EEVblog #87 – Let’s hop on the Electronics Design Merry-Go-RoundPosted on May 16th, 2010 19 comments
Dave demonstrates how much fussing around can be involved in selecting just a couple of cost optimised parts for a new design, using Digikey, Mouser, FindChips, Octopart and Atmel websites.
what about the free samples for the prototype?
It’s a professional issue, how to decrease costs to be competitive. So you have to search and search and search…
Some development systems are in the range of almost nothing like:
Formerly there were no current sensors as a single chip, now there are complex ones like the INA219/220 etc etc.
So for very cheap solutions, the old opamp circuits (e.g. one is shown in the LMV932 datasheet) are preferred.
For selection of other very cheap components i always look at modern PC motherboards…
PS: I like your blogs.
How did you film the PC screen?
It was well done and easy to read.
If you use firefox, the digikey sort by price greasemonkey script is great for ordering multipage results by price/quantity:
100% spot on. It is comforting to know that the pros suffer as the rest of us do. I have spent countless hours — if not days — researching parts for projects. As Thomas Edison said: Genius is 1% inspiration, 99% percent perspiration. Today he would probably qualify it with “80% of that time being spent combing over datasheets.”
Apologies if you already touched on these (was working on a project while the video was rolling), but I would like to add:
- Distributor parametric searches (e.g Farnell) often miss data; as such, narrow parametric searches can result in suitable components not being displayed.
- Costs can vary widely across distributors. Shop around.
- Although international, distributors can be limited as to what they can sell you in a particular region. E.g. even though an item is available to US customers, it may not be available to UK customers. (Often the case with test equipment.)
- There are many more distributors than just Farnell, Digikey and Mouser, but you may need to buy in quantity as they typical only distribute to the manufacturing sector as opposed to the hacker/maker/hobbyist set. (I needed a very difficult to source latching relay, and I needed to buy 35 or so just to meet the minimum order).
- As such, you develop an appreciation for Farnell, Digikey and Mouser as they will sell you only 1 of something.
- Don’t know about the rest of the world, but shipping a free to UK customers from Farnell.
I know that I am getting near the end of the component selection process when I am absolutely sick to the stomach of reading datasheets…
Over here in New Zealand, shipping is free from farnell on orders over $100. Otherwise it is around the $10 – $15 mark. New Zealand Dollars that is.
I myself am going into my first major design, and am looking at exactly the same things, microcontrollers, etc. Mostly I look at enclosures, and the other add-ons like grommets. These seem to be the most expensive part of the project.
One thing I found, it is always cheaper to use bare chips, than to use modules. Or even bare bones modules with support chips, compared to a fully featured module.
My best example would be the lantronix range. The ENC28J60 from microchip can replace the wired range without much trouble (throw in an EEPROM for storing the website). The wireless range is a little harder to replace, but I looked into the WiFly GSX (RN-131G), which is about half the price.
@Dan , Here in NZ shipping is free from RS on any order, and Digkey offer free shipping over $120, Farnell are usually overpriced on everything.
I bought a couple of logic gates from RS. How do they compare in terms of price?
I knew about digikey’s free shipping. I plan to make the most of it at some stage.
To me it seems strange that you want to get the design perfect the first time. Don’t you build a prototype first, then optimise the part selection?
@Dan RS are good price wise, they will match prices often also.
The term I have always used for this process is catalog engineering.
I can not get this video via my prefered method, podcast.
Be careful with filter part search for
micro controller, for example, if you think
you need only 4Mhz part and you filter for
that, you may be stuck with old parts with
bigger die/price than new part with little
die/price running up to 20Mhz.
Same problem with voltage range, don’t restrict
yourself to 5V part if you have 5V rail on
your board because new part run from 1v8 to 5V.
Enjoyed this video…it’s like you screen-captured a half hour from my PC at work.
Some people might smirk at agonising over an 80cent part but you do really feel like God kills a puppy everytime you concede 10cents to the cost of your project.
You managed, i think, to include the important criteria.
Sometimes you have to really quiz your boss, client or market to get a good feel about how much you should agonise over price. This also becomes important compared to the quantity you can get made at one time if making more than say… 10. Yes. You can be sure your competition is trying to get keep cost down on their widget as well.
As you say, component size can have consequences elsewhere. It may force you to load components on the other side of the board or for the PCB to become a 2 or more layer board.
Component size and lead type/pitch especially for large runs of SMD boards might mean considering a different board loader company with better/different capabilities. Establishing a good relationship with a board loader takes time. Also smaller SMD lead pitches might require laser cut solder paste shims adding significant cost initially. (no one remembers these costs once youve made thousands of the thing)
I like the “Catalog Engineering” comment. Sometimes engineering is knowing whats available from whom at what cost. For this reason i sometimes tack on other interesting components to the order along with the ones i need, to try to build a “library” of parts. Then i might have them when the next design requirement comes along or can offer some trivia about the part or technology during design discussions. Because the board loader keeps the stock of most parts these days, these sorts of parts aren’t usually kept in any real qty at the office.
I agree with the comments about not relying 100percent on parametric filtering. Even general searches can fail. If it turns up 0 on several key word searches, I go to the paper version (if i have it) to discover they do have it but have given it some generic or esoteric name.
On getting it right the first time or iterating, it often depends on the time to market available. Also, for larger SMD runs, the cost of solder paste shims is a significant first run cost. And the PCB manufacturer will have a setup fee everytime you change your design significantly. You feel like a bit of an idiot if you’re iterating because of hasty decisions the first time round. God kills a litter of puppies and a whale everytime you iterate because of errors.
I’ll admit if i have the time i’ll get a nine day turnaround prototype PCB and hand solder the components myself (yes even fine pitch. no not bga or bump… lol but i did hand solder a QFN once toasterless – not recommended). I think i need to convince work the get a small SMD oven and a PCB router.
btw, the WiFly modules are great. Developed by a mob here in Sydney. We’ve been devloping code on them at work, thankfully with the underlying c code SDK and not the console API I/F.
Sometimes you have to watch it with CamStudio. It won’t like it if you’re recording over a certain time limit (> 1hr?) as i’ve frustratingly discovered. Also if you’re using a USB headset and plugging stuff in and out of the same hub while recording, the audio gets out of sync from then on.
Hi Dave, I seem to be late catching up on your blogs… or you are just making them too fast. This may be too late but did you consider using your extra opamp (configured as a difference amp) for your high side current sensor? If the CCMR of the differential opamp is to much for you there is a nice trick ala Bob Pease… look for his artcile titled “What’s all this error budget stuff, anyhow.”
Hope it all worked out for you,
The ATtiny48/88 does support 2 PWM outputs (and Atmel’s parametric table now shows this).
I guess it’s a prime example of manufacturers not putting out accurate information and wondering why a product isn’t selling.
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