hybridfree/eevblog-posts huggingface dataset:
purpose of capacitors in circuit - Page 1
Forum section: electronics / beginners

author: zze110
author_rank: Contributor
timestamp: March 08, 2015, 03:12:15 am
content: Hello,I have a schematic I am trying to read and I'm somewhat unsure what I'm looking at. I have attached a picture from wikipedia that matches the circuit almost exactly.The difference is each line: SCLK, MOSI, and MISO have 68pF capacitors connected between the bus line and ground (not in series with slave device). From what I can guess this is a parallel termination to avoid signal noise? However, I've only seen this done with a resistor before.Why use a capacitor? How does this behave differently from using a resistor?

author: zze110
author_rank: Contributor
timestamp: March 08, 2015, 04:12:37 am
content: Thanks!I'm guessing by "source side" you mean right next to the SPI master device? This is really unknown stuff for me. Didn't learn anything about this in school.From what I can tell the capacitors are physically placed directly in the midpoint of the traces.Drew another picture that describes where the capacitors are placed. Obviously it isn't perfect center because there is more than 1 slave device.

author: zze110
author_rank: Contributor
timestamp: March 08, 2015, 04:37:04 am
content: Now it all makes sense!Thanks for your response. Guess I need to learn more about EMI stuff.
Purpose of diode at output of single supply op amp - Page 1
Forum section: electronics / beginners

author: bonz
author_rank: Newbie
timestamp: October 20, 2024, 02:43:52 pm
content: Ran across this schematic which uses single supply op amps (OPA2374) to provide the positive and negative portions of an AC signal. What is the purpose of the diode at the output of the single supply op amp? Wouldn't the output go to (and stay at) ground level when input swings to negative (on the positive op amp and vice versa on the negative)?I have searched for this online and all I see is uses of this with dual supply op amps which make sense to keep the output from swinging below 0v, but I found nothing on the single supply op amps.I appreciate your answers in advance.

author: MrAl
author_rank: Super Contributor
timestamp: October 20, 2024, 03:03:34 pm
content: Hello,With many op amps that run off of a single supply, their outputs can not go all the way to 0.000 volts, instead they only get down to maybe 0.025 volts to 0.200 volts. With that added diode, it drops around 0.600 volts, so the output can get all the way to 0.000 volts even with a single supply.That's one possibility although one diode is usually enough for that and the pulldown resistor is usually smaller than that 1 Megohm that we see here.It can also just be there to prevent a negative output.

author: magic
author_rank: Super Contributor
timestamp: October 20, 2024, 03:11:04 pm
content: Ask whomever you got this schematic from.(The noninverting one could be a peak detector, the inverting slightly less so. Either way, net labels look like they may be ESD test fixtures?)

author: langwadt
author_rank: Super Contributor
timestamp: October 20, 2024, 04:04:29 pm
content: some kind of push-pull drive for a center tappet transformer?

author: Zero999
author_rank: Super Contributor
timestamp: October 20, 2024, 05:27:06 pm
content: They're precision rectifier circuits.The capacitors provide filtering, but lets concentrate on the DC response.The diodes are connected in parallel, so can be treated as single diodes.The top one is half wave and the bottom full wave but R6 on the output attenuates the positive cycles because when the op-amp's output is negative, the input is connected to the output via R& and R5.precision rectifier.asc(1.95 kB - downloaded 45 times.)A solution is to the full wave rectifier is to select the feedback resistors so the op-amp inverting amplifier's attenuation matches that of the output resistor and add an amplifier to raise the gain back to unity.precision rectifier.asc(1.95 kB - downloaded 15 times.)
Purpose of external capacitor between gate and source of a MOSFET - Page 1
Forum section: electronics / beginners

author: syntax333
author_rank: Regular Contributor
timestamp: May 15, 2020, 04:00:47 pm
content: Hi, the soft-latching circuit is bothering me since I cannot understand the purpose of the capacitor placed between gate and source of the p-channel of MOSFET in this soft latching circuit.Can anyone point me to right direction? I know the purposes of resistors in the circuit but capacitor I do not.

author: Peabody
author_rank: Super Contributor
timestamp: May 15, 2020, 04:16:44 pm
content: I'll offer one idea. Whenever the battery is disconnected from the circuit, all capacitors become discharged. And this includes the capacitor we call the mosfet gate. When the battery is plugged in and power comes up, you can get a significant GS differential - enough to turn on the mosfet - because the source rises immediately, but the gate can only come up through the high-value resistor. The capacitor is there to transfer the source voltage immediately to the gate. A capacitor acts as a low-impedance pathway to a rapidly changing signal. So for a very brief period, it's as if the source and gate are tied together, so there can be no GS differential, and that keeps the mosfet off. Then after that, the resistor takes over and maintains the same situation. So basically, it's there to prevent the mosfet from turning on by itself when you first connect power to the circuit.That's just one guess, and I don't know if it makes sense. In any case, you are substantially increasing the effective gate capacitance, so subsequent transitions would tend to be slow. That's probably not an issue in this situation.
purpose of parallel RC circuit across MOSFET (fan control) - Page 1
Forum section: electronics / beginners

