enl

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enl last won the day on June 18

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About enl

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    Machining, welding, electronics, woodwork, making, education, tools, toys

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  1. Best advice I can give you is to breadboard it. The LM3915 is pretty rugged, as long as you don't mix up the power supply pins, and everything else except the analog switch is, as well. The frequencies are low. This is very bread-boardable. The 4000 series IC's are not as static sensitive as some, but they do take some care. ALL unused inputs should be connected to ground or V+. I generally use about a 10K resistor, rather than direct connection, primarily because there are some failure modes that can occur during power cycling if the inputs are direct connected to V+ or ground, and the resistor limits current generally preventing damage. The unused analog pins should also be connected to ground.
  2. See, for example, https://web.stanford.edu/class/archive/physics/physics105/physics105.2002/datasheets/Analog_Linear_OpAmp_ICs/LM3915.pdf pages 8-21 I like this IC family, and have used them many times for many things. I miss them, but not much.
  3. Does anyone have recommendations for a current probe for use with an oscilloscope? I borrow a Tektronix from work when I need one at home, but a friend now needs one for field work and needs to be able to look at moderately short pulses (1 microsecond-ish), and he needs to buy out of pocket. The low end Tek, which would do the job, are about $700, but there must be other options that are decent these days for 1mA resolution. The specs for the Hantek CC-65 don't really do it, other than price. Suggestions?
  4. I am not sure what you are trying to ask, or what processor you are working with, but it appears that you don't have a good understanding of fixed point representations The value from the DS18B20 is a signed (2's complement) fixed point, 16 bit value. Cutting off the last four bits using a right shift that shifts zeros in to the left removes the sign. The shift can be done so as to preserve the sign by using the appropriate arithmetic right shift (arithmetic right shift RRA in assembler on the MSP430, or right shift operator in C on CSS). This will give an integer in 16 bit 2's complement. The rounding will ALWAYS be the floor (truncate to smaller value; round down) operation. To get round towards zero, you can use a condition such as (in C): if (t<0) t+=16; t=t>>4; or t=t>>4; if (t<0) t++; to do the job. If you want 'conventional' (grammar school) rounding (round down for the fraction <1/2, up for fractions >=1/2), then t+=8; t=t>>4; would be the cannonical way. If you want symmetrical rounding such that if the fraction of |t| < 1/2 is toward zero, and if hte fraction of |t|>=1/2, round away from zero, then, again, the easiest way is a condition: if (t<0) {t+=7;} else {t+=8;} Really, you need to know the desired behaviour. There are a lot of reasons why the default action is desirable (always round to negative infinity), in particular because then each count represents a range of one degree, rather than the range for zero being two degrees.
  5. Depending on the flash unit, the max current during charge may be quite high, 5A or more, judging by my Vivitar. The LM317 will current limit (the exact value depends on the version and manufacturer of the device), and the supply you are sourcing the LM317 from may also limit current. If the LM317 isn't warming up, it is likely the supply, not hte regulator. Another possibility is that the supply for the lm317 isn't high enough voltage for the regulator to do its job. It is not low drop out, and the max current goes down as the drop across the regulator goes down. Again, the exact voltage depends on the version, but typical is 1A max at 2V (from the onSemi data sheet) and a 2.5 input-to-output for the rater 1.5A output.
  6. Could you tell us the issue so that others can avoid it, or recognize it when a mistake is made?
  7. "if (bar[0]==NULL)" won't look at the pointer value, but instead the memory the pointer references, so that is right out, unless you want to know if the parameter is an empty string (only the null terminator) "if (bar == NULL)" should work, in particular if you explicitly pass NULL in since you are comparing a value to itself, as should "if (!bar)", since NULL should be 0. I just checked both (using gcc on a windoze machine) and they work as expected, so I can offer no insight as to why you would have a problem. I would suspect that you are seeing a symptom of some other issue than pointer comparison.
  8. In my first reply to the "true random number" thread, the last code block gave weird behaviour. The code editor opened, but refused to close. The code shows in a code block, but, when editing the post, the block can not be selected and acts like regular text.
