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  1. hevans1944

    Help needed on simple short circuit protection

    Rude? I am sorry you took it that way, but this sounds like a re-fit to an existing product, ergo, the original design is in some manner defective, or least incomplete. I am aware that even though you are talking about minuscule currents (10 ma?) driving the three paralleled potentiometers...
  2. hevans1944

    Soldering Connections For My Replacement 3.5 Stereo Plug

    Back in the day we had to make our own: rubber baby syringe bulb plus a short length of Teflon tubing stuffed into the business end of the syringe. A piece of 10 of 12 gauge solid wire was used to push the solder sucked into the tube (where it immediately solidified) into the bulb proper. We...
  3. hevans1944

    Help needed on simple short circuit protection

    What happens to this ill-designed product if the power to the potentiometers is "accidentally" shorted to ground? Does it fall out of the sky? Will people be injured? Will there be a gigantic high-current arc through the short from the unspecified 3 V DC power rail? How fast must the circuit in...
  4. hevans1944

    Sensor for solar irradiance

    Well, if you had read the datasheet at the link I posted for the LM358 you would find, on page 5 under paragraph 6.5 Electrical Characteristics, Voltage Range, that the output can only vary between 0 and [(V+) - 1.5 V]. Hmmm. Lessee... 5 - 1.5 is... wait for it! 3.5V! OTOH, if you had used the...
  5. hevans1944

    Soldering Connections For My Replacement 3.5 Stereo Plug

    I just now remembered why I threw those cans away. The padded ear-cups rotted away! I looked but couldn't find suitable replacements. The tinsel cord terminated at the cans in metal tips like those shown in Peter's link, held to each can by set screws. So, it should have been easy to change out...
  6. hevans1944

    Choosing Wire Gauge

    No. I have a tough time trying to crimp a ring terminal onto 4 gauge wire. I do like fine-stranded 4 gauge welding wire for high current applications when I can find it at the right price (cheap) at Mendelson's. I purchased out of my own pocket about a hundred feet of it and took it to work one...
  7. hevans1944

    Sensor for solar irradiance

    Well, doh! I warned you about this in post #9. What value of resistance did you use for Rfb? Is the photocell hooked up with the correct polarity? Remove the op-amp (okay to leave the resistor Rfb in place) and measure the voltage where the photocell connects to Rfb. Use the other lead on the...
  8. hevans1944

    small motors

    Back in the day, we would dip the whole machine in solvent... after removing all the parts that could be damaged by solvent of course: motor, rubberized belts, spools of thread (don't forget to remove and clean the bobbin under the bottom plate). If you use solvent, test it on non-essential...
  9. hevans1944

    Why I prefer electronics to plumbing

    @donkey Before replacing faucet washer, discard the faucet and replace it with valves that use "O"-ring seals. You may thank me a few years down the road, or curse me when you can't find the right size "O"-ring and have to replace the faucet again.:p
  10. hevans1944

    Choosing Wire Gauge

    Good thing your house wiring doesn't run on 12 V DC.
  11. hevans1944

    Sensor for solar irradiance

    Yep. This is exactly what you need. The Linear Technology LT1679 quad op=amp is a good choice. It closely approximates an "ideal" op-amp for your application. More on "ideal" op-amps later. The open-loop gain of the op-amp is very large, about one million for the LT1679, so it typically takes...
  12. hevans1944

    How to design analog circuit

    Water is an excellent dielectric... if you can keep it clean and pure. But water is also a highly polarized molecule that dissolves a lot of stuff, becoming an electrolyte instead of an insulator rather quickly. Try measuring the conductivity of various water samples (tap water, distilled water...
  13. hevans1944

    Choosing Wire Gauge

    I believe you are right! I just copied the first pretty picture I found on the Google image page. Turns out this was from an automobile forum where the length in the table takes into account the voltage drop. Here is a better table more suited to electronics work: This still doesn't take into...
  14. hevans1944

    200vdc 1A supply, adjustable 180-220vdc

    I love PICs. Reliability is not an issue with them AFAIK. Going to bed now.
  15. hevans1944

    looking for feedback on feasability of this idea...

    You will make more progress if you do a little thermodynamic analysis of the situation first. Heat in versus heat lost.
  16. hevans1944

    Choosing Wire Gauge

    Maybe this table will help or visit this Google page: It also depends on how much voltage drop you can tolerate. The ampacity table just tells what is a safe amount of current a given wire gauge will carry for a given distance based on the temperature rise in the wire. The longer the wire...
  17. hevans1944

    I have the qualification electronics and i don't know it's occupation

    Personally, I would NOT hire anyone with just a degree or diploma of any kind. I would want to see some passion from that person with respect to their interest in electronics. Passion demonstrated by hands-on involvement after school, on their own time, to improve their practical knowledge of...
  18. hevans1944

    small motors

    I am with everyone else on this. Sewing machines, like fine old watches, need periodic cleaning and lubricating, including the (usually) oilite bearings in the motor. Find the owner's manual for instructions on how.
  19. hevans1944

    200vdc 1A supply, adjustable 180-220vdc

    Well, if you need it right now, I can't be of much help... I have Hamvention® to attend this weekend, grass to cut, junk to sort out and throw away before moving to Florida... Yada, yada, yada. But I am curious to know how you control the intensity of the LED colors using just relays. Do the...
  20. hevans1944

    Sensor for solar irradiance

    Oops! I forgot about that little factotum. I once owned an HP calculator that I wanted to power with solar cells, so off to Radio Shack to purchase a few at truly outrageous prices. I was successful at tacking on 30 AWG solid wire-wrap wire to the first cell, but abandoned the project soon...
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