author: JeanF
author_rank: Regular Contributor
timestamp: November 05, 2020, 10:08:58 am
content: Hi,the 12V fan inside the handle of my cheap generic 858D+ hot air station is driven like this:The PWM from the microcontroller has a frequency of 500 Hz.Can someone help me understand the purpose of the 1µ / 2k7 parallel RC circuit across the MOSFET?If I'm not completely asleep it should act as a high-pass, with a cutoff frequency of about 59 Hz. So I don't get what it's doing here.I've seen RC snubbers across transistors sometimes, but all the ones I've seen were series RC, not parallel.When the station is on standby, the fan is of course not running but emits a very annoying whine.The 12V rail and ground look good. I can see a ~1V pk-pk sawtooth ripple around 3 kHz, with a lot of jitter on the drain of Q1.It looks like it comes from the internal circuitry of the fan because when I swap the internal squirrel-cage blower with a 12V PC fan, the whine and ripple disappear.With the original fan plugged back again, if I remove the 1µ cap only the audible noise is almost completely gone. If I remove the 2k7 resistor only, or both R and C, the noise completely goes away.So could I just remove the RC circuit as a quick & easy fix for the annoying whine, or am I completely missing something here?Thanks

author: Zero999
author_rank: Super Contributor
timestamp: November 05, 2020, 10:42:14 am
content: It's wrong. The resistor and capacitor should be in series. As drawn, the capacitor will discharge, resulting in a huge current surge flowing through the MOSFET, when it's turned on and the 2k7 resistor will allow around 4mA to leak through the fan, when it's off.If the fan has a plain, ordinary brushed DC motor, it should have a freewheeling diode in parallel with it and no RC snubber on the MOSFET. If the fan has a brushless DC motor, then no freewheeling diode or snubber are required.

author: JeanF
author_rank: Regular Contributor
timestamp: November 05, 2020, 01:15:19 pm
content: Thank you.The fan is brushless. I removed both the 2k7 resistor and the 1µF capacitor and reassembled everything. Now it's silenton standby mode at least; when actually using hot air it's a bit noisy, but for the price, I really can't complainThere seem to be many variations of these and I don't know if other variants have this "feature". For the record, the PCB in mine is populated with a mix of THT and SMD parts and has a blue solder mask. The only marking on the silkscreen is "858D2"
Purpose of potentiometer before non-inverting pin on Op-Amp - Page 1
Forum section: electronics / beginners

author: jrjradler
author_rank: Newbie
timestamp: November 28, 2022, 12:06:19 am
content: A circuit I'm replicating ties the output of one op-amp (OPA277) to the input of a potentiometer - that output then acts as the input to the non-inverting input of another op-amp (INA149). I believe it's trying to create a modified howland pump - I'm just a bit confused about what the potentiometer does and if I can replace it with a smaller 0603 resistor.I attached a photo of the circuit in question.Here is a link to the OPA277 datasheet ->https://www.ti.com/lit/ds/symlink/opa277.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1669593970133&ref_url=https%253A%252F%252Fwww.mouser.ca%252FHere is a link to the INA149 datasheet ->https://www.ti.com/lit/ds/symlink/ina149-ep.pdf?HQS=dis-mous-null-mousermode-dsf-pf-null-wwe&ts=1669583195718&ref_url=https%253A%252F%252Fwww.mouser.ca%252F

author: Doctorandus_P
author_rank: Super Contributor
timestamp: November 28, 2022, 12:22:57 am
content: Start by drawing a schematic.Not many people are interested in figuring out a PCB layout and interpreting the results.And with a bit of luck, if you have drawn the schematic, the reason for the pot may be obvious.

author: EPAIII
author_rank: Super Contributor
timestamp: November 30, 2022, 09:05:40 am
content: Some more reading:https://www.allaboutcircuits.com/technical-articles/the-howland-current-pump/https://www.ti.com/lit/an/snoa474a/snoa474a.pdfWhat does the original circuit do and why are you trying to copy it but with changes?

author: mikerj
author_rank: Super Contributor
timestamp: November 30, 2022, 10:28:23 am
content: Quote from: jrjradler on November 28, 2022, 12:06:19 amThe INA149 is not just an op-amp, it has integrated gain setting resistors so the trim pot is actually in series with a 380k resistor within the INA149. This means the trimmer will be adjusting gain on the +ve side, presumably to get the best CMRR. Drawing the schematic including all circuits immediately connected to the INA149 will likely yield clues as to why they found this gain trimming was required.
Purpose of Strange pcb track - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 09, 2015, 06:48:37 am
content: I have attached some of PCB's showing strange PCb track. (zoom out file to 50% for clarity).What is their purpose. Shouldn't they be straight way connected?

author: ataradov
author_rank: Super Contributor
timestamp: March 09, 2015, 06:51:47 am
content: A very typical trace length matching.

author: Psi
author_rank: Super Contributor
timestamp: March 09, 2015, 06:53:01 am
content: It's either to get a specific resistance or to adjust the delay in a signal bus so all the signals arrive at the same time.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: March 09, 2015, 06:54:30 am
content: This is to have a precise delay in the transmission of the signal.

author: Falcon69
author_rank: Super Contributor
timestamp: March 09, 2015, 07:05:19 am
content: i always wondered what that was about. i see them all the time on computer motherboards.

author: Psi
author_rank: Super Contributor
timestamp: March 09, 2015, 07:12:40 am
content: Yep, when dealing with GHz parallel buses it doesn't take much difference in track length before some of the bits from one clock cycle arrive too late, which, as you can imagine, causes some issues

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 09, 2015, 03:26:25 pm
content: It is very fast DIO board (upto 50Mhz).I have noticed that tracks which had small distance between them, only those where made wiggled.Tracks which had large distance very straight lines.So I think correct reason would beThis is done to have signals to arrive at the same time at the end of the line.