  9. (continued, due to editor throwing a fit on last code block in previous post) Your example: ( {1839765.71, 1839765.79} ) ... But only move the last digit (from 1 to 8) Presuming that you mean the last digit is selected from [1, 2, ..9], could be written as randomd(1839765.71,1839765.80,9); Again, note that the randomd() function DOES NOT include the right endpoint, so b is one least count greater in the function call than in your example. If you want the upper bound included, the function gets an n-1 for the division in offset.
  10. Notation: [ and ] indicate that the endpoint is included, ( and ) indicate a range that is open (endpoint not included) First, I will presume you have a way to produce a random sequence of values (standard function or your own). Depending on the toolchain and libraries you use, the most common results of this are: A float (or double) [0..1), an unsigned (int or long int) over the full range of the type, or an int in a specified interval [0..n). The function to produce a bounded integer can be written several ways, but the two most common are // return a random value from the interval[0..n] unsigned random (unsigned n) { // rand() returns an unsigned int over [0..MAXUNSIGNED] return rand()%n; } as shown above, and // return a random value from the interval[0..n] unsigned random (unsigned n) { // rand() returns an unsigned int over [0..MAXUNSIGNED] return (int)((((double)rand())/MAXUNSIGNED)*n); } The second version (yes, I over-parenthesized to make the structure clear) first generates a real over [0..1) then scales to the desired range and truncates to an int. This is preferred for good behavoiur in some applications, especially with the common congruential pseudorandom generators, but is slower then the other version. For most things, it isn't important. (warning: the code is off the top of my head and untested...) If you are generating an integer in a range, such as [20..28)--8 values in the set--, or, more generally, [k..k+n) with n values: // k is least in interval // n is number of values to include // random(n) is a function that produces values in the interval [0..n) int r=k+random(n); If you are generating a real value, as in your example, the principle is the same // generate a double in specified interval from [a..b), selected from n values double randomd(double a, double b, unsigned n) { // this could be simpler in practice, but the structure here is to show method // the method requires care it it is critical that it produces best values in // that can be represented, starting with the applications definition of 'best' unsigned ri=random(n); double range =b-a; double offset=range*ri/n; // this is the offset from the starting value // ri/n will be a real from [0, range/n, 2*range/n,... (n-1)*range/n] return a+offset; } If you want a value selected from all reals in the interval: // generate a double in specified interval from [a..b) double randomd2(double a, double b) { double range =b-a; double offset=range*(rand()/MAXUNSIGNED); // this is the offset from the starting value return a+offset; }
  11. A good bench is at the top of the list. I have an industrial assembly bench as my primary space with a work area of 1500mm by 700mm. It came with outlets mounted in the shelf faces, the front of the work area, and the back f the work area, but I ended up adding several more duplexes (4, for a total of 8 more) as well as a few 2A USB sources and an IEC320 strip (I scored a bunch of 600mm IECmale to female cords at Eli Heffron's back in the late '80s. They still come in handy) Power is key, and not just for electronics work, These power the scope, logic ananyzer, several meters, computer, monitors, power supplies, and several projects. The bench has a lighted magnifier-on-a-stick which gets a LOT of use (I have about a half dozen mounted around the shop and the office. I am getting old and have had several eye injuries) as well as the optivisor and a bunch of loupes. My go-to style loupe is the jewelers style (black conical with a single lens) of 2.5 to 5X. The 5X and 10X Bauch and Lomb that clips onto my glasses gets a lot of use, as well. One good one costs as much as several cheapies, but the cheap ones are useless due to distortion. Go good with glass lenses. I also keep several powers of cheater reading glasses around as well as safety glasses with cheaters. A stereo microscope gets a lot of use. High power isn't the key for electronics. It lets you work in a more comfortable position and focus without strain. I would love a Mantis, but can't justify the cost, so I have a 7.5 to 75X Nikon that spends most of the time at the 7.5X end. It also gets used for machinist work (I made a mount for the lathe and for the mill), and for measurement and for photography. If you can find one (craigslist is your best friend) an arm mount beats a base any day. It isn't too hard to make a mount, but it is nice to have it come with one. My monitors are mounted to the back rail of the bench. Dual monitors (if I upgrade the machine, I'll go for three next time) of