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  1. hevans1944

    Need help with this academic problem

    Oops! That's the equation for capacitors in series. Since Cx and 1200 μF are in parallel, it's simple addition: C = Cx + 1200 μF. But I see you got the correct answer for Cx = 800 μF despite my "help":D
  2. hevans1944

    Need help with this academic problem

    Well of course it would be limiting, but that's no reason to delay starting the journey. I am a proponent of "hands on" learning, where experiment and theory go together synergistically to increase knowledge. Start slow and small and build from there. The first thing you need is one of those...
  3. hevans1944

    How to choose and where to get proper electronic fuses

    At the currents you are anticipating, along with the probability of accidental shorts while experimenting, I would recommend using a panel-mounted reset-able thermal-mechanical circuit breaker such as found on this Google page result. PTCs are good for non-frequent "trips" but don't provide any...
  4. hevans1944

    Need help with this academic problem

    The key to solving this problem is realizing that, since the capacitors to the right of the voltage source are in series, they all have the same charge, Q = CV. The rest is, as you said, academic. Thank you for clarifying your intent. I noticed that your previous post was in 2013. Don't be a...
  5. hevans1944

    Call Progress tone

    Correct, for dial, ring tone, and busy signals only. For Special Information Tones it is a sequence of three tones with no interruption between tones in the sequence followed by a recorded voice message: boopbeepbleep <short pause> "We're sorry! Your call cannot be completed..." IIRC there are...
  6. hevans1944

    Need help with this academic problem

    Using Q = CV calculate the charge stored in the 500 μF capacitor that has 16 V potential across it. This same charge will also be stored in the 100 μF capacitor and in the parallel-connected capacitance 1200 μF and Cx. Using V = Q/C find the voltage across the 100 μF capacitor. Add this to the...
  7. hevans1944

    help repair router adapter

    This one from Sears would seem adequate. Cost is $22.18 plus shipping. There may be others, cheaper. How much is your time worth?
  8. hevans1944

    AC 117 Volt is it possible to put a DC socket??

    Or you can just purchase an inverter that runs off of 12 V DC and produces some sort of AC output at 117 V AC. Many of the cheaper inverters don't provide a very good sine wave output, and this may make the power transformer in your amp unhappy. Best to try before you buy if at all possible.
  9. hevans1944

    Clean square waves using a 555 timer?

    Just for reference, below is a copy of the original waveform with it's overshoot and following "ledge". The horizontal axis time base is 100.0 ns per major division in the original versus 200 ns per major division in @dorke's hardware "simulation" without an output load and without...
  10. hevans1944

    I need assistance on one way transmit

    Simple is always better. I forgot that AM/FM "pocket radios" are dirt cheap now. Easy to build a little broadcast band one-transistor transmitter and modulate it with the 555 pulses. The circuits were all over the "hobby magazines" in the 1970s, and earlier than that if you built your own...
  11. hevans1944

    I need assistance on one way transmit

    You are quite correct. Here is a nice article by Texas Instruments describing what is allowed in the US for unlicensed purposeful operation at low power levels. It explicitly forbids any purposeful radiation from 399.9 to 410 MHz, and 433 MHz is quite close to that band of frequencies. However...
  12. hevans1944

    Clean square waves using a 555 timer?

    The only things in the netlist are transistors, resistors, and a few capacitors that are external to the model. Nary an inductor in sight. There is a library reference to standard BJTs which are used to define two transistor types in the model. I looked at the ASCII lib file in Notebook and saw...
  13. hevans1944

    I need assistance on one way transmit

    If the receiver is powered, which it would have to be to light an LED, you could construct for the transmitter a low-frequency, low-power, RF oscillator driving a loop antenna at a sub-milliwatt level. A simple regenerative receiver tuned to the transmit frequency could easily detect this signal...
  14. hevans1944

    Very Fine Cable?

    It called "solder-strippable wire" and Google is your friend for finding it.
  15. hevans1944

    Rectified AC Power

    The 36 V output is the rms (root mean square) voltage of a sine wave. An AC sinusoid with X rms volts has the same heating effect on a pure resistive load as X DC volts. The peak voltage of a sinusoid, which is what a rectifier would charge a capacitor to, is the square root of two times the...
  16. hevans1944

    name of this part

    It is called a keyhole hanger. It looks purpose-built, so you may not be able to find an exact duplicate. Shorter versions are readily available. Google "keyhole hanging strap" for ideas.
  17. hevans1944

    Clean square waves using a 555 timer?

    I am sorry that I missed your point. Sarcasm now noted vis a vis R vs RC vs no load on the output. So, in an attempt to simulate the overshoot problem in LTSpice, I joined the LTSpice Yahoo! public forum today and went looking for accurate 555 models. Attached is the first transistor model I...
  18. hevans1944

    Clean square waves using a 555 timer?

    The datasheet graph clearly shows the output is at least 1.3 V less than Vcc at 25 C, in agreement with @dorke's analysis in post #72, and rising to more than 1.6 V at 100 mA load.
  19. hevans1944

    Clean square waves using a 555 timer?

    Still, it all adds up to a big bux investment eventually. I haven't added to my stock of resistors and capacitors lately, except for a onesie-twosie purchase of some polyester dielectric caps for a specific project. So, maybe I will model that 555 output stage in LTSpice AND build a model of the...
  20. hevans1944

    Clean square waves using a 555 timer?

    Yeah, but even Amazon now sells twenty 10μF tantalum caps for $13.37, so about 67 cents each. Not too hateful IMO. Free delivery if you have a Prime membership.
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