| ??? 01/19/07 18:37 Read: times |
#131130 - Yes I do ... Responding to: ???'s previous message |
Erik Malund said:
As for your remark about saving $0.17 on a $0.20 component, well, isn't that a worthwhile effort?
I know of no '51 derivative that sells for $0.20 and you, constantly, refere to previsous statements and this thread IS about testing '51s. Well, Jan expanded the discussion to include passives and linears. I agree my query applies, originally, only to the 805x-core MCU's, and, as you say, none of which I'm aware cost only 20 cents. However, if you receive ten parts and seven are defective, and you learn that right away, you can return them, and, since they may cost $17 rather than $0.20, you've saved some bucks now, not to mention the panic, schedule slip, and embarassment that occurs when 7 out of your 10 MCU's are broken, and particularly so after they're soldered into that $2500 board. I remember that you once said that you didn't need to test LCD's beyond the functions that you use in your application. Well, that's probably true if all you care about is "getting them out the door" since that will suffice for a demonstration. If several functions fail, however, isn't the entire device broken? Would you ship a defective device in your product? If some of the bits don't fail until it's had a chance to warm up, aren't you concerned it will have some effect? Would you ship a product when the carry doesn't work just because you don't use it in the current code? What if the next field-fix requires it? apples and oranges you refer to the carry in a LCD (which I do not use any of). nope ... that was the carry in an MCU ... we are discussing MCU's, right? It's like a car. If you don't plan to use reverse gear today, perhaps you don't care that it doesn't work, but what about next Monday, when you have to back out of your parking space? To the point: if a display works in my system before and after "it's had a chance to warm up" why would I spend time and money on testing whether the "storage for oddball characters you create yourself" works or not, since I do not, and never will, use it. My point is that if any function in an integrated circuit is broken, it's the whole integrated circuit that's defective. How it makes itself felt is not relevant. You have a very low opinion of distributors, is that reflected by your use of surplus you referred to a while ago? (was it LCDs?) Yes, I've been "screwed" by distributors one time too often. Once bitten, twice shy, as the saying goes. No ... I use surplus components when I can (a) save more than 75% on a small quantity, AND (b) verify that they actually are fully functional. I learned this, not from surplus suppliers, but from main-line distributors, who shipped me IC's that were defective. I've had much more trouble with Arrow and Avnet as a supplier than with DigiKey and Mouser, the latter pair being in the surplus business. I mentioned that surplus LCD matter in the context of an LCD tester I built long ago and recently loaned to a colleague for use by his students in a microprocessor-related course, most of whom would be purchasing their LCD's from a surplus vendor, since distributors seldom want to sell just one of something. I have had NONE ZERO NADA problems with one component in 1,000,000 failing NO such failure have cost enough to justify extensive pre-testing; HOWEVER I have had very costly replacements because of bad designs by others. The likelyhood of a costly 'accident' being due to design is far greater than it being due to the component.
Go ahead, 'design' without adhereing to min/max temp etc and then blame the component manufacturer. This exactly happened with a 'design' done by someone using 'typical' values from a datasheet, getting by with it for a couple of years and then BOOM the 'design' failed - of course it was the new components - not the design, the fact they were within min/max did not matter. Erik I don't know why you bring up this last issue. Nobody has suggested that one should design a circuit outside the limits specified by the manufacturer. Do you "shake-N-bake" all your products to ensure they work throughout the entire temperature range? Are you feeling guilty? RE |
