gmane.comp.hardware.microcontrollers.pic

Re: [OT] jumpstarting takes a few minutes of "charging"?

Sean Breheny — 2012-05-17T00:55:26

I agree, Bob. The resistance of good clamps on fairly clean metal is
going to be maybe 1 or 2 milliohms per connection. This would be 8
milliohms max for the entire circuit. 4 AWG wire is about 0.25
milliohms per foot so if the set of cables is 10 feet long, the entire
path length is 20 feet or 5 milliohms for the wire. The total path
resistance is then 13 milliohms. If you went down to 0 AWG wire, the
resistance of the wire would be 0.1 milliohms per foot so the total
contribution from the wire would be 2 milliohms making the entire path
10 milliohms which is significantly less. Going to even larger wire
would let you approach 8 milliohms total. Actually, 8 milliohms for
the clamps is probably higher than the real value anyway, which makes
the cable even more important.

I think that people are not giving enough consideration to the current
it takes to charge the dead battery. Assuming that it is merely low
and not damaged permanently, it will probably draw 200 or 300 Amps
when connected to the other car. T

Re: [OT] jumpstarting takes a few minutes of "charging"?

Bob Ammerman — 2012-05-16T23:31:39

----- Original Message ----- 
From: "Mark Hanchey" <mark< at >pixeltrickery.com>
To: <piclist< at >mit.edu>
Sent: Wednesday, May 16, 2012 6:45 PM
Subject: Re: [OT] jumpstarting takes a few minutes of "charging"?

This is not true. The resistance of the cable is in series with that of the 
connections and thus it is the total of the two that controls the current 
flow.

Re: [OT] jumpstarting takes a few minutes of "charging"?

Mark Hanchey — 2012-05-16T22:45:43

It isn't so much the resistance of the cables as it is the poor 
connections at each end. Measure the surface area contacting both ends 
and compare it to the size of the cable, if it isn't at least the same 
amount of surface area then it doesn't matter how large the cable in 
between , it is like connecting a 100 ohm resistor to a 2 inch thick 
copper cable, the limit will still be the resistor and increasing cable 
size isn't going to change that.

This is all about safety.  Hydrogen gas can be an issue but the real 
reason for not placing both cables on the battery is because the  clamps 
easily come loose from the terminals. If the two ends touch you now have 
an  arc  of current equal to that of an arc welder  with the clamps 
bouncing around from the arcs and the user trying to stop the shorting 
out,  plastics, wires, and anything near by can easily catch fire from 
the high temps the arc creates. I have seen what happened when a 
mechanic dropped a wrench and it fell across battery terminals, not a

Re: [OT] Looking for Linux expert

Neil Cherry — 2012-05-16T22:42:32

Hmm, think that was a tomato sauce stain. Oh, yup it was an -i.

Re: [EE] "Black sun" effect in CMOS camera sensors

Alex Harford — 2012-05-16T16:39:49

Are you preparing to take some pictures of the upcoming Transit of Venus? :)

Re: [OT] jumpstarting takes a few minutes of "charging"?

Spehro Pefhany — 2012-05-16T13:43:33

Maybe you didn't look? Cheap cables have the characteristic you
mention because they are too light to deliver the starting current
without a large voltage drop.

I've seen ones as light as AWG8 or even AWG10!.

Good ones are AWG4, 2 or even AWG 1. Naturally, the price tends to
go up with the gauge, because there is more copper (and also the
clips tend to be better made). If you want them long, of course
the gauge has to be larger again for the resistance.

There's almost an order of magnitude difference in milliohms per
foot between the worst and the best. That's WAY more than the
difference between "starts instantly" and "not a chance".

Here's one:
http://www.amazon.com/Coleman-Cable-08862-25-Foot-Ultra-Heavy-Duty/dp/B000PJD7HY/ref=sr_1_4?ie=UTF8&qid=1337175552&sr=8-4

Something like this is a more reasonable trade-off to keep in all
the cars:
http://www.amazon.com/True-Power-Booster-Jumper-Cable/dp/B002RJK3Q8/ref=pd_sbs_misc_6


BTW, in the really old days, we used to move the cars so that
the bumpers co

Re: [EE] "Black sun" effect in CMOS camera sensors

M.L. — 2012-05-16T12:40:59

Thanks, Brendan

On Tue, May 15, 2012 at 1:01 PM, Brendan Gillatt
<brendan< at >brendangillatt.co.uk> wrote:

Re: [OT]:: Annoying monitor problem

RussellMc — 2012-05-16T12:28:47

Displays some of a million of so photos when screen is not being
otherwise employed.
The longer it is since you were there, the better you remember it :-).


