| Electronics > Beginners |
| How to look for parts |
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| cuccureddo:
Hey all. I'm developing my very first circuit, nothing complex, just a first attempt. Anyways the thing i'm struggling the most with is looking for parts. How am i supposed to do that? Let's say i need like an opamp or a binary counter how do i look for it? I tried going on digikey or mouser but i got literally overwhelmed. I've been asked for informations that, at this stage, i dont know/havent tought yet like temp range, package format and all sort of things. And even if i refine the search parameters enough to get a list then i have to read through something like 20 datasheets I mean it cant be right can it? Is it just like that or am i doing something wrong? Is there a "catalog" i can use which is divided into sections like for example digital circuits, amplifiers, semiconductors etc It took me quite a long time just to find a simple 7490 I know this is a very noobish question, but i feel... lost thank you |
| allanw:
Try sorting by price or by quantity available. If you don't need a very specific op-amp for example, just picking a popular one that has the performance you need is probably good enough. Otherwise it's basically impossible to pick from among the thousands of IC's that perform the same task. |
| EEVblog:
Unfortunately that's pretty much what design engineers spend most of their time doing, trying to find the most suitable part for the job. You'll generally have enough basic requirements like package type, speed or power consumption etc in order to get the list down to a manageable first level. But for common parts this can often still be hundreds or thousands of parts as you've discovered, so you need to whittle it down some more. You can do this by selecting "in stock" parts only, and then you'd sort by price and maybe some extra fields like power consumption. Even with hundreds of parts still left, you might pick purely by price. And you'd also look for it being a generic part number too that is available from a bunch of different manufacturers. Then it's common to search through say 5 different datasheets before finding a suitable part. Your example 7490 is usually pretty simple, as generally they are "jelly bean" parts that perform the same across all manufactures, so it won't matter which one, just pick the first on the list. So you'd just search by package type, in stock, and price. You might then use octopart.com or findchips.com to make sure it's available from different suppliers. Dave. |
| DJPhil:
As I understand it, even for the professionals this is a pain, and often constitutes the largest portion of design time. Don't feel bad, this is one of the more difficult things to master. It's further complicated by the speed that ICs are constantly being revised, discontinued, or released for the first time, and that makes it hard to stay current. Thus the concept of the 'jellybean' is born. When you want to breadboard a circuit to test an idea or slap something together quickly to solve a problem it's a good idea to have some inexpensive standbys handy. These get used when you simply need 'Opamp, Mk. 1, standard grade' and are usually very cheap. The goal is to always have a few handy, so you keep a stock and replenish it like you would a resistor of a commonly used value. This doesn't always work well if what you're doing requires high performance, but if you're hobbying your way along it can be a good way to start. Engineers (or hobbyists, labs, companies) that have different areas of focus or specialization will have different ideas of what makes a good jellybean opamp, for example, because different component trade-offs are valuable to them. Someone who's doing a bit of everything might have a dozen or more different jellybean opamps to cover their bases. Being a hobbyist, I personally like this way of doing things as it seems like a fair system for working in the free sample services of the manufacturers. I've got no qualms about asking for a sample of a dual voltage, low dropout, low quiescent current regulator with independent standby and soft power on, but I can't keep a straight face when thinking about asking for samples of an LM317 for 'evaluation' that's been in production for years and years. (P.S. I just made up that regulator, so nobody ask me where to get one :D) Discrete logic is harder to do this with due to the overwhelming variety of tasks you'd have to cover. Others can likely give good advice on this, I've got no real experience in digital logic or mixed signal parts. You can also look for circuits online that perform similar tasks to the one you're designing for and see what parts they use. Failing all else, you can always ask for advice here! If you describe what you're trying to do I'm sure there's someone who has the experience to recommend a few part numbers. Some of my jellybeans: Opamps for audio = assorted TL07X and TL08X (where x equals 1,2,4 for single, dual, quad), LM833 Opamps general = LM324 quad Opamps precision = OP07 Comparator general = LM339 quad 3 pin Vreg = LM317T positive and LM339T negative (TO-220), LM317L (TO-92), and a handful of fixed 7805 and 7812 Oscillator = any 555 clone, any 556 clone (dual 555), I'm using NE556 To everyone: what do you guys keep handy at all times? Hope that helps :) |
| cuccureddo:
Thanks guys, that was helpful. I'm still kinda lost and overwhelmed, but at least i know i'm not alone ;) I'll try to follow your tips and see if i can shorten the list a bit. I mean if i have to dig like 5-7 datasheets that's quite doable, but 20 for each IC no way :D Yes asking around is another solution, but i would like to keep that as a last resource because it's a bit like cheating. By that i dont mean that is a shame to do so, just that you "sweat" less hence you learn less. But ye sometimes it's the only way :P Thanks again |
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