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> Then again, maybe that's because I'm still thinking like a consumer. When
> I buy something, I want it to *not* brake. The manufacturer, on the other
> hand, has a vested interest in making it so flimsy that it won't last 5
> minutes. That way they get more repeat business. (In addition to the
> materials savings, obviously.)
I think more people would steer away from a brand if it got a reputation for
breaking all the time, usually manufacturers have exact targets for how many
devices are returned failed after certain amounts of time. They are
carefully calculated (to produce a device that doesn't break too often, but
is also sensible to manufacture) and then the product is carefully designed
and tested to meet these targets. The bad reputations usually come from
mistakes rather than deliberate design intention. Still this is usually a
result of poor design/testing procedures, which are obviously related to
cost.
> Personally it makes me angry that somebody would deliberately design
> something to be defective so that they can make more money out of me.
I doubt anyone designs something intentionally to fail, no matter what it
might seem like as a consumer. It's quite hard to design something to be
fine within warranty but then to fail just after, you risk a huge
replacement bill if you try that tactic, plus you'll get a very bad
reputation.
> (I still don't understand why digital devices *need* thousands of analogue
> components in them in the first place, but anyway...)
On our boards nearly all of the discrete components are part of the power
supply or to round off the data signals to improve EMI/EMC performance.
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scott wrote:
> Interesting, the cost breakdown to make an iPhone:
>
> http://tinyurl.com/28v49e8
>
> Somewhere else (I lost it now) they mention assembly costs are around
> $9.50.
Tht's not the cost of making an iPhone. That's the cost of the hardware that
goes into making an iPhone. It leaves out stuff like patent licenses, and of
course the sunk design costs etc.
--
Darren New, San Diego CA, USA (PST)
Serving Suggestion:
"Don't serve this any more. It's awful."
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On 10/14/2010 7:53 AM, Invisible wrote:
> Now, see, I would have thought just surface-mounting the 2,157
> individual resistors would cost more than $10... But what do I know
> about anything?
Well... once you buy the machine to do it, it doesn't really use too
much electricity (except, maybe the heater to keep the solder bath warm,
and only takes a few minutes to pick and place the components. But the
initial outlay for the cost of the machine is a high cost.
--
~Mike
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On 10/14/2010 9:46 AM, scott wrote:
> On our boards nearly all of the discrete components are part of the
> power supply or to round off the data signals to improve EMI/EMC
> performance.
[A large chunk of this response is mostly directed at invisible]
Right. Filtering the signals. Caps are used a lot of time in digital
circuits to prevent switching noise from corrupting signals via ground.
When some digital circuits (TTL in particular) switch they create a lot
of noise on the ground plane that must be dealt with. Too much
fluctuation between power and ground, and the circuit begins to behave
erratically. Also, its a good idea to limit current. Resistors are used
to stabilize signals, pull up or pull down an input or output, bleed off
excess voltage so FETs don't retain a charge, etc... You need RC
networks to run a clock crystal, etc... Just connecting together a pile
of digital components won't work. You need supporting components to make
sure everything is stable in the system, especially when dealing with
large-scale digital systems like an iPhone. Keep in mind, that device is
also going to require a oscillators and filters for the RF parts, as well.
It gets even more interesting when you start dealing with designing
circuit boards, where you actively need to avoid traces from running
parallel to each other for too much distance, lest they build a
parasitic capacitance between them. In systems with very tight voltage
and current tolerances, the length of traces and thickness of traces
becomes very important as well. Traces can also act as inductors.
Some of the discrete components may be in there to also counteract some
of these effects caused by the traces themselves on the board. You'll
notice caps and resistors will often be very close to the pins of an IC
to minimize any effect the circuit trace may have.
--
~Mike
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> [A large chunk of this response is mostly directed at invisible]
>
> Right. Filtering the signals. Caps are used a lot of time in digital
> circuits to prevent switching noise from corrupting signals via ground.
> When some digital circuits (TTL in particular) switch they create a lot
> of noise on the ground plane that must be dealt with. Too much
> fluctuation between power and ground, and the circuit begins to behave
> erratically. Also, its a good idea to limit current. Resistors are used
> to stabilize signals, pull up or pull down an input or output, bleed off
> excess voltage so FETs don't retain a charge, etc... You need RC
> networks to run a clock crystal, etc... Just connecting together a pile
> of digital components won't work. You need supporting components to make
> sure everything is stable in the system, especially when dealing with
> large-scale digital systems like an iPhone. Keep in mind, that device is
> also going to require a oscillators and filters for the RF parts, as well.
Well, the iPhone runs on battery power, so yeah, the power supply is
probably a little unstable. I'm thinking more about desktop PC
motherboards. Why do *they* need so many million capacitors?
> It gets even more interesting when you start dealing with designing
> circuit boards, where you actively need to avoid traces from running
> parallel to each other for too much distance, lest they build a
> parasitic capacitance between them. In systems with very tight voltage
> and current tolerances, the length of traces and thickness of traces
> becomes very important as well. Traces can also act as inductors.
>
> Some of the discrete components may be in there to also counteract some
> of these effects caused by the traces themselves on the board. You'll
> notice caps and resistors will often be very close to the pins of an IC
> to minimize any effect the circuit trace may have.
Meh, well, fortunately I don't have to care about such things.
(Presumably a few attofarads only starts to matter once you're operating
into the GHz range anyway...)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 wrote:
> I'm thinking more about desktop PC
> motherboards. Why do *they* need so many million capacitors?
That's what *makes* them digital.
--
Darren New, San Diego CA, USA (PST)
Serving Suggestion:
"Don't serve this any more. It's awful."
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Darren New <dne### [at] san rrcom> wrote:
> Orchid XP v8 wrote:
> > I'm thinking more about desktop PC
> > motherboards. Why do *they* need so many million capacitors?
> That's what *makes* them digital.
Capacitors are not digital. You are confusing them with transistors
(which, technically speaking, aren't digital either, but can be used
for that purpose when their multiplying factor is ignored).
--
- Warp
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On 23/10/2010 06:42 AM, Warp wrote:
> Capacitors are not digital.
Perhaps it would be more accurate to say that no single component is
digital, more that a particular circuit design can be digital. (I've
seen logic gates used to make an analogue circuit, for example...)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> Orchid XP v8 wrote:
>>> I'm thinking more about desktop PC
>>> motherboards. Why do *they* need so many million capacitors?
>
>> That's what *makes* them digital.
>
> Capacitors are not digital.
Nothing is digital. Digital is an interpretation of an analog signal. To
"make an analog signal digital" requires analog components. You have to
drive the analog signal so it doesn't linger between the fully-on and
fully-off states (however those may be defined).
And yes, capacitors can be digital in a voltage-driven circuit.
--
Darren New, San Diego CA, USA (PST)
Serving Suggestion:
"Don't serve this any more. It's awful."
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Darren New wrote:
> Warp wrote:
>> Darren New <dne### [at] sanrrcom> wrote:
>>> Orchid XP v8 wrote:
>>>> I'm thinking more about desktop PC
>>>> motherboards. Why do *they* need so many million capacitors?
>>
>>> That's what *makes* them digital.
>>
>> Capacitors are not digital.
>
> Nothing is digital.
As an example, even your keyboard needs debounce circuits, and power
supplies have to be careful not to let the inductance fry things when you
toggle the switch.
--
Darren New, San Diego CA, USA (PST)
Serving Suggestion:
"Don't serve this any more. It's awful."
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