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  1. hevans1944

    Clean square waves using a 555 timer?

    Thank you. Looks like an excellent resource for the hobbyist.
  2. hevans1944

    Clean square waves using a 555 timer?

    Thank you, @dorke, that explains the steady-state performance very well. But in order for the output to, briefly, spike to Vcc and then fall back requires an inductive reactive component to temporarily store the requisite energy. My guess is this parasitic inductance lies somewhere between the...
  3. hevans1944

    Clean square waves using a 555 timer?

    If you are limited to using the 555 as your oscillator... well the upper frequency limit is now up to one megahertz. See this Intersil datasheet. It's still a crap shoot what the output waveform will look like. There are "better" oscillator circuits but none quite so versatile as the 555 if you...
  4. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    I think it would work. The one I used was several hundred dollars and was made for crimping wires to pins inserted in a high-density circular bulkhead connector. I re-purposed it to crimp ferrules, but the tool you found is not only inexpensive it also appears to be designed to crimp wire...
  5. hevans1944

    Clean square waves using a 555 timer?

    So, can we go back to a "standard" astable 555 circuit running at twice the desired frequency and add a Schmitt trigger inverter followed by a D-flop to get half the 555 frequency with a guaranteed 50% duty cycle? All this stuff is now available in single-function itsy bitsy teeny weeny...
  6. hevans1944

    Coil problems...

    Well, electronics is very much an art. So get out your air-brush and "touch up" the finished project to your taste.
  7. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    Since you have already demonstrated the capability to have PC boards manufactured on a previous thread, I would go the professional PCB route. But do a prototype first. Do what you did before and upload schematics and board layouts for our inspection, criticism, and inspection. A few iterations...
  8. hevans1944

    Bench Power Supply

    The LM317 maintains Vreg (or Vo) by varying its conduction from Vi to Vo. When the load at Vo draws sufficient current from the LM317 it will bias the 2N2905 PNP transistor on through the voltage drop across the 22 Ω resistor. As PNP collector current rises, it turns on the power NPN by forward...
  9. hevans1944

    Coil problems...

    Thanks. That link was from a woo-woo reply on Moebius loops. It's fixed now.
  10. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    Ha! If going to that extreme, build the op-amps, too, using discrete transistors and resistors and perhaps a few capacitors. And diodes! Loved your post on the XL741 @chopnhack! You can learn a lot about 3-terminal regulators by actually using them and discover that adding an op-amp or two or...
  11. hevans1944

    Voltage regulator question

    And do shield your electroinics. I prefer die-cast aluminum Bud boxes with covers secured with machine screws (actually they provide self-tapping machine screws IIRC). These (or clones) are also available with a woven wire gasket in the cover, but it probably isn't necessary to go that far...
  12. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    There is much, much, more... some of it in private conversation. @chopnhack has professional chops in many areas, including home construction and maintenance: drywall installation and repair, plumbing installation and repair, electrical installation and repair, and fine woodworking including...
  13. hevans1944

    Voltage regulator question

    Are you kidding? EMI-proof the ignition radiation from a 1949 Ford tractor? You would have to enclose the whole tractor inside a Faraday cage and surround that with a mu-metal shield. Or maybe instead do the same thing with your electronics. Hard to say what will work down on the farm, but your...
  14. hevans1944

    Coil problems...

    Commonly, floral wire was made from painted soft-iron wire because of cost and malleability considerations. Please see if a small permanent magnet will attract the wire you have. If so, it is iron wire. However, I agree with @Arouse1973 that you may not have removed the insulation sufficiently...
  15. hevans1944

    Woo Woo need a diode ?

    Amen to that! I hate woo-woo "science" and generally will not respond to those who pursue it. In 2013 I got back into amateur radio by obtaining an Extra Class license (AC8NS). So, to see what had happened since my original Novice Class license expired in 1967, I attended the 2013 Dayton...
  16. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    I must confess I don't own any NTE576 power rectifier power diodes. I have lots of 1N400x types, lots of small-signal 1N914 and 1N4148 types, and even a few germanium diodes I recently spotted at Mendelson's and just had to buy at ten cents each. I will have to eventually purchase the higher...
  17. hevans1944

    Clean square waves using a 555 timer?

    This is a good idea. If the bread-board fixture is introducing problems you should see some sort of difference in the calibration square wave when the probe, with the blue wire attached, is connected or disconnected from the bread-board. Not sure if this will help determine how to eliminate the...
  18. hevans1944

    Clean square waves using a 555 timer?

    So, I guess @Colin Mitchell is "vindicated" in his opinion that the 555 is a "very nasty chip". I've heard it called worse than that. Personally, I like it, whether in the low-power CMOS version or its original flavor, perhaps with some chocolate sprinkles. It clearly states on at least one...
  19. hevans1944

    How do I calculate the ESR of a capacitor please?

    Actually it says "b. Power Supplies: - stabilized, regulated, low-ripple, constant and variable output (voltage, current), switched mode." This is probably important enough to go back and ask your instructor very specifically whether a switched mode power supply is a requirement or whether a...
  20. hevans1944

    Zeroing out a LM317 reference voltage with a zener - PSU build

    My thoughts are: you are over-thinking this. I can see using a separate switch to enable and disable separate power supplies, all powered from separate transformer windings, but it is penny wise and pound foolish to create an elaborate switching scheme to create series and parallel...
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