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1846  Using Arduino / General Electronics / Re: Why use 2 decoupling capacitors? on: August 30, 2012, 10:22:50 pm
In my few years at the Electronics... I don't believe I have Ever seen a board fail due to too many Bypasses,, But I've seen a bunch that failed because of too few and more than a few of mine suffered that initial condition.
Having said that I utterly fail to find any sense in deciding how few you can get away with using in a design. The parts cost much less than the possible time figuring out why it doesn't behave "exactly" the way you thought it should. MY Very simple Rule is a 100 to 330 uF electrolytic at the Vcc connection, a .1uF cap per Ic and a 10uF cap for any board and increased by one every 3 IC's.
What Hasn't been mentioned well here is the inductance of the power supply leads and more important the traces carrying power on the PCBI. It's like a whole series of little inductors... in series with both power and grounds distributed across a board.
The Very best boards I Ever worked on had 4 layers top and bottom were grounded, more as an EMI shield that anything else, there was a Vcc plane, Split as necessary for ADC's and other more sensitive or low noise devices and an internal ground plane, Granted they were early Military stuff but there were no board issues and they were high speed synthesized radio PCB's... with 100 Mhz system clocks.
My design philosophy is very simple... You Don't have to populate the pads and holes... But it is sure hard to "Stick" em on later.
Place the parts on the board or at least the footprints... Stuff them all on the first copy and then remove the ones you think... extra, and see that your power supply is clean with an O'scope... If not start putting them back until it is.


Doc

Doc
1847  Development / Other Software Development / Re: [MOD] Arduino Enhanced Release 1.0.1B for Windows (installer, drivers, etc) on: August 30, 2012, 05:08:37 pm
Where is the "New Code" the "New shiny WINAVR"... I downloaded the Aug 13 version...

Doc
1848  Development / Other Software Development / Re: New Library for BiColor LEDs on: August 30, 2012, 04:52:37 pm
I apologize for "loosing" you but my "Rant" was about users that ASSUME that they KNOW everything.
If for example, you consider a 60Hz 10V PP signal... AC Right?, NO WRONG, a repetitive signal of 10 Volts amplitude only... repeating @ a 16.67 Ms interval.
The AC signal requires a reference of +5V. to recover the "Negative" part. It is still a 10V PP signal.
The basic concept of AC is a negative going signal... A Voltage that alternates polarity.
However polarity is a thing related to a "reference" point, usually 0 volts.
The point is that this signal Will pass through devices made for AC only.
Your alternating dc voltage will pass through a transformer... DC won't. Even a single pin from an Arduino coupled through a capacitor
with a repeating pulse present will pass both the transformer and the capacitor and be present at the other transformer winding... DC won't.
The capacitor isn't required but I included it to drive home the point about AC vs DC.
So it clearly isn't DC any more. To prove it is simple. It requires an external "reference" a pair of equal value resistors from Vcc to ground.
Measure from the center point of the resistors to the pin outputting the "Pulse" you will measure an AC 5 V PP signal.... at least on an Oscilloscope.
A DVM  will "average" or really mangle the signal But it is AC.

Doc
1849  Development / Other Software Development / Re: New Library for BiColor LEDs on: August 30, 2012, 03:31:22 pm
Pulsating dc and ac are the same, a variable flow of electrons. The primary difference is the "Reference"... If "AC" is "Referenced" from the most negative level them you could say "It''s Just pulsating DC.
Whether it is sinusoidal, square rectangular (duty cycle not 50%) triangular.
Come to think about the definition a little and you will see that the prime requirement for AC... The one Difference that sets AC apart from noise is just Periodicity.
It is the periodicity that sets it apart and allows it to do useful and predictable work is it's periodicity.
If you put in place a device that passes AC only, a capacitor or a transformer will pass your "DC" very well.
As to the library it does produce a signal that makes the LED light up Yellow... So the difference is?.. The LED works the same as if it had AC on it
Just the point of reference... Put it in the right place and your "DC" signal becomes "AC".
Place a diode in series and you remove 1/2 of the DC signal... Just as a diode would with AC... and you have DC again... pulsating but of one polarity... The signal cannot pull down when the input goes to it's lowest point because the diode will not conduct in the reverse direction.

Doc
1850  Using Arduino / General Electronics / Re: Driving a high power transistor on: August 29, 2012, 11:27:29 pm
A handful of BS170's, 2N7000's, or VN2222's are great too.

Doc
1851  Using Arduino / General Electronics / Re: voltage divider calculations on: August 29, 2012, 09:41:52 pm
That is the Finest Kind of learning... Also the way I've worked out Many, many different issues... I usually do my finest work in the shower... and I used to go to work with most of the previous day's issues worked out.

