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  1. BobK

    how to convert 5mV to 15V

    To convert a 5mV power source to 15V, practically impossible. To convert a 5mV signal to a 15V signal, using a power source, not too difficult, an op amp or comparator would do the trick. Bob
  2. BobK

    UV LED Exposure Box

    Did you look at all at the output ratings (mcd). The small LEDs output 1000mcd, the large ones output 30000mcd. So 1 high power one will replace 30 of the small ones. Bob
  3. BobK

    measuring time interval signals using a watch

    Yet they all seem to understand miles per hour and miles per gallon. Bob
  4. BobK

    measuring time interval signals using a watch

    I am sure you can answer this: If you counted 30 pulses in a minute, how many seconds between pulses? Now can you write down the equation to convert from pulses per minute to seconds per pulse? Bob
  5. BobK

    Reverse the voltage?

    Thanks, I'll have to get the free version and try it out. With TI having consumed National, I would think they might have a good library of analog parts. Bob
  6. BobK

    Reverse the voltage?

    CDRIVE, What is the schematic / simulution package you use to produce the circuits you post? They really look good. Bob
  7. BobK

    A Level Project - Powering Two Amp/Speaker Setups

    Don't just switch the polarity of the power! Check it, and get it correct. If you connect it wrong you could destroy the amplifier. Your voltmeter should tell you the correct polarity. Do you know that the switching power supply is in working order? What voltage does it measure when not...
  8. BobK

    Op-amp help please!!!

    Yes, I agree with everything you said. My point has always been the that only difference between a "dual supply" and "single supply" op amp is how close the inputs and outputs get get to V-, and I see nothing in your post that disputes that. Bob
  9. BobK

    Op-amp help please!!!

    Because you told me op amps only work with a single supply when you provide a low impedance virtual ground, and this circuit does not do that. (I don't think it would not work, I am disputing your previous statement) Bob
  10. BobK

    Op-amp help please!!!

    @Laplace Okay, please describe to me why this circuit does not work. You will note that there is no vrirtual ground in the circuit, and it is using a "dual supply" op amp. Also explain why it would start working if I put two 15V supplies instead of 1 30V supply. The specification: The...
  11. BobK

    Need Transistor to relay help ASAP

    Hurrah! Bob
  12. BobK

    Op-amp help please!!!

    Okay, then, tell my what is different about single supply op amps that allows them to work without a low-impedance virtual ground? Bob
  13. BobK

    Voltage Divider feeding Op-Amp Confusion.

    Another way of looking at it is to consider the Thevenin equivalent of the R1/R2 divider. It is equivalent to a 1.25V source and a 975R series resistor. So that resistance is in series with the 1K R3 and therefore the gain of the amp is - 1K / 1.975K or 0.506. Multiply this by the 1.25V...
  14. BobK

    Op-amp help please!!!

    I like to think of the other way around. All opamps work off a single supply. If they did not, why don't they have 3 power connections? The difference between dual supply and single supply opamps is in how close to V- the inputs and output can go. Older one like the 741 can only get within...
  15. BobK

    How to added up a Resistor Value using misc values

    Why do we keep spoon feeding this troll? If he had bothered to look at the results of the search I did for in the very first response to this thread, he would have found what he was looking for. But apparently that is too much work. Bob
  16. BobK

    Near signal detector

    How loud is this thing? Might it be disturbing to the turtle? Bob
  17. BobK

    How to added up a Resistor Value using misc values

    Let me google that for you: http://www.lmgtfy.com/?q=parallel+and+series+resistor+calculator Bob
  18. BobK

    Need Transistor to relay help ASAP

    Okay, just wanted to make sure you got it the right way, because it would be would go up in flames if the wrong way. Bob
  19. BobK

    Need Transistor to relay help ASAP

    Well, it should be less than 600ma at 24V I hope. It also just occurred to me that, since you were not familiar with which lead is which on the transistor symbol, you also need to pay attention to the diode. ------------------|<------------------ cathode -------------- anode And on...
  20. BobK

    Need Transistor to relay help ASAP

    The 3.3K base resistor was chosen to make sure the 2N4401 is saturated at the maximum current spec of 600ma. By the way, hopefully you determined that the relay coil draws less than that. I don't think you ever gave us the specs on the relay. Bob
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