author: ataradov
author_rank: Super Contributor
timestamp: March 09, 2015, 04:07:32 pm
content: Tracks that run in parallel close to each other are differential pairs, to the length alignment is necessary to ensure that the signal in two wires travels the same distance and arrives with the same delay.

author: c4757p
author_rank: Super Contributor
timestamp: March 09, 2015, 04:10:32 pm
content: I doubt those are differential pairs...

author: ataradov
author_rank: Super Contributor
timestamp: March 09, 2015, 04:11:53 pm
content: It looks like the place that is show on the picture is the part where they have already been separated. Although they do look strange. There seems to be plenty of space here to keep them running in parallel.
Purpose of these diodes in inverting opamp feedback - Page 1
Forum section: electronics / beginners

author: haseeb zaib
author_rank: Contributor
timestamp: November 03, 2021, 10:53:44 am
content: Hi, I was reverse engineering a circuit for learning purposes and I came across this strange configuration of op-amp. I want to ask, what is the purpose of these diodes? (please explain little bit) are they being used to stop feedback current/voltage ? I was looking at log opamp but it seems to me this is something different.I have also ran this circuit in ltspice but I still don't understand it.on inverting input the voltage could vary as shown in image, but on non-inverting input the voltage is being given by voltage divider which equal to 5V-5.1V

author: vk6zgo
author_rank: Super Contributor
timestamp: November 03, 2021, 11:25:43 am
content: Quote from: haseeb zaib on November 03, 2021, 10:53:44 amI have seen a similar schematic, but that only used one diode.The idea is to produce an amplifier with a non-linear transfer characteristic.Back in the day, it was common to use an array of diodes to obtain such a characteristic for video "gamma correction" circuits.

author: Zero999
author_rank: Super Contributor
timestamp: November 03, 2021, 12:04:53 pm
content: It's an inverting amplifier, with a gain of 10, with the input and output referenced to 5V.VOUT= 5+(5-VIN)*10D1 and D2 limit VOUTto two diode drops below 5V.

author: haseeb zaib
author_rank: Contributor
timestamp: November 03, 2021, 01:20:28 pm
content: thanks alot, for taking the time and doing this simulationI understood it way better. In the actual circuit, the voltage was also limited to around 4V, similar to it was in a simulation. when I removed the diodes it went to 0 volt.thanks once again
Push and Pull current from voice coil linear actuator from ADC output of 0-5V - Page 1
Forum section: electronics / beginners

author: faizan_zaheer
author_rank: Newbie
timestamp: December 07, 2024, 11:19:06 am
content: Hi membersI am Faizan. I am designing a circuit for driving a voice coil linear actuator with R=18 ohms and operates fully at a 5V supply. I want to make a current source and sink circuit so that I can source and sink current from the voice coil to produce back-and-forth linear motion. Right now, I am using an op-amp with a transistor as a current source buffer which provides variable voltage supply by varying input voltage between 0-5V at op-amp input generated by ADC and it also varies source current according to voltage set.But, to produce reverse backward movement, I need to place negative voltage on a coil or sink current from it after supplying it with 5V. How can I design a circuit to both source and sink varying current from it by varying voltages from 0-5V with a 2.5V split? The Howland current pump is the way but it will always maintains a fixed current regardless of the input voltage to the load? Thanks.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 07, 2024, 04:18:14 pm
content: H-bridge motor driver?L9110H will handle 800mA continuous.

author: Benta
author_rank: Super Contributor
timestamp: December 07, 2024, 05:06:10 pm
content: Quote from: Terry Bites on December 07, 2024, 04:18:14 pmThat would work for bang-bang control.For linear control, I'd suggest a bridge-coupled audio power amplifier.

author: Tim S
author_rank: Contributor
timestamp: December 09, 2024, 06:08:28 pm
content: Voice coil motors are not easy to implement, they require something to push/pull against otherwise all they do is shoot end to end like a doorbell solenoid.Options are1) use a spring to push it to one end then drive against the spring. The position is dependant upon current flow. The spring must be arranged to exert a constant force over the range which excludes sticking it on the end. The spring cannot move more than 10% of it's length - the shorter the better.2) use a position feedback and servo to the required position. Difficult as you will need a linear position feedback.Whatever you do, analogue class B like a speaker driver is the way to go. Things may get warm, but get it working on analogue first.Good luck!

author: mawyatt
author_rank: Super Contributor
timestamp: December 09, 2024, 07:19:30 pm
content: An LM1875 might work in a bridge configuration. The Juntek 1698 has a pair of LM1875s that is used for a DC Coupled Buffer Amp for AWGs. Should be easy to configure to check out how these LM1875s behave driving a Voice Coil Motor.Best
Push button Delay Circuit - Page 1
Forum section: electronics / beginners

author: avc4eva
author_rank: Contributor
timestamp: March 16, 2015, 12:24:55 pm
content: Hi all,I have a question regarding a circuit i need to design:I want to able to use a simple on/off momentary switch which when held for say 3-5 seconds interfaces with GPIO of MCU and turns on/off MCU (similar to the functionality of a smartphone when turning on/off).I was thinking i would need some kind of LC circuit, the simpler the better, but should have consistent timing.Or if anyone has any other suggestion to implement something similar to the of found in smartphones that would be great.Andrea.

author: Unknown
author_rank: Unknown
timestamp: March 16, 2015, 12:32:15 pm
content: If the sleep current of the MCU is not too high you can use a GPIO with an interrupt that wakes up the MCU directly.