Doc
1852  Using Arduino / General Electronics / Re: Resistor Color Code Finder App on: August 29, 2012, 09:28:04 pm
Lefty, I agree with you 100% There is a great color code reference in Chapter 22 of the ARRL handbook...
Table 22.4
Resistor Color Codes
Color Significant Decimal Tolerance
Figure Multiplier             (%)
Black 0             1 { ? (0) }
Brown   1 10     1
Red      2 100    2
Orange 3 1,000
Yellow  4 10,000
Green  5 100,000                 0.5
Blue 6  1,000,000                0.25
Violet  7 10,000,000            0.1
Gray   8 100,000,000           0.05
White 9 1,000,000,000
Gold                   0.1         5
Silver                 0.0         10
No color                          20
This is a rough cut and paste from the handbook but the information has been in the "Public Domain" for so long, I have no issues with repeating it
There will not be a 3 or 4 band resistor with a 3rd band greater than blue or 000000 6 zero's. Not in the EIA standard list.
There is a big bunch of resistors that can be purchased from Amazon, for $29.00 you get 4550 resistors, All 1% metal film and Blue bodies, that for my old tired eyes, even with one of those headband magnifiers @ full strength... makes me grab my Fluke 179... just to make sure.

Doc
1853  Using Arduino / General Electronics / Re: SMD variant of the RFP30N06LE on: August 29, 2012, 08:18:02 pm
I Quote from the Fairchild sheet I enclosed...
Quote
N-Channel Logic Level Enhancement Mode Field Effect Transistor
However had you read the next 3 pages and paid attention to Vgth you would have noted that .8V was enough to cause a 1mA current to flow, and had you looked at the graph on page 3 top left side of the page you would have seen that 2.5V Vg @ 1V Vds was enough to cause 400 500 mA to flow... Clearly a good part for a 150 mA load... from 3V3 logic too.
The mistake iis easy enough to make If your electronics knowledge is spotty... The rest of the data sheet is quite clear however. That's why there are characteristic curves for the device on the other pages.
I was Very surprised that you chose to ignore the "Logic Level" Statement at the top of the page. And Yes certainly a ULN2003 will work, with 6 unused sections and some other drawbacks as well... Vcesat
is about 1.5V Vs  40 mV for the Mosfet... @ 500 mA for the '2003 and 150 mA for the BSS138 so they aren't quite in the same class... The '2003 was originally developed as a Print head driver for the old "Dot Matrix" printers. Many years ago... Thus only 7 drivers, the eighth pin was part of the character spacing. and not used except in a few of the real "Letter Quality" printers Panasonic KXP1135 is one and I still have one stored in my garage that is nearly new... One of the very few besides the Okidata model 82 that could do 7 part NCR forms.
Like C and C++ reading a data sheet requires that you understand what you read... at least a little.
If I was too hard on anyone I apologize. I read the data sheet carefully before I said it would work fine.  The comments about the other Fet and the subsequent recommendations for "Driver IC's" were really out there
Much like using a 10 kiloton bomb just to kill the flys in the back yard, Workable but hardly desirable.
I have been doing Engineering for about 30 years total and I WILL NEVER make a recommendation that won't work... or for that matter one I haven't already done.
I would be really ashamed of myself for telling someone something that was clearly wrong.
If I ever say I don't know... it's because I couldn't get the information or figure out how to solve the question at hand...
Some questions I don't even bother with... because there are too many "Experts" involved already.
If there are any other questions... pm me, i Will answer as quickly as I see the email notification. I hope this helps... a little

Doc
1854  Using Arduino / General Electronics / Re: SMD variant of the RFP30N06LE on: August 29, 2012, 12:10:08 am
Did you read the data sheet AT ALL?. The BSS138... Data sheet enclosed. Btw did you read what the OP wanted to do with the FET?... Something about a 150 Ma Light???
Quote
That link is to a MOSFET that is nothing like the RFP30N06LE - it has a max drain current of 0.2A rather than 30A, an on resistance of 1.4ohms not 0.047 ohms, it requires 10V of gate drive to turn on properly (not 4.5V).
                    Not quite it is a LOGIC LEVEL MOSFET...
The OP wasn't looking for a 30A SOT23 package... just a little bitty Mosfet for a pilot light...

Quote
I'm wanting to make a SMD version of this. I need to turn a 12 volt light on/off that draws about 150 mA.
(OP's FIRST POST... it's the caption... Under that BIG picture of the Mosfet.
This device would WORK PERFECTLY FROM A 3V3 Logic output... The first requirement for an "Expert..." is the ability to read a data sheet... Before you quote a worthless opinion. IMHSHO

Doc
1855  Using Arduino / General Electronics / Re: Motor driver problem, do I need more capacitors? on: August 28, 2012, 05:10:40 pm
Lucky you didn't let the magic smoke out of the power supply supervisory circuitry .... That could well have let the magic smoke out of Everything else connected to the power supply too. It's usually the 5V source that supervises everything else, If the math behind the transformer design is right all will be fairly well controlled by controlling the 5V high current output. As to Capacitors I'd use the biggest one that fit 10KuF or .01F would not be out of line... At least on something I would build. a 10,000 uF cap isn't really very big even at 35V working voltage.

