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DonQ

Member Since: September 30, 2010

Country: United States

  • You forgot one of the most important things about "regular" LEDs (the ones without special blinking circuitry or UV-phosphorescent LEDs). That is taking advantage of difference between "Forward Current" (otherwise known as "Max Average Forward Current") and "Peak Forward Current". Some LEDs have "Peak Current" many times greater than "Max Average Forward Current". For example: An LED may have a "Forward Current" of 20ma and a "Peak Current" of 100ma. That means that if you are running it off of DC, then you do your calculations based on 20ma and if you exceed this current on a continuous basis, it will overheat and die. But, with that same LED, you can send a short pulse of 100ma without blowing up the LED, and during that time the LED will be 5 times as bright. If you continue at this current, it will quickly overheat and burn out. What good is that? Well, the human eye judges brightness by PEAK brightness. So if you send a 20% duty-cycle current of 100ma, it will average out over time as an average current of 20ma, but your eye will see a brightness the same as if it were driven continuously at 100ma.

    You can observe this in many common devices. Many LED stop-lights on automobiles use this fact. If you scan your eyes quickly back and forth, you can see the blinking. Some traffic lights do this. LED clocks use this fact, along with multiplexing the digits, to save circuitry AND to make brighter numbers. You can tell of they're blinking by using the same eye-scanning technique.

    Realize that this does not work with many of the more efficient LEDs which work by exciting a phosphorescent emitter with UV light from an otherwise invisible LED. The phosphorescent coating integrates the UV from the pulsing LED and the eye does not see a blinking source at all. Duty-cycle changes the light output almost linearly in that case. Other LED-based products that have internal ICs would also not work with this duty-cycle trick.

    Just for a little more info... The failure mode for exceeding "Peak Current" is that the little wire connecting the top end of the LED die instantly melts. The failure mode for exceeding the "Forward Current" is that the entire device overheats and dies a normal overheating death. A proper duty-cycle allows both limits to be met, and the human eye does what it does and judges the brightness by the peak brightness.

  • Another Eagle "trick" is to set the color for vias to BLACK. That way, the vias take the color of the layer they are on, instead of always being green. They will also not appear unless the layer they are on is enabled for display. I have a 12-layer blind and buried via board that would be indecipherable if not for this "trick".

    Also, @OldFar-SeeingArt, ...(or as often seen on the net: walla!)

  • +1... loss of valuable resources due to an inane fad.

  • Checking a few instruction manuals, different Host/Client combinations seem to use all the options from full CRC, to XOR checksum, to completely ignoring the checksum/CRC altogether.

    The way the protocol is supposed to work is that the host will inquire if the client supports CRCs, if so then it uses them. If not it is supposed to fall back to a Checksum. Even with a checksum, there is no law saying that the host needs to pay attention, so apparently some don't. The standard way of responding to a bad CRC/Checksum response is to resend the record. This is much quicker than resending the whole file like the "Verify" flag does.

  • You can also select the "External editor" option. This doesn't get you things like single-stepping or monitoring variables, but at least it lets you enter code in a reasonable editor.

  • Not the point. The point was whether or not the article SAID it did. The article DOES say that it does. Nowhere was Optiboot mentioned. Maybe Optiboot doesn't, don't know, but again, that never was the point.

    Also, quoting the Omimex manual for Sparkfuns STK500 Compatible USB Programmer: "Boot loader implements the standard protocol XMODEM with CRC16 for firmware update." The Atmel manual states that it uses a checksum on each record sent, both are options for the Xmodem protocol. Completely ignoring the checksum/CRC response is also an option, but not recommended.

    Any competent Xmodem host will resend a record if the client responds that the checksum/CRC failed. Program downloaders have been routinely doing this since the '70s. If Optiboot doesn't, it certainly should!

  • Quoting the article

    "each frame of the STK500 bootloader has a cyclic redundancy check"

    I don't know if this is true or not, but I know that it is NOT correct that "the article never said anything like that..."

    Having a bootloader without some sort of checksum or CRC is unlikely, and it would probably exist at the record level rather than at the file level.

  • Your numbers are only good for constant acceleration, and with no friction. Fuel burns, rocket gets lighter, a=F/m so acceleration goes up (and the integral gets more complicated). Also, many solid fuel rockets are burned in a way where the burning surface area increases during the burn. So not only does m decrease, but also F increases, sometimes by many multiples. Low sub-sonic air friction increases approx with the square of velocity, but decreases with altitude. Super and trans-sonic friction is not so simple. Can't do those numbers in my head anymore, but I suspect that they're different than what you got. Just sayin'.

  • Not a flame, just the facts. The original poster noted the declining quality of many current 'data-sheets'. I am simply agreeing, with recent examples.<br />
    <br />
    NC, no connection, means, and has meant for many years, no - decades, that there is No Connection to circuitry inside the chip. One of the examples I gave went further to expand the definition as "No internal Connection" and "these may be driven or left floating". To distort this to mean that you should not make any connection to this point defies logic. <br />
    <br />
    There are a wide variety of other terms that are available for "Do Not Connect", "Do Not Use", "For Testing Only", etc. Perhaps the examples I gave could have used "/Power-Supply Shutdown" on one, and "Vcc" for the others, rather than "NC".<br />
    <br />
    It is apparent that many of the people who are writing these 'data-sheets' don't consider them important enough to even turn on the spell-checker, much less actually insure that the information is accurate. <br />
    <br />
    In any writing, it is important to write in a way that is easy to understand. In technical writing it is important to write in a way that is difficult to mis-understand. Technical writing is an art, an art that many people simply do not have.<br />
    <br />

  • jdf2525 "I don't know if it's just that I'm getting old and cantankerous"<br />
    <br />
    Oh! Don't get me started... It's not just you. I've just about given up on even spending the time to read data-sheets. I recently made a board with 3 different chips that the data-sheets didn't know what NC means. It means, and has meant for many years, No Connection. It does not mean <br />
    "don't connect or else things will blow up." <br />
    <br />
    One, a 12A switching supply (2 on the board), had 3 pins (out of 133 in an LGA package) to be used to reinforce the physical mounting. These were further explained as "no internal connection". This was true for 2 of the 3, the third pin forcefully shut down the output. How long did it take me to find that? when the LGA pins are under the chip on a 12 layer board? when the data-sheet explicitly says "no internal connection"?<br />
    <br />
    Another, a Flash memory, went even further to state that the NC pins could be driven or left floating. As per normal human practices, these pins were merged into the ground plane, along with several interspersed labeled ground pins. The only thing is, two of these NC pins were actually unlabeled VCC pins, resulting in a direct short through the chip to the ground plane. How long did it take to find that?...<br />
    <br />
    Another chip on this board, a 1517 pin (not a typo!) BGA, had one set of pins labeled NC, and another labeled DNU (Do Not Use). Do you think I am going to believe what the data-sheet actually says as I wire up a $4000 chip? <br />
    <br />
    Timing diagrams are even worse. Polarity matters! Phase relationship matters! TIMING matters! That is why it is called a timing diagram. The information provided in some 'timing diagrams' is completely un-helpful. Pretty pictures... yeah, I get it, you can work "Paint" or something similar. A pencil scribble drawing with correct information would be much more useful.<br />
    <br />
    The data-sheet is supposed to be so that you don't have to get a chip, breadboard it, and randomly try wires and interface circuitry till you can get it to work. Instead, all too often today's data-sheets are created by people who really don't care. Standards aren't what is needed. What is needed are people who care, and who have at least half a clue.

No public wish lists :(