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  1. BobK

    GUI (Graphical User Interface ) problem

    If you want a graphical UI on a TV, a Raspberry Pi is probably your best bet. Bob
  2. BobK

    Newbie question regarding 8w LED bulbs...

    Well, the 3 1W LEDs would produce a little less heat since they are more efficient, and it would be distruted over a larger area, which would require less heat sinking to keep it at the same temp as the 3W. So 3 x 1W is the winner. Unless space is a problem. Bob
  3. BobK

    Transistors

    A common collector circuit has current amplification but no voltage amplification. In fact, it is also known as a voltage follower, because the voltage at the emitter follows the voltage at the base - the Vbe drop. Bob
  4. BobK

    to make an LED blink

    If these methods worked at all, I don't think you will get satifactory results. Why not just use a blinking LED? Bob
  5. BobK

    Newbie question regarding 8w LED bulbs...

    State of the art is better than 100 lumens / watt. The bulb you pointed to is 50 lumens per watt. Bob
  6. BobK

    Newbie question regarding 8w LED bulbs...

    You can buy the LEDs without the electronics for less money. Look for 3W LEDs on Ebay for instance. One of these might be enough. Two would probably produce more light than the IKEA one you linked, since it is not particularly efficient. Then you want a constant current driver for them...
  7. BobK

    Inductor question

    More windings will increase the magnetic field if the same current is used, more current will increase the magnetic field if the same number of windings are used. The voltage needed to supply a given current depend on the resistance, which depends on the length (and inversely on the diameter)...
  8. BobK

    Transistors

    Read the first sentence of my last post. If beta is 100 and the transistor is operating in the linear region, then if the base current is 0.1mA, the collector current should be 10mA. Bob
  9. BobK

    seeking advice on a tiny repair project - replacing a capacitor

    Are there any markings on the part? How about posting close-up well lit photo. Bob
  10. BobK

    Measuring the inductance of a wirewound resistor

    Since I am your uncle, I'll take a stab at it. How about making a voltage divider driven with a frequency that makes the inductive reactance >> than the resistance? Then you should be able to ignore the resistance, and measure the reactance at that frequency. Bob
  11. BobK

    Transistors

    The beta of a transistor is the ratio of the collector current to the base current. But beta is not a constant, it changes depending on whether the transistor is in cutoff (basically no collector current), saturation (the most collector current you can get given the voltages) or the linear...
  12. BobK

    Transistors

    Think of it this way. You have a hose nozzle that has a very sensitive level that controls the flow of water coming out out of the hose. You "press" that lever by shooting it with a squirt gun. The small flow of water from the squirt gun then controls a large flow of water out of the hose...
  13. BobK

    Forward voltage help!

    It is not clear at all what those drivers do. It says constant voltage and constant current, which is impossible to do at the same time, and it does not appear to be configurable, so I have no idea what it will do. Bob
  14. BobK

    Inductor question

    Magnetic field is proportional to the number of windings and the current. More windings = more resistance = less current, so it is not that simple. Bob
  15. BobK

    Inductor question

    Inductors are normally wound that way. The inductance is proportional to the square of the number of turns, so adding 1 layer to a 1 layer winding gives you about 4X the inductance. Bob
  16. BobK

    timer

    Yes, you can make a timer from a capacitor and a string. If the string is length l, the period is 2*pi*sqrt(l / g). The capacitance and voltage rating do not matter, though a larger weight is helpful. Bob
  17. BobK

    Inductor help

    The equation for an inductor is dI/dt = V/L So, with a fixed voltage across the inductor, the current will rise linearly. This is with ideal components, i.e. a voltage source that has no current limit or internal resistance, and an inductor with no series resistance. In the real world it...
  18. BobK

    Astable multivibrator calculations and Multisim

    An analog simulator uses numeric integration to solve the equations at each delta t. Spice keeps reducing the step until the results converge, and it will tell you if the step becomes too small without converging. Don't know about multisim through. Bob
  19. BobK

    Voltage controlled thru opamp playing up?

    Never mind. Bob
  20. BobK

    Voltage controlled thru opamp playing up?

    Is it possible you cut and pasted the code for 1 channel to do that 2'nd channel and missed a change so that the 2'nd channel is messing with the 1'st? Bob
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