hybridfree/eevblog-posts huggingface dataset:
What should this opto-circuit do ?? - Page 1
Forum section: electronics / beginners

author: MathWizard
author_rank: Super Contributor
timestamp: May 07, 2025, 07:48:47 pm
content: I'm making a schematic of a used INSTEK PC-3030 PSU I bought, and I found this 4N33 Darlington opto-coupler (I don't have a spice model). It's part of the 1k and 10k potentiometer settings for V,I and for the constant voltage, or constant current, overload LED indicator circuits.But I don't get what it's doing. The PCB is 1 sided, with through hole parts, so I'm 100% sure there's a 220k from the emitter to the base pin, but the emitter goes nowhere else. The D509 really is a 1N4148, pointed into the collector, it comes from the output pin of a 555.I haven't gone on to the next PCB yet to see where all the jumpers go, but besides some leakage currents, it can't be doing much. Applying a 50V sinewave to the BJT equivalent, can get 4mA from base to collector. But the 4N33 is really an opto.BVCEO Collector-Emitter Breakdown Voltage 55 VBVCBO Collector-Base Breakdown Voltage 55 VBVECO Emitter-Collector Breakdown Voltage 7 VBVEBO Emitter-Base Breakdown Voltage 7 Vhttps://www.ct-micro.com/uploads_zip/4N33.pdf

author: srb1954
author_rank: Super Contributor
timestamp: May 07, 2025, 09:05:51 pm
content: Maybe the collector-base junction of the photo-transistor is just being used as a photo-diode without any amplification from the transistor portion. This results in a lower, but more temperature stable, current transfer ratio and considerably faster response time than when used in photo-transistor mode.

author: thm_w
author_rank: Super Contributor
timestamp: May 07, 2025, 11:16:07 pm
content: Is J1082-2 connected to anything obvious like Gnd?Curious where it is going to.

author: MathWizard
author_rank: Super Contributor
timestamp: May 08, 2025, 07:40:05 am
content: It goes to the high-side of the current sensing/emitter degeneration resistors for the power transistors. Each channel can do 30V, I'm not sure what the supply +HV to -HV is, maybe 40-45V with no load.All the low power circuits have their own +/-15V and +/-24V rails, I'm not sure what the lowest resistance is, back to the +/-HV rails yet, but they float around it.Oh nevermind, the great mystery is solved, I mixed up pin 4 and 6, so the emitter does have a path to a lower voltage, and the regular base is just tied to the emitter w/ the 220k.But also all the GND's on that lefthand side PCB are actually the -24V rail, and the connector on the next PCB has 2 extra wires, so the jumper connectors in that picture are wrong.
What size caps usually have inrush current limiting ? - Page 1
Forum section: electronics / beginners

author: lordvader88
author_rank: Frequent Contributor
timestamp: September 14, 2018, 04:04:23 am
content: I'm making some linear PSUs with old transformers, and using over 2200uF caps . A lot of old stuff never really used any type of inrush current limiting at all did they ? Like old amps, TVs.When does it become a worry or just reduce the life of caps, or rectifier diodes ?

author: Cliff Matthews
author_rank: Unknown
timestamp: September 14, 2018, 11:29:44 am
content: Transformer inductance limits inrush but with SMPS, only diodes (and maybe a filter) are the only things before fusing.

author: Zero999
author_rank: Super Contributor
timestamp: September 14, 2018, 12:25:16 pm
content: How big is the transformer? The mains fuse/circuit breaker tripping might also be a problem.

author: David Hess
author_rank: Super Contributor
timestamp: September 15, 2018, 09:53:44 pm
content: The only common problems were damaging the diodes or causing problems with other equipment. Slow blow fuses were often required.

author: tautech
author_rank: Super Contributor
timestamp: September 16, 2018, 08:27:21 am
content: Quote from: lordvader88 on September 14, 2018, 04:04:23 amCorrect.QuoteThe diodes/bridge must be beefy enough to handle the inrush cap charging currents and they are calculated WRT the cap size/value. Check some bridge/diode datasheets to see the specs they put on peak currents.Linear stuff is not normally a problem as Cliff Matthews points out.SMPS on the other hand is where the impedance of the mains supply is so low as to provide currents above the peaks diodes can handle for just a few mains cycles into what's often a low ESR bulk rectified mains cap.Hence thermistors are commonly used so to limit current inrush to levels diodes can manage.....and they also allow the engineer to select a lesser diode package due to lower current peak startup loads.Further, as the voltage rise the SMPS starts working also adding additional load to the mains diodes.I suspect common mode chokes may soften the power ON load on the diodes by adding impedance to the mains supply.Someone can help you with the equations to determine peak currents vs time (mains cycles) vs capacitance that provides for the info to correctly select diodes with.
What size dispensing tip for 0402 SMD?  - Page 1
Forum section: electronics / beginners

author: peps1
author_rank: Regular Contributor
timestamp: August 13, 2013, 08:10:16 pm
content: Hey guys,I'm new to SMD but have some Arduino Mini Pro boards coming with a couple of 0402 package components that need to be soldered (got very frightened when those components came today and I saw just how small they are!!!)I was just wondering what gauge dispensing tips I should order to give me a fighting chance!(any other tips on dealing with such tiny packages would be very welcome too)

author: Corporate666
author_rank: Unknown
timestamp: August 13, 2013, 09:12:47 pm
content: We use 15 gauge (luer lock) nozzles for all dispensing - they are predictable. Much smaller and you need a ton of pressure to get any flow.We control the dot size with air pressure and dispense time.I'm guessing you are using a pneumatic dispenser since you're asking about this? I'd start around 50psi.. the lower the pressure, the more leeway you have in dispense time.

