Electronic Parts Deciding?

[TheNetImp]

I have a few ideas for a few projects.  I may know the "kind" of part I need, but how do you find out what parts exist to use for your project?  For example there are lots of different kinds of voltage regulators.  Is there a single resource that you can go to to figure out which one you should use for your project?

[Torsten Wagner]

I would say it comes down to the following chain for me...

1. Read the specs... e.g., there might be several dozen of 5V
regulators but they are not all the same, they differ slightly for
different parameters.
2. As soon as I decided which group still fits and if I still have the
luxury to choose, I go for one which is the most easiest to source for
me... either locally or checking that there is a huge stock in an
online store. The reason is rather simple, if I want to rebuild the
project or if it ever gets some publicity and people want to build it
too, it would be good if everyone can get the same parts. Thus, I do
not care if it's a quick and dirty one time solution and buy randomly
basically what I can find in local stores. If its part of a bigger
project I try to make sure mouser, RS, and Co. have them in stock.
3. Go for standard over fancy.... sure its nice if you can get hands
on a very seldom but perfectly fitting part, however, if you go with
standard parts even if this might need more PCB space or sightly less
performance, however, if you face some problems, chances are higher
others faced the same probs and found a solution already. Again online
resources helps here... if RS has only 10 uC in stock of package A but
10.000 of package B you should ask yourself why is that.

All this is more true for more complex parts, you might not face any
problems for discrete parts and only seldom problems for single
transistors, voltage regulators, etc. However, for e.g., uC, ADCs,
DACs, OPamps, etc. I would say, never go for a very seldom package or
very seldom used model. Sooner or later you might have trouble to
source them.

Well another problem esp. related to Japan is the fact that
transistors and other parts are completely different named compared to
what is used in US or Europe, that troubles me if I try to buy stuff
locally, (is this NJM-XYZ the same as the good old BC171 ?!)

Totti

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[James Andrews]

I guess I was more asking how do you find all that information?  Where does one go to figure out what parts exist in order to read the specs?   Are some sources better than others?  I personally couldn't tell if something is more common than not.  How does one figure that out?

[tALSit de CoD]

I usually go to mouser.com and search there. I *always* filter out things that aren't in stock, then sort by cheapest first. Then I check to see if they have decent stock of the one I looking at and go from there.

// talsit.org

[MRE]

If you know essentially what you want, then online catalogs are great.
I usually use Digikey.

To take Totti's example of a 5 volt regulator:
Going to digikey and entering "5 volt regulator" in the search bar initially gives you a lot of stuff that may or may not fit. Obviously, pneumatics is not what we are looking for ;)
But as we search down, we see several types of Voltage regulator options: LDO, Linear, DC to DC switching, and special purpose. There are yet more DC-DC converter categories below.
So, from here we decide on an LDO. Low drop out regulator. There are nearly 4000 options.(that does not mean 4000 unique parts. Most parts have more than one entry in the catalog. For example delivered on tape/reels, or bags, or individual packaging.)
Selecting LDO brings us to several search filter boxes specific to voltage regulators, and in particular, LDOs. In the "Voltage Output" option, we have a long list of choices, but only one that is 5V and ONLY 5V. Click that, then "Apply Filter". Next lets decide that we want output current near 1 amp. Selecting the 1A option and apply the filter again.
Now you should start thinking about the kind of package you want (not shipping... how is the part designed to be connected.) Lets say you want a large transistor style package with a metal tab, and legs you can solder through a pcb. Now.. learning all the transistor package types takes time. And most of us do not know them all. I will tell you that the package you want is called a TO-220 package. Select it and apply filters.
FINALLY we have a just one part (with two different shipping package methods) to choose. AT this point, we should inspect the datasheet (at the far right of the chart, a page icon with a teal D on it) to see if it fits our needs. Often, we strike out, and have to go back, widening the search before narrowing down once again.

[MRE]

If you are not sure what you are looking for, or even what major parts are available, or what they do:

1: Build lots of kits. Read the instructions carefully. A good set of instructions will take the time to explain each major function block, and the parts within them.

2: once you have a good solid foundation of essential components and most common packaging types, you can then google around for the unique items you are looking for.
Good key words for googleing:
* adding "IC" to the end of something will often return more relevant results. For example "power amplifier" and "power amplifier IC" give you very different results.
* the same is true with "sensor," "component", "DIY", "schematic" and "project"

3: Explore a LOT. Look at other project schematics. What are the major function blocks? What parts are they using? Why? Hack-A-Day is your friend. You can find loads of projects, and the vast majority includes some electronics.

[James Andrews]

I had actually started looking at Digikey, and I found the search functionality daunting.  I hadn't heard of mouser.com but their search functionality was a little better than Digikey's and I think I found what I want.

I should explain my background a little bit.  When I was in highschool I went to a vocational school and took the electronics course.  Spent 4 years making and breaking mostly analog circuits.   HS Graduation happened during the recession of the early 90s, most of the electronics shops moved out of the NE down to TN where the pay rate was less.  Those that stayed weren't hiring.  I ended up getting into web development in 96 and put electronics behind me mostly.  So buying a bunch of kits gets me nothing knowledge wise imo.  I know what kind of parts I want and how they work, but since my time in HS the form factors are not necessarily the same, there are more types of components to choose from. back then we use to look up components in books 8cm thick.

