<DocScrutinizer05>
actually for *electrons* (physical direction pragma) it would be push and pull swapped. At least that's what I consider "push" and "pull"
<DocScrutinizer05>
(seen from pin3)
<nicksydney>
so if i change "“Holes” are push and pull around" to "electrons push and pull around" makes more sense ?
<DocScrutinizer05>
unless you write from a C3 point of view. then you could say C3 pushes electrons to V+ and pulls them from ground. But usually it's the active component (NE555) for which the activities are defined
<DocScrutinizer05>
the one's push is the other's pull ;-)
<DocScrutinizer05>
whe I push you, you may say you pulled me
<nicksydney>
yeah i'm more inclined to view it from the NE555 point
<DocScrutinizer05>
ooh, and actually not holes but electrons are "moving from ground to C3"
<nicksydney>
will be a useful reference for myself down the track as will not be able to remember everything i learned :)
<DocScrutinizer05>
:-)
<nicksydney>
the whole exercise of learning this circuit is because i'm thinking of making RA8875 driver board...and one of thing that really confuse the hell out of me was producing the different voltage required for the Backlight
<DocScrutinizer05>
aaah yes
<nicksydney>
the board will have RA8875 for interfacing with 4.3inch screen + BLE (for communication to Android) + temperature + barometer and for MCU was thinking M3 or M0
<DocScrutinizer05>
best you forget about electrons (and even holes) and just think "current" (keeping in mind this is technical current pragma, + -> - )
<DocScrutinizer05>
current always flows from + to minus, or from higher to lower voltage, whatever fits your model best
<DocScrutinizer05>
only for electron beams in CRT ans the like, you need to know the electrons actually come from minus and move to plus
<nicksydney>
DocScrutinizer05: ok got it...will think about it as just normal current going from + to lower voltage
<DocScrutinizer05>
but even experienced EE usually don't bother about electrons
<DocScrutinizer05>
actually often I tend to forget when I better should remember
<DocScrutinizer05>
e.g. when pondering highly obscure stuff like electromigration (electrons bouncing metal atoms along the wire, literally!)
<nicksydney>
because this schematics http://postimg.org/image/o370v7dvz/f3d8104a/ shows that there is VLED+ and VLED- which makes me think need to understand about producing negative voltage and that's where i learned the termed 'Charge Pump' so it eventually brought me to learn about using 555 to produce negative voltage to understand the basic
<DocScrutinizer05>
seems to me like VLED- is pretty standard connected to GND
<DocScrutinizer05>
no need for negative voltage in there
<DocScrutinizer05>
*usually* GND = V-
<nicksydney>
ahhhh.....right....that's why when i was looking at that schematics again and trying to put the pieces together i realised that there is no diode present for the negative voltage
<DocScrutinizer05>
there's just a resistor for sensing the current
<DocScrutinizer05>
R8/R9
<nicksydney>
what is "sensing resistor" used for actually ?
<nicksydney>
DocScrutinizer05: so "*usually* GND = V-" does that mean that when the backlight is connect the connection will be the VLED+ for BL+ and GND for BL- ?
<DocScrutinizer05>
L4 and D2 create a high (relative to input) voltage to feed backlight VLED+ with it. On R8 there's a small voltage (some 0.x Volt) proportional to current through LEDs, and the chip U4 is sensing that via pin3/FeedBack
<DocScrutinizer05>
nicksydney: the connections are like shown in schematics
<DocScrutinizer05>
U4 is specialized chip to drive backlight
<nicksydney>
yeah i was thinking of replacing U4 with TPS61040 as that AIC1896 is not easy to get ... but again i could be wrong
<nicksydney>
R5 and R8 is a voltage divider correct ?
<nicksydney>
while R9 is to limit and pull current to GND ?
<DocScrutinizer05>
pin1/LX pulls current through L4 to store energy in that inductivity. Then U4 switches pin1 to open state, so the inductivity creates high voltage pushing through D2 into C23/21
<DocScrutinizer05>
yes, basically that's a voltage divider. But R8 and R9 (if populated) are parallel and can be considered one
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<DocScrutinizer05>
(voltage divider) here it doesn't serve that purpose. The purpose of R5 is to make any current going through Zener D4 (when voltage > maybe 13V) immediately pull up U4:3 to stop the oscillating of that chip and thus reduce output voltage it creates
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<DocScrutinizer05>
so basically R8 and R8 pull current to GND
<nicksydney>
ahhh ok let me see if i get this right.....when current flow from FB and since R5 and R8 is connected to GND ...the current is "pulled" towards GND by the resistor which leaves less current to be "pulled" via D4 ?
<DocScrutinizer05>
no
<DocScrutinizer05>
FB is an input
<DocScrutinizer05>
D4 is normaly highimpedance aka "open"
<DocScrutinizer05>
simply forget it for now
<DocScrutinizer05>
voltahe upper end of R8/9 goes higher the higher the current
<DocScrutinizer05>
this voltage goes to FB input via R5
<DocScrutinizer05>
when voltage goes too high, U4 reduces frequency to regulate the current to LEDs
<DocScrutinizer05>
that's normal operation
<DocScrutinizer05>
now think something strange happens and voltage on VLED+ (and top of D4) rises above any sane limit to maybe 13V or more
<DocScrutinizer05>
D4 is a Zener that "closes"/connects the path for electric current when voltage along D4 goes >12V (that's why it's written there)
<DocScrutinizer05>
current flows from VLED+ resp C23/D2 to D4, through D4 and directly into FB
<DocScrutinizer05>
FB sees very high voltage and immediately stops activity of U4
<nicksydney>
"current flows from VLED+ resp C23/D2 to D4, through D4 and directly into FB" so it means that the Zener Diode "REverse breakdown voltage" can be reached ?
<DocScrutinizer05>
yes, exactly
<DocScrutinizer05>
on >12V plus whatever voltage is at lower end of D4
<nicksydney>
now this is interesting.....as learning something new again :)
<DocScrutinizer05>
:-)
<DocScrutinizer05>
afk o/
<nicksydney>
so the current 'push' and 'pull' between D4 and the FB uses that to determine when to 'supply' more current or not
<DocScrutinizer05>
there's no push/pull between D4 and FB. FB is an imput
<DocScrutinizer05>
1/LX is the active output of U4
<nicksydney>
ok let me go this step-by-step....
<nicksydney>
1/LX will provide current and the current flows 'through' D2 to supply to VLED+
<DocScrutinizer05>
LX connects to GND to increase current through L4. Then it does stop the current (high impedance) and thanks to "inertia" the current in L4 has to go through D2
<DocScrutinizer05>
so LX pulls current through L2, and L2 then pushes current through D2
<DocScrutinizer05>
this cycle happens like 1 mio times per second
<DocScrutinizer05>
and less often when FB goes high enough, so current through LEDs gets reduced when it's going too high
<DocScrutinizer05>
(actually it might adjust time of LX pulling, instead of frequency LX is pulling)
<DocScrutinizer05>
effect is the same: current reduction
<nicksydney>
so when this happens --> "and less often when FB goes high enough, so current through LEDs gets reduced when it's going too high" .... that's the time when the voltage will be higher than 12V and reverse voltage of D4 happens and this makes current "flow" through D4 but the R5 and R8 resistor limit the current for the FB pin..is that correct how my thinking is ?
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<DocScrutinizer05>
without R5 the current through D4 would go straight to ground via very low resistance R8/9
<DocScrutinizer05>
thanks to R5 the FB input goes high level very easily as soon as D4 allows a small current to flow
<nicksydney>
DocScrutinizer05: so R5 is there to make sure "some current" does not flow through directly to GND so as can be picked up the signal by FB
<DocScrutinizer05>
yes
<DocScrutinizer05>
we want volatge from R8/9 on FB, for current feedback, but we also want allow D4 to immediately and efficiently "shut down" the device when overvoltage detected on VLED+
<DocScrutinizer05>
R5 allows voltage from R8/9 to go to FB with little attenuation (FB is very high resistance input), but doesn't allow all of current through D4 (when overvoltage) vanish directly to GND via R8/9
<nicksydney>
I understand the part that current flows through D4 and R5 "stops" some current from goingt o GND to be picked up by FB but I'm lost when you say "R5 allows voltage from R8/9 to go to FB "
<nicksydney>
i think the question that my head is ringing with "Where does the voltage from R8/R9 comes from as current are trying to push itself all to GND" ? :)
<nicksydney>
sorry if the question sound stupid :)
<DocScrutinizer05>
when current flows along a resistor, it creates a volatge along the resistor. This means for 100mA via LEDs there will be +1.2V (vs GND) on upper pin of R8/9
<DocScrutinizer05>
those 1.2V go straight to FB, via R5
<DocScrutinizer05>
it's not like current has a direction and needs to break to make it through the curve towards R5
<nicksydney>
i see....so current has a destination and voltage does not have any ..methamorphically speaking
<DocScrutinizer05>
hmmm, I have to ponder this, it#s not easy for me to understand :-)
<DocScrutinizer05>
it might be correct but I haven't understood it completely yet
<DocScrutinizer05>
may it helps when you compare a electric circuit with your heating pipes and radiators and the pump for the water
<DocScrutinizer05>
some radiators may be parallel to each other, others may be in series
<DocScrutinizer05>
the battery or power supply is the pump creating some pressure difference
<DocScrutinizer05>
the on/off-valves are resistors
<nicksydney>
"pressure difference" that's the word i was looking for...yes that makes sense ...because FB has less pressure the voltage "move" to that pin ?
<DocScrutinizer05>
also the radiators are rsistors
<DocScrutinizer05>
yes, some electricity moves there, but since it's a dead-end pipe basically that omly has a pressure gauge mounted to it (FB input), not much electricity is flowing through the R5 resistor to FB, and at FB you already have same pressure like at top pin of R8
<DocScrutinizer05>
for the pressure to propagate, not much volume has to move around, so any valve/resistor that's in there will probably not matter much since not a whole liter of water flows through it. It's more like one ml per minute that gets lost somewhere in pressure gauge
<DocScrutinizer05>
basically zero current is flowing
<DocScrutinizer05>
via R5
<DocScrutinizer05>
when D4 eventually "opens the valve", *some* water will flow via R5 down to the huge GND pipe and back to the pump, but the pressure on upper end of R5 will be hig, compared to lower end of same R5
<DocScrutinizer05>
if R5 wasn't there, all water would go straight to R8 and GND and not much pressure would be seen at FB
<DocScrutinizer05>
I mean if R5 was a straight pipe (aka wire)
<nicksydney>
gotchat
<nicksydney>
*gotcha
<DocScrutinizer05>
without any connection otoh the pressure at R8 couldn't get to FB at all
<nicksydney>
so with connection that is there (R5) the pressure was slow down so it can reach FB
<DocScrutinizer05>
*theoretically* we could also use an ideal diode instead of R5, that would only let current flow from R8 to FB but not the other way round
<nicksydney>
so that's why PIN3 is connected between D4 and R5
<DocScrutinizer05>
but there are no ideal diodes, they always bite a bit out of pressure/voltage even in forward direction of current. Usually ~0.7V
<DocScrutinizer05>
and diodes are more expensive than resistors
<DocScrutinizer05>
and then there's also some non-ideal parts in D4 behaviour, it might not be completely "tight" even on voltages lower than Zener voltage
<nicksydney>
what will happen if PIN3 was connected between R5 and R8 ?
