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  1. BobK

    5v solar usb charger

    Get a multimeter. It will be far cheaper than blowing out your phone or speakers by "winging" it. Bob
  2. BobK

    Problem with 13.8v to variable output circuit using LM317T regulator

    The resistor is the schematic is 510 Ohms. The resitor you link to is 510K = 510000 Ohms. Try using the correct resistor and see if things improve. Bob
  3. BobK

    Buttons!

    Sounds like a job for a 3D printer. You could design caps for a tact switch like Steve suggested. Bob
  4. BobK

    Is my IR photo interupter dead? Can you test them

    Did you try blocking the path and see if that made a difference on the signal line? It is possible that the signal goes high when it is blocked. Bob
  5. BobK

    Automated counting system

    You could build such a thing, but how do you know whether 1 or 2 parts were dropped? Bob
  6. BobK

    Power rating on resistors

    You can always use a higher wattage resistor in place of a lower one. Bob
  7. BobK

    How to get a strong signal over a long distance

    1 KB and 1MB are not data rates, they are amounts of data. A rate is an amount per unit time. If you want to transmite 1KB in 1 second or 1 MB in 1 second, then yes, the 1MB will be much harder to achieve. But if you want to transmit 1KB in 1 second and 1MB in 1000 sec, the data rate and...
  8. BobK

    Infared Transmitter

    LEDs have a viewing angle specification that tells how directional they are. Bob
  9. BobK

    LED's unknown forward voltage & current measurements

    Without knowing one of the two, you really can't. The only way to know you have gone too high is when they blow out, and that is likely way above the current at which they will have a long lifetime. Bob
  10. BobK

    Limiting car audio volume

    Or a 1000V supply to the volume knob. Bob
  11. BobK

    Designing Schematics for inverting 741 OPAMP

    The GBP of a 741 is 1MHz, so the gain at 20KHz will be 50, not meeting your spec. Also the 741 is a very bad choice for single supply operation. Bob
  12. BobