electronic and electrical components etc.

[KeepItSimpleStupid]

Honestly, I don't think I can get much cheaper than that.

 

[Semaphöre]

I wouldn't discount the eBay ones so quickly then...if it doesn't work you're only out $5, and it should at least last long enough to survive a school project presentation. They do tend to take a while to ship (still faster than USA->Canada!!!!), which could be problematic under a deadline. I've ordered a lot of electronics from those Chinese distributors (though never a meter) and they always seem to work well enough for what I'm trying to do.

Another option is to check a local surplus store, I remember finding some old analog panel ammeters at one such place for practically zilch.

 

[PG1995]

Thank you, KISS, Semaphore.

Forget the power meter. In post #8 I mentioned this digital meter which can read voltage and current. The description says that it has a built-in shunt. I have never such a meter before. You can also find many meters of this kind here on ebay.

I need two meters for my project. One meter could expect the maximum voltage of around 22V and maximum current of about 1.5A, and the other meter should be able to read maximum voltage of 10V and current 3.5A. Could you please help me to select a suitable meter which doesn't really 'harm' the normal operation of circuit ? Thanks.

Regards
PG

 

[dr pepper]

I have a kit of breadboard wires I got from ebay, they were only a couple of quid, in this country they are expensive, 15 quid for the same set.
None of my breadboard layouts are anything like as neat, might also be the reason why I've blown a few parts prototyping with them.
I have one of those meters too, but mines a 2 wire, havent used it for anything yet I just got it as I was buying some other gear.

 

[PG1995]

Hi

Could you please recommend some online store for electronics and electrical components, especially ICs?

I was searching for a small latching relay which could be used in a small project where maximum voltage expected is about 25V and maximum current expected around 2A. Could you please help me to find one because I wasn't able to? Thanks.

 

[cowboybob]

Mouser (https://www.mouser.com/Search/Refine.aspx?Keyword=latching+relay), Digikey, etc.

A DPDT relay can be wired to latch. Crude, but effective.

 

[KeepItSimpleStupid]

Knowing what side of the pond your on helps with these sorts of queries. Latching comes in single coil and dual coil and various voltages, mostly DC.

 

[PG1995]

Thank you cowboybob, KISS.

I just need on/off operation and I will be turning the relay on and off using a microcontroller. The MCU I'm using outputs almost 3.3V and normal output current could be taken to be about 15-20 mA. During on operation the relay should be able to handle up to 2A current. I hope it's clear.

The webpage mentioned by cowboybob is a good one. The following link could be used to refine search:
https://eu.mouser.com/Electromechanical/Relays/Low-Signal-Relays-PCB/_/N-5g38

Regards
PG

 

[cowboybob]

Forgot to mention that an OpAmp (with an NPN as the current handling switch) can be configured as a latch, as well,

Easily driven by a uController's digital outputs.

 

[PG1995]

Hi

Could you please let me about some US-based popular online stores which sell electronic components? I suppose Digikey happens to be the one. Is it delivery service good? Some stores take such a long to deliver stuff? Thanks.

 

[cowboybob]

PG,

I've used Mouser, Digikey and Jameco (plus other lesser known sources).

They all have various delivery options (up to Next Day, at least in the US) and, thus far, excellent service.

<EDIT> Punctuation.

 

[PG1995]

Thank you, Bob.

Yes, I need the delivery in the US. It looks like Digikey, Jameco, and Mouser are the most famous ones.

I would prefer the delivery the next day or within three days from the date of order. I hope they don't sell for high prices than the regular. If you have any suggestions, please let me know. Thanks.

Regards
PG

 

[cowboybob]

For the stuff and quantities (seldom more than 10 of any one item) I usually buy, the pricing differentials are insignificant, to me anyway.

Of the vendors, I find Digikey and Mouser have a selection process I don't much care for (the "filtering process" gives me too many options, especially as to manufacturers). Just my particular negative. Generally speaking, the circuits I put together are never so sophisticated that "general purpose" components aren't adequate to the task. Thus, Jameco is, for the most part, where I shop, that is if Radio Shack doesn't have it , (who have way high prices but I can get it within 20 minutes ).

Truth be told, I'm still partial to using paper catalogs and, having found the part I want, I then go online and order it/them.

 

[PG1995]

Hi

The following are all single supply op-amps. I need the one with maximum voltage swing which can get as close to the supply rails as possible. I will be using +5V supply to power it up. Could you please help me to choose one? To me, #3 looks good and note that #2 is same as #3 except that there is an additional op-amp in #3. Thank you.

1: https://drive.google.com/file/d/0B_XrsbDdR9NEMlNKY0JRckFZalk/edit?usp=sharing (LM324/LM324A/LM224/LM2902/LM2902V/NCV2902)
2: https://drive.google.com/file/d/0B_XrsbDdR9NEcFprWlpPd1Q0MlE/edit?usp=sharing (LM158/LM258/LM358)
3: https://drive.google.com/file/d/0B_XrsbDdR9NEZmtPMUNGaENobkk/edit?usp=sharing (LM158/LM258/LM358/LM2904)
4: https://drive.google.com/file/d/0B_XrsbDdR9NETGpkQW9hOWU3QXc/edit?usp=sharing (OP290)

Regards
PG

 

[cowboybob]

3: looks good to me. Only better than 2: because of the dual opamp per chip feature (if that's needed).

 

[MrAl]

Hi

The following are all single supply op-amps. I need the one with maximum voltage swing which can get as close to the supply rails as possible. I will be using +5V supply to power it up. Could you please help me to choose one? To me, #3 looks good and note that #2 is same as #3 except that there is an additional op-amp in #3. Thank you.

1: https://drive.google.com/file/d/0B_XrsbDdR9NEMlNKY0JRckFZalk/edit?usp=sharing (LM324/LM324A/LM224/LM2902/LM2902V/NCV2902)
2: https://drive.google.com/file/d/0B_XrsbDdR9NEcFprWlpPd1Q0MlE/edit?usp=sharing (LM158/LM258/LM358)
3: https://drive.google.com/file/d/0B_XrsbDdR9NEZmtPMUNGaENobkk/edit?usp=sharing (LM158/LM258/LM358/LM2904)
4: https://drive.google.com/file/d/0B_XrsbDdR9NETGpkQW9hOWU3QXc/edit?usp=sharing (OP290)

Regards
PG

Hi,

None of those op amps will do rail to rail effectively. There's always a fairly large drop for the high state output so that with a 5v power supply only the output will be about 3.5 volts max. They will get close to ground though, and if you really need a near 5v output there is a trick that can be used but it requires sacrificing the 0v output so the lowest output will get much higher, and that's still not rail to rail. There might be more mods we can use, but they already make rail to rail output op amps so why not find one of those as they are quite common these days.

 

[MrAl]

Hello again,

Another option is to build a small voltage boost circuit to boost the power supply voltage of the LM358 which would then allow the output to get to +5v or more.

Interestingly, this might be able to be done with the other section of the LM358
https://www.electro-tech-online.com/threads/lm358-booster-for-rail-to-rail-output.141736/

or alternately with a small low current boost circuit.

 

[PG1995]

Hi

I was playing around with an old computer power supply in order to find a suitable inductor for my project.It has got four inductors. Please give the linked picture some time to get fully downloaded. You can zoom in or zoom out using "View" in menu bar.

I'm confused about inductor #1. You can see that its winding is bi-color. It could mean that there are two sets of windings and it could be a coupled inductor or a transformer. So far I haven't taken those inductors out of the supply frame but careful look at inductor #1 reveals that it has got more than four terminals!

What is it really and how many terminals it has got?

Is it possible for you to make a guess at the inductance value of inductor #2? I'm trying to salvage an inductor with inductance greater than 1mH and which can carry 3A of current.

Regards
PG

 

[MrAl]

Hi,

It is very hard to guess the value if not impossible because the permeability of the core can be anything from 100 to 5000 which would represent a change in inductance of about 50 to 1. The best you can do is pull them all and measure them.
Might get some idea if you look at a power supply schematic which is similar, but it's questionable until you measure it.
1mH sounds kind of high but then again they usually operate these supplies around 10 to 20 kHz.

 

[KeepItSimpleStupid]

I can't make much stuff out with the dust and resolution. The bottom of the PCB should give you an idea of the number of terminals. My comments will therefore be generic.

The core material makes the inductance frequency dependent. Recently, I wound an inductor suitable for 100 kHz and about 5 mH.

Switching supplies usually have a common mode inductor at the the line input. It will have 4 terminals and would like a transformer, but the windings are in seres with the line. These are used to prevent radiation into the power line.

Switching multiple output supplies may directly regulate one winding and linearly regulate others or they could be switching for all of the voltages.

Transformers wound on toroidal cores are common.

Mr Al's comments are "right-on" Another "problem" is that the permeability has error bars of +-30%. This is where a transformer manufacturer has an advantage. A particular ferrite lot, may be much closer and therefore once they successfully make one and determine the permissibility, the others are virtually the same.

If your in the US, I could measure them for you.