author: avc4eva
author_rank: Contributor
timestamp: March 16, 2015, 12:34:46 pm
content: Quote from: exapod on March 16, 2015, 12:32:15 pmYes this is the idea, however i want that typical 3-5s hold delay from smartphones to place into off/sleep.

author: Unknown
author_rank: Unknown
timestamp: March 16, 2015, 12:41:54 pm
content: You can do that in software with timers or rtc if you have one.

author: avc4eva
author_rank: Contributor
timestamp: March 16, 2015, 12:47:11 pm
content: Quote from: exapod on March 16, 2015, 12:41:54 pmTrue, however if the device is off/sleep that is difficult.

author: Unknown
author_rank: Unknown
timestamp: March 16, 2015, 01:45:59 pm
content: The first interrupt from the button wakes up the mcu, you set the rtc/timers for a 5s interrupt and go to sleep.At this time if the user releases the button another interrupt is fired, the mcu wakes up you cancel the 5s interrupt and go to sleep.If the user doesn't release the button the 5s interrupt wakes up the mcu and you are "on".

author: avc4eva
author_rank: Contributor
timestamp: March 16, 2015, 01:47:19 pm
content: Quote from: exapod on March 16, 2015, 01:45:59 pmAh great idea, thanks for that help!Andrea
push-on hold off - Page 1
Forum section: electronics / beginners

author: chota.sanjiv
author_rank: Contributor
timestamp: September 06, 2016, 12:56:24 pm
content: Hi Guys,I am using the attached circuit to implement push-on and hold off logic for my circuit, I now need to modify this so that rather than VCC_TOP I can use the same logic for GND so that by default its +12v and on hold it becomes GND and again o a single press it becomes 12v, I have a very limited knowledge of analog electronics and this is giving me a headache, please help.regards,Sanjeev

author: TomS_
author_rank: Frequent Contributor
timestamp: September 07, 2016, 06:36:02 pm
content: One of Daves earlier videos covers a soft latch power circuit, I wonder if this could help?edit: oh, I just figured out what you meant by "hold off". I assume you want some similar functionality to a typical PC power button. Press it and it turns on, but hold it for a few seconds and it turns off? Thats probably implemented using a microcontroller or other similar type of device rather than an analogue circuit. Maybe a tiny micro like a PIC10 would do a better job? Certainly fewer components and less head f**kery.

author: JS
author_rank: Frequent Contributor
timestamp: September 07, 2016, 10:10:11 pm
content: You won't get over 1s time constant with a simple RC reliably.You can still use your power on circuit as is and sense (in a sensible way) the push of your switch, if you are driving a µC from it you already have the pullup (the sensitive was in the case the voltage of the power device could be higher than the µC input)If you don't have a micro but you do have a 5ish volts rail you may think into getting a tiny one in (8pin pic maybe). If µC are ruled out for some digital-free fetish or something you could add a counter or an reasonable RC time constant with some help, a comparator or something...JS

author: JS
author_rank: Frequent Contributor
timestamp: September 07, 2016, 11:05:22 pm
content: Just found this...https://kitnic.it/boards/github.com/kasbah/push-on-hold-off/Seems much like the one you found for me, I don't know... maybe I was wrong then.JS

author: kasbah
author_rank: Contributor
timestamp: September 08, 2016, 01:04:59 pm
content: The board JS linked is my design. In the repo link there is a LTSpice simulation as well and some good folks in this forumhelped me out with it.I don't understand your problem description though. Could you try and describe the behaviour you want in different words?
push-pull crossover + op amp as buffer - Page 1
Forum section: electronics / beginners

author: fady232
author_rank: Contributor
timestamp: April 24, 2025, 01:56:23 pm
content: Hello all, can someone tell me if i understood this circuit properly?:This circuit is basically identical to the last post i did, but with a difference, there is an op amp acting as voltage buffer, what he does here is this:at pin "+" i connected the sine wave and the pin - is connected to the output.Now what amplifier gonna do is a comparison beetwen the pin + voltage and pin -, and will try to match its output in order to make pin - voltage as close as possible to pin +, in this way with the op amp we compensate the drop of bjt internal diodes etc, cus we use our input as reference.Secondly we got a low impedance as output.Is this correct? for what other reason this circuit is used?

author: BillyO
author_rank: Super Contributor
timestamp: April 24, 2025, 02:41:16 pm
content: The Vbeof the transistors is already compensated for by the R2, D1, D2, R1 bias circuit. In this case the op amp is there to provide a high impedance input.

author: Zero999
author_rank: Super Contributor
timestamp: April 24, 2025, 02:41:53 pm
content: Well the op-amp helps to compensate for the non-linearity of the buffer because it has a high open loop gain.Note that the OP37 is not unity gain stable and will likely oscillate or ring, when configured at a unity gain buffer. The gain must be greater than 5 in order to ensure stability.https://www.analog.com/media/en/technical-documentation/data-sheets/op37.pdf

author: Xena E
author_rank: Frequent Contributor
timestamp: April 24, 2025, 04:59:51 pm
content: Check V3 and V5 connection in your diagram?X

author: Terry Bites
author_rank: Super Contributor
timestamp: April 25, 2025, 12:18:30 pm
content: Its to boost the output current (by lowering the output impedane) of the opamp.It also removes the heating caasued by the opamp's output stage to extenal devices.Heat=drift.It will not fully eliminate all crossover distortion. You wouldnt use this in an audio system but it could work very well at DC.

