.onsemi.com/pdf/datasheet/2n3055-d.pdfI still can't figure out the pinout though. There's nothing printed on it.

author: BradC
author_rank: Super Contributor
timestamp: December 18, 2022, 08:27:34 am
content: Quote from: naujoks on December 18, 2022, 07:57:15 amA couple of things. First the obvious. That data sheet isn’t for a 2955. Secondly, the pin locations are not symmetrical. The pin out you are looking for is on page 4 of the 5 page data sheet you linked. It’s just not the right pinout for the transistor in your photo because it’s the wrong data sheet.

author: Ian.M
author_rank: Super Contributor
timestamp: December 18, 2022, 08:43:05 am
content: The actual manufacturer's datasheet is available here:https://pdf.dzsc.com/20090603/200904230247507431.pdfBy convention, through hole power transistor pinouts are the bottom ('pin') view, unless otherwise indicated.If in doubt, as the collector is invariably the case or tab of power transistors, you can locate the base pin using a DMM on its diode test range.

author: naujoks
author_rank: Regular Contributor
timestamp: December 18, 2022, 02:45:29 pm
content: Using those sheets I think I correctly identified the B and E.Afterwards I also noticed, that the pins are not exactly in the centre of the transistor, so putting the two next to each other I was also able to see which way it's supposed to go.

author: TimFox
author_rank: Super Contributor
timestamp: December 18, 2022, 03:35:11 pm
content: I believe the TO-3 dimensions were chosen so the device could fit into an octal tube socket.Having the B and E terminals on the center line would be an unwise choice, for obvious reasons.
Polarity on this laptop DC jack - Page 1
Forum section: electronics / beginners

author: SolderOcelot
author_rank: Contributor
timestamp: November 09, 2018, 10:18:48 am
content: I want to measure if there is voltage between the DC jack and motherboard. This DC jack has 5 legs. Which is +? Which is -? What are the other ones, just support?https://www.dropbox.com/s/27etfzauw4wt669/dc-jack.jpeg?

author: capt bullshot
author_rank: Super Contributor
timestamp: November 09, 2018, 10:41:41 am
content: Looks rather obvious. For pins are connected, and one isolated.So I'd guess the connected ones are "-" and the left over "+" as this is most common. Might be reversed, that's what you use your DMM for to determine this.

author: wraper
author_rank: Unknown
timestamp: November 09, 2018, 10:43:21 am
content: 4 legs are connected to ground (-), it's quite obvious because they consist of single piece of metal. One leg separated with a piece of black plastic on the bottom right corner is +.

author: SolderOcelot
author_rank: Contributor
timestamp: November 09, 2018, 11:04:02 am
content: Honestly it did look obvious to me too but I just wanted to make sure
Polarized capacitors - Page 1
Forum section: electronics / beginners

author: paul18fr
author_rank: Contributor
timestamp: August 25, 2014, 12:31:07 pm
content: DearDoes polyester film capacitors are polarized ? I'm looking for 1nF to 100nF ones (to play with my breadboard and/or my new Arduino i.e. from 3V up to 12V max) and they seems not being electrolitic ones ...ThanksPaul

author: Pedram
author_rank: Regular Contributor
timestamp: August 25, 2014, 12:32:40 pm
content: no they are not

author: paul18fr
author_rank: Contributor
timestamp: August 25, 2014, 01:37:32 pm
content: thanks for the quick answer,Effectively and after a "hard" search on internet, such polarized capacitor does not exist for 1nF; I understand (nut am I right ?) that "polarized" feature comes from the manufacturing process (and absolutely not from any design consideration) ; for such low capacity it's better to use ceramic capacitors.Paul

author: DanielS
author_rank: Frequent Contributor
timestamp: August 25, 2014, 05:37:29 pm
content: The "polarized feature" is because high-capacity capacitors use electrolyte to increase their energy density. Biasing them the wrong way causes electrolysis and fairly rapid failure.Small-value capacitors do not require electrolytics' density since value requirements can often be met by straight electrostatic potential such as the very common multi-layer chip capacitors.Over a decade ago, a 1µF ceramic capacitor used to be impractically large so 1uF electrolytics were still somewhat common but today, you can get over 10µF in 1210 MLCC format and this made sub-10µF electrolytics almost history.

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2014, 05:45:02 pm
content: Polarization comes from the process by which the capacitor works. Polarized capacitors rely on an electrochemical reaction which produces the insulating dielectric layer.
Poly caps used with SMPS - Page 1
Forum section: electronics / beginners

author: Sylvi
author_rank: Regular Contributor
timestamp: January 08, 2019, 11:08:47 pm
content: HeySMPS module app notes always specify ceramic caps all around, sometimes chokes, even electros, but never poly caps.There are many polypropylene caps used in DC link applications with high-frequency impedance curves that look exactly like MLCCss, so why does no one every use them? Is it just because of cost? Size?I know poly caps are physically much larger but they do not have the variable capacitance versus voltage that MLCCs suffer, nor does their value change with temperature - so much more like an expensive C0G-N0P ceramic. These days, the range of polyprop cap-voltage has been extended down to quite low voltages at decent capacitance values, and also to large-C at high-V. They are super rugged compared to ceramic so more likely to see them in railway duty - haha - why not pro audio and consumer electronics?

author: David Hess
author_rank: Super Contributor
timestamp: January 08, 2019, 11:29:37 pm
content: Plastic film capacitors are larger, more expensive, and more difficult to solder. They work fine as replacements for ceramic capacitors.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 09, 2019, 12:05:34 am
content: Film is only economical above 100V or so, and when more AC current is needed than electrolytic can handle (which is cheaper per uF).As it happens, aluminum polymer has very much the same characteristics as lowish-Q film caps (say, self-healing MKS style), scaled to lower voltage ratings and larger values. Still kind of expensive, but well worth it when you need it.Tim
Poly electrolytic vs ceremic caps (SMD) for voltage rail ripple - Page 1
Forum section: electronics / beginners

author: gjvdheiden
author_rank: Contributor
timestamp: March 23, 2023, 11:08:38 am
content: To stabilize a supply voltage, I wan't to use a 10u and a 4.7u capacitor. I also got small ceremic caps for decoupling higher freq stuff. The rail is 5V.I ordered a cemeric (Samsung) and a poly electrolytic (Nichicon) cap from DigiKey.I was wondering, is there any obvious reason why (not) to choose the cemeric or the poly ones for voltage rails?

author: Kleinstein
author_rank: Super Contributor
timestamp: March 23, 2023, 11:16:20 am
content: With a power full supply, e.g. from a rechargible battery one may want to be a bit careful with the ceramic capacitors. From mechanical stress they sometimes fail short, especially the larger cases and near mounting holes or similar areas where board stress is high.

author: gjvdheiden
author_rank: Contributor
timestamp: March 23, 2023, 03:21:27 pm
content: Learned something, thank you.