On 3/5/2016 6:47 PM, firstname.lastname@example.org wrote:
Exactly. A car isn't like a PC -- there are LOTS of little processors
scattered around the vehicle. Often, designed by different groups
and pieced together. Legacy systems being used in places where a
complete redesign wasn't considered necessary.
Does each little box keep it's own settings? Do they expect some
"master" to provide "configuration data" that they can use? When?
each time the ignition is switched on? Each time a door is opened?
Each time "fresh power" is sensed?
El cheapo microcontrollers may have very tiny amounts of nonvolatile
memory -- often with strict limits on how often it can be erased/rewritten.
So, while the controller that draws all those pretty graphics on the
screen for you may have significant horsepower, the one that remembers
your mirror position may be a real dog!
Wanna bet even the dealer doesn't know the fine details? ("Which version
of the software are you running...?")
Virtually none of the settings are easy to re-set. You have to scan
for stations to *find* those that can be received in your current
locale -- for AM, FM and XM. Then, have to decide which of those you
want to save as your presets. Your spouse has to repeat the exercise.
If any of your presets are from your "vacation home" or out-of-town
workplace, you can't set them until you are AT those locations.
Readjusting seat and mirrors takes time -- plus telling the car to
"store" those settings.
Typing in the names of each GPS "destination" using a touchscreen
keypad. "Hmmm... what's Bob's address? I can't seem to SEARCH for
'Bobs House'..." Do you even remember what all of the destinations
Drag out each of your cell phones and pair them with the vehicle.
Any BlueTooth headsets? Transfer your telephone books to the vehicle.
Plus all of the "optional configuration" stuff. "Hmmm... did I have the
autoheadlight sensitivity set to LOW? Or MED?"
And will you remember that you want the "Auto Door Unlock" setting to
be "Off" instead of the default "All Doors When Driver's Door Opens"?
(Because the default would allow someone standing by your passenger door
in a secluded parking lot to let himself into your vehicle despite
the fact that you are rushing to gain the security of that vehicle
for JUST yourself!) Yet, you want the "Key and Remote Unlock Mode" to
be "All Doors" instead of the default "Driver Door" (think about it)
Do you even remember the procedure to set each of these? Or, will you
be scrambling to paw through 500+ pages of "owner's manual" hoping
to track down each setting's explanation and method of setting?? Or,
pestering the dealer for help?
[Our _Owner's Manual_ is ~450 pages. The _Navigation Manual_ is
almost the same size. The _Owner's Guide_ a mere 150!]
On Saturday, March 5, 2016 at 9:27:47 PM UTC-5, Don Y wrote:
Irrelevant because those microcontrollers don't have individual
security codes. Off to the wilderness again.
Taken car of by the car manufacturer.
The dealer doesn't know the fine details because they don't need to.
How to enter a security code for the radio, or some master security
code for the theft deterrent system, that they would know.
Yawn. Maybe on you're car. Last IDK how many cars I've owned,
the radio remembered the presets when power was lost. After all,
the non volatile memory necessary to do that costs about 10 cents.
The only thing I have to enter on the BMW X5 is the date and time.
Show us the car example where all that is lost when power is interrupted.
And I'll show you a car company with no customers.
On Saturday, March 5, 2016 at 11:50:44 AM UTC-5, Sam E wrote:
Assuming "ECU" means the emission control monitors or engine computer,
there are no security codes for it. Some cars might have a security
code for the radio, the owner's manual would cover that. I can tell
you the BMW x5 here, there are no codes. After a loss of power, only
the date and time need to be set.
Current "memory that can hold its contents during a power outage"
is FLASH (in ages past, there was core, bubble, BBSRAM, MNOS, etc.).
FLASH has limited write cycle performance -- you can't read and write
it "casually"; it "wears out".
Additionally, writing FLASH takes a LONG time (in terms of CPU
time -- like thousands of times slower than writing to RAM).
And, you must have recovery algorithms in place in case the write
*fails* (which means it can take even LONGER)
So, using FLASH means a more involved data retention strategy:
- keep "working" copies of all data in (volatile) RAM
- periodically (when?) flush those values to FLASH (for safe keeping)
- if the working copies are "suspect", reload them from FLASH
- verify the integrity of data stored and retrieved to/from FLASH
Deciding when to move things into/out of FLASH becomes a separate
design challenge; what if two values are related to each other
in some way? Then, you must ensure you move BOTH of them into
(or OUT OF) FLASH at the same time. Otherwise, you risk the
system getting confused (inconsistent state).
