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  1. Merlin3189

    Calculating resistance and Base current

    Sorry, I was assuming Vout was the voltage on the collector! (I couldn't read the diagram - it looked like omega 2t or something. I've been spending too much time on Bhuvanish's questions! And why is Vout on the input?) BTW I still can't work out what Collin was hinting at. Ok, so Vout isn't...
  2. Merlin3189

    Calculating resistance and Base current

    It all depends on the LDR and I agree, I can't find one with a low enough On resistance. But if this is a theoretical exercise, it doesn't seem unimaginable to have an LDR with the required range.
  3. Merlin3189

    complex number

    1- You are using the complex plain, with 1j being the unit vector East and 1 being the (orthogonal) unit vector North. (This is a reflection & rotation of the conventional axes, but you can use that.) You were going 3+4j, you rotate 90deg counterclockwise by multiplying by -j (because you chose...
  4. Merlin3189

    I'm new to Logic gates and digital electronics and could use some help please!

    I would applaud your intention here, but say that it is a bit misguided. To build a 4 bit counter needs 4 flip flops, as Heavans has said. Now learning to build a flip flop from gates is a good idea, but once you've done it (and played around with it and understood how it works, which is a...
  5. Merlin3189

    Help understanding Varactor fm modulation circuit

    First - If anyone else has this circuit with some component values or further description, I hope they may chip in. This comment I would say is technically wrong. If it is a phase modulator, as I believe, the point is that the crystal is undisturbed and generates its fixed frequency. This...
  6. Merlin3189

    Help understanding Varactor fm modulation circuit

    I can't pretend to even begin to understand that circuit, particularly with no values to show the relative magnitude of the impedances and no signal ground. However, there is a phase modulation technique (used to create FM signals) using an RC filter. At the cutoff frequency of an RC the...
  7. Merlin3189

    imaginary and real world signals

    I don't know what exactly your prof has in mind when he says this: it's a complex subject, so I imagine it's difficult to explain!:D I think what he may have meant by "play" is that we can do maths on the "Imaginary" numbers (just as we can with "Real" numbers), but when we measure things we...
  8. Merlin3189

    Ni-cad's

    In my experience overcharging is a problem. The chargers that come with cheap (I have no experience of expensive ones!) electric drills, screwdrivers, torches, toys, etc. have no regulation, control or timer. If they are capable of charging in less than about 14 hrs, then they will be...
  9. Merlin3189

    complex exponential signals

    Quite so! This is Euler's Relation. A complex exponential can be written in terms of sin and cos. And sin and cos can be written in terms of complex exponentials. e^ix = cos(x) + i sin(x) sin(x) = {e^ix - e^-ix} / 2i cos(x) = {e^ix + e^-ix} / 2 The complex exponential form is used when it...
  10. Merlin3189

    Can a 6v light bulb blow a 12v transformer

    Yes the inrush current is certainly worth thinking about. With a 6V instead of a 12V bulb, presumably the inrush current could also be double. Inrush is pretty certainly the time when filaments fail, but why do they fail due to this current, when they have happily survived it for thousands of...
  11. Merlin3189

    The Standard of Engineering Graduates

    Do you worry about who's designing your cars,aircraft, buildings, bridges, oil refineries, ...? (I don't worry about most of the electronic technology, because I just wish most of it didn't work! Like mobile phones, game boys, i-anythings,..) Just recently I've come across two posts (not here...
  12. Merlin3189

    Different answer using inverting op-amp and KCL?

    Well done Heavans! I hadn't spotted that until you said. We just think about putting this sort of ground for a voltage reference, but of course current may flow. It's easy to forget.
  13. Merlin3189

    Can a 6v light bulb blow a 12v transformer

    Not so LOL myself - I'm always unhappy about the cost of electricians! (Though I do sympathise with them. They seem to spend more time going on expensive courses to update their certification and knowledge of the regs, than they spend working. So the bill has to cover all those costs.) But...
  14. Merlin3189

    Can a 6v light bulb blow a 12v transformer

    Yes, we all have our own opinions. It would be interesting to see the electricians detailed calculations which led him to that conclusion. Perhaps I'd be convinced?
  15. Merlin3189

    stepper motor with ultra low torque at rest?

    It may be worth looking up a Permanent Magnet Synchronous Motor. Many years ago I used one of these as a stepper motor and it had to remain energised to hold it's position. When not energised there was no detent at all I think. I can't remember how many poles it had, not many, 6 I think, but I...
  16. Merlin3189

    Can a 6v light bulb blow a 12v transformer

    I'll also join BobK's camp - very unlikely. As to possible, well maybe it just could have been the final straw, or final bit of a straw for a transformer already on its way out.. If there had been a drastic difference in the current carrying capacity of the wires (filament vs transformer...
  17. Merlin3189

    Trying to find out the name of a type of component.

    Although it is probably not what is wanted here, the description, " a component that conducts current at or above a voltage value", made me immediately think MOV (metal oxide varistor) or voltage dependant resistor. These used to be routinely soldered across power supply inputs to protect...
  18. Merlin3189

    discrete signals

    Apologies Harald, I did not read your posts carefully enough. Having reread them I think I would agree with you and your detailed treatment. I think maybe we agree, that discete/continuous and digital/analogue are more about the way information is encoded in a signal than the appearance or...
  19. Merlin3189

    even and odd signals

    Without more context I can't think of much to say about odd and even functions. The distinction seems to be largely one of how you can treat them in various mathematical tricks - whether you can integrate from -infinity to + infinity in one go, or whether you need to do it in two halves, for...
  20. Merlin3189

    transformation of independent variable

    Time shift could be a delay and all circuits have delays. But generally these transformations are not so much things that "happen" to signals, but mathematical operations we perform, either in processing the signals or in calculating what happens to them. Time reversal and time shifting are...
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