                           Russell

Re: [OT] jumpstarting takes a few minutes of "charging"?

Lee Jones — 2012-05-16T11:55:12

It's the resistance of the cables, the resistance of the clamps,
the cleanliness of the battery posts, and the comparative size
of the batteries & supply vehicle charger & taret vehicle starter.

I carry cables made with size 0(?, same size as my welder's ground
wire) copper wire & top-notch clamps.  Clamps have strong springs.
When I put the clamps on -- both ends -- I wiggle them around to
ensure that the surface oxidation is broken and there is good
contact (to battery terminal or to heavy frame member).

With my old V8 Surburan supplying current, I can immediately crank
any new politically-correct car. If target vehicle won't crank, it
is a poor connection at the clamp ends.


They are.  Look at car parts stores that cater to professional
vehical repair stations.  That means not Autozone, not Pep Boys,
not O'Reilly/Kragen.  However, you may be able to special order
decent jumper cables from them.  Remember, if you want quality,
you have to pay for it.

You can also get raw cable & clamps for jumpe rsets

Re: [OT]:: Annoying monitor problem

Rodney Pont — 2012-05-16T10:51:01

Re: [OT]:: Annoying monitor problem

Patrick Moody — 2012-05-16T10:17:10



On a related, but not really helping with your problem note; What's the
point of the blank-screen screen-saver before the monitor is powered down?

In the post-CRT computer monitor era, I'd argue that any screensaver is a
total waste of energy and reduces the lifespan of the monitor. If it's not
in use because the machine has sat idle for some time, I think you should
just switch it off and forget about having a screensaver entirely.  The
sooner you turn off the back-light when the monitor is not being used, the
better.  LCD pixels kept in the same state on an LCD don't wear out and
LCDs don't suffer screen-burn like CRTs used to, so the screen-saver is
totally unnecessary for this.  Also, when a blank-screen screensaver is
activated, the back-light remains active unnecessarily using up some of its
finite lifetime.

Apart from for some marketing purpose if your monitor is facing your
potential customers, can anyone give me a good reason for the
continued existence of screen-savers since the screen-burn pr

Re: [OT]:: Annoying monitor problem

Yigit Turgut — 2012-05-16T09:23:06

Try with an external video card see if it's related to it. If it's,
changing the motherboard will probably do the trick (if they still
want to operate onboard vga).

On Wed, May 16, 2012 at 12:10 PM, Ruben Jönsson <maxruben< at >rjjournal.net> wrote:

Re: [OT]:: Annoying monitor problem

Ruben Jönsson — 2012-05-16T09:10:18

My dell monitor has an integrated two port USB hub. That could be the cause of 
the "bing-bong" sound when powering down. If the monitor has a USB hub, try to 
remove the USB cable between the computer and the monitor and see if that 
helps. However, the USB hub should not affect the screen, but you never know...

Also, has he tried to update the video drivers? 

/Ruben





===========================================
Ruben Jönsson
AB Liros Electronic
Box 9124
200 39 Malmö Sweden
www.liros.se
Tel +46 40142078
============================================

[OT]:: Annoying monitor problem

RussellMc — 2012-05-16T08:13:53

A friend reports a monitor problem as below.
Any comments on a fix would be of interest



         Russell

_____________________________

Russell,

We have a number of different machines with LCD and CRT monitors.  Mostly but
not exclusively Dell hardware.  All running WinXP SP3.  All set for exactly the
same screen-saver and power saving settings  - blank screen after 5 minutes,
power down monitor after 10 minutes.

Most systems work as expected/intended.  After the programmed period the
screen-saver kicks in (and the monitor screen goes black), and then after a
further specified period the computer powers down the monitor without further
ado.  On moving the mouse the monitor powers up and the desktop appears on the
screen.

Two of the systems however don't work like this.  They enter screensaver mode
(with a black monitor screen) OK but when the computer attempts to power down
the monitor, the standard Windows "bing-bong" change of hardware status sound is
heard (actually it goes bing-bong longer-

Re: [PIC] direct-connect PWM outputs?

Bob Ammerman — 2012-05-16T01:28:22

You certainly cannot connect the two pins together.