Then, you have to decide *where* the data will reside, physically.
Which of the 10, 20, 30 little "smart boxes" (CAN nodes) scattered
around the vehicle will hold each datum? And, as those boxes can
be replaced, over time, how do you ensure the data they contain
remain pertinent? Or, are automatically invalidated ("Hey, this isn't
the same car that I was in last time I was powered up!")
OTOH, just letting all of the data sit where it would NATURALLY want
to sit -- in RAM (which is actually BBSRAM -- "Battery Backed"!)
eliminates a lot of these issues.
Take the disk drive out of your PC and you remove an entire
layer of software from it!
On Sunday, March 6, 2016 at 1:57:20 PM UTC-5, Mark Lloyd wrote:
Apparently there are some here that don't think so. Not only has that
memory been around for a long time, the cost of it to hold some trivial
settings is probably 10 cents. Let's see, spend 10 cents on a few
bytes of memory or have inconvenienced, pissed off customers? What
would Jesus do?
The opposite problem exists, there. Most (inexpensive) things designed
to charge (big!) batteries do so by simply ensuring they can develop a high
enough open circuit voltage to "push" current into the targeted battery
(i.e., more voltage than the nominal CHARGED voltage of the battery).
They typically have no "smarts" to tailor the charge current to the
actual sensed state of the battery (i.e., limit the amount of current
when the battery is low and taper/cut off the charge current when the
battery reaches "full charge" (over charging a battery shortens the
life of a battery).
Instead, they are usually simple "trickle chargers" -- a voltage source
behind a current limiting resistor (sets maximum charge current).
Often, that "limiting resistor" may be the windings of the transformer!
As big batteries have lots of "electrical inertia" (bogus term), this
arrangement works out OK -- the battery dictates how the charger operates
because it is so much more "massive" than the charger's capabilities.
The charger just gets a little warm as it's struggling to coerce the
battery to raise its float voltage.
Because the battery has so much say in the matter (very low impedance),
the charger doesn't need to be filtered *or* regulated -- one or more
diodes to insure the output of the charger is always "positive"
(instead of "AC"). Instead of "pure" DC, you end up with half (or full)
-wave rectified AC:
HALF __/ \____/ \____
\ /\ /\ /\ /\
FULL \/ \/ \/ \/ \
(the lowest point in each waveform is "0" volts)
But, the peaks in each of the above waveforms are typically higher
than the nominal 12V desired (14.4 charged?).
When you attach the charger to a battery, the battery smooths out
those peaks -- makes them *pure* DC (because the battery has such a
low impedance, it controls the circuit's behavior). Only over time
will the "DC" seen at the battery slowly start to creep up -- as
it accepts charge from the charger.
Eventually, the charger will try to push current into a FULLY CHARGED
battery and the battery will resist (a function of the chemistry of
the battery) -- dissipating that extra power as heat *in* the battery
(gas formation in some chemistries).
Without the battery in place, there is nothing to hold the output of
the charger at this nice "pure DC" level (dictated by the battery).
And, if the load represented by the rest of the car is tiny
(because you've deliberately turned everything off -- except for
the "quiescent currents" of the memory circuits and any other
circuits that remain powered when the car is "off" -- keyless
entry, burglar alarm, etc.) COMPARED TO THE CAPABILITY OF THE CHARGER,
then these peaks appear everywhere the "battery" signal is delivered
throughout the car.
So, you now have to imagine what measures each of the little bits
of electronics took to protect themselves from "high voltage"
appearing on their inputs.
And, what measures the charger manufacturer SKIPPED to ensure
its output always was "reasonable" -- given that it EXPECTS to
be connected to a battery!
I can, for example, design a charger that puts out *30V* with
"no load" but that has a high enough output impedance that attaching
it to damn near ANY 12V battery immediately causes that voltage
to appear as 12V (or, whatever the battery dictates). The charger
will keep hoping to drive the battery up to its 30V (which is when
the current would fall to *0*). But, I could rely on characteristics
of the particular battery(ies) being charged to never let that happen!
