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I've been doing EMC stuff since around 1987.Thanks Tim. So we should go for an R-C circuit with an acceptable limit on
the slew-rate, and not bother with the ferrite bead at all, do you think?
Sorry for my ignorance - that was the first EMC testing I have been involved
in, and it is a black magic to me TBH.
Didn't you get two replies to this yesterday? Including mine:All,
Off a PIR motion detector I get a 24 volt output and when it detects
someone the pulse drops to zero for about 4 seconds. I want to trigger
a 555 timer to output about a 1/2 second pulse. What is the standard
way to take this long trigger and shorten it? Thanks.
Terry
Good idea but they are usually pricey, above 5 cents a pop. Then you canI am not aware of any but you might consider a dual and configure the
second transistor as the diode- this should just work at low supply
voltages and the low reverse EB voltage stress.
Yes, looks like the MMBT versions in SOT23 will be around a while. TheOn still lists various surface-mount versions -- is it just the 2N
version, or the die?
Well, if *everything* i know is wrong, then *maybe* something i do NOTI've decided I'm going to write a book. Screw it, I sit here
and claim I have a theory that explains everything, dammit,
I ought to have the hairs to put my mouth where my mouth is.
Now the big question, which will, of course, be everyone's
first objection: If I know everything, howcome I can't figure
out how to get money?
Well, I have an answer, and of course, from the POV of the
people who have the money, it sounds just like nothing but
more of the same whining from the people who don't have the
money.
The people who have the money will resist the theory because
it tells how the people without money can theoretically get
money, but the people with the money are terrified that if
they let loose of any of their money at all, it will all
be sucked up by the infinite abyss of the money hole, and
they will die horribly, a pauper in the streets like the
ones they're so desperately trying to avoid becoming in
their own right.
So, I guess I'll have to resort to the old-fashioned way,
of getting a job - although I would like to think that it's
within the realm of possibility within known reality that
I could find some employer who wants me for my mind instead
of just my body. ;-)
Or - one of the things of "magic" that so few people actually
try - to simply ask for some:
How does one go about getting an advance to write a book? I
am lazy, after all, and it does happen, and there might be
some eccentric out there, or it could be about as successful
as the left-handed microwave oven. Which, by the way, if
anybody takes that one to market, I'd appreciate a buck or
two thrown my way for thinking of it.
But, I'm certainly not going to sit here and wait for somebody
to show up with a check! I think I can handle "starving writer"
for awhile - actually, that's what I already am, because
if anyone were to look into it, my current "job title" (I'm
a contractor, so don't really have a title or anything, except
maybe "misc.") is "Tech Writer," and I'm poor, albeit not
literally starving.
And if worse came to worst, standing on the street with a sign
that says "Bum" pays about $15 bucks an hour. ;-)
So, off to the grindstone!
Cheers!
Rich
Look in "HDL Chip Design," as it includes both combinatorial and sequentialSo do you have any pointer to
that , i am sorry,i've been trying a lot to look around , figure out
and implement a circuitory but wasnt successful at all even after
looking at books!
Use a one-transistor one-shot.All,
Off a PIR motion detector I get a 24 volt output and when it detects
someone the pulse drops to zero for about 4 seconds. I want to trigger
a 555 timer to output about a 1/2 second pulse. What is the standard
way to take this long trigger and shorten it? Thanks.
Terry
Yeah, there ya go.you can use a rgulator for constant current source. for example in 7805
datasheet, you can find a sample circuit. for switching, i have not got
much idea but maybe you can use a microcontroller to adjust the time.
It's probably because there isn't a standard 18 pin SSOP package, soHi there
Will anybody out there please tell me what's the difference between an
18pin and a 20pin PIC16f628?
All I can figure out is, 20pin dip is having one extra Vdd and Vss
pins. I don't understand the need of those duplicate pins!
Even an elector in West Virgina is already refusing to vote for Bush:Talk about denial- the latest news is that over 30 major newspapers that
endorsed Bush in 2000 now endorse Kerry. Kerry has even been endorsed by
a major Conservative magazine because they conclude Bush is not
conservative- he is a fraud. The whole literate world has turned against
Bush- he has no support left.
Dang! Email Microchip. They may give you a reward for pointing out thatHi there
Will anybody out there please tell me what's the difference between an
18pin and a 20pin PIC16f628?
All I can figure out is, 20pin dip is having one extra Vdd and Vss
pins. I don't understand the need of those duplicate pins!
Thanks
Thanks for your info Graham. In fact it is a SPDIF signal (unbalanced), asSteve wrote:
"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:417d0686$0$43607$ed2e19e4@ptn-nntp-reader04.plus.net...
Steve <me@privacy.net> wrote:
Hi,
During EMC testing (for CE) of our product, the single output data
line
failed the radiated emissions test. It is a digital audio square
wave -
0.5V
pk-pk at 12.28MHz - and at 100MHz or so the emissions were just over
the
allowed limit.
snip
I'm thinking that we could put pads on for a 0805 ferrite bead, and
then
take the board for EMC testing with a bunch of alternative spec
beads so
we
can try them out while we are there. But is this likely to be
successful, or
is there a better way?