good size are a requirement to maximize workflow and reduce eyestrain from focal changes. It doesn't seem like it should matter, but it does. A lot. They also get use with the microscope camera for a lot of things when I prefer not to be staring down the eyepieces. A decent workholding vise is nice. I made several for specific purposes, including board-holding. If I was to name the MOST important thing, it is light. A lot of glare free light. I have about 5000lm/m^2 at the bench, from multiple directions, most diffuse sources, and have about another 10000lm available task lighting (fixed fluorescent and lamps on movable arms). About 20% of this os LED floods, to give some shadowing and contrast, the rest being quite uniform from flourescent.. I use high color rendering index lights (90+) daylight (6500k) mostly. I have a few fixtures in the shop with warm (4500K) so it doesn't feel so clinical, but hte key is a LOT of light. Magnification comes right with this. As I also use the space for woodwork and machining, I also have a bunch of vises for these tasks. A decent drill press vise can serve a lot of masters. The one I get the most use from is an ancient, swap meet, palmgren 2-1/2" angle vise. Second is a dirt cheap ($2?) yard sale job with 1" and 1-1/2" jaws that rotates (no brand.... just "Japan"). The jaws on that needed a little dress with a file, and the vacuum holddown went to the trash, but it works a treat for everything from holding a probe in place to holding a micrometer suspended in mineral spirits during rebuild. I never had mch use for a panavise or equivalent, though I have had several, as they never seem to be rigid enough or be able to get to the position I need them in.
  12. Am I reading correctly that this is with the LM35 not connected to the input pin? In other words, there is nothing connected to the input pin? If this is the case, then the potential on the pin will float, generally to about half of the power supply, give or take (depends on the device) and, being configured as an input, it will have very high impedance, so it will pick up noise. You would be measuring more the properties of the multimeter and its interaction with the floating input than a real potential.
  13. Most of his talk was not about C++, but about how to social engineer others into adopting in a non-supportive environment. It was a religious rather than technical exposition, as many Java talks, for example, also are. As to the data, I buy it. The technical points made are that strong typing reduces run time bugs is true, under the umbrella that only certain flavours of bug are caught, but these flavours lead indirectly to bugs of kinds not caught directly. Another advantage of strong typing is that, properly used, it can let the compiler do better optimization. His test case, a lightweight class, is probably where the advantages are greatest, but this is where, for many embedded applications, the other benefits to C++ are most available. I am not convinced that many of the 'more advanced' C++ tools and abstractions will give the same benefits, other than, with proper design, reduced debugging.With improper design (as one of the questioners put it, 'naive') there are likely to be losses. Some tools impose run time penalties that are unavoidable (often space rather than time) even with strong typing, but many of the standard tools (vector, for example) minimize this hit and save enough in other ways to be a net gain. Well designed standard tools pretty much always beat implementation specific, since they are designed (usually) by a specialist whose sole point is to get the best performance (by some metric) on the specific hardware. C++ provides a LOT of these tools. There are cases where a special purpose tool is better, but these are often brittle when changes are required, and the next revision has a net loss, either in performance (time or space) or in increased debugging. For reference, I tend to be a 'well written C is valid C++' kind of programmer, and use the C++ tools sparingly, especially in embedded work, and am NOT a C++ guru. I am, in fact, quite out of date with regards to the state of the C++ art. I still use the tools as they are appropriate, though. As for the social engineering aspects of the talk, nothing new. Read Dale Carnagie for the same. It is an effective model for understanding others and working with them. Nothing that hasn't been in writing for a good century, and known much longer, though in this case there is the extra fancy four quadrant graph of belief presentation.
  14. Ah. I went through the log and saw that I had added the site as an exception on one machine (one I generally use for such) in 2015. Tried accessing from the shop machine today. I am surprised I haven't noticed before, but, then again, the shop machine has all of three bookmarks in the browser, since it is generally used only for the shop gear.
  15. It appears that 43oh is rejecting https connections (browser: mozilla, system windoze8, urls tested: https://www.43oh.com/ https://forum.43oh.com/ )