author: peps1
author_rank: Regular Contributor
timestamp: August 13, 2013, 09:18:08 pm
content: Quote from: Corporate666 on August 13, 2013, 09:12:47 pmNope, just using a normal syringe....but, the one I got didn't come with any form of tip or nozzle, just a rubber stopper.

author: mazurov
author_rank: Frequent Contributor
timestamp: August 13, 2013, 09:56:33 pm
content: You don't need paste - just tin the pads making sure not to pour too much, apply small amount of liquid flux to the tinned surface and hot air. If you still want to use paste, thin it with IPA to almost liquid state and apply with a toothpick. You can also apply paste to the part itself.For 0402 I wouldn't even bother with reflow, it's big enough to be soldered with an iron. Tin one pad, solder one side by melting the tin on the pad and placing the part. Remove iron, turn the board around and solder other side. Liquid flux is your friend.

author: peps1
author_rank: Regular Contributor
timestamp: August 13, 2013, 10:40:43 pm
content: Thanks for the tips.Unfortunately I have a tremor in my right hand that may make hand soldering such small packages hard.....hence why I quite liked the idea of SMD, as the parts tend to get dragged into place with the reflow if a bit wonky.

author: metalphreak
author_rank: Frequent Contributor
timestamp: August 14, 2013, 01:59:02 pm
content: You are really limited to what size will actually allow solder paste through especially when doing it by hand. Compressed air makes things easier but there is still a limit to how small you can go. I find that the paste tends to stick to the nozzle rather than the pads sometimes as well.You'll need larger tips doing it by hand than with a dispenser. Trying to push the plunger with enough force AND keep a steady hand is impossible. Also, you'll find that paste will keep squeezing out even after you stop pressing the plunger. Going with the toothpick idea might not be such a bad thing?
What size Teflon sleeve tubing are you using for 1/4 - 1/2 Watt Resistors - Page 1
Forum section: electronics / beginners

author: Johnny10
author_rank: Frequent Contributor
timestamp: April 29, 2024, 11:13:36 am
content: What size Teflon sleeve tubing are you using for 1/4 - 1/2 Watt Resistors and where are you buying?Thanks

author: RoGeorge
author_rank: Super Contributor
timestamp: April 29, 2024, 11:59:27 am
content: You mean, like the green isolation in this pic?Only rarely did that, and usually not with teflon tube, but with isolation leftovers after stripping casual wires.

author: Zoli
author_rank: Frequent Contributor
timestamp: April 30, 2024, 06:15:59 am
content: On a previous job I've usedAlpha Wire; teflon(PTFE) tubing is listed under accessories. If you don't need too much, maybe you can get away with samples.

author: GLouie
author_rank: Regular Contributor
timestamp: May 01, 2024, 03:22:38 pm
content: It can be useful for bodges, and mini-oil spouts. We kept some Alpha with, I think, ID of 0.032inch (0.86mm), as it seemed to handle the leads of most smaller components. Anything larger and I used heat shrink.I see Mouser sells it for about $1.62USD a foot in 100 ft. spools.https://www.mouser.com/ProductDetail/Alpha-Wire/TFT20020-NA005?qs=tCP6PqRLZF6eDp%2FdXGvd8A%3D%3D

author: floobydust
author_rank: Super Contributor
timestamp: May 01, 2024, 03:57:27 pm
content: Looking at through-hole resistor lead sizes:2-5W parts are 0.8mm1W parts are 0.8mm1/2W parts are 0.7mm, some cheap ones 0.4mm1/4W parts are 0.45mmI use Alpha WireTFT-200-18ID 1.07mm, 0.305mm wall.It is a bit big but works easy on bends and over 1/4W parts. Wow $CAD $250/100ft roll or $0.21/inch stuff is expensive.Did not tryAliexpressbut much is too thick wall. Used in 3D printers too.There is also PTFE heatshrink tubing.
what solder alloy for tinning wires? - Page 1
Forum section: electronics / beginners

author: electrolust
author_rank: Unknown
timestamp: July 19, 2020, 04:58:15 pm
content: I bought a solder pot as I need to tin a lot of wires. For PCB soldering I use 63/37. What (leaded) solder alloy should I use for tinning wires? Does it even matter?

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2020, 05:44:47 pm
content: Any eutectic solder, 60/40, 62/38, whatever will work.I'm more curious as to why you want to tin them in the first place. It's mostly a recipe for trouble (If we're talking stranded wires).

author: electrolust
author_rank: Unknown
timestamp: July 19, 2020, 06:46:37 pm
content: Thanks.1. luminaire disconnects. these accept push-in wire, normally expected to be solid but they can also accept tinned wire. they are spring loaded clamps, with a barb to prevent pull-out, so they should be reliable for tinned wire.2. i build a decent number of cables using high density circular interconnects that have solder cups. these are much easier to do if the wire is pre-tinned.

author: ceoxrad
author_rank: Regular Contributor
timestamp: July 19, 2020, 07:17:47 pm
content: for the first use case I would suggest to use crimped ferrules instead.Solder will wick up the strands and make a fragile spot and can cause troubles in the long run, also it tends to cold flow under pressure.Something like this

author: Benta
author_rank: Super Contributor
timestamp: July 19, 2020, 07:46:17 pm
content: Quote from: electrolust on July 19, 2020, 06:46:37 pm1: Really bad idea, a crimped ferrule is much better. You risk major insurance liability if a tinned connection starts a fire due to cold flow and arcing. And the tinning will make the cable fragile around 3 mm from the joint, breaking after a relative low number of bends.Use these, plus an inexpensive crimp tool:

author: electrolust
author_rank: Unknown
timestamp: July 20, 2020, 06:48:41 pm
content: i did already try ferrules, but they are not available in the size i need for disconnects -- as they necessarily grow the wire gauge and my wire is already at the max size for the connector i need to use. the wire disconnects are specifically rated for tinned wire in addition to solid wire, however with only 1 insertion and no removal allowed. whereas for solid wire they have a max cycle count insert/remove. you strip the wire back and part of the insulated section gets buried in the disconnect, tightly, thus providing mechanical stability. (not like a ferrule where the insulated part is a very loose fit into the insulated part of the ferrule.)and for solder cups of a circular connector, ferrules obviously don't work.
What laser specification i need to use to etch a thin layer of copper - Page 1
Forum section: electronics / beginners

author: loris
author_rank: Newbie
timestamp: May 26, 2020, 01:44:55 pm
content: Hello , i am a french student mechanical engineer and i am working to engraving a thin layer of Copper or Gold or Tin (about 5-10um thick) on polymere with a beam spot size of about 50um. My reaserch oriented me to use a 532nm Q-switch YAG laser due to the fact that these materials absorbed very well this wavelenght emitted by the laser. I have found some suppliers for this kind of laser, but they proposed a lot of choice of laser with many technicals specifications. I know that the higher energy per pulse, the greater the depht engraved and the lower the repetition rate, the slower the process speed. But how can I chose between all thess parameters, wich one is the best for my apllication (I need a speed process of about 2000mm/min). I saw these lasers from teem photonics :https://www.teemphotonics.com/laser/532-nm-laser-500hz-350ps/Thanks in advance for your answers, and sorry for my english.

author: ebclr
author_rank: Super Contributor
timestamp: May 26, 2020, 03:21:49 pm
content: This machine uses the kind of lazer your professor sugestshttps://www.aliexpress.com/item/4000335225866.html?src=google&src=google&albch=shopping&acnt=494-037-6276&isdl=y&slnk=&plac=&mtctp=&albbt=Gploogle_7_shopping&aff_atform=google&aff_short_key=UneMJZVf&&albagn=888888&albcp=7303158455&albag=86143156931&trgt=883147839739&crea=pt4000335225866&netw=u&device=c&albpg=883147839739&albpd=pt4000335225866&gclid=CjwKCAjw_LL2BRAkEiwAv2Y3SXLAcOsHeccn_lBw_eL_LjXUYLHx24sPKMS_UQDtAj37Uifv4omlvBoCYE8QAvD_BwE&gclsrc=aw.ds

author: loris
author_rank: Newbie
timestamp: May 27, 2020, 06:44:17 am
content: I need a head laser wich could be mounted on a machine, so I need something much more professional, like the head laser on the link I post before. The Laser you suggest me is deliver with no technical specifications on a cheap website... Moreover I need a head laser to engrave copper or gold or tin and not to remove a tattoo.
What SPI Flash Chip is this ? - Page 1
Forum section: electronics / beginners

author: HansGruber
author_rank: Contributor
timestamp: August 25, 2021, 06:47:48 am
content: I tried to google for ORA15. ORA16, ORAI5, ORAI6 but I can't figure out what manufacturer or model this SPI Flash IC is...This is the best quality picture I can provide.

author: HansGruber
author_rank: Contributor
timestamp: August 25, 2021, 11:45:35 am
content: After looking for too long I can't find anything. Feels like I can see a "MT" at the bottom left, could be microchip technology but I can't find anything that would match the logo displayed there. The package is WSON-8.

author: AaronLee
author_rank: Regular Contributor
timestamp: August 25, 2021, 12:46:38 pm
content: Quote from: HansGruber on August 25, 2021, 11:45:35 amIt's not Microchip, rather it's Micron Technology's old logo. Here's an example of a different chip with that same MT logo:https://commons.wikimedia.org/wiki/File:Micron_Technology_MT48LC32M8A2-3048.jpgHave a look at this document:https://media-www.micron.com/-/media/client/global/documents/products/customer-service-note/csn11.pdf?la=en&rev=3d4f5be99b6044febb3e8e5ea5947c50Figure 2 seems to match well with the marking on your chip, even though the package type doesn't. If that same system applies to your chip, then the top line is the date/rev/country information, and the second line is the key to figuring out the part number but the photo isn't clear enough to make it out.

author: DrG
author_rank: Super Contributor
timestamp: August 25, 2021, 01:27:01 pm
content: Excellent projective test with that picture - Hermann Rorschach would be proud.FWIW I get:with RW161 (if that is what it is) linking tohttps://detail.1688.com/offer/652979628245.html?spm=a261b.11197608.mof001.36.70b169b0XjCJ6Ufor example, suggesting M25QL256

author: AaronLee
author_rank: Regular Contributor
timestamp: August 25, 2021, 10:16:03 pm
content: Yes, that looks to be it. RW161, plugged into Micron's Decoder yields part number MT25QL256ABA1EW9-0SIThttps://www.micron.com/products/nor-flash/serial-nor-flash/part-catalog/mt25ql256aba1ew9-0sit
What the cap is going on with my caps!?! - Page 1
Forum section: electronics / beginners

author: haxtormoogle
author_rank: Newbie
timestamp: February 13, 2014, 08:15:53 am
content: Check this craziness out!http://wtfmoogle.com/?p=3585My random use caps are popping in my part bins without ever being used!Are these really that bad of a brand of caps that they fail like this? O.OHave I been duped with some bad Chinese caps?How can they even pop without ever being used?!?What should I replace my caps in my parts bin with now that all the caps are ruined?

author: Simon
author_rank: Unknown
timestamp: February 13, 2014, 08:25:23 am
content: what is their temperature rating and where are you storing them ?