Have you taken any measures to limit the slew-rate of the digital
audio
signal?
Even a simple R-C filter might be helpful.
Hi Ian,
Thanks for your suggestion. TBH we've dismissed that approach in the
past
since a decreased slew rate could increase jitter on the signal. Jitter
is a
problem to audiophiles (real or perceived), so limiting the slew-rate is
not
something we want to do if we can at all help it.
It's a classic case of Errrrr But !
Whatever the ferrite does will have pretty much the same effect as an RC !
Otherwise it wouldn't pass the EMC test.
You really shouldn't have a problem with a dig AES ? out btw if proper
screening
and earth return is applied.
Graham
No. It is a value of a resistor which is a load only when the rise time (Dv/Dt)Clarence wrote:
"John Popelish" <jpopelish@rica.net> wrote in message
news:41753A07.B1F4C5DE@rica.net...
KM wrote:
John Popelish wrote:
KM wrote:
I have use a LC3803 Linear regurator to design a flyback regurator.
A
tronsformer is wind with single primary and double secondary coil
(one
for 3volts and one 7volts) the FB was return from 3 volt output. It
is
found that the output of 7 volts when unloaded is floating high to
13v
when only 3volts output are loaded. It is found that the overshoot
is
causing the raise. What is the possible solution to this?
Are the 3 and 7 volt outputs both positive?
Do the 3 and 7 volt outputs share a common return?
What are the rated full load currents for each output?
both are positive
No, there are individual return separately
That rules out sharing currents in the 3 volt winding.
the rated full load are 2.2A for 3 Volts and 1.2 A for 7volts
respectively.
I think I would try winding part of the 7 volt winding bifilar with
the 3 volt winding and putting the rest on top of that. And you will
probably need to add some minimum load to the 7 volt output so that it
is never completely unloaded.
--
John Popelish
How about a "Snubber" on the unloaded winding to control overshoot? I can
not
imagine a supply design without some form of rise-time load for a lightly
loaded output. Ripple control is most important at low currents.
Isn't that what a small resistive load across the filter cap amounts
to?
The Siliconix Vishay 2N3819 JFET datasheet has curves of gate leakageHowever, none of the datasheets I could find listed the maximum
voltage that can be placed across a 2N3819 (from drain to source).
E.g. http://www.fairchildsemi.com/ds/2N/2N3819.pdf
[ snip ]
I'm curious though, what happens to a JFET when that voltage
rating (drain-gate) is exceeded? Does it avalanche like a MOSFET?
Would it survive?
I have your design..... He wasn't specific about the level he wanted in theOn Tue, 19 Oct 2004 20:27:24 GMT, "Clarence" <no@No.com> wrote:
Hassan wrote:
Hello;
I want to design a switching power supply with:
Vin=24 Vdc and Vo=15V @ 7A
Possible to use:
http://www.mpja.com/productview.asp?product=14335+PS
Heavy duty.
---
What is it about "design" that you don't understand?
--
John Fields
Whether you use digital or analog means, the difficulty is proportional,On Wed, 20 Oct 2004 21:01:13 -0700, Fox zhou wrote:
As shown in the following chart, there is a trigger signal (a pulse)
may occur at any time in the cycle of a 100MHz square wave (10ns
period, 50% duty cycle). I want to measure the delay time between the
rising edge of the square wave and the trigger falling edge. (t marked
in the chart).
|t|
--------__________
______-----_____-----_____
|<-10ns-->|
| 1 cycle |
I'd like to hear any ideas from you to solve this problem.
I'm trying to use the logic gate to capture this interval and charge
the capacitor this period of time. Then the elapsed time is recorded
in the capacitor a voltage. But it seems difficult to acquire the
logic and control the charging and discharging. Do you have a
Chart: [missing]
Just use a Tektronix scope with at B sweep.
Cheers!
Rich
---"John Fields" <jfields@austininstruments.com> wrote in message
news:cr9bn0lruhi5sobk9so5ssrqfimfa4dna9@4ax.com...
On Tue, 19 Oct 2004 20:27:24 GMT, "Clarence" <no@No.com> wrote:
Hassan wrote:
Hello;
I want to design a switching power supply with:
Vin=24 Vdc and Vo=15V @ 7A
Possible to use:
http://www.mpja.com/productview.asp?product=14335+PS
Heavy duty.
---
What is it about "design" that you don't understand?
--
John Fields
I have your design..... He wasn't specific about the level he wanted in the
original posting. I see someone else ask as well.
Or are you only showing that you didn't understand?
You started it, you can just live with it!On Wed, 20 Oct 2004 00:09:36 GMT, "Clarence" <no@No.com> wrote:
As usual had nothing of value to contribute!
---
Same old "John Fields", huh, Clarence?
'best' - under what constraints?I'm looking for the best circuit to switch batteries from a parallel
arrangemnt to a series arrangement for stacking the voltage.
There can be no best way when you do not specify:Any pointers as to the best way to switch these batteries into the
stack and handle the large voltages would be appreciated.
Pulse transformers, optocouplers, relays, optic fibers will all work.I'm confused on how to drive the gates as they will each be 12V higher
than the next one.