Doc
1856  Using Arduino / General Electronics / Re: Driving a high power transistor on: August 28, 2012, 04:59:14 pm
Not So... With a Darlington the base drive would be on the order off 10 mA X 1000 (Hfe) = 10A. A 330 ohm base resistor and a TIP140 is a 10A NPN Darlington with a Min Hfe of 1000. The real issue is that it requires 1.4 volts base to emitter to fully turn it on. A single device solution with one 1/4 watt 330 ohm resistor. If the Emitter of the transistor is grounded... I would run a small wire from the 12V ground to the transistor emitter to your Arduino and keep the other wiring to the transistor and load separate form the Arduino. You really don't want the ground current for the high current load to flow in the Arduino ground path. A wire from the Arduino ground to the emitter of the power transistor (return) and a wire from the switched port to the resistor connecting to the base of the Darlington transistor (control).

Doc
1857  Using Arduino / General Electronics / Re: SMD variant of the RFP30N06LE on: August 28, 2012, 04:38:59 pm
Keep the total dissipation below the Fet limits and you should have no trouble... The only real concern is the Vgth of the mosfet... which will usually allow 100+ mA @ 3Vgs which would be my worst case assumption. Based on the "Assumption" that you are using a "regular" Arduino and not one of the 3V3 variants... Then I would be REAL concerned that the Vgth be less than 3 volts... 2V - 2V5 being in the OK range.

Doc
1858  Using Arduino / General Electronics / Re: Best Anti-Static Soldering Mat? on: August 28, 2012, 12:36:53 am
I actually did loose one and only one... it was a windy dry day, I walked into the lab from lunch and poked my finger into a board I was cycling off and on... Everyone in the room heard the snap as my finger discharged through a gate package... Never again but it Can happen although I do agree an ic is relatively safe there... In the board... Now If I could just keep from dropping crap on them... Solder is my great enemy, clean the iron and the bits are guaranteed to go to the PCB... Especially If it's Sunday and the shops where the Real parts are sold... Are closed.

Doc
1859  Using Arduino / General Electronics / Re: Current limiting a RGB-LED on: August 28, 2012, 12:28:06 am
If you replace the Zener with a TIL431 and a 10K pot wiper to adj cw to cathode and ccw to anode you would have a variable current generator. and an NPN Darilinton would give some real current although it might require more than 10-12 Volts to insure compliance over the full range and remember the small one, 2N3904? is only good for a hundred mA or 325mW dissipation. bforeee the magic smoke gets away...

Doc
1860  Using Arduino / General Electronics / Re: Need some help with the concepts of pull-ups/downs. on: August 28, 2012, 12:14:53 am
Well Young Man, It has been my experience that any reasonable education will come in handy, sooner or later... My biggest fear is that I will forget which answers the questions are for... Think about it. My Very last rant on pull downs, I promise other that to question once in a while... Is that I take a different approach... Kill 'em All and let no one but me.. When I am doing something new I usually use 470 ohm "terminators or pull up/down's... I never really worry about current drawn, I use op-amp Voltage followers on analog measurements and when I am through I start the real engineering and that is to remove components until it's operation is either departing from the design spec's or has flat quit... Put that part back and then test it and try to break it... whatever you can think of that it might see in use... If it works good it's good enough to field test... Maybe many times I have had a piece of equipment fail miserably in the field after heat and cold testing both heat soaked and transitioning between hot and cold... Just roll over and die from something I thought could never happen... about 90% of the time. Granted many seem really out there... as far as time and parts, knowledge and experience... have taught me to remember that "Murphy Was an Optimist". What I recommend here worked for me or I wouldn't advocate it. However there is one real final teacher that few of us know to heed regardless of exposure... Pain is the real teacher... It's the one we knee jerk remember rather than the intellectual or reasoning parts we like to think we use...did you ever wonder why people stick their fingers in light sockets... at least once? it's simply because they have been told not to... By someone who was told not to... Why would I want to go to the trouble of finding one to begin with?
Actually that isn't really fair however it might be true... we do things like that because we are constantly testing our boundaries... That's how we learn.
I can't remember but one board I ever produced that went into production with anything as small as 470R But I do use them until I know that the noisy thing I am concerned about is under control.

 I use them and the lesson that taught me their use went out with spare pins tied high or low. It was also the only project I ever put in a nema plastic enclosure... Steel after that. Again I've wasted a perfectly good space somewhere with my blathering... IT Was Fun though. IMO

Doc
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