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2025, 04:44:09 pm
content: Quote from: Xena E on April 24, 2025, 04:59:51 pmThey're correct.
Push-Pull Output with 500mA@12V - Page 1
Forum section: electronics / beginners

author: Domonoky
author_rank: Newbie
timestamp: March 06, 2019, 02:23:12 pm
content: Hello,I have a project where i need an output which can push up to 500mA at 12V and also sink up to 500mA of current. And the circuit for this should use as minimal power as possible while nothing is connected to the output. As this is battery powered and should run as long as possible in standby.The Output does not need to switch fast. There is now PWM or so planned for this.The input for this circuit is a 3.3V signal from a flip flop with also has a push-pull output, but only +-20mA @ 3.3V.Can anybody recommend a circuit/chip for this Levelshifter/Push-pull type thing which uses as little power as possible ?In a first try is used a MCP1416 MOSFET driver, which works, but uses ~0.5mA when nothing is connected to the output. Also it looks like i have broken one when i pushed to much current into it, even with the PTC fuse in front of the MOSFET driver.Any help is welcome

author: Jeroen3
author_rank: Super Contributor
timestamp: March 06, 2019, 03:34:23 pm
content: Mosfet drivers probably can't do continous 0.5A. See if you can find a half-bridge driver and some small mosfets.Or an integrated half bridge driver for that matter. (eg: motor driver)

author: Zero999
author_rank: Super Contributor
timestamp: March 06, 2019, 04:47:02 pm
content: Yes, it won't be able to drive 500mA continuously.You could try a higher current MOSFET driver. Both sections of the TC4424 wired in parallel should be able to take 500mA continuously, without any problems, especially the DFN package on a large copper plane.

author: magic
author_rank: Super Contributor
timestamp: March 06, 2019, 06:43:37 pm
content: If you can live with only about 1-11V output swing under load, some low power CMOS opamp or comparator like TLC3702 (20µA supply current) could be used to amplify the waveform and buffered by a bd139/bd140 totem pole to drive the current.
push pull solenoids - Page 1
Forum section: electronics / beginners

author: cncmark
author_rank: Newbie
timestamp: April 25, 2016, 09:05:56 pm
content: hi guys new to the forum and electronicsi design,build and program cnc machines i have built a few nowand i'm a builder 24/7 long story so if i can help anybody just callfor a project i am doing i need to use two solenoids to push and pull either a diamond coated wire or a very fine band saw blade like a vibrating sawi was going to use some 12v or 24v push pull solenoids with a 10mm movement but havent got a clue on what switching unit or controlling the speedso i kneel before you all being a humble builder and beg for helpmany thanks marky

author: retrolefty
author_rank: Super Contributor
timestamp: April 25, 2016, 09:30:25 pm
content: An H-drive is a popular method of applying bi-polar DC voltage to a motor and should work for solenoids. Lots of inexpensive E-bay driver choices available.

author: max_torque
author_rank: Super Contributor
timestamp: April 25, 2016, 09:37:37 pm
content: Quote from: retrolefty on April 25, 2016, 09:30:25 pmer, unless you are using mechanical means to return the sol to its starting position, an AC signal isn't going to help! (conventional solenoids only act to increase their inductance, so either polarity results in a single direction of motion!) A "voice coil" actuator is what you are after, as it uses a permanent magnet to bias the magnetic field to produce a bipolar force

author: sokoloff
author_rank: Super Contributor
timestamp: April 25, 2016, 09:41:21 pm
content: If you're trying to do a reciprocating saw motion, I'd look to copy what existing saws do, and it's not a pair of push-pull solenoids. They typically use an eccentric drive.Look into a jigsaw or sewing machine mechanism if that's close to what you're trying to build.

author: cncmark
author_rank: Newbie
timestamp: April 25, 2016, 11:40:27 pm
content: hi guys many thanks to you all i have to use two independent units like solenoids i will read through your suggestions so i dont talk without getting my brain in gearcheers marky

author: woodchips
author_rank: Frequent Contributor
timestamp: April 26, 2016, 06:41:13 pm
content: Might be much easier if you use a stepper motor.

author: bitslice
author_rank: Frequent Contributor
timestamp: April 26, 2016, 09:14:57 pm
content: Quote from: sokoloff on April 25, 2016, 09:41:21 pmThinking the same, maybe mount the blade on a sliding rod and use something eccentric to push it back and forth.Appreciate the OP only has some solenoids, but the alternative hardware is a few quid
push-pull vs open drain - Page 1
Forum section: electronics / beginners

author: rookie
author_rank: Contributor
timestamp: August 09, 2019, 08:05:08 pm
content: Hi !I'm trying to understand the difference between push-pull and open-drain in the context of multiple inputs connected on the i/o line. For example, I know open drain allows multiple inputs to drive the line low, something that is not possible in push-pull configuration. But I don't know the technical (electronics) reason behind this. Something something p-mos/n-mos... Can someone enlighten?

author: ataradov
author_rank: Super Contributor
timestamp: August 09, 2019, 08:17:52 pm
content: Because in an open drain configuration an output transistor can do two things:1. Not drive the output.2. Drive the output to ground.The high level is ensured by the outside pull-up resistor.There will never be a conflict of levels. If either of the devices drives the line low, it will be low no matter what others are doing.In a push-pull configuration the output is actively driven, so if one device decided to drive high level and another one decided to drive low level, there will be a conflict. The end result is unpredictable and depends on the exact design of the output stages.

