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  1. hevans1944

    decoder for 8051

    I will re-visit this thread next month to see if there has been any progress made.
  2. hevans1944

    decoder for 8051

    So please do what was asked to demonstrate you understand how an instruction is assembled for the 8051 from an 8-bit op code, plus one or two byte operands (if needed). Why not encode MOV R4, #5 and MOV R3, A, and MOV A, @R1? See my complete post #57.
  3. hevans1944

    decoder for 8051

    Okay. Let's reset this thread to the beginning: This microcontroller uses an 8-bit (one byte) operational code (op code) that allows for 256 separate instructions. Of this number, 255 are actually defined op codes. For each of the defined op codes, none, one, or two additional bytes are...
  4. hevans1944

    LED min and max Current and Voltage

    The forward voltage depends on the LED physics and, indirectly, is a function of color. Shorter wavelength LEDs require a larger bandgap, i.e., more energy to force electron-hole pairs to radiatively combine in a forward biased PN junction to emit photons with energy (inversely proportional to...
  5. hevans1944

    Power supply purchase

    This appears to be a very nice switching power supply that can provide constant-voltage or constant-current, depending on front-panel switch selection. The price is very good, too. The only caveat would be the switching noise, both in the output, conducted on the power line, and radiated...
  6. hevans1944

    LTSpice switch

    Okay, but what about the first paragraph, where I gave you instructions on how to work out the states on paper? You don't need a software simulator for that: just your own powers of reasoning and observation. Once you have the state transitions figured out, then (and only then) should you try to...
  7. hevans1944

    DVM meters with Square waveform mode

    I think we are done here. Why don't you ask a moderator to close this thread and allow you to open another?
  8. hevans1944

    The need for resistance

    Dustin, Electronics is all about having fun!
  9. hevans1944

    DVM meters with Square waveform mode

    Probably not. Matched terminations are used to prevent signal reflections on transmission lines (a coaxial cable is a transmission line with a characteristic impedance). Unless an output generator has zero source impedance, the signal across any load will be attenuated by the ratio of the...
  10. hevans1944

    Testing a electrolytic Cap

    Electrolytic capacitors are a real PITA. First of all: they AGE, whether in use of not. Second, they dry out as they age, increasing their ESR. Third, they fail catastrophically: leaking, bulging, sometimes even exploding. When in doubt, replace with factory new stock purchased from a reliable...
  11. hevans1944

    DVM meters with Square waveform mode

    Ideally a waveform generator has a low impedance so that whatever load it is driving does not appreciably attenuate the waveform, or if appreciable attenuation does occur, the attenuation is predictable. For example some waveform generators have 50 Ω output impedance; when connected to a matched...
  12. hevans1944

    LTSpice switch

    You have to start somewhere, so assume that V3=10 V is applying an active-high CLR to all three D-flops. Until V3=0 V the CLK input, V1 will do nothing. So, initially, A1:Q=1 and A2:Q=1 and A3:/Q=0. With this information, determine these three outputs for a succession of clock pulses, assuming...
  13. hevans1944

    DVM meters with Square waveform mode

    It's meant as a "feature" to sell cheap digital multimeters. It's up to the buyer to figure out something useful for it.
  14. hevans1944

    floodlight HELP

    Does the 12 V beacon require 12 V DC or 12 V AC? Do you have a model number for the beacon? Does it have a motor-driven reflector that rotates around an incandescent lamp?
  15. hevans1944

    How would one make a power supply for a 30,000w xenon lamp

    Oh, well then... If we are talking hypothetical, I suggest you ask Scotty to loan you some di-lithium crystals to drive your arc lamp. These could be so much better than a bank of three-phase hockey-puck thyristors (SCRs) and 100 V AC @ 1000 A grain-oriented silicon steel transformers.
  16. hevans1944

    How would one make a power supply for a 30,000w xenon lamp

    I would not want to be anywhere near that puppy if you put in enough power to "pop" it, even with the orange plastic shield bolted firmly in place. Anyway, I think the orange plastic shield is intended only for protection during transport and would melt if left attached while the lamp absorbed...
  17. hevans1944

    Circuit help

    If you use a SPDT pushbutton switch, you can de-bounce it using the /R and /S (active low) inputs of the other flip-flop in the SN74HC109 package. Tie unused J, /K, and CLK pins to ground. Connect NO and NC switch contacts to /R and /S inputs, along with 10 kΩ pullup resistors connected to Vcc...
  18. hevans1944

    DVM meters with Square waveform mode

    Just because some instrument has a "feature" doesn't mean that "feature" is useful. If I want a variable frequency, variable duty cycle waveform to test something I also want to (1) be able to select the waveform (2) adjust the frequency and (3) set the duty cycle (or pulse width)... preferably...
  19. hevans1944

    Circuit help

    I haven't seen a specific device mentioned yet. What is the part number of the J-K flip-flop?
  20. hevans1944

    dirt devil 7.2 volts hand held vacuum

    So you found the transformer at a store? Why didn't you just purchase it as a replacement for the one you lost?
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