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  1. BobK

    Ultra-Capacitor Powered Car

    Why is regenerative braking needed to drive 50m at a constant speed? Bob
  2. BobK

    Controlling multiple TVs with buttons

    Break one of the wires to the speaker on each TV and run two ends to a switch. Bob
  3. BobK

    Tracking a toy car in a game

    A GPS only gives you accuracy of about 10m. This is huge to a toy car, probably larger than the area they are running around in. An overhead camera might be a better idea. If you control the background, and make each car a different color, the processing to determine where the cars are could...
  4. BobK

    Capacitors

    If you are playing with circuits on a breadboard, what voltage are you using? In most cases, there will be no voltage larger than that across any capacitor. The exception is boost circuit like the photoflash Gryd3 mentioned. These will create larger voltage from small ones, and generally...
  5. BobK

    parallel led array

    Well, you were told wrong. As long as the voltage across the LED matches the LEDs specification it will put out the same light whether in parallel or in series. But 2 in series uses exactly half the power of 2 in parallel. I have given you the best way to get the most light out of the LEDs...
  6. BobK

    Short circuited tablet battery?

    Ah, you probably zapped some of the protection circuitry in the battery. That explains why no fire! Bob
  7. BobK

    Turning supercapacitors into batteries

    Depends strongly on the max voltage of the supercap. Assuming a 5V one, which might be useful for this purpose, and are commonly available: For the battery, a 18650 cell with 4000 mAH has 4 * 3.7 * 60 * 60 = 53280 Joules of energy A supercap will have 1/2 C V^2 For 5V we have: 1/2 C * 25...
  8. BobK

    Short circuited tablet battery?

    You are lucky it did not catch fire. If you did this with the battery out, just replace the battery. If it was I n the phone at the time, the phone was probably damaged. Bob
  9. BobK

    How to switch something as soon as power is applied

    A better solution is to exp!ain the feature and why they want it. In my Prius you don't even notice when the car starts unless you are paying attention to it. Hacking the car to reduce its gas milage sounds like a dumb idea to me. Bob
  10. BobK

    Allan Timer Circuit

    What does it do? It should be easy do duplicate it with any microcontroller. It looks like it drives 2 relays through 2 opto-isolators. Bob
  11. BobK

    parallel led array

    Morticia can type faster and more accurately than I, but she lacks the electronics knowledge that I acquired while studying with the good Dr. Frankenstein. Bob
  12. BobK

    Hacking a microwave oven

    Did you read any of the warnings in this thread? There are lethal voltages in a microwave oven even when it is not plugged in. I would not take apart a microwave oven until it had been disconnected from power for about a month. Bob
  13. BobK

    parallel led array

    The brightness of an LED is roughly proportional to the current, though it falls short of this linear relationship as the current approaches the maximum. Or, to put it another way, LEDs are slightly more efficient when run at maybe 1/2 the max current, where they will put out more than 1/2 the...
  14. BobK

    parallel led array

    Also, how did you calculate your 2.7Ω resistor. I come up with 1.6Ω to run a 1400mA 1.4V LED from a 3.7V battery. (3.7 - 1.4) / 1.4 = 1.64 With a 2.7Ω resistor you are running them at about half power, which is perhaps intended. Also, 1.4V * 1.4A is less than 2W, not 5W as advertised. If...
  15. BobK

    Turning supercapacitors into batteries

    The other thing that distinguishes a capacitor from a battery is the discharge curve. A capacitor will lose voltage linearly as discharged. A battery holds its voltage, or declines at a slow rate up to a point then falls off rapidly. This makes the battery more suitable to power a device...
  16. BobK

    Electric arcs and spark gaps: Are they active or passive devices?

    How about a normal diode, active or passive? I would call the spark gap active for the same reason I would call the tunnel diode active, it exhibits hysteretic behavior, meaning how it acts depends on the past. Bob
  17. BobK

    parallel led array

    The way you are doing this is the most wasteful way you could come up with. You are using only 38% of the power from the battery to power your LEDs. The rest is going into heat in the resistors. Want 2X the battery life? Put 2 LEDs in series. The voltage is 1.4V so 2 is 2.8V, which is fine...
  18. BobK

    pwm opinions

    Please draw a schematic for us. The MOSFET you are using should not even get warm at 3A if you are using it correctly. If you can't provide a schematic, at least assure us that the voltage on the gate is at least 10V higher than the source. I suspect t that you are using either insufficient...
  19. BobK

    pwm opinions

    Schematic please. Bob
  20. BobK

    Split Voltage for Driver IC & Backlight

    No need, Analog Kid already gave you the simplest solution. It will supply 3V to the backlight and 1.5V to the driver. Theoretically, both batteries would by supplying the back light and only one supplying the driver, so you might think that one would run down faster than the other, but the...
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