author: MarkF
author_rank: Super Contributor
timestamp: August 09, 2019, 10:16:55 pm
content: Here is a crude visualization using relays and switches.The resistor is NOT part of any gate.
Push switch doesnt stay on - Page 1
Forum section: electronics / beginners

author: Faringdon
author_rank: Super Contributor
timestamp: September 26, 2023, 10:28:18 am
content: Hi,Is this switch designed to stay on of current flows through it?http://www.manplug.com.my/products-switches-push-5_2.htm...its in the line wire to a fan unit......the unit has blown...but how does this switch ever stay on?

author: themadhippy
author_rank: Super Contributor
timestamp: September 26, 2023, 12:28:50 pm
content: looks like a mommentry (on) off switchQuoteit dont,it turns on a self hold relay ,bonus added safety feature is that it wont start on its own after a power failure.
Putting a foam grip on handle without using plastic shims?  - Page 1
Forum section: electronics / beginners

author: Aston01
author_rank: Newbie
timestamp: August 28, 2022, 03:18:58 pm
content: I bought an Aixun T3A and it came with a couple of uninstalled foam grips, but every video I've seen shows foam grips like that being installed with a pair of plastic pieces that look a lot like shoehorns.Do I need to order those plastic pieces from somewhere or is there another way?

author: c099
author_rank: Newbie
timestamp: September 13, 2022, 02:14:03 pm
content: I used a little bit of soap water.
putting good caps in paralell with bad. - Page 1
Forum section: electronics / beginners

author: ME
author_rank: Frequent Contributor
timestamp: May 04, 2025, 02:24:22 am
content: I have this dead stabilock SI4011 coms test set that fails a few self tests ,It has some smd electrolytic caps that measure almost open , ie>10 ohm esr ,can i tack new caps in paralell with the bad ones for testing , untill my new caps arrive?.

author: CaptDon
author_rank: Super Contributor
timestamp: May 04, 2025, 03:09:44 am
content: As a temporary test sure.

author: Konkedout
author_rank: Frequent Contributor
timestamp: May 04, 2025, 03:22:06 am
content: In general I think that electrolytic capacitors tend to fail open rather than short, so that is probably OK.

author: PinheadBE
author_rank: Regular Contributor
timestamp: May 04, 2025, 10:12:04 am
content: Why bother ?If you got new parts anyway, do no take any risks, and remove the old ones.If those leak, you will have much more work to clean all the mess
PV Array SPD Question - Page 1
Forum section: electronics / beginners

author: Viral
author_rank: Newbie
timestamp: October 17, 2023, 12:47:51 pm
content: I've been working with PV system for quite awhile now, and for most of the time i took things for granted. But now, when i was in a position to explain some things to a new guy, i realized i have not clue.Between PV solar array and ON-Grid Inverter we connect a box consisting of following: String fuse, Separator and SPD.1 String boxes contain SPD with two module while 2 String combiner boxes contain SPD with three-module. Why there are 3 modules ? It's not supposed to be a module between DC+ and Ground and 1 module between DC- and ground. Why is there a "Y" configuration of these capsules with the center connected to PE.See attachments.Thank you.

author: jwet
author_rank: Frequent Contributor
timestamp: October 22, 2023, 10:37:25 am
content: The difference between the two depends on what you're trying to accomplish and what code you're trying to meet. In 3 phase systems, this gets much more complicated, how many fault "modes" are you covering- each pair or each pair and ground, etc. Are you just covering line to line or line to neutral for each and line to line. Its the difference between two and three MOV's. Depending on what standard, you're trying to comply with- each looks at this differently- some of the standards/code bodies are: (NEC) National Electric Code, NEMA (National Electrical Manufacturers), IEEE (Institute for Electrical and Electronic Engineering and several mil-specs- 23200 and 16400 are two I know and likely some IEC and DIN standards that I don't know, might come into play. Its a philosophical thing about what the goal is.1. The two terminal device will clamp the input at some differential potential independent of all else. It will protect the load from large excursions in input.2. The three terminal device will clamp between the two lines as above but also clamp how far one or both can get from "ground".Sometimes ground doesn't exist and sometimes the latter doesn't matter. In some cases like the Mil Specs for ships or large outdoor metal structures, they insist on the first case but only want to be able to sense the second case for safety. They just don't want to run current through the hull/structure for electrolysis reasons, they just want a warning indication.Find out what standard applies for what you're doing- this is called protection "modes" in most of the standards. The second type is more conservative but is not universally wanted as in the ship example above.Complicated- ain't it?
PV panel to trickle charge 12 V battery, also while in use? - Page 1
Forum section: electronics / beginners

author: analogo
author_rank: Regular Contributor
timestamp: November 04, 2024, 07:21:45 pm
content: My watering system is powered by a 12 V AGM battery. A microcontroller wakes up every now and then and, if the sensors say that water is needed, it activates a pump (via a relay with NO connected to the 12v battery) for a few minutes. This set-up as been working flawlessly for the past few years. With a small annoyance: every few weeks I need to unplug the battery, recharge it, plug it back.Could I simply attach one of those small photovoltaic panels with integrated charger for auto batteries (random example:https://www.amazon.com/dp/B0C9Z4NHJH), and have it trickle charge my battery,without disconnecting the circuit? Or will it cause issues when the microcontroller is awake and the pump violently starts sucking current out of the battery?

author: SmallCog
author_rank: Frequent Contributor
timestamp: November 04, 2024, 10:45:59 pm
content: You can charge your battery whilst in use, probably. Only hiccup will be if your microcontroller isn't tolerant of the higher voltages that the battery will be charging at. Figure on it seeing up to 15V to be safe (but it shouldn't) however I presume you're already using a buck module or something so you're likely going to be OK.Some of those little panels like you linked are unregulated and rely upon being quite small compared to the quite large vehicle battery to prevent over charging.I'd use a solar regulator and a panel, a decent brand panel (eg Symmetry) costs hardly anything and they're commonly used industrially.Be sure that your chosen regulator has a charge profile compatible with your battery, smaller Gel/VRLA/AGM batteries can have lower charge voltages than vehicle batteries. I'd personally use a little PWM reg for something like this.

