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  1. BobK

    Stabilising wienbridge sine wave using FET

    Nope, here is what you get if you use a shifted sine wave: The green is the voltage across the LED, the blue is the current through the LED, which is roughly proportional to the light output (but not exactly). The problem is that an LED is not a linear device. You can see that it puts out...
  2. BobK

    Stabilising wienbridge sine wave using FET

    You could possibly achieve a sinusoidal output from the LED by varying the voltage a small amount just below the nominal forward voltage, but the output signal would be considerably smaller than using a full wave, which let's you go from zero to full brightness. IR remotes use a square wave and...
  3. BobK

    can you power a 12v circuit from a car battery?

    You can use it as is. Bob
  4. BobK

    Wires and Power Supplies

    Is that picture your final wiring? The + side of the strips are not connected to anything! Bob
  5. BobK

    electric Bike

  6. BobK

    Stabilising wienbridge sine wave using FET

    You still haven't explained why you need a sine wave, and, as Duke pointed out, the output of the laser didoe will not be a sine wave with sine wave input. So, why a sine wave? If you don't really need a sine wave, as Duke pointed out, (and as I did much earlier), a crystal oscillator plus...
  7. BobK

    electric Bike

    What, and have it catch fire when you ride up too steep a hill? Bob
  8. BobK

    Apple vs the FBI

    I just looked an iPhone 6s teardown. In addition to the Apple A9 processor + ram chip it has this: Toshiba THGBX5G7D2KLFXG 16 GB 19 nm NAND Flash So the flash is a separate chip as I surmised. Now, it is possible that this chip is programmed to do the security check. Flash chips do in fact...
  9. BobK

    Apple vs the FBI

    Couldn't they simply remove the flash chip or chips from the device and read them something other than an iPhone? I doubt that the program that erases everything after 10 wrong keys are entered would be inside the flash chip. The data is presumably encrypted, but there are only 10000 possible...
  10. BobK

    Trickle Charge Batteries

    All that is needed is a voltage source significantly higher than the batteries full charge voltage and a resistor. The resistor should be calculated to drop (Vin - Vbatt) at a current of C / 20. This will cause a higher charging current when the battery is depleted, which is okay, going down...
  11. BobK

    Trickle Charge Batteries

    You can charge them forever at C/20. Any higher and it gets complicated. Bob
  12. BobK

    How do I multiplex lots of switches/LEDs with my Arduino

    For the outputs, you send a bit stream representing all of the LEDs then send a latch command. The LEDs that had a 1 in the bit stream will be on. You need do nothing else until you change anything, then you do it all over again. No flickering. Bob
  13. BobK

    1.2w/10mA LEDs

    Are you sure the blue LEDs are driven by a constant current source? That would be odd, given the size of the resistors. A voltage source of probably 5V seems much more likely. Bob
  14. BobK

    Wiring LEDs with different V & mA?

    Do not use the solutions with 3 LEDs in series. This is garbage, it will do nothing to regulate the current in the LEDs. In order for a resistor to regulate the current it must drop a couple of volts. The solutions with 3 LEDs in series have 4 volts on each of 3 LEDs giving 12V leaving...
  15. BobK

    Help with resistors

    Lavaguava's info about paralleling batteries is not correct. Once batteries of the same chemistry are paralleled they cannot have different voltages (since the terminals are tied together) so most of what he said cannot happen. If one discharges faster than the other it will stop discharging...
  16. BobK

    -12Vdc Circuit design

    Most likely your AC source is rated by peak-to-peak voltage and you have entered the RMS voltage. That would be true if you are using LTSPICE. To model a 9V RMS AC source in LTSPICE you have to enter 12.7V as the voltage. Bob
  17. BobK

    Transistor hfe

    There is something that the OP does not seem to get no matter how many times he is told. In a linear power supply, the efficiency is given by: Vout / Vin And the power dissipation of the circuit is given by: Iout * (Vin - Vout) That is it. It has nothing to do with any characteristics of...
  18. BobK

    Lullaby circuit

    I was thinking that there might be baby cards that already play a lullaby. No reprogramming needed. No problem fitting it in a small space. Bob
  19. BobK

    Lullaby circuit

    Look for a greeting card that plays a lullaby. These have very tiny modules in them. Not very loud though. Bob
  20. BobK

    Chosing the Right Tweeter

    You would never wire a woofer and tweeter in series. They would interact with each other in bad ways. Bob
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