Unless, of course, there is NO battery present -- in which case,
you'll happily see 30V on the output of the charger!
I'd *guess* the charger you cited would work -- cuz the automotive
electronics designers assume the folks servicing these things aren't
rocket scientists and want to ensure there aren't nuisance problems
(because someone disconnected a battery cable before disconnecting
a *shop* charger).
OTOH, the folks making the charger (People's Cheap Battery Charger
Factory #884A) only marginally care that their product appears to
work IN THE APPLICATION FOR WHICH IT WAS DESIGNED. What recourse
do you have if something goes poof in the night?
[I.e., try using it as a 12V "battery eliminator/substitute" and
I'm sure you will be disappointed]
[[By contrast, a 9V "transistor battery" is 9V -- no "peaks" to
Might work, but some battery chargers will not continue to charge
without being able to sense voltage from the battery - even after you
get them "kickstarted" and voltage regulation on many cheap chargers
into a basically open circuit is next to non-exixtant - so who knows
how high the voltage might go.
There are battery minder/chargers that plug into the cig lighter that
would likely do the job - with the 2 aforementioned caveats to keep in
On Fri, 04 Mar 2016 17:36:34 -0500, email@example.com wrote in
Something I just thought of: On newer model cars, the cig lighter
receptacle is "off" unless the car is in the "on" or "accessory" key
position. ISTM that if the cig lighter receptacle of "off", none of
those charger or memory devices will work. Is that correct?
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
Yes. So, you have to put the car in ACCessory mode. As I mentioned
upthread, in our vehicle, that turns on all sorts of things (digital
dash, navigation system, etc.). So, you're suddenly powering
more than JUST the "settings memory".
A 9V battery sourcing tens of milliamps will last hours. That
same battery at an amp would last ~5 minutes. And, that assumes
its a "fresh" battery -- and, not one made in People's Really Good
Battery Factory #773.
Additionally, there's some concern over how power is switched/gated
to that outlet. Is it a mechanical switch (relay)? Or, a solid
state device (FET)? Did the circuit designers expect current to
flow *in* through the "lighter" socket?
Not aware of any vehicle that will not accept pwer in - not aware of
any vehicle where the "accessory outlet" (the device formerly known as
a cigar or cigarette lighter) is switched by anything fancy. - but
that doesn't mean they don't exist. - and more and more vehicles have
a non-switched "accessory outlet" somewhere in the vehicle.
On 3/6/2016 4:55 PM, firstname.lastname@example.org wrote:
Dunno. I haven't designed any automotive electronics for a decade.
But, back then, there was a growing concern for using "smarts" to
replace *wire*, moving to 48V systems, etc.
There are two "Power Outlet"s in our vehicle. Both are switched
(and, may, in fact, share the same 15A fuse!)
I've not yet purchased a shop manual so I can't tell, for sure,
how things are wired.
But, if *I* have to swap a battery, I'll drag out a lab supply,
program it for 12.0V, set the current limit to a few amps (to
be safe) and jumper to the battery cables (I'm not sure if
anything would get upset if I connected to the frame instead
of battery minus -- as *something* is watching current OUT of
On Sunday, March 6, 2016 at 2:34:45 PM UTC-5, CRNG wrote:
If it's off, then it's not going to work. I think many cars though still
have cig lighters that are on all the time, because people want to use
them to charge phones, etc while they may be away from the car.
You could still hook one of the devices to the car another way, like
at a jump start terminal, if it has one under the hood, etc.
On Thursday, March 3, 2016 at 12:47:23 PM UTC-5, Micky wrote:
Happens to all of my cars too. Even worse is when you blow them all away
I was out of town a few weeks ago and trying to find something to listen
to on the radio. I was using the scan feature where stations play for
about 5 seconds and then move on. If you like the station, you can press
scan again (within that 5 seconds) and the head unit stops scanning.
My Honda also has a button that will lock in the strongest local stations,
filling up FM1, FM2 and AM. 18 stations in all. That button is right next
to the scan button. Guess which button I pressed when "scan" found a station
that I liked and I quickly tried to press the scan button to stop the
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