author: J-R
author_rank: Super Contributor
timestamp: November 05, 2024, 09:44:23 am
content: What is the Ah capacity of the battery?

author: analogo
author_rank: Regular Contributor
timestamp: November 05, 2024, 02:17:20 pm
content: Quote from: J-R on November 05, 2024, 09:44:23 am12Ah, it's a Panasonic LC-PA1212P1.Is the capacity of the battery relevant?
PWM (10 bit) vs DAC (5 bit) - Page 1
Forum section: electronics / beginners

author: Moriambar
author_rank: Unknown
timestamp: August 25, 2018, 08:43:11 am
content: Hi,I am a newbie here and in the EE world (kinda). Looking at our beloved Dave videos, I came about to appreciate PWM as a DAC alternative. Anyway picking up aPIC16F15325, I found out that it has a 5bit DAC function, as well as several 10 bit PWMs.So my thought is: if I can be able to be way more precise with a simulated DAC via pwm, why include a DAC functionality from the start? So I thought that perhaps I misunderstand something and 10bit PWM is not better than 5bit DAC.Well I tried searching the info online but I'm lost. Can anyone point me in the right direction, please?

author: Kleinstein
author_rank: Super Contributor
timestamp: August 25, 2018, 08:53:40 am
content: Using PWM as a DAC is usually slow and often needs an extra filter (e.g. 3rd order active filter with 1 OP). The real DAC inside the µC is likely much faster and lower power. There are still quite some application that can get away with using PWM and thus a DAC is not such a common part in µCs.

author: Moriambar
author_rank: Unknown
timestamp: August 25, 2018, 08:58:15 am
content: Thanks! So basically either you go for "built-in, quick, low power, but with less steps" or you can go for "slow, precise, not so low powe, but needing extra filtering steps", right?Cheers

author: mikerj
author_rank: Super Contributor
timestamp: August 25, 2018, 12:14:21 pm
content: Quote from: Moriambar on August 25, 2018, 08:58:15 amIn this case yes. Other micros have higher resolution DACs built in, 12 bits is now reasonably common.

author: Rerouter
author_rank: Super Contributor
timestamp: August 25, 2018, 12:21:27 pm
content: Another thing with the DAC is that you can change the reference voltage or use an external one at an arbitary voltage, So in the end you end up with more than 5 bits worth of steps with some clever programming

author: MasterT
author_rank: Frequent Contributor
timestamp: August 25, 2018, 12:28:11 pm
content: Keep in mind that to clock out 10-bits over PWM takes 1024 periods, even with 16 MHz PWM, max update rate less that 16 kHz.

author: Moriambar
author_rank: Unknown
timestamp: August 25, 2018, 06:42:30 pm
content: Quote from: RerouterI did not think about that, you're right! Thanks!Quote from: MasterT on August 25, 2018, 12:28:11 pmRight, of course!

author: fonograph
author_rank: Frequent Contributor
timestamp: August 26, 2018, 03:55:55 am
content: Quote from: MasterT on August 25, 2018, 12:28:11 pmThats true only if no noise shaping is used.Snake oil music format DSD uses 1 bit PDM 64 periods to get 20 bit resolution with 7th order noise shaping and dither.
PWM amplifier - Page 1
Forum section: electronics / beginners

author: merseyless
author_rank: Contributor
timestamp: July 24, 2013, 08:29:11 am
content: I'm working on a circuit where I'm taking a PWM input from a Arduino and amplifying it to an arbitrary voltage between 25v and 10v, I need to then smooth it out to get the average voltage and then feed that final voltage into a 20mA load.So far I tried using a BJT to amplify the PWM signal, but when I fed it into the filter, it would charge and discharge the filter asymmetrically due to the need for a resistor between the emitter and ground.So I tried using an opamp as a comparator, as the voltage from the arduino for pwm is between 5 and 0v, I used a voltage divider and fed 2.5v into the inverting, and fed the pwm into the non-inverting, and let it swing between the arbitrary voltage and ground. the only problem with this is that the filter I have designed draws 0.5ish amps. Which the Opamp does not like one bit.Arduino PWM sits at around 500Hz, so I made a 3 stage 50Hz low pass filter using 22uF cap and a 160ohm resistor.So, where do I go to from here?

author: Alana
author_rank: Frequent Contributor
timestamp: July 24, 2013, 08:46:29 am
content: Tried half of h-bridge chips powered from your 10-25V and a voltage shifter if control logic is not on 5V level?Oder idea is to use something like TDA2010 audio power amplifier as an op-amp.
PWM.. an AC voltage or DC?????? - Page 1
Forum section: electronics / beginners

author: elex_enthusiast
author_rank: Regular Contributor
timestamp: May 27, 2013, 01:34:38 pm
content: i am a bit confused if a pwm an AC volt or a DC?... and i am wondering if it is posible to measure its true rms value by an AC function of my DMM..please explain....