<DocScrutinizer05>
as long as this leak is negligible compared to the flow of current that R5 allows to drain to GND, it doesn't matter
<DocScrutinizer05>
then overvoltage protection would not work at all
<nicksydney>
my best guess is it will not be picked up by FB
<DocScrutinizer05>
when PIN3 was connected between R5 and R8, then overvoltage protection would not work at all
<nicksydney>
because the voltage between R5 and R8 is very high for FB ?
<nicksydney>
"<DocScrutinizer05> those 1.2V go straight to FB, via R5" ... is that the 1.2V ?
<DocScrutinizer05>
current via R8 would increase *marginally* when D4 opens up completely, since R5 limits the current to insignifican amount. Thus voltage across R8 wouldn't increase any noticeable amount, and thus FB doesn't see any change
<nicksydney>
ahhh so i was correct :) ... the FB does not detect any changes and like you say the overvoltage protection would not work
<nicksydney>
got it !
<DocScrutinizer05>
so D4 and R5 are useless when FB is connected to R8
<nicksydney>
ok ok now i see
* nicksydney
jumping like a rabbit as he can see how things works now
<DocScrutinizer05>
:-D
<nicksydney>
it's complicated but yet easy to understand !
<DocScrutinizer05>
yeah, this actually is a nice educational circuit
<DocScrutinizer05>
it shows a few concepts
<nicksydney>
for newbie like me all circuit are educational circuit :)
<nicksydney>
so that means there is no point having R9 as R8 (changing the value) will be more than enough ?
<DocScrutinizer05>
yes
<nicksydney>
in terms of selecting the correct R value normally how do you go about determining it ?
<DocScrutinizer05>
as long as the value is correct to create the right FB volatge when current through LEDs is nominal, it doesn't matter if it's one or two parallel resistors
<nicksydney>
i mean if you have to start designing this kind of circuit how to determine what is the correct resistor value to use ?
<DocScrutinizer05>
determining R8: find datasheet for U4. It has a formula that goes like: FB-voltage must be 1.3V, so for 100mA you need 13 Ohm, according to I*R=U rsp R=U/I
<DocScrutinizer05>
U=1,3V, I=0.1A, -> R=13Ohm
<nicksydney>
so normally in the datasheet it does tells you that if say for example you use L4 with 10uH you will get 100mA and then you can use that current value to calculate the voltage required to get the resistor right ?
<DocScrutinizer05>
when FB volatge must be 1.1V (datasheet needs to tell you), then your R is 5.5 Ohm for 200mA
<DocScrutinizer05>
L4 is fixed by design of U4 basically. They will tell you what L4 type to use
<DocScrutinizer05>
it's not really related to current you want to get for your LEDs
<DocScrutinizer05>
that circuit is for regulated output voltage, for backlight you need regulated output *current*
<nicksydney>
ahhh we need "regulated output current" to control the amount of current that are available for the LED as we don't want too much current as that will create problem...got it !
<DocScrutinizer05>
and the 6.8uH is for very low output current, the diagram says 10V@15mA
<DocScrutinizer05>
you need to study the complete datasheet, it wil have proper instructions how to use the chip and which external components to get
<nicksydney>
ok cool....going to write down what i learned today in my notes otherwise will forget again
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<eintopf>
nicksydney: cool
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* whitequark
ponders at "powdered alcohol" that recently appeared on the net
<DocScrutinizer05>
whitequark: congrats, your moscow streets get nicer now. Don't dare to think otherwise! The project manager clearly stated that those who don't like this project are not of a sane state of mind
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<whitequark>
apparently, ethyl alcohol trapped in cyclodextrin crystals
<whitequark>
DocScrutinizer05: what?
<DocScrutinizer05>
"official" graffiti
<whitequark>
what?