author: mariush
author_rank: Super Contributor
timestamp: February 13, 2014, 08:25:55 am
content: IS there such a thing as good no brand name chinese capacitors?Shitty caps => blows

author: haxtormoogle
author_rank: Newbie
timestamp: February 13, 2014, 08:36:38 am
content: Quote from: Simon on February 13, 2014, 08:25:23 ammarked vent 85*c +-20%my lap is kept at standard room temp 24-7

author: amyk
author_rank: Super Contributor
timestamp: February 13, 2014, 12:52:58 pm
content: That's really,reallybad electrolyte decomposing.http://www.badcaps.net/forum/showthread.php?t=9910

author: electronics man
author_rank: Frequent Contributor
timestamp: February 13, 2014, 04:03:09 pm
content: where did you buy them

author: Rudane
author_rank: Regular Contributor
timestamp: February 13, 2014, 04:06:23 pm
content: I've seen caps do this before, and I still don't know what caused it. I suspected it was either a cheap manufacturer or a bad run (Friday afternoon).

author: dfmischler
author_rank: Frequent Contributor
timestamp: February 13, 2014, 04:10:59 pm
content: Good caps list
what the heck is this connector called - Page 1
Forum section: electronics / beginners

author: amateur_25
author_rank: Regular Contributor
timestamp: December 24, 2016, 01:00:06 pm
content: what the heck is this connector called

author: mariush
author_rank: Super Contributor
timestamp: December 24, 2016, 02:09:36 pm
content: It looks like something JST would make.Maybe JST XH :http://www.jst-mfg.com/product/detail_e.php?series=277There's loads of them ... you could go at distributors like Digikey and Farnell and filter by pitch and cable diameters and number of wires in connector and rows and so on and look at pictures to see what resembles your connector.

author: Codebird
author_rank: Regular Contributor
timestamp: December 24, 2016, 11:42:19 pm
content: Got it:http://www.batteryspace.com/connectoradaptor4pinfemalejstxhconnector.aspx- that's a JST XH, and it looks exactly like the the one in the picture.That wiring color scheme is familiar. Whenever I've encountered those four together, there has usually been a stepper motor on the end.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: December 25, 2016, 03:08:52 pm
content: Molex 4 pin connector.
What through hole device can I use instead of a SOT23 format BF862 please? - Page 1
Forum section: electronics / beginners

author: Chris Wilson
author_rank: Super Contributor
timestamp: December 02, 2018, 02:06:52 pm
content: What through hole device can I use instead of a SOT23 format BF862 please?https://www.nxp.com/docs/en/data-sheet/BF862.pdfshows the specs.The circuit it would be used in is hopefully attached. Thank you!

author: ogden
author_rank: Super Contributor
timestamp: December 02, 2018, 02:13:46 pm
content: Quote from: Chris Wilson on December 02, 2018, 02:06:52 pmIt's just LED current limiter. You can use resistor.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 02, 2018, 02:16:14 pm
content: If the inputs are the voltages shown, just use 1k resistors. They're literally using them as (8 to 20mA) current limiters.Ew, a step-up gate drive transformer, and no winding details (core, but not winding).Ew, ancient fatass transistors too. Those 1 ohm gate resistors aren't going to do anything.I've seen Tesla coil circuits better than this, which is saying something...Ed: ew, and using a 6N136 in phototransistor mode. Just use a 4N35, except those aren't fast enough.It just gets worse the more I look at it...Tim

author: bson
author_rank: Unknown
timestamp: December 02, 2018, 02:17:59 pm
content: You should be able to drop in any N channel JFET with a suitable Ids at Vgs=0. For example, J110 (10mA @ Vgs=0), J111 (20mA @ Vgs=0), both available in a TO-92 package. But it really depends on what LED current you want. The quiescent current also isn't a hard specification, so we're talking ballpark. I believe the max LED current for the 6N136 is 25mA? The J110 probably is a good starting point.J110, J111 in TO-92:https://www.mouser.com/ProductDetail/InterFET/J110?qs=sGAEpiMZZMv4z0HnGdrLjo0W1AxRZQdlXPGpjxX7bVahwwoTN%2fTXPg%3d%3dhttps://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/J111?qs=sGAEpiMZZMv4z0HnGdrLjpo3FY8YkyPv%2ff16NpPbr4w%3dBe warned, these devices areESD sensitive.Always make sure you're grounded when handling discrete JFETs.
What to do with an unused half of an LM13700 OTA? - Page 1
Forum section: electronics / beginners

author: jpalicke
author_rank: Unknown
timestamp: December 31, 2014, 01:44:49 am
content: Hey guys, quick question.I'm building a clone of a guitar compressor pedal, specifically an MXR Dynacomp/Ross Compressor, and instead of using the CA3080, I'm using an LM13700. What's the proper way to deal with the unused half of the OTA? Tie the inputs and control pin to ground? 0 differential voltage and 0 control current should equal 0 current coming out right? Or is there a better/safer way to do this?

author: c4757p
author_rank: Super Contributor
timestamp: December 31, 2014, 02:19:02 am
content: Tying unused inputs straight to ground isn'talwaysa good thing, but it looks like if you tie the transconductance control pin (1 or 16), the diode bias pin (2 or 15), both inputs (3/4 or 14/13) and the buffer input (7 or 10) all to V-, you should be able to shut off the whole amplifier and reduce its current consumption to practically zero.Hooray for devices with the internal schematic in the datasheet!

author: jpalicke
author_rank: Unknown
timestamp: December 31, 2014, 02:44:26 am
content: Excellent, many thanks!

author: zmix
author_rank: Newbie
timestamp: January 01, 2019, 04:19:45 pm
content: Quote from: jpalicke on December 31, 2014, 01:44:49 amI realize that this thread is quite old now, but since the OTA is a current output device have you considered paralleling the two halves?I have a Chinese Dyna-Comp clone that does just that, presumably for lower noise and distortion.I'd like to experiment with this as well, does anyone have any thoughts about it?