author: w2aew
author_rank: Super Contributor
timestamp: May 27, 2013, 01:56:37 pm
content: Quote from: elex_enthusiast on May 27, 2013, 01:34:38 pmIt's neither, really. AC means that the voltage/current changes polarity. A PWM signal typically is a logic signal that turns on and off. So, a PWM signal is more accurately described as a pulsed DC signal.Most True-RMS reading DMMs will AC couple the signal when set to AC, so they won't give you the right reading because the DC component is taken away. If you put the meter in DC mode, it may read the average voltage properly (depending on the meter, and the frequency of the PWM signal). But, the average voltage of a PWM signal is not the same as the RMS value.Some True-RMS DMMs may specifically state that they measure true-rms AC+DC. If so, then they should read the RMS value correctly, as long as the frequency of the signal is within the capability of the meter.I just did a video on this.https://www.eevblog.com/forum/beginners/back-to-basics-video-what-is-rms-voltage/

author: c4757p
author_rank: Super Contributor
timestamp: May 27, 2013, 02:06:11 pm
content: You can compute the RMS value.avg = duty * peakrms = sqrt(duty*peak^2) = sqrt(avg*peak)So measure the average (filter it with an RC filter if the meter is confused), and you should know the peak (what voltage is the circuit running at?), then find sqrt(avg*peak).

author: elex_enthusiast
author_rank: Regular Contributor
timestamp: May 28, 2013, 03:42:38 am
content: Quote from: w2aew on May 27, 2013, 01:56:37 pmso does it mean that the ac+dc function of my fluke 287 can determine the rms vlaue of a pwm signal?...i thought it was only good for mixed signals

author: c4757p
author_rank: Super Contributor
timestamp: May 28, 2013, 03:47:28 am
content: Quote from: elex_enthusiast on May 28, 2013, 03:42:38 amYes, it can, as long as the frequency isn't too high. Looks like the 287 has a 100 kHz bandwidth - try to stay below 50 kHz or so. It's a square wave, so it has high frequency content that will be lost.What do you think "mixed signals" means??

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 28, 2013, 04:18:14 am
content: It's both. Usually, only the DC component is what ultimately matters, but it's possible to make real use of the AC component. For example, if you have a piezo attached to the PWM output of a microcontroller, you could use low duty cycles to reduce the volume.
PWM and old school... - Page 1
Forum section: electronics / beginners

author: MMDuino
author_rank: Regular Contributor
timestamp: April 20, 2015, 11:22:31 am
content: DearsHow could i generate PWM through 3 pins rotary by using only transistors, OPamps, 74xx and 40xx.. i mean without microchips...??could anyone help me in this issue...

author: bugs
author_rank: Contributor
timestamp: April 20, 2015, 11:26:57 am
content: Is this a school assignment?

author: Cherry
author_rank: Contributor
timestamp: April 20, 2015, 11:33:54 am
content: Maybe you can ask professional people's advice.

author: Delta
author_rank: Super Contributor
timestamp: April 20, 2015, 11:40:52 am
content: If you aren't using microchips, then opamps, 74xx and 40xx series logic are out of the window! And what on earth do you mean by "through 3 pins rotary"?PS. Do your own bloody homework!

author: Simon
author_rank: Unknown
timestamp: April 20, 2015, 11:42:10 am
content: errr 555 timer ? there are other more elaborate ways with opamps but you'd need to understand the various circuit topologies to put together am opamp version

author: madires
author_rank: Super Contributor
timestamp: April 20, 2015, 11:43:44 am
content: LM339 or TL494 for example.

author: MMDuino
author_rank: Regular Contributor
timestamp: April 20, 2015, 11:44:54 am
content: Indeed, it's bloody homework!

author: rob77
author_rank: Super Contributor
timestamp: April 20, 2015, 11:46:07 am
content: you mean a 3pin rotary encoder with quadrature output ? that would be a challenge without a micro.if you just need a PWM generator, then 555 - google for "555 servo tester"

author: Zero999
author_rank: Super Contributor
timestamp: April 20, 2015, 11:47:20 am
content: I think some of the meaning has been lost in translation.Presumably by no microchip, you mean no microcontroller?Are you talking about using a potentiometer to control the duty cycle of a PWM signal?Here's how to do PWM with commonly available ICs:555 TimerLM393, comparatorCMOS logic gateshttps://www.eevblog.com/forum/projects/pwm-signal-from-555-timer/msg17855/#msg17855You need to be logged in to see the images above.It's also possible to so this with discrete transistors but I don't have the circuit handy at the moment.
PWM Breakout board question - Page 1
Forum section: electronics / beginners

author: Youkai
author_rank: Regular Contributor
timestamp: March 18, 2023, 03:08:48 pm
content: I'm looking into using a PWM breakout board for a project I'm working on. Something likethis.I'm going to be using this to control 6 servos. I'm curious why there is a V+/GND/PWM for each channel. Is there a reason to run the V+ and GND through the board instead of using the related rails on my circuit? It seems like that would unnecessarily send a bunch of power and heat through the board. Am I missing something?If I'm not going to use the boards power and ground would it make more sense to get the bare chip? If I do end up using the board does spacing the servo's out along it make a difference as far as heat dissipation goes?

author: fourtytwo42
author_rank: Super Contributor
timestamp: March 18, 2023, 03:20:54 pm
content: That is to match the standard pinout of a servo lead. It would not be advisable to provide a separate ground circuit as servo's can be sensitive to noise between the pwm signal and ground. To be sure both vcc & ground bounce can cause misoperation, the best way to avoid this is to stagger the start of movement rather than trying to start all servo's at once. Ensure there is adequate decoupling on +5V.The continuous current is not high enough to heat the pcb unless you are operating the servo's continuously (they are not designed for that anyway).