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  1. L

    quadrature singal

    http://www.eecg.toronto.edu/~kphang/papers/2001/dong_IQphase.pdf What is the intended frequency when the control voltage is +10V? -10V? 0V? Is there a 180 degree phase shift over the +/- range? Is 'A' meant to be adjustable/settable over some range?
  2. L

    AC vs DC in project

    Batteries are safe but can be a hassle. Using "an electrical outlet with a rectifier" just sounds so wrong. Have you considered using an AC adapter? Radio Shack sells these in a range of voltages and are about as safe as using batteries.
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    diode bridge

    The word 'dynamo' usually refers to a generator employing a commutator to produce DC current. If that is what you have, then a diode bridge should not be necessary for your setup. However, if your dynamos are generating AC then visualize the problem of just connecting two in series: frequency...
  4. L

    The Value of a Missing Resistor?

    I would not worry about the resistance of R1 and R2. If you know the current through R1 then you can calculate the voltage across R1. This will be the same voltage across R2, from which you calculate the current through R2. Add these currents together to get the current through Rx. Subtract...
  5. L

    DIY Brainwave Monitor

    Did Wyatt Earp ever miss? Not easily.
  6. L

    Simple circuit help

    For dial-up consider using a transistor switch for each LED with a resistor and LED at the collector, and a base resistor driven by the potentiometer. For the second LED add a diode in series with the base resistor. For the third LED add two diodes to the base resistor. The design will be...
  7. L

    DIY Brainwave Monitor

    http://openeeg.sourceforge.net/doc/
  8. L

    Hello Im new this is my first post, I have lots a questions.

    Your power supply has the appropriate voltage and sufficient current capability for your needs; however, this being an audio application, I would check that adequate electrical filtering is included to suppress AC hum. Even though the unit may have large electrolytic capacitors, who knows for...
  9. L

    Digital electronics

    A universal gate is a gate which can implement any Boolean function without need to use any other gate type. I agree with (*steve*), there are only two.
  10. L

    LED Help!

    The cheap and dirty way is to multiplex the LED's. For instance, wire the LED's in banks of eight (assuming you are not using the external interrupt RBO/INT): connect RB0 to LED1, LED9, LED17, LED25, LED33, LED41, LED49, LED57; connect RB1 to LED2, LED10, LED18, LED26, LED34, LED42, LED50...
  11. L

    DC and Low Pass Filters

    My first thought on reading that was, "No, it's not magic; it's just physics." It also illustrates the difference between engineers and physicists. The linear circuit analysis textbooks that engineers study introduce the capacitor as an ideal circuit model along with the differential equation...
  12. L

    DC Current Booster

    It would be interesting to investigate using a charge pump to lower the voltage. Charge pumps are normally used to double, triple, etc., a smaller voltage. This approach will not increase current but it will conserve charge, which seems to be your goal. The approach is to use the 5V capacitor...
  13. L

    DC and Low Pass Filters

    DC is as low in frequency as you can get. So DC has no problem passing through a low pass filter.
  14. L

    Fast Counter Design

    Have you considered using one of the arduino external interrupts? Then just have the interrupt handler increment a register. When you say the signal has positive and negative peaks of 10 usec duration, it suggests there may need to be some signal conditioning for the input.
  15. L

    Large Variable Capacitor

    @Vivake: When you said "create" I thought that meant "build" your own large capacitor plates. Normally gyrators are used to simulate inductors by using capacitors, but it is possible to simulate a variable capacitor with a gyrator using an inductor and variable resistor. For instance, see the...
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    Large Variable Capacitor

    Capacitance is proportional to surface area, so in order to get more capacitance the device needs to be made larger. For a mechanical approach the size of the plates need to be made much larger. For digital switching with FET switches the largest component capacitor would need to be 0.5 uF...
  17. L

    hex to octal converter with display

    Since this is a homework assignment, do you suppose the professor gives extra credit for finding a commercial chip? Or is designing a segment decoder from scratch part of the assignment? My guess is the learning experience demands the student build the truth table for each segment, construct...
  18. L

    hex to octal converter with display

    For 4-to-7 hexadecimal decoding the convention is that the B & D digits are displayed as lower case. 0 1 2 3 4 5 6 7 8 9 A b C d E F
  19. L

    thevenin's help

    Thévenin's theorem for linear electrical networks states that any combination of voltage sources, current sources, and resistors with two terminals is electrically equivalent to a single voltage source and a single series resistor. The single voltage source is the open circuit voltage (no load)...
  20. L

    Follow ME

    I would try something like a high frequency pulse infrared emitter mounted in a cap. Then in each corner of the room mount filtered infrared sensors with each sensor having several infrared detectors at a different angle into the room. The tricky part would be getting simultaneous signal...
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