author: Lee Leduc
author_rank: Regular Contributor
timestamp: January 01, 2019, 05:47:59 pm
content: Hope this helps.I contacted a TI application engineer with this question a while back:"I need to properly terminate an unused OTA section of an LM13700.I'm thinking that connecting the amp bias input (pin 1 or 16) to V- (pin 6)should disable the input. I also plan to leave the buffer inputs open.Is this a good approach or is there a better way to do this?Thank you."This was the response.Lee,That will work well. Pin 1 or 16 can be open, but connection to pin 6 ensures no bias current.Regards,Ronald MichallickLinear Applications
What to do with broken RPIs? - Page 1
Forum section: electronics / beginners

author: nardev
author_rank: Unknown
timestamp: June 14, 2018, 11:57:37 pm
content: I have like two RPIs which suddently jsut stopped working. I don't remember doing anything unusual, always keeping them properly, distanced from other things, in anti-static bags etc.I'm wondering if anyone tried to fix RPIs, what is the way to inspect RPIs? Visually everything looks ok.The RPi2 B actually has two LEDs, green and Red powered up and nothing is happening.On the RPI mini, nothing is happening. One day i decided to turn it on and i plugged it to USB and, nothing..Ok, what can i do with this, other than throwing it to a trash? Any way to fix this?

author: Macbeth
author_rank: Super Contributor
timestamp: June 15, 2018, 12:41:03 am
content: You can keep using a RPi if for example it's USB has failed or its Ethernet port has failed and neither of these cause an issue for you. If the HDMI has failed you can still get access over SSH. It will be a useless OSMC media device, but could well be a very useful data-logging device with a nice web interface, or whatever you use its GPIO ports for.With your RPi2 are you sure it has failed and not just the MicroSD card? It's very common for a RPi MicroSD fail - they are not generally designed for lots of random reads and writes. If you are getting both lights blinking means it's trying to read the card so the PSU and processor must be working.

author: nardev
author_rank: Unknown
timestamp: June 15, 2018, 02:07:19 am
content: It's strange for RPI2, the SD card works with another RPI and doesn't boot this one. So, it must be something else.
What to do with extra pins on 74xx - Page 1
Forum section: electronics / beginners

author: RJDog
author_rank: Contributor
timestamp: February 23, 2017, 03:34:37 am
content: I am designing a circuit which requires multiplexing some digital signals... I originally designed the circuit by trying together the outputs of some tri-state non-inverting buffers (74HCT125), but then I discovered there is actually a 74xx that does what I want already... 74HCT157. Neat!Anyway, 74HCT157 has four discrete circuits... I only need two, so what do I do with the pins for the other two circuits? Tie all the pins to ground? Leave them unconnected? What is generally accepted as the de-facto way to handle this situation?

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: February 23, 2017, 03:55:51 am
content: With CMOS gates such as the Quad two-input mux 74HCT157 its best to tie the inputs to all unused gates or logic blocks to ground or Vcc and leave unused outputs open. This stops the unused inputs from floating into the active range and possibly causing the gate/logic to oscillate and so draw excessive power.If you have unused inputs on the gates/logic which you ARE using then you have to tie them either high or low depending on the logic involved in order for your circuit to work correctly. Unused outputs on same should, again, just be left open.This rule holds for both CMOS logic families and real TTL families such as 74LSXX, 74XX, 74Sxx, etc but in the case of TTL the power draw with unused gates can be minimized by tying the inputs high directly to Vcc or through a 1K resistor. As many as 20 inputs can be tied to the same resistor.

author: RJDog
author_rank: Contributor
timestamp: February 23, 2017, 02:07:10 pm
content: Thanks; I figured tying the input pins to ground would be a good idea, but wasn't sure, and really wasn't sure about the output pins. I guess nothing's going to hurt it by not having a load on the output.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 23, 2017, 02:10:14 pm
content: Tying them to VCC will consume slightly less current than GND, but either option is better than none.In a pinch, TTL inputs can be left open. They will float to logic high. They will be susceptible to ambient noise, though.Tim
What to do with fifty 15kR - 50W power resistors? - Page 1
Forum section: electronics / beginners

author: japasetelagoas
author_rank: Regular Contributor
timestamp: September 25, 2017, 04:48:09 pm
content: Hey everyone,I've seen a carbox with maybe 50 Dale power resistor in the junkyard, is there anything useful that could be done with these resistors?Maybe a dummy load or something else?15kR - 50W - 1%Thanks

author: kalel
author_rank: Frequent Contributor
timestamp: September 25, 2017, 05:27:37 pm
content: I guess that to reach the power rating a high voltage would be needed. Of course, then a heatsink is needed also. I'm not sure how many W you could dissipate without adding anything.

author: edavid
author_rank: Super Contributor
timestamp: September 25, 2017, 05:38:17 pm
content: Quote from: kalel on September 25, 2017, 05:27:37 pmHere's the datasheet:https://www.vishay.com/docs/50013/rh.pdfThe unmounted power rating is 12W @ 25C.

author: ElektroQuark
author_rank: Unknown
timestamp: September 25, 2017, 05:41:39 pm
content: A 300R 2500W resistor?

author: Benta
author_rank: Super Contributor
timestamp: September 25, 2017, 05:44:51 pm
content: Dunno what you mean by "15kR". Those are 1 ohm resistors and can come in extremely useful as dummy loads. Especially as they are 1% tolerance. Go for it.

author: ElektroQuark
author_rank: Unknown
timestamp: September 25, 2017, 05:46:18 pm
content: 15kR -> 15K OhmThe image must be a generic one.

author: japasetelagoas
author_rank: Regular Contributor
timestamp: September 25, 2017, 08:08:46 pm
content: Quote from: EdoNork on September 25, 2017, 05:46:18 pmExactly.

author: innkeeper
author_rank: Unknown
timestamp: September 27, 2017, 01:20:29 am
content: i have a crap load of precision resistors and caps. maybe we can do some trading if it helps your parts inventory, if your reasonable distance from me and it makes economic sense.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: September 27, 2017, 01:26:17 am
content: Quote from: japasetelagoas on September 25, 2017, 04:48:09 pmBetter grab all you can, those are not cheap. Someday you will find a use for some of them. Give some away on the forum, or sell them.

author: bjcuizon
author_rank: Frequent Contributor
timestamp: September 27, 2017, 03:03:53 am
content: Make a 50 ohm HF dummy load if you got more than 50 resistors.

author: Ian.M
author_rank: Super Contributor
timestamp: September 27, 2017, 03:27:42 am
content: 3.5W dissipation at 230V means they'd be useful as an anti-condensation heater for small mains powered enclosures.

author: innkeeper
author_rank: Unknown
timestamp: September 27, 2017, 04:05:01 am
content: heaters for a 3d printer heated bed?Fishing weights?slingshot ammo?throw them under your tire for extra traction when stuck in the winter time.non environmentally friendly replacement for water skipping stones.
What to do with some physicaly large and high value electrolytics. - Page 1
Forum section: electronics / beginners

author: peteb2
author_rank: Regular Contributor
timestamp: September 11, 2016, 11:49:34 am
content: Along the way i have been gifted six physically gigantic 3900u/500V and two 330,000u/40V electrolytic caps. I normally don't deal with things like these and I doubt if even the 3900uF units could be used in the powersupply of a valve amplifier of all things so what experiments or projects could these things be put into. They are used but i haven't even bothered to even test them yet. They have charge bleed resistors already installed across their bolt terminals.What i really want to know is am i just wasting time or perhaps i could build some kind of dangerous as hell thing and blow it and them up for a YouTube video or build something that could actually be usable...Ideas anyone...

author: ovnr
author_rank: Frequent Contributor
timestamp: September 11, 2016, 12:08:37 pm
content: Well, hook the 500V ones up in parallel and charge them with a bridge rectifier + lightbulb. Proceed to short them out. Enjoy the fireworks.Or just chuck them on eBay. Few things that don't involve explosions need those caps.

author: DTJ
author_rank: Super Contributor
timestamp: September 11, 2016, 12:10:54 pm
content: Battery tab spot welder.

author: Chris Mr
author_rank: Regular Contributor
timestamp: September 11, 2016, 12:23:13 pm
content: or make thermocouples by discharging across your two wires - requires much testing to find safe levels!

author: Cliff Matthews
author_rank: Unknown
timestamp: September 11, 2016, 02:56:52 pm
content: Safe call on the bleed resistors, I've got some big 250 and 450v Cornell-Doublier caps up safe on a shelf. It's been 6 months, so just checked the averages: only the 450v caps have floated to around 20v while the 250v caps are only at 2v, strange beasts... Maybe you could make a surge generator similar to the one used in Joe Smith's testing?

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: September 11, 2016, 03:24:29 pm
content: If your interested in practical electronics you might try turning these capacitors into a battery pack to use in place of a lead acid motorcycle battery. They would have the advantage of not having to buy a new battery for your bike.
What to do with TN LCD during 1s timed sleep? - Page 1
Forum section: electronics / beginners

author: dusan
author_rank: Regular Contributor
timestamp: May 01, 2025, 07:05:21 am
content: I want to make a clock with TN LCD display. They need to be driven using AC to prevent damage. To save energy I put MCU to 1s deep sleep during which the output holds their state but only either high or low, not AC. Is it a problem that the display will be static for 1s? Or how else should I drive TN LCD during MCU sleep?

author: Psi
author_rank: Super Contributor
timestamp: May 01, 2025, 07:23:20 am
content: Can you use a sleep state that leaves a timer running with output compare to produce the AC waveform in hardware?Usually you use a MCU with LCD controller built in, or you use an external LCD controller IC.You could try just waking up to change the pin state every 30ms and then going back to sleep.A modern MCU can wake up and sleep pretty fast. So you may find that even waking up that often still means you are sleeping for the vast majority of the 1 seconds.

author: xvr
author_rank: Frequent Contributor
timestamp: May 01, 2025, 03:03:34 pm
content: Quote from: dusan on May 01, 2025, 07:05:21 amIf all pins of LCD will be in the same state (preferably turned off) there will not be a problem for LCD - it just turned off. But it could be a problem to clock userIf pins will be driven to last active state LCD will eventually burned out.QuoteYes, you can use LCD with built in driver chip. But it will consume power (and LCD backlight will consume much more power), so 1s slepping of MCU will be not enough to reduce total consumed power.If you really concerned about power saving - use e-ink display. It can be compleately turned off between updates.
What to look for in an op amp for precision Howland circuit. - Page 1
Forum section: electronics / beginners

author: DanioIO
author_rank: Contributor
timestamp: March 04, 2015, 07:20:44 pm
content: Hi,Im trying to make a precision bidirectional current source to about 1MHz using Improved Howland circuit. I have 4 matching transistors, but my question is "What op amp I should select". This will be only single module for me so i can buy a expensive op amp. So what op amp parameter should i look for?

author: krivx
author_rank: Frequent Contributor
timestamp: March 04, 2015, 07:31:54 pm
content: I think you'll need to post a schematic and specification of what you want. What are the matched transistors for? I am used to seeing the Howland circuit just with an opamp and passives...

