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  1. hevans1944

    Transformers in parallel

    The secondary voltages must be closely matched or there will be heavy circulating currents between the two secondaries when they are connected in parallel. I learned this the hard way some fifty years ago when I tried connecting several 6.3 VAC filament windings in parallel. There was enough of...
  2. hevans1944

    Van de Graaff Generator

    You never "deliver" voltage to a capacitor, spherical or otherwise. Voltage is the result of charge being moved from one plate to the other plate of a capacitor: V = Q/C, where V is the voltage in volts, Q is the charge in coulombs, and C is the capacitance in farads. In the case of the...
  3. hevans1944

    Thévenin equivalent circuit

    Don't forget to include the 520 V that is dropped across the 260 Ω resistor. This voltage is in series with the voltage dropped across 40 Ω resistor to determine the open-circuit voltage between nodes A and B.
  4. hevans1944

    RPM sensor for rotating shaft

    Why can you not measure the AC output frequency directly? Just use a zero-crossing pulse generator and feed the 120 Hz pulses to a microcontroller that measures their frequency (or, more easily, their period) and controls the "load" resistance accordingly.
  5. hevans1944

    Van de Graaff Generator

    Google is your friend here. The answer is: You might also want to visit this page. Define "normal capacitors" please. The continuous discharge from a Van de Graaf occurs because a continuous charge is being delivered to its "spherical capacitor" by the moving belt (or chain in the case of a...
  6. hevans1944

    Missing parallel resistors

    Ouch! Last year I wondered why the NiMH cells in my KX3 transceiver wouldn't take/hold a charge, so I opened the KX3 up and discovered one of those cells had corroded and made a mess inside one of the two 4-cell battery compartments. I didn't want to send the KX3 back to Elecraft again right...
  7. hevans1944

    Missing parallel resistors

    My first introduction to a slide rule was something my father used as a navigator/bombardier during WWII. I never did figure out how to use all its features, but it was circular, about six inches diameter, and therefore equivalent to about an 18-inch linear slide rule. See a picture of it here...
  8. hevans1944

    Hammond Organ Schematics

    You could try to telephone to see if they are still in business: (708) 352-8011.
  9. hevans1944

    Missing parallel resistors

    You aren't wrong, but I don't usually bother to calculate what I need to put in series or in parallel with a given resistor to obtain a specific value. I just use my ohmmeter and plug away with whatever values I happen to have in my "junque box" of FOUPs (Fine Old Used Parts).:D This only works...
  10. hevans1944

    type of diode/protection

    I suppose a rectifier diode (1N400x family) inserted in series with each supply, with the anode of each diode on the positive terminal and the cathodes tied together and connected to the swing motor would also work... at the expense of one diode forward drop (about 0.7 volts) decreasing the...
  11. hevans1944

    Missing parallel resistors

    Well, @Mr Musabe have you figured out how to "fill in the blanks" or do you want us to do that for you too? Since this is homework, that ain't gonna happen... at least not by me. If you post your results however, someone here will check them for you, and possibly point you in the right direction...
  12. hevans1944

    Hammond Organ Schematics

    Check this site to purchase Hammond service manuals and owner's manuals.
  13. hevans1944

    type of diode/protection

    Perhaps you could wire in a simple DPDT toggle switch with a center-off position (ON-OFF-ON). Common terminals wired to swing motor, contact terminals wired to battery pack on one side and to wall wart supply on the other side.
  14. hevans1944

    Incident with a motor pump

    When you replace the motor, you might consider wiring a Cinch-Jones male connector with spade prongs on a short lead to the motor and a female Cinch-Jones connector to the power cord. Then, when Bozo trips over the cord again, it will simply disconnect from the motor.
  15. hevans1944

    Missing parallel resistors

    I agree with @davenn. The dashes under R3 in rows a, b, and c imply that no value is assigned there, that R3 is not part of the problem. The remaining blank spaces in rows a, b, c, d, and e are easily solvable as Dave pointed out.
  16. hevans1944

    Getting a led to turn on when voltage is under 3 volts on a battery

    It's box mod (for modification), not box mode. A fairly recent description of vaping can be found here. The box-type power units are a favorite of "cloud chasers" because they are capable of driving a very low resistance atomizer coil, usually a drip coil, to produce copious amounts of vapor. I...
  17. hevans1944

    Looking for 3-axis magnetometer chip

    @evol_w10lv : It sounds like you know what you are doing, and are aware of the limitations of the sensors required for an inertial nav system. Depending on your application and reliability/accuracy requirements, a GPS receiver could be much more reliable than a magnetometer to make corrections...
  18. hevans1944

    Sensor for automated retail kiosk

    Hasn't this problem already been solved by vending machines that dispense a product? The buyer presses on a "door" that opens backwards to provide access to the product after vending while a mechanical mechanism operated by the door simultaneously prevents access to unpurchased product. How is...
  19. hevans1944

    Looking for 3-axis magnetometer chip

    A three-axis magnetometer is not the best choice for a navigation aid. The Earth's magnetic field varies all over the map (literally!) with changes in latitude, longitude and altitude. Plus you need some mechanism to "null out" the effect of nearby ferromagnetic elements, assuming those remain...
  20. hevans1944

    Common Cathode Triple digit display pinmap help!!!

    Yep. Just imagine you have the task of connecting each segment and decimal point and cathode to a pin without crossing any wires. Once you find out where the pins are for one digit the pins for other two should fall right into place. This ain't rocket science, it's just wires. OTOH, if you find...
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