However, you should have some sort of low-pass filter on your PWM.  This is 
often just a simple RC network. You can just have separate resistors to the 
top of the filter capacitor from each of the PWM outputs.

However, you certainly can get the effect you want in software. You can even 
use 8-bit samples but you have to average them rather than simply adding 
them before sending them to the PWM. I don't know if you are using C or ASM, 
but it is basically trivial to do the averaging if you are in ASM. It is a 
little slower in C.

Re: [OT] jumpstarting takes a few minutes of "charging"?

Lyle Hazelwood — 2012-05-16T00:32:30

Many "consumer grade" jumper cables have reduced copper and added
extra insulation to make the cables look as thick as better cables.
Long ago I invested in a long, very heavy set of cables, and a decent
zipper bag to store them in. Never regretted it, and the bag has done
it's job by protecting the cables between uses. The only other item in
the bag is a pair of safety glasses, just in case.
They have never failed to start a car immediately after connecting.
And I do insist that anyone without eye protection takes a few steps
back. ;)


On 5/16/12, Dwayne Reid <dwayner< at >planet.eon.net> wrote:

[PIC] direct-connect PWM outputs?

Lee Mulvogue — 2012-05-16T00:27:20

 

Simple and possibly(?) dumb question; if I connect two PWM output
pins of a PIC together, can it cause damage to the PIC?  ie., will
"input" power being applied to an "output" PWM pin smoke it? 

I am producing sound via PWM, and currently add two samples together
in code before outputing to one PWM channel, but it would be a lot
simpler in most respects to just send the two samples to their own PWM
channel and hard-mix them; the higher the output level the better, so
was just going to essentially solder the two pins together; bad idea? 

Currently my two samples are only 7bit resolution, feeding an 8bit
PWM, as they can add together to get a max of 255.  If I use two
separate channels, I can increase them to 8bit.  Not a huge deal for
the sounds I'm producing, but would make creation, processing etc much
easier. 

Lee

-------------------------
Msg sent via Webmail - http://hosting.myob.com/

Re: [OT] jumpstarting takes a few minutes of "charging"?

Dwayne Reid — 2012-05-16T00:15:10


Yep.  The starter needs significant current to operate.



Also Yep.  A discharged Lead-Acid battery that is otherwise in good 
shape (not sulfated) has an extremely low impedance and will consume 
just about as much current as you can give it.  That causes 
significant voltage drop in the jumper cables, which contributes to (1) above.



A battery that is being charged at a high rate gives off Hydrogen 
gas.  You want to keep sparks as far away as possible from that gas.


I had an unfortunate incident during High School where I was in close 
proximity to a rather large car battery that was being charged.  The 
charging lead became dislodged somehow and the battery promptly 
exploded.  Luckily, the lab was in fairly close proximity to the Gym 
showers and I was quickly dragged to where I could be rinsed off.  No 
damage done, other than to clothing.  Large holes did appear <grin>.

dwayne

Re: [OT] Looking for Linux expert

smplx — 2012-05-15T23:45:14


On Tue, 15 May 2012, Neil Cherry wrote:


"Damn this dirty T shirt. I could have sworn the 'i' was an 'f' in that 
'rm' command"

:-)

Regards
Sergio Masci

Re: [OT] Looking for Linux expert

Neil Cherry — 2012-05-15T22:51:53

I *Like* that a lot. It's also properly positioned for when you
really need it!

Re: [OT] Looking for Linux expert

Tamas Rudnai — 2012-05-15T22:22:43

Hello Dwayne,

What was the problem like? VI could not open the file, or could not save
it, or need a crash course on vi?

If could not open or save the file, what did it say? Do you need super user
(root) privileges for editing these files? With an "ls -l path/filename"
you can check that...

VI crash course:

The basic concept of VI is that you can use it on very very old terminals
with no modern keys on it like arrows and insert key etc.
It has several modes, but the default is the navigation mode, so using
h,j,k,l keys you can place the cursor pretty much anywhere. 'w' and 'b' are
jumping words and there are many many more for this.

To enter edit mode you typically type 'i' or 'a' and from that point you
can type. When finished press <ESC>. 'a' is for Append, 'i' is for
Insert... With 'o' you can create a new line and start typing a text. If
you would like to replace a word, type cw you are replacing a word (change
word). Do not forget the <ESC> key after editing, that changes back to the
navigation mod