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  1. hevans1944

    How to control the speed of a 24vdc pump from circulating water temperature?

    Probably. I was born in Welch, West (by God) Virginia. That's coal mining country. Don't think my grandfathers or grandmothers were immigrants, but some of my ancestors might have crossed the pond from Wales.
  2. hevans1944

    Simple transistor / LED circuit problem

    ALWAYS use a current-limiting resistor in series with ANY LED. See EP's resource on driving LEDs.
  3. hevans1944

    Finding C & L from XC and XL

    I just noticed that you use Z = √(R² + (XL - XC)²). This calculates the magnitude of Z but omits the angle that Z makes with the positive x-axis when impedance is plotted on Cartesian coordinates with the real component on the x-axis and the imaginary component on the y-axis. Just sayin'... it's...
  4. hevans1944

    Finding C & L from XC and XL

    I distrust circuit simulators and seldom use them, especially for simple RLC circuits. Best to learn how to use complex algebra and use that to check the simulator. Note that, impedance is a complex quantity that has a real component and an imaginary component, expressed usually in the form of...
  5. hevans1944

    Finding C & L from XC and XL

    I had to correct the equation for C, My algebra must be rusty, Corrected result: C = 1 / (XC x 2 x pi x f). I have already edited my original post to show the correction. Sorry 'bout that.
  6. hevans1944

    Finding C & L from XC and XL

    Just use algebra. XL = 2 x pi x f x L requires you divide both sides of the equation by (2 x pi x f) to "cancel" those terms on the right side of the equation, leaving just L = XL / (2 x pi x f). Similarly for XC = 1 / (2 x pi x f x C) first take the reciprocal of both sides: 1 / XC = (2 x pi x...
  7. hevans1944

    Maplin Electronics in the USA?

    Hmmm. I am guessing @usalabs doesn't like the increased security and vigilance here in the United States of America, prompted in part by the destruction of the World Trade Center by a few disgruntled individuals whose only "weapons" were a few box cutters and a few large commercial airplanes...
  8. hevans1944

    Resistor Replacement

    Why would you assume the burnt resistor is the same value as the other resistors whose color codes you can read? The two missing color-code stripes could be anything! All you really know is the first digit and the tolerance. A schematic of the circuit, with values labeled, would be useful.
  9. hevans1944

    Variable speed water pump controller

    I didn't have any trouble opening the page. Lots of people in the forum do motor mods, usually for DC motors. Variable frequency drives are available for AC motors to provide variable speed control, but both the special motors required for variable frequency operation as well as the...
  10. hevans1944

    Induce current in air?

    Gee, do you want me to read them out loud to you? Did you even visit the link I posted? Start there and find others yourself. Make Google your best friend for this. Also, read page 10 of this PDF link.
  11. hevans1944

    Electronic stimulator

    Actually, it would help a lot if you describe what you are trying to DO. Is your goal to learn electronics and LTSpice simulation? Or do you want to actually design and build a muscle stimulator? There are hundreds of "monkey see, monkey do" projects on the Internet. And there are dozens of...
  12. hevans1944

    Induce current in air?

    There is a device called a plasma torch that ionizes air by means of an intense RF field inside an open coil. Air is blown through the center of the coil, becomes ionized to a plasma state as a result of absorbing RF energy, and exits the coil as a hot gas suitable for wherever you need to use a...
  13. hevans1944

    General Purpose Programmer

    You need to understand how a "universal" programmer works before attempting to purchase one. The typical programmer has a 40-pin Zero Insertion Force (ZIF) socket with each of those 40 pins connected to a software programmable "pin driver" circuit. The pin driver is capable of receiving binary...
  14. hevans1944

    General Purpose Programmer

    See if your devices are on this list. If so, the somewhat pricey Chipmaster 7000 might work for you. Or maybe upgrade to this one. Try this link for programmers (hardware) and programming services. Do you know who the manufacturer is for the M27C64A EPROM is? Who made the P87C51SBPN OTP/ROM...
  15. hevans1944

    Boost Car Radio Signal

    Your best bet might be to purchase a really good after-market radio and have it professionally installed. Not much you can do for your existing radio without pulling it and having it tested to see if it still meets original factory specifications. If you go to that much bother, and it's a really...
  16. hevans1944

    Help me to understand this circuit

    Thank you for the extended analysis, @dorke. I don't know what V_808 is supposed to do. And I failed to notice that Q8 is N-channel while Q7 is P-channel MOSFET. So, if power is present, Q8 turns on and grounds the gate of Q7, presumably turning Q7 on and allowing voltage to appear at the anodes...
  17. hevans1944

    Boost Car Radio Signal

    As with real estate, it's all about location, location, location. Underground or in a parking garage or in a tunnel is bad. Atop a mountain is usually good. You can disconnect the car radio antenna and substitute an antenna with more "gain" but it will be directional and probably not very...
  18. hevans1944

    Will this be safe to test? Homemade Laptop Power bank

    Best to carry a looong extension cord with your MacBook Pro Retina and power it from a wall outlet. That's what my wife does with her MacBook Pro Retina when we travel. At home, the wall outlets are located conveniently close to the MacBook power supply. I suppose transferring to a school more...
  19. hevans1944

    Help me to understand this circuit

    Everything to the right of the inductor, the MOSFETs, the Schottky diode, etc. are part of a monitoring circuit used to identify the presence of the input voltage. Since the output of this buck converter circuit is regulated by feedback voltage-divider resistors R3 and R4, introducing a diode to...
  20. hevans1944

    Boost Car Radio Signal

    Absolutely! You simply increase the power of the transmitter.:eek:
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