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  1. K

    Simple RC circuit problem

    I am always coming up with new problems in electronics. Take a simple RC circuit and apply a triangle wave. Doesn't the signal divide down. This means there is a change in current. But on the other hand, the capacitor following the equation I = C dv/dt will have a constant current. So, must not...
  2. K

    Bad 7912's

    There are only a few combinations to try with a 3 terminal regulator. I tried them all with a variable negative regulator. The only good aspect to any of the combinations was the power supply voltage at the output. This won't work.
  3. K

    Power MOSFETs

    What do you suppose the gate capacitance amounts to. If they say it's in picofarad range, that is real low. I have seen picofarad capacitors and they seem much larger than the would be gate capacitance. So I wonder if the specification is intended for calculation purposes only. That is the...
  4. K

    usb project

    What is the protocal of the USB. How does it synchronize and what is the amount of data it can transmit in one synchro. How does it compare to HDLC? I bet it is very similar.
  5. K

    I wish I knew

    Yeah. The magnet I taped to the tube was placed in a strategic location to give me a more horizontal DC line. I don't blame Madell for this skew. I just figure it is all part of the tube manufacturing and the solution I implemented is acceptable.
  6. K

    Bad 7912's

    I have heard comments of 7912's not functioning properly and I am the next victim. What is going on with these bad parts. I didn't ask, but I think the person I talked to got their parts from another distributor. Has anybody experienced bad regulators before. Although the likelihood of getting...
  7. K

    Convert Current

    Check out the Projects section for 12V 500ma. I have given the answer to your problem. It is a simple voltage regulator that will take your input and deliver the voltage and current. This will take some design work but maybe I can steer you in the right direction. Use the TIP31A available from...
  8. K

    I wish I knew

    I wish I knew that Electronics Lab offered a cheap oscilloscope. The one I bought off Ebay is a Madell. There is an interesting story behind it too. Right after a purchased the thing the horizontal went out. They were very kind in their repacement attitude and I received a new one. The only...
  9. K

    regulated 12 v dc and 500 mA current o/p

    If you have a low peak to peak at the capacitor, don't you still have the peak to peak at the input. This means there is a large peak to peak dropped by the diode. But it doesn't matter because the DC potential at the capacitor keeps it reverse biased. Just for you audioguru, I like to think of...
  10. K

    cyclic timer

    Are you going to use the motor to control a valve? The motor can be caused to turn slightly by applying a small voltage. You want the small voltage to change polarity so I would use a two polarity supply. The logic will will supply a high or low when you need the motor to turn. It will have one...
  11. K

    regulated 12 v dc and 500 mA current o/p

    I found the reason for the drop in rectified voltage. It was the diodes. You must select diodes with a high enough impedance to filter. The peak to peak across the diode is high but the diode remains reverse biased because of the DC potential. This way you can have a high peak to peak across the...
  12. K

    0-20 (3A) and 0-40 (1.5)A Power Supply (Elenco)

    Doesn't that mean that the drain voltage will remain constant like a voltage source with the current changing with the signal.
  13. K

    0-20 (3A) and 0-40 (1.5)A Power Supply (Elenco)

    Has anybody ever tried connecting a resistor to the power supply through a MOSFET. If you set the VGS to maximum then you can get the power supply voltage at the drain. Then you can apply a signal through that resistor and the drain will hold it's voltage. So you can have a changing current...
  14. K

    transformer windings

    Not only that. I found that my meter is only good at measuring sinusoidal waveforms with respect to ground. Sometimes I have to decouple the signal to measure RMS. I even get false readings sometimes. I'll go to measure the voltage, read the voltage, pull the probes away and still measure a...
  15. K

    project ideas

    Drive a motor and sense the feedback. You can have direct servo control or A/D and tune the motor at the correct voltage to get the speed right. Try a different load and adjust the voltage.
  16. K

    Ask about design a Frequency Synthesizer

    What you want is a variable oscillator. Start with a standard oscillator and try to vary the frequency using different components. Keep the active component the same or use several. You can switch power to components if you need. The component remains inactive until you switch power to it by...
  17. K

    regulated 12 v dc and 500 mA current o/p

    I constructed this regulator. One of the problems is that the DC after rectifying and filtering is a little low. I should be getting something closer to the peak value. Has anybody experienced this? I know that the DC should be close to the peak value after filtering. Where is the loss? I think...
  18. K

    regulated 12 v dc and 500 mA current o/p

    The basic requirements for a voltage regulator are feedback and a main current transistor that is controlled with the feedback. The feedback goes to the base of the control transistor. The collector of the control transistor goes to the base of the main current transistor and the input through a...
  19. K

    PC oscilloscope useful or not

    It seems the only thing to a PC oscilloscope is the display. Else, the electronics hardware is the important part.
  20. K

    Looking to build a scoreboard

    You can run a cable as long as you want. A scoreboard is a simple undertaking. How much power did you want to display? Do you want to light bulbs? I think a start is to determine whether you want run the power to the display or power up the display from where it sits. You just modulate the...
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