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  1. Archie Medes

    Analog zero-point synced AC PWM: is there a better way?

    Cheers dlgoff, that looks pretty handy
  2. Archie Medes

    Analog zero-point synced AC PWM: is there a better way?

    Cheers for the detailed explanation BoB Yeah, that is what I meant by setting the period with the pot and cap on the 555 comparator inputs. I would prefer a controller that gave me both period and duty control, and was wondering if your suggested device offers that (I haven't got around to...
  3. Archie Medes

    What's in an electronics hobbyist's toolbox?

    Can't see this one mentioned: Magnetic trays. The kind auto-mechanics use. Annoying when you brush a bunch of carefully laid out screws everywhere, and you wanted them to go back into the holes they came out of. I prefer pushing screws into foam, but trays are useful when working in awkward...
  4. Archie Medes

    Analog zero-point synced AC PWM: is there a better way?

    Thanks for your reply BoB, I will check out the drivers. I can set PWM period with the pot and cap on the trigger/threshold input of the 555. 1 second with half-waves gives me 100 points of resolution at 50 Hz. Unless you mean that I can vary the period without altering the circuit, which would...
  5. Archie Medes

    Analog zero-point synced AC PWM: is there a better way?

    Hi, Thinking of a circuit to control the AC power to a heating element. I wanted something fairly linear, and analog. I don't have anything against using a programmable controller, I just wanted to think of an analogue solution, seeing as I don't need to learn how to write a program. The...
  6. Archie Medes

    Sheet resistance of metal mesh

    I'm afraid you would have a better understanding of it than I would. I don't actually know anything about the physics of photovoltaics. My grid suggestion would only give a reasonable answer if the resistance of Rv and Rh were both significantly higher than the junction resistance, and whether...
  7. Archie Medes

    Transform difference equation into continuous function?

    Ahh, thank you Looks like the thing lacking from my understanding in this case is the derivation of series expansions of functions. Right now is the first time I have read the formal definition of the Taylor expansion of a function. I have used expansions to solve problems, and I'm fine using...
  8. Archie Medes

    Transform difference equation into continuous function?

    Thank you for the help, I'm mostly there, I can now solve R(t) for a given T(t). I was not interested in that sine function per se, it was just a simple bounded continuously changing function that I could use for R to follow on a graph. What I'm still unclear about, is this part: How did k...
  9. Archie Medes

    Transform difference equation into continuous function?

    I realise I can pretend so to speak, the graphs illustrate that. I want the actual continuous function though (not because I need it, but because I'm curious), and I'm having a brain lapse. I was hoping someone could point me in the direction of what to look up. I am basically looking to do...
  10. Archie Medes

    Sheet resistance of metal mesh

    Never done a problem like this, but here's my thoughts The mesh is basically a rectangular grid of individual resistors, from which the extremities (apart from that at B2) can be ignored. I am also assuming there is no electrical connection between the three busbar ends beyond the final finger...
  11. Archie Medes

    How much charge does the battery deliver?

    Ceq = 1/(1/C1 + 1/C2) = C1*C2/(C1+C2) nevermind, you picked it up, and I can't delete this
  12. Archie Medes

    Find the Current Flowing through each resistor

    A few things: Voltage polarity is due to potential difference. Your equations don't seem to be loop (mesh) equations. The direction to assign a current for analysis is arbitrary, as long as you don't swap it's direction mid analysis. If you guessed the correct direction, the result will be...
  13. Archie Medes

    Calculate the voltage between points A and B

    I sometimes find it easier to re-sketch the circuit as branches, with all the elements facing one direction:
  14. Archie Medes

    Transform difference equation into continuous function?

    Homework Statement My question: Can I turn this difference equation for R below, into a continuous function R(t)? I have no idea if, or how, I can. And I'd like to. Equation derived from the following manufacturer statement on the thermal response of a thermistor to a fixed temperature: The...
  15. Archie Medes

    Manufacturing Help -- Need a highly viscous material

    Lanolin Viscosity adjusted by solution with hydrocarbons
  16. Archie Medes

    Metallurgical questions about alloying of Sn with Cu/Ag/Au

    Thank you I forgot to stress it is the silver I am most interested in, because I can't find information on it either, whereas gold and copper information (anecdotally at least) seems much more available. Reason I ask is for fashioning custom soldering heads. I want to know how silver behaves...
  17. Archie Medes

    Metallurgical questions about alloying of Sn with Cu/Ag/Au

    Hi My question relates to electronics soldering, where the main metal in the solder is Sn, with small amounts of Ag and/or Cu If a rod of Cu, Ag, or Au is placed in molten Sn, which of the rods would melt away fastest? Is there a threshold temperature up to which the solid metals won't...
  18. Archie Medes

    I How do you answer "So what's the practical application....?"

    The way to select the right example is by first asking the questioner about themselves and their lives. If people want a one-size-fits-all answer, well whoever comes up with one will make an absolute fortune in education.
  19. Archie Medes

    I How do you answer "So what's the practical application....?"

    Yes, but is the question "why do you pursue knowledge?" or "what does that knowledge end up used for?" It doesn't matter that there is no existing use for something, or that one can't be thought of. The fact people are building it means it exists as a tool.
  20. Archie Medes

    I How do you answer "So what's the practical application....?"

    You told me it is wrong, yes, but I'm not agreeing with you. With logic, sorry, I was thinking of programming logic, which is very simple. Part of set theory is being used eh? Wow, so it is a tool after all, even if all the applications haven't been figured out yet
  21. Archie Medes

    I How do you answer "So what's the practical application....?"

    Done plenty of logic, and love proofs. Knowing how they work doesn't change them from being tools
  22. Archie Medes

    I How do you answer "So what's the practical application....?"

    A hammer doesn't tell a carpenter what to nail
  23. Archie Medes

    I How do you answer "So what's the practical application....?"

    But it isn't different at all. Engineer has a problem, uses the relevant mathematics to solve it. I mean, no wonder laypeople are having difficulty understanding it, if people are over complicating it with their philosophical pursuits!
  24. Archie Medes

    I How do you answer "So what's the practical application....?"

    I thought the question is the general public asking what the practical use is? But I also honestly don't see it as anything other than a toolbox. Why do people use mathematics if not to solve problems? The pursuit of it, well, that is another matter.
  25. Archie Medes

    I How do you answer "So what's the practical application....?"

    You can extend it beyond craftspeople to anyone at all. We all use tools, and we all have tools that we love, and tools we wish we had.
  26. Archie Medes

    I How do you answer "So what's the practical application....?"

    Then the problem is your ability to communicate with less educated people, because it isn't hard. You're not putting yourself in their shoes. If they are asking you to explain how the mathematics works, that is a different story.
  27. Archie Medes

    I What methods other than Taylor Series to solve this eq?

    Ahh thanks A quick search for solving 5th degree polynomials brought me to the Quintic function page on wiki, where it says the impossibility was proven by the Abel–Ruffini theorem at the beginning of the 19th century
  28. Archie Medes

    I What methods other than Taylor Series to solve this eq?

    Are you talking about the substitution provided by BvU? What is the name of the theorem/proof (sorry if poor terminology) that explains it, so I can read up? Thanks
  29. Archie Medes

    I How do you answer "So what's the practical application....?"

    That is why i put it in terms of craftsmen People might not be engineers or scientists, but pretty much every adult uses some kind of tools in their day to day life, so they know how to appreciate a good toolmaker. And they can also appreciate that scientists and engineers do important stuff...
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