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 04, 2015, 07:36:59 pm
content: I think he means matched resistors ..

author: DanioIO
author_rank: Contributor
timestamp: March 04, 2015, 07:37:49 pm
content: I meant 4 matching resistors. Im basing my circuit on a schematic included below.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 04, 2015, 07:45:28 pm
content: You do not balance for different gain selections?

author: DanioIO
author_rank: Contributor
timestamp: March 05, 2015, 06:11:01 am
content: The op amp in buffer configuration will eliminate the resistor feedback error.

author: Trey
author_rank: Contributor
timestamp: March 05, 2015, 04:26:44 pm
content: Is that the circuit diagram from the TI paper (SNOA474A)? I haven't read it all, but believe it has some guidance on components (e.g., 5 - Choice of Amplifiers).Of course that is a 2008 paper, so there are some newer op-amps available. There are a number of factors including how much drive you need, how precise, etc. If you stick with standard chip pinouts, you can of course start with a lower-priced chip while you're prototyping (and more likely to burn it up), then progress to a more expensive one when you're happy with the basic design.

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: March 05, 2015, 09:35:25 pm
content: the Howland VCCS relies on feedback so your op amps have to have enough excess gain at your operating frequency to boost your R to the output Z you want the output to meetasking op amps to do much at 1 MHz is pushing beyond commodity op amp capability, and beyond simple dominant pole gain block circuit approximationsspecs on your accuracy, compliance range and minimum output full complex Z requirements at frequency are needed in a analysis that would include a number of other component and PCB circuit parasitics toothe more detailed spec and analysis may show you can meet your need with todays faster op amps but then you really need to tools to see if they misbehave in your build - oscillating near their 100+ MHz GBW product is common, needs fast scope, fet probessome "current feedback" op amps or transconductance circuits can operate with fair accuracy open loop - to higher frequenciestaking output from AD844 TZ/comp pin, or using the OPA660
What to look for when buying old, discontinued ICs - Page 1
Forum section: electronics / beginners

author: Legion
author_rank: Frequent Contributor
timestamp: May 19, 2014, 01:26:51 pm
content: I wanted to get some old sound chips like the SN76477, SN76489, YM2413, etc. The only places I've found them readily available are Chinese / HK sellers on eBay. Besides feedback score, is there anything I should look for when reviewing listings? At $10 each I'd like to avoid having to buy 10 to get 2 good ones. If there's a better place to get these I'm open to suggestions.

author: AKM
author_rank: Contributor
timestamp: May 19, 2014, 01:59:42 pm
content: From my limited experience, they are all pretty much the same. I usually buy old chips and modules athttp://www.utsource.net/;at least it arrives within 3 weeks.If you ever decide to buy from them this year, use the coupon code UT2014 for 10% off.

author: Kjelt
author_rank: Super Contributor
timestamp: May 19, 2014, 03:03:24 pm
content: Unfortunately the only thing to watch for is to test it when it already arrives, and if not good file a complaint open a dispute.Older ic's are often refurbished in China that is soldered of their original product cleaned and sold with a picture of a brand new one.The worst that could happen is that the chip is cheap replacement, or even totally counterfeit and rebadged.All possibilities where you can not defend yourself against when buying overseas through the net.

author: Legion
author_rank: Frequent Contributor
timestamp: May 19, 2014, 04:06:21 pm
content: Quote from: AKM on May 19, 2014, 01:59:42 pmThanks for the coupon code. I'll check them out.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 19, 2014, 07:04:44 pm
content: Don't just check the seller's feedback score, focus on the negative and neutral feedbacks. You want to see how the seller handles the problems and what kind of problems occur.Ed

author: marshallh
author_rank: Unknown
timestamp: May 20, 2014, 01:08:15 am
content: UTsource is a big one, I have ordered several types of chips from them.Results range from clean pulls (it was pulled from old product, pins are nice and straight, ready to go) to NOS (partial trays of TSOP produced several years ago)

author: dentaku
author_rank: Frequent Contributor
timestamp: May 20, 2014, 10:44:07 am
content: I've never looked at utsource until now.They have XR2206 chips, which is interesting. I already have an SN76477N for making weird sounds but a nice function generator might be nice tooIt's what the XR-VCO is based on.http://www.birthofasynth.com/Thomas_Henry/Pages/XR-VCO.html
What to look when looking for a FET or MOSFET equivalent - Page 1
Forum section: electronics / beginners

author: gkmaia
author_rank: Frequent Contributor
timestamp: December 11, 2019, 06:51:08 pm
content: What are the key ratings to consider when replacing a FET or MOSFET for and equivalent apart from voltage and current ratings?

author: magic
author_rank: Super Contributor
timestamp: December 11, 2019, 10:22:23 pm
content: SOA, threshold voltage, RDS(on), gate charge, zillion of things...What kind of application, what kind of FET?

author: gkmaia
author_rank: Frequent Contributor
timestamp: December 11, 2019, 10:32:42 pm
content: I suspected you could look at a zillion things, but if you were to simplify these zillion things to a couple that are the most critical ones apart from voltage and current what would those be?

author: Circlotron
author_rank: Super Contributor
timestamp: December 11, 2019, 10:40:04 pm
content: The most critical things vary, depending on the application. If you tell us the application we can narrow things down a *lot*.

author: aheid
author_rank: Regular Contributor
timestamp: December 12, 2019, 09:59:21 am
content: You can simplify somewhat but it is highly dependent on application. Attributes which are important in some applications can lead to detrimental aspects for another application. For example a good switching MOSFET typically won't work well in the linear regime. IIRC high voltage tolerance leads to higher capacitance, which is very bad for other applications.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: December 12, 2019, 10:16:54 am
content: The thing I always double check is Gate Threshold VGS(TH)

author: magic
author_rank: Super Contributor
timestamp: December 12, 2019, 01:24:27 pm
content: Probably mostly the things I listed before.Load switching: RDS(on) and VGS(on)PWM: ditto plus perhaps gate chargeLinear: SOA, power dissipation vs temperature, maybe VGS(th)
What to put in the place of desoldered microphone? - Page 1
Forum section: electronics / beginners

author: Bob Sava
author_rank: Regular Contributor
timestamp: June 18, 2021, 03:26:48 pm
content: After de-soldering a microphone, to keep the circuit from picking up any noise, should I solder a resistor or leave it open?

