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  1. BobK

    Battery charging regime for low charge rate?

    Charging NiCd batteries is not simple. http://batteryuniversity.com/learn/article/charging_nickel_based_batteries. Bob
  2. BobK

    Help with reading schematic

    I think a "compassator" is an electronic component that has empathy with other components. Bob
  3. BobK

    watts vs joules energy

    dV/dt = I / C At 1A a 16666 uF capacitor will charge at a rate of 60V / second. Bob
  4. BobK

    12v to 440v step up

    If by decent amps you mean at least 1 Amp, you will need to draw about 40 Amps from your battery. The Cold Cranking Amps is what the battery can supply for 30 seconds, so I don't think that figure is of any use to you. How much current do you need and for how long? Bob
  5. BobK

    Calculate switching frequency for IGBTs

    Start with what your requirements are, then look for a part that meets them. Bob
  6. BobK

    555 Timer Circuit and 4017 Decade Counter

    I see a trailing effect, it just doesn't go across the entire range, it trails off for about 5lights behind the moving section. Bob
  7. BobK

    Help with reading schematic

    If you are looking for an adjustable voltage power supply that is not it. Try looking in the LM317 datasheet. Bob
  8. BobK

    basic electronics question - help

    Hi and welcome to the forum. This should tell you everything you want to know about using LEDs. https://www.electronicspoint.com/got-question-driving-leds-another-work-progress-t228474.html Bob
  9. BobK

    Diode identification

    You are quite lucky they were 24V zeners. If they were 5V you would have seen some smoke. The resistor was there to limit the current if you placed a voltage too high on it. Bob
  10. BobK

    Does order ever matter in a series circuit?

    Hand your professor a sealed box with an LED and resistor in series and a + and - lead coming out and ask him to determine whether the + lead is connected to the LED or to the resistor. Bob
  11. BobK

    Multiplying Resistance

    Unpowered? No wonder you are having problems! The schematic leaves off the power connections, but you must have them. A 741 will require a dual power supply, i.e. one that is positive wrt gound and one that is negative. Use two 9V batteries connected in series with the middle being...
  12. BobK

    DC Booster IC

    Have you taken out the 10 Ohm resistor? At 5V that is going to drop the voltage by half at 250ma which will get you only about 100 ma out at 9V. Edited: more like 50ma, I forgot that the input voltage was going to be 2.5V after dropping in half. Bob
  13. BobK

    Multiplying Resistance

    I agree with you that this looks wrong. For one thing the spectrum analyzer is showing a waveform at about 80Hz rather than 40Hz. And the harmonics are not falling off as they ought to at 12db / octave. First of all, what op amp are you using, and with what supply voltage(s). Are you...
  14. BobK

    DC Booster IC

    Yep, they really do need about 9V to work. At 9.5V you are going to want 50 Ohms to limit the current to 30ma. If all 14 segments are active this would be 0.42A which given the the boost from 5 to 9V at say 75% efficiency would require about 1A from the batteries. This is really pushing it...
  15. BobK

    Help on leds

    CREE and LUXEON are high powered LEDs used for lighting. Bob
  16. BobK

    noob question on current rating

    The thermostat does not draw 5 amps, it can handle switching of 5 amps. Only the bulb is drawing significant current. The power supply should be able to deliver an excess of what the bulb will draw. bob
  17. BobK

    Multiplying Resistance

    Earlier in this thread you posted a circuit that you said was not working. I simulated it and it did exacly what I expected. Perhaps your expectations are wrong. Why don't do try a fixed frequency filter and tell us exactly: 1. What is the intendeded cutoff frequency. 2. What is the...
  18. BobK

    Where to start with arduino controlled electromagent

    Quickly is an imprecise word. In our world quickly could mean measured in nanoseconds. It would not be used to describe what I saw on that video :) Bob
  19. BobK

    Is Differential Amplifier badly inaccurate?

    An instrumentation amp can allow for common-mode voltage well outside the power supplies to the op amps. But you do not need that. Once again, if you stay within the common-mode specification from the datasheet it will work. I don't know why you are being so paranoid. Bob
  20. BobK

    DC Booster IC

    How are you connecting the 7-segment displays? Are you sure they want 9V? Do you have a link to the part? Bob
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