<whitequark>
what the hell are you talking about
<DocScrutinizer05>
"Putin" painting walls with graffiti showing Krim in russian colors, and of course the logo i´of his party next to it
<whitequark>
you clearly are informed much better than me
<DocScrutinizer05>
see? German TV news are not all that bad
<DocScrutinizer05>
;-D
<DocScrutinizer05>
I seem to recall they said "2000 walls"
<whitequark>
I do not watch TV of any country
<DocScrutinizer05>
I can well understand that
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<whitequark>
hmmm, so, powdered alcohol. I'd need α-cyclodextrin
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<whitequark>
sigma-aldrich is selling it for like 300EUR/kg
<whitequark>
apparently, I can make it myself with starch and some enzymes. α-amylase is going for $20/120ml, but their price list is weird
<whitequark>
now, I'd also need α-CGTase. not sure where to get that yet, hmmmm
<whitequark>
grmbl. no vendors here. alibaba otoh has some
<whitequark>
no, I don't need a *bucket*
<whitequark>
(╯°□°）╯︵ ┻━┻
<whitequark>
why can't I buy a completely trivial purified enzyme in reasonable quantities, is it 2014 or so
<whitequark>
why the fuck are we, as a society, focused on fucking rectangles with fucking displays
<whitequark>
gah
<whitequark>
won't work.
<whitequark>
fascinating: apparently, a pinhole camera performs a spatial Fourier transform on the incoming light
<whitequark>
I'm not sure I understand how that works
<nicksydney>
DocScrutinizer05: just put a sample oder from TI for the TPS chip let's see if they approve it for the project :)
<DocScrutinizer05>
hm?
<nicksydney>
going to design the pcb to test it on when it arrive
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<DocScrutinizer05>
ooh
<DocScrutinizer05>
good luck!
<nicksydney>
going to divide and conquer...once the power part is working than i will work on the RA8875 chip
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<nicksydney>
this is the block diagram for the board http://postimg.org/image/4xfx9luyr/3ebfbd85/ .. not my design ..this is from RA8875 demo board ... not going to use ROM in my design
<DocScrutinizer05>
whitequark: why do you want to build cyclodextrin (if that's the right name, I dunno). Seems that stuff is widely available for relatively low cost
<DocScrutinizer05>
and used in roundabout everything nowadays, like "Febreze air freshener"
<DocScrutinizer05>
also washing powder that claims to keep laundry fresh (read smelling) for 2 weeks
<DocScrutinizer05>
literally everybody and his dog is using that stuff for smart as well as nonsensical purposes
<DocScrutinizer05>
after all, when they already offer their own DDoS exploit, then way deny and reject it?
<DocScrutinizer05>
s/way /why /
<qi-bot>
DocScrutinizer05 meant: "after all, when they already offer their own DDoS exploit, then why deny and reject it?"
<DocScrutinizer05>
never waste an opportunity for an exploit borne from ignorant use of deprecated technologies
<DocScrutinizer05>
hmm, maybe I just need to tackle this a tiny bit smarter: "hey, have you recently checked the vulnerability of your FireFox? To check, set 'accept cookies: never' and then visit this pake: $URL. When after 60min the page hasn't detected the vulnerability in your FF, then it's probably safe to simply abort the test. Nevertheless redo every other week, new vulnerabilities could sneek in to FF with updates that get installed
<DocScrutinizer05>
automatically!
<DocScrutinizer05>
page, even
<DocScrutinizer05>
might fly
* DocScrutinizer05
wonders what's best channel to start this game
<DocScrutinizer05>
media channel
<DocScrutinizer05>
/.? reddit? some other silly fora? Twitter?
<DocScrutinizer05>
BOFH is quite inspiring sometimes
<DocScrutinizer05>
;-P
<DocScrutinizer05>
>>never waste a wrong connection<<
<DocScrutinizer05>
>>don't say 'sorry, wrong number', say 'Cindy? Cindy isn't available for you anymore! Cindy is completely pissed of you and I shall tell you to fuck off<<