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  1. L

    weird question... i think

    One thing you could do is mess with the earthquake satellites..... http://www.kurzweilai.net/spacecraft-saw-ulf-radio-emissions-over-haiti-before-january-quake Spacecraft Saw ULF Radio Emissions over Haiti before January Quake December 9, 2010 by Editor Geoscientists say that the DEMETER...
  2. L

    transformer observation

    How about if you do a bifilar primary winding with a copper/iron pair. Then measure with just the copper wire being used, leaving the iron wire unconnected. Then measure using the iron wire, leaving the copper unconnected. Then explain those results.
  3. L

    transformer observation

    The source of the magnetic field is ampere-turns. Using iron wire certainly does not increase the number of turns. Also, there is no reason that using iron wire will increase the current flowing through the iron vs copper wire. So you really don't have a "theory" - what you have is an...
  4. L

    transformer observation

    What is the magnetic coupling between the spools? Is this an air-core transformer? If this is an iron-core transformer, then your stated results make no sense. For an air-core, the iron wire may be partially substituting for an iron core, whereas with copper wire it would remain as true...
  5. L

    RS232-RS485

    Check out the technical library at B&B Electronics. http://bb-elec.com/technical_library.asp They also have all the 232/485 interface products that you might need. Interfacing a 232 device to a 485 device can be fairly simple; however, interfacing a 232 device to a 485 network can be tricky...
  6. L

    Help with electronics question. Urgent!

    1.(a) - Does the {gain x bandwidth} constant have any relevance here? 1.(a)(i) - Does a 20kΩ resistor to ground have the same impedance as a 20kΩ resistor to virtual ground? 1.(a)(ii) - Google 'differential amplifier' http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar7.html#c1...
  7. L

    laser alarm problem

    The 4017 counter will not meet the stated design specifications. What you need is a CMOS RS latch or SR flip flop (Google 'RS Latch'). Connect the comparator output to the S input. Use the switch for the R input. The 741 on a 9V power supply may not reliably drive a CMOS logic input due to...
  8. L

    50 IR LEDs powered by 9v battery??

    What is the design advantage to multiplexing a flood light? I just don't see it. Is there some principle of physics at work there of which I'm totally unaware?
  9. L

    Capacitor Question

    The answer depends upon how far you are willing to have the voltage fall over those 10 seconds. As stated by a previous poster, C = Q/V = (dQ/dT)/(dV/dT) = (I x dT)/dV. In this formula, I=4mA, dT=10 seconds, and dV is the change in voltage over dT the time increment. Let's say your battery...
  10. L

    50 IR LEDs powered by 9v battery??

    In the first place, you would not run 50 mA through the LED -- that is an absolute maximum rating. A current of 20 mA is more reasonable. Also the data sheet shows a maximum forward voltage of 1.6 V, with a typical value of 1.3 volts at 20 mA. So at most you could string 5 LEDs in series...
  11. L

    Looking for ideas for electronic dog whistle

    For the transducer why not try an audio tweeter?
  12. L

    op amp circuit

    The purpose of the given circuit is to generate a negative signal edge to ground in order to trigger a 555 monostable from sound pickup by the microphone. In what way do you expect that function to be improved by an op amp?
  13. L

    Something simple...

    I would be interested in seeing test results for the voltage across the motor with no capacitors versus a full complement of capacitors (10,000uF). It seems clear how capacitors help with a purely resistive load but I still can't visualize how capacitors help with a motor.
  14. L

    How to convert 6V~3w input to 5V 500mA output (USB)

    I also have a 6V-3W hub generator which powers an array of 16 18,000 mcd white LEDs as a bicycle headlight. If the bike goes very fast the generator has enough voltage to also switch in series a 1 watt LED with a focused beam. I use a Schottky diode bridge rectifier to maximize the DC voltage...
  15. L

    USB Solar Charger Current Question

    The 7805 is a linear series regulator. Have you thought about using a shunt regulator instead? If the open circuit voltage of the solar array is 6.0 volts, try using a silicon power diode in series to drop 0.7 volt followed by a 5.1 volt zener power diode to shunt the current to ground. Then...
  16. L

    simulation tool

    Here is an example of using Mathcad for circuit analysis of your original circuit. The potentiometers are replaced by two resistors with a parametric variable, i.e., R2 becomes (x)R2 and (1-x)R2 where x has a range from 0 to 1.
  17. L

    Something simple...

    Trying to visualize how the capacitor will interact with the back-EMF of the motor, I can't decide whether the capacitor will be a help or a hindrance. Rough approximations suggest that for a motor drawing several amperes of current, a capacitor would need to be sized in excess of several...
  18. L

    Something simple...

    As a rough estimate let's say the resistor needs to drop 10 volts (28-18=10) at 2 amps. R=E/I=10/2=5 ohms. Your 25K resistance is a bit high. What I would try in place of the resistor is a string of power diodes in series, with each diode dropping 0.7 volt. You should not need more than...
  19. L

    A few questions regarding theory.

    Laplace said that 4 x 3,600 = 14,400
  20. L

    nodal analysis

    The description given is confusing. You say, "This is the transformed circuit." What was it transformed from? As shown it is set up for either node or mesh analysis. For mesh analysis you would use the loop currents shown, summing the voltage drops around each loop and obtaining 3 equations...
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