Taking the original voltage regulator scenario.  My wife and I both have a lot of 5VDC re-chargable devices.  Every year we go on trips via car, and end up having devices that lose charge along the way.  iPad, iPhone MyFi etc...  We bought a dual USB lighter adapter, that supplies 2A max.  We can put both phones in, but not a phone and an iPad.

When my wife bought her car she bought it without certain options.  This left sections of the dashboard un-used.  I want to add 4-5   USB charging stations.  Each capable of charging at 2A.  The problem is it needs to be low profile, I can't go sticking a bunch of TO-220 package voltage regulators on a board and hope to fit it in the space I have.  My thought of a solution is 4 sot-223 type packages wired in parallel each contributing 500mA towards the 2A, maybe even a 5th to get 2.5A just to give myself some space.

I can see a lot of other use for a similar device in the house on the kotatsu with all our devices.

When I was on digikey I found it hard to search but mouser gave me the uA78M05 chips which will probably do the trick, again I won't know until I get my hands on some and give it a try.  Also my first time working with SM components.

It's too bad there isn't a better way to reference parts than haphazardly searching e-commerce sites.

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[MRE]

In the project you described, a good solution is a DC to DC converter. It requires a largish coil at 4 amps. But the advantages are
- low heat. Good for behind your dashboard
- low losses. Not so important in the car, but more efficient when chargng while parked.

Taylan designed a board for 4 outlets, just under 4 amps total output, and its iPhone/pad ready. Apple does crazy shit to the charge system to force official chargers.

Its a bit big for behind a dash, but you can find a spot and root the usb sockets to the right place.

Also, its optinized for large car batteries.

Imo, assembling kits can ALWAYS teach you something new: new tech, new parts, new technique, new design methods.
Seasoned peos at least LOOK over other designs to glean new skills. No one can ever know everything.

Take a look at Taylan's design. We may still have a few kits. If not, we have at least one assembled unit. I guarantee you will learn something.

And yes, Digikey can often be a total PITA to slog through. But its also the most complete index of parts anywhere on tthe web.

[MRE]

Fnarg.
Thats "seasoned PROS"

Although, these days even pros are po.

[James Andrews]

I'd be worried that the coil may be too large for the space that I have, I litterally have maybe a couple cm at best.  Hence my thought for sm parts.  I'll check out the DC to DC converts though.  I am aware of apple's charging scheme, but I am not sure so much if it's to force their chargers, since I've used non apple chargers to charge my phone before.  I thought it was to control the rate at which the iPhone/iPad draws current.  I wouldn't want an iPad trying to pull 2A from my laptop.  Either way, that is part of my research is to make sure that I get 2A and figure out the resistor configuration that does that.  I'd like to at least take a look at the design, but if there's a completed unit I can look at that'd be cool too.  Thanks.

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[MRE]

Yeah, absolutely.
Taylan will lijely step in and throe some advice at you, since its his design. And I think Lady Ada has a blog post specifically about the apple resistor network required.
Yes. You are right. Its to identify charging rates, and to some degree the type of device, so tgat you dont plug a wimpy phone charger into an iPad. In principal a good design practice.

The only problem is that it causes most Apple products to only work on apple approved chargers (including aftermarket, "certified")

You cant just wire up a power supply and expect it to work.
Tried solar chargers for a guy biking across Japan. His older iphone worked, but not the newer one. Eventually had to make a custom dongle that attached to any usb cable and turned it into an "Apple" cable, which could then plug into the solar panels.

[James Andrews]

I have watched lady ada's video, it's out of date though, as it was made pre-ipad  I am worried the resistor values will only get me 1A instead of 2.

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[MRE]

Yeah... cars are a hard environment to design for: no space, no ventilation, 12 volts not really suitable for digital electronics.

LDO or dcdc switch is the way to go. Old school linears are to hot and wasteful.

[MRE]

Lots of these floating arohttp://www.amazon.com/gp/aw/d/B003GAAQXM/ref=aw_d_iv_pc?is=lund

Found a 9 dollar device on amazon as well.
Buy one, cut it open and measure the resistors.

[James Andrews]

Yeah that's what I was thinking actually.  I just was waiting for $$ to come my way.

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[AbH Belxjander Draconis Serechai]

I have a yet to be  used picoPSU sitting in a bag that I need to replug for a molex plug

as I want to run 2 low power motherboards off a common ATX mainboatd amd fit them both into a custom case

Would my bringing that with me to a hackerspace meeting help for you to read some of the part information from it?

[Taylan Ayken]

It mat not be suitable for a car dashboard as the DC-DC converter block is a bit huge. Actually they are smaller as this one has the IC, the coil and the FET encased in a heatsink. Good think is it has 4 USB ports, bad thing is they were set at 500 mA to have some headway as the converter had an internal limit set at 3 A. But mess up with resistors and change two of them to 1 A or only one to 2 A. If the size fits.

5 V output with 2 A with a DC-DC converter is easy for a car, you may even be able to use the internal FET of the buck IC but have to check on that. Coil will not be that huge, maybe 1 cm above the board. I have to actually design sth to be able to tell you how big the coil will be. And even with that you have axial-radial decision which affects the size.

No need to crack open a case to get resistor levels: Cut a USB cable, find the 5 V and GND cables, measure the remaining (D+ and D-) cables' voltages wrt GND. Then try to come up with a voltage divider that gives you those values, try to use resistors in the kohm range. That is about it.

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From: MRE <epre...@gmail.com>
To: tokyohac...@googlegroups.com
Sent: Wednesday, November 7, 2012 1:18 PM
Subject: Re: [THS:21044] Re: Electronic Parts Deciding?

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