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  1. BobK

    Battery charging bank help

    If you want to use that battery holder, you will have to break the existing connections, then connect all the pluses together to the red wire and all the minuses together to the black wire. That would put all the batteries in parallel. It does not matter that the batteries are facing different...
  2. BobK

    Battery charging bank help

    Soldering directly to the terminals is not a good idea, unless they have tabs welded to them. You might be able to find battery holders, which would make it easier. Bob
  3. BobK

    Another LED-diodes topic

    My wife just bought little string of LEDs that run off 4 AA cells. They have a single 18Ohm resistor, then they put a pairs of blue of yellow in series, and pairs of red and green, then then parallelled all those pairs. I have no idea why this works as well as it does, but they do seem to...
  4. BobK

    Electronic Door Activated Socket

    For someone with your level of knowledge to mess with mains wiring at a boarding school sounds like criminal negligence to me. Bob
  5. BobK

    Battery charging bank help

    Connect both of the batteries + terminals to the + input on the board and both of the batteries - terminals to the - input on the board. Which is what the seller is saying here: Bob
  6. BobK

    LM741 Integrator and Audio Amplifier circuits

    An operational amplifier takes the difference in the voltage of it's two inputs (+ and -) and multiplies it by a very large number (like 100000) and then outputs that voltage. All of the magic in using them comes from applying feedback from the output to the - input, which gives you great...
  7. BobK

    (woo woo) transformers 1:5 ratio - were to buy

    Fuunny that someone performed an earth shattering feat like that, and I never heard of it, when the media is all of the guy who flew an ornithropter design just a few hundred yards was all of the media. Bob
  8. BobK

    confused about hookup of a gate.

    If you are trying to measure resistance in circuit with power on, don't do that. You mention connections to Vcc, both inputs and the output, but no connection to ground. Is it connected? Bob
  9. BobK

    Total Voltage / Current Draw

    All is explained here: https://www.electronicspoint.com/got-question-driving-leds-t256849.html Bob
  10. BobK

    astable multivibrator

    The resistors you are asked to add are between the LED and V+. These are needed to limit the current in the LEDs. Bob
  11. BobK

    astable multivibrator

    More likely it is wired wrong. Also, you need a resistor in series with the LED load, you did not mention having one. Please post a schematic and pictures. Bob
  12. BobK

    LED Driver circuit

    Ah, the equation would be different here in the U.S. 24V 5A would only be 120W you would need 25 of these to run 3000W. Your cheapest option is the one you mentioned intially and we are not allowed to discuss here. If you want to take the risk and make sure these things are well protected...
  13. BobK

    powering a LED help

    No, a constant current driver is just that, it will raise the voltage high enough (within limits) to make 350mA flow. If you put a 20mA LED on it, bad things will happen. Bob
  14. BobK

    Non isolated mains LED bulb = illegal?

    If this bulb is like others I have bought, I don't think the exposed heatsink is actually exposed metal, it is coated with something which perhaps provides enough insuation. Bob
  15. BobK

    Need advice on adding a USB power port to tablet

    You will not get to 12V 2A from a 5V USB charger. They max out at 1 to 2A which is 10W at most, your 12V 2A charger is putting out 24W. You could probably get away with using a USB connector on the 12V 2A supply, but it would be misleading, encouraging someone to plug a 5V charger into it...
  16. BobK

    Amplitude and Frequency

    No, they are not harmonics. A two- or three dimensional object can vibrate in many different ways that are not harmonically related. These are called modes of vibration, and each mode will have a fundamental and harmonics. This is why bells, for instance do not produce a sound with only a...
  17. BobK

    Help for switching operation

    Actually the way I read it, what the OP describes is ~A & B. This easily done with logic gates. Bob
  18. BobK

    Amplitude and Frequency

    A jar or glass is going to have more than one resonant mode. Bob
  19. BobK

    Help with light-sensing automatic LED bicycle headlight

    LEDs can be used to detect light, but there are better sensors, i.e. photoresistors, photodiodes and phototransistors. That is not what an accelerometer does. An accelerometer measures acceleration (not speed) of itself, not of other objects. Bob
  20. BobK

    Non isolated mains LED bulb = illegal?

    This is a brand sold at Lowes, (big box hardware store in U.S.) so I suspect it has regulatory approval. Bob
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