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  1. hevans1944

    Frankenstein's Components.

    Amazing what you can do with a little bit of transformer steel and some insulated copper wire. Tally ho, Bertus!
  2. hevans1944

    CRT

    I wonder why you are mucking around with a CRT monitor when cheap LCD/LED monitors with higher resolutions are available? The ZZIT noise is probably arcing in the fly-back transformer. It can only get worse, now that the insulation has started to break down, but if you can quickly restore the...
  3. hevans1944

    What happens if you put a BJT in a 12V AC circuit?

    I haven't read any of the datasheets yet on the photomos relays cited by @Harald Kapp, but just the name leads me to believe these are "ideal" interfaces between the real world and any electronic processor. As for the AQH2223, as Harold mentioned these are photo-coupled, zero-crossing, triac...
  4. hevans1944

    10.7 MHz oscillator with transistor

    Everything that you need to know about ceramic filters can be found on this web page, along with links to other sources of information. Until these spiffy little devices came along, the filters they implemented were made from discrete quartz crystals, hand tuned to specific frequencies. It was...
  5. hevans1944

    7805 regulator capacitors

    @HellasTechn, you seem to be ignoring the datasheet recommendations concerning the capacitor values you should use. The input capacitor is a high-frequency bypass capacitor, needed ONLY if there is substantial distance between the 12 V "smoothing" capacitor and the three-terminal "7805" linear...
  6. hevans1944

    Improvised Alternatives to a High Voltage Probe for Oscilloscope

    I have NO practical experience with atmospheric ion generators, allegedly generating either positive OR negative ions or both. You are on your own as to what you want to believe, or how you think ions can be generated and presumably diffuse through air like smoke. Your original question was how...
  7. hevans1944

    Improvised Alternatives to a High Voltage Probe for Oscilloscope

    They sell better that way because it has been shown that positive ions are not good for your health or sense of well-being. Just because you can emit electrons into the atmosphere with a corona needle generator doesn't mean you are creating a significant quantity of negative ions. However...
  8. hevans1944

    Improvised Alternatives to a High Voltage Probe for Oscilloscope

    All is not lost yet! The main reason HV attenuating probes cost so much is that they are built to higher expectations of accuracy and frequency response. However, getting a voltage divider rigged up to allow you see slowly changing charge/discharge wave forms is not difficult. All you need is a...
  9. hevans1944

    Improvised Alternatives to a High Voltage Probe for Oscilloscope

    I implied no such thing. Since you "modified" an ion generator, it is a pretty sure thing that your original device was originally intended to make positive ions, by removing one or more electrons from atoms or molecules in a conductive gas environment. So, yes, expect your DIY capacitor to...
  10. hevans1944

    Improvised Alternatives to a High Voltage Probe for Oscilloscope

    No, AC square waves ARE NOT in effect pulsed DC. AC means Alternating Current. DC means Direct Current. Pulsing has nothing to do with it. Perhaps you should consider taking an introductory course in the study of electricity. Hoping is what I used to do after placing a tooth under my pillow...
  11. hevans1944

    Improvised Alternatives to a High Voltage Probe for Oscilloscope

    You haven't provided enough information for a meaningful response. How can the capacitor you built be "charged with a 20kV AC square wave from a modified domestic ion generator?" Capacitors are "charged" with DC not AC. What model and manufacturer was the domestic ion generator before you...
  12. hevans1944

    Need help for value of resistor

    The 1N4148 virtually replaced the venerable 1N914 signal switching diode in most logic applications. I have been using it since the 1970s and have never found fault using it to replace the 1N914. However, both diodes are fast signal diodes, not power diodes. You need to be aware of this...
  13. hevans1944

    Need help for value of resistor

    This IS a hands-on forum, riiight? Get the damned scope out from under the work bench and connect its input across the relay coil using capacitive coupling. Pulse the relay coil with a logic-level MOSFET and measure the so-called fly-back wave form. Take some pictures, post them here with a...
  14. hevans1944

    help me identify these components

    Oh, really? So, why don't you do your OWN fcking homework and look up those part numbers using your favorite Internet search engine? After you find the parts, be sure to post a link to their datasheets. We help those who help themselves in this forum. What have you done besides butchering those...
  15. hevans1944

    Sensors to detect and locate a fire

    The subject of this thread, autonomous robots, reminded me vividly of the opening scene in the movie I, Robot. The character played by Will Smith was saved from drowning when the robot that saved him "calculated" the probability of a successful rescue was greater for Will Smith's character than...
  16. hevans1944

    Sensors to detect and locate a fire

    Excuse me? Quoting you was definitely intentional, no intoxication involved. Was there something inappropriate about your statement that I quoted? Why would you say, "or are just intoxicated?" I thought I was making it clear that the original poster didn't have a clue about how to design, much...
  17. hevans1944

    Sensors to detect and locate a fire

    Yeah, your cockamamie idea sounds good at first reading because there was no critical thinking involved. Who wouldn't want a robotic fireman on duty twenty-four hours a day, every day, all year long? Of course we have to assume this automaton is at least as well-trained as the human being it...
  18. hevans1944

    Sensors to detect and locate a fire

    Seems to me that you also need to distinguish deliberate open flames, say from a fire place or kitchen stove-top burner, or even from someone lighting a cigarette with a match or lighter, from out-of-control flames that must be put down quickly. Perhaps an image recognition system, working in...
  19. hevans1944

    Newbie question...

    Unfortunately, I have to agree that you have encountered wires soldered to wire-wrap pins. Back in the day, we would sometimes do this to ensure a permanent connection. Wire-wrap connections are intended to be made ONLY with solid wire. The sharp corners of the wire-wrap pins penetrate the...
  20. hevans1944

    Obsolete Dual Diode Specs

    I shared in your curiosity, but I just was not as fortunate as @73's de Edd, who has been there, done that, and probably ate the cat too. OMG! How could I have forgotten selenium rectifiers!? Grandfather had stacks of these with vertical convection air-cooling fins, mounted on the wall of his...
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