author: fcb
author_rank: Super Contributor
timestamp: June 18, 2021, 03:58:08 pm
content: It depends. If it's a condenser microphone then leaving it o/c will be fine. You might find that some AGC in the system winds the gain up - again it depends on system.If you're concerned about it floating about then perhaps add a 1K5 in it's place (I've seen a few of condenser mic's are powered from 3.3V via a 1K5 or so), else you could put a capacitor of perhaps 100nF (risk it acting as microphone if you're unlucky).Prob's just try it.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 19, 2021, 01:34:12 am
content: A resistor to ground reduces the chances for hum pickup if you care. Probably leaving it open is fine.
What to replace Philips/Signetics PLS ICs with - Page 1
Forum section: electronics / beginners

author: giosif
author_rank: Frequent Contributor
timestamp: October 27, 2020, 07:08:59 pm
content: Hello,I have a few PLS ICs pulled from a sick Tektronix 2710 SA which seem to have died.Does anyone know if they can be swapped with something more modern / with better availability on the market?Programming them shouldn't be a problem, but I'm looking for functionality parity (ideally, physical format as well - i.e. PLCC).Thanks!

author: grumss
author_rank: Contributor
timestamp: November 06, 2020, 08:21:16 pm
content: Yes i have the the same issues with my 2710, be very interested if anyone comes up with some suggestions..
what to search for / where to buy - Page 1
Forum section: electronics / beginners

author: schwarz-brot
author_rank: Regular Contributor
timestamp: December 20, 2013, 10:40:12 pm
content: Hi folks,i am searching for a special kind of 2.54mm pitch female pinheader: those stackable ones with extra long pins which can be seen on some arduino shields, for example like this:http://www.ebay.de/itm/1x-5x-10x-Buchsenleiste-1-reihig-8-10-Polig-gerade-RM-2-54mm-Female-Buchse-/151044623060?pt=Elektromechanische_Bauelemente&var=&hash=item232af60ad4But I need these with, say, 50 contacts or thereabout and breakable to the desired lenght like normal pinheaders would be. All I can find are some very pricey precision types for wire-wrap prototyping. Also these would only fit IC-Pins, no normal pins.Any suggestions?

author: sachleen
author_rank: Contributor
timestamp: December 21, 2013, 05:20:22 am
content: I've been looking for breakaway female headers too. I've only found the round "machine pin" type but never the square type. You can just cut those to whatever length you need but you have to cut in the middle of one pin.

author: sleemanj
author_rank: Super Contributor
timestamp: December 21, 2013, 05:32:10 am
content: They are simply called long pin headers usually, like other headers 40pins long is the typical manufactured lengthhttp://www.ebay.com.au/itm/40-pin-1-row-0-1-Long-Pin-Female-Header-DE3886-/370921937473?pt=LH_DefaultDomain_0&hash=item565cab9a41&_uhb=1As for breakable, you'll only get that in machined pin sockets, which are expensive. Cutting the normal headers to length is no problem but you lose a pin, just score and break along the middle of the pin you don't need and snap, then trim off the edges.

author: minime72706
author_rank: Frequent Contributor
timestamp: December 21, 2013, 05:33:22 am
content: You'll be hard-pressed to find break-away female headers, especially with long leads. That might be a custom order to Tyco or Samtec!I'm curious so I'll do some looking around myself.
What to use?  - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: November 19, 2020, 07:34:37 pm
content: Guys I have a bad cap but not sure what yType to replace it with. It’s in the COUPLING section of a transmitter.Schematic shows Molded Mica 300mmfd 500VW

author: CaptDon
author_rank: Super Contributor
timestamp: November 19, 2020, 09:08:32 pm
content: Looks like an older style mica capacitor.300pf??? Ceramic disk would be my go-tochoice.

author: Zero999
author_rank: Super Contributor
timestamp: November 20, 2020, 07:50:37 pm
content: MMFD stands for micromicrofarads. 1 micro = 10-6and when multiplying exponents, they add so if 1µ = 10-6, then 1µµ = 10-6×10-6= 10-12, which equal to 1p, so 300MMFD = 300pF. In other words, MMFD is an archaic way of writing picofarads. It goes back before pico was an accepted SI suffix.https://en.wikipedia.org/wiki/Metric_prefix#List_of_SI_prefixes
what too look for - Page 1
Forum section: electronics / beginners

author: p.larner
author_rank: Frequent Contributor
timestamp: October 19, 2023, 12:45:05 am
content: i have a gigabyte GA-78LMT-USB3 (rev. 5.0) motherboard it has no serial or paralell ports on its backpane,just two lots of pins on the mainboard,i need a cable that plugs into these with a socket+mounting plate to tit the rear case expanson holes,what are they called and what do i look for and order,cheers.

author: themadhippy
author_rank: Super Contributor
timestamp: October 19, 2023, 01:08:41 am
content: This sorta thing?https://cpc.farnell.com/startech/plate25f16lp/cable-parallel-port-header-lp/dp/CS24156?st=parralel%20platehttps://cpc.farnell.com/startech/plate9m16/header-9pin-serial-10pin-motherboard/dp/CS23826?st=serial%20plateBest to double check the wiring as not everybody follows the same wiring config

author: coromonadalix
author_rank: Super Contributor
timestamp: October 19, 2023, 01:33:14 am
content: same here seing the manualcheck the pinout, normally it should do fine ...

author: p.larner
author_rank: Frequent Contributor
timestamp: October 19, 2023, 01:59:18 am
content: got the 25pin one what about the serial 9pin one?.

author: p.larner
author_rank: Frequent Contributor
timestamp: October 19, 2023, 02:03:43 am
content: sorted it cheers.