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  1. BobK

    5 Digit Digital stop watch using a MC14553b and TIL 311

    That would improve the duty cycle, but not the accuracy. A 555 timer is not likely to give you .01 second accuracy over 10 minutes. Far from it in fact, you would be lucky to get accuracy of 6 seconds over 10 minutes (1%). You need 1 part in 60000 accuracy. Only a crystal can do that. Bob
  2. BobK

    220V voltage to digital voltage

    You need a diode to ground, parallel to the zener to conduct in the negative half of the AC cycle. Also, the .47uF capacitor is going to limit the current to about 40ma. How current do you require? Bob
  3. BobK

    Looking for resistor value and capacitor value for passive low pass filter remove RF

    Nerve condution is not electrical conduction. It is a chemical process in which the permeability of the nerve to ions changes and this propagates down the nerver fiber. And this travels way slower than the speed of light, a max of about 120 m/sec. Compare to 3x10^8 m/sec for light or...
  4. BobK

    Bottleneck 555's 0.2A Stuck project

    The 555 is not seeing the high current, so take out the red line to pin 4. On the other hand, the ground lead of the motor, the source and drain of the MOSFET, and the anode of the diode are seeing the 10A, so these wires should be red. Bob
  5. BobK

    Patents / Freedom

    In my dreams! But, in my younger days, I invented a voltage controlled sawtooth generator using just a BJT as a constant current source and a UJT relaxation oscillator. It was quite amazingly good in linearity considering how simple it was. Bob
  6. BobK

    Non invasively monitor AC backup generator power.

    The jack has 3 connectors, left, right and ground. Bob
  7. BobK

    Patents / Freedom

    I think you should preface that advice with the "I am not a lawyer" disclaimer :) Bob
  8. BobK

    Patents / Freedom

    Patents expire after 17 or 20 years (depending on when filed.) So, no, you would not have to pay royalites on the Moog patent you reference. You are in violation of the patent if you use any of the claims it contains. Patents are generally written as broadly as possible. I did not read...
  9. BobK

    hi! i need a programmer for my pic16f84

    A pickit 2, for $35, is not only a programmer but also in in circuit debugger, which you will not get with a DIY programmer. And how much is your time worth? How many hours will you spend trying to get a DIY programmer to work? How much more time will you spend debugging without and...
  10. BobK

    Programming Help

    Try zeroing the timer just before turning it on. bob
  11. BobK

    transistor switch for LED's

    Use a lever switch. The card would simply hit the lever when fully inserted. These can be found in SPDT easily. Here is one that might work: http://www.digikey.com/product-detail/en/ZMA00A150L04PC/CKN10157-ND/2044493 Bob
  12. BobK

    GSM based simple project

    You will need a microcontroller and a GSM module. Check out the schematics of the GSM shield and how it connects to the Arduino for some idea. Bob
  13. BobK

    Help using TIP42c

    The 2n3904 is rated at 200ma, so you don't want to go any higher than that. It has a gain of about 100, so choose a base resistor to provide 2ma at 5V. I.e. 5 = 0.002 R R = 2500 Bob
  14. BobK

    transformer

    Unless he wants 2 isolated outputs. Which is what I assumed when he is talking about cutting the windings. Bob
  15. BobK

    Help using TIP42c

    Well, 500mA at 27R is 6.75W. So you need a 10W resistor. I would go to a MOSFET if I were you. Bob
  16. BobK

    transformer

    What 2 outputs are you looking for? Do they share a common ground, or must they be isolated from each other? Bob
  17. BobK

    Fitting an exponential curve to inductance graph

    You don't need to plot any exponential curves. All you need to know is how long it takes for the current to rise to 62.3% of the final value. That time is the time constant, you can read it directly off the scope. But I would not rely on getting better than about 10% accuracy. For example...
  18. BobK

    How to limit amplifier output power

    Unless you plan on using ear-splitting volumes, don't worry about it, just don't turn it up too high. Bob
  19. BobK

    Fitting an exponential curve to inductance graph

    Well, you never actually reach the full current, so determining the point at which it reaches the full current is pretty difficult. The way you would determine the time constant (and thus the inductance) is to find when it reaches (1-1/e) or 62.3% of the final current. Bob
  20. BobK

    need help about pointers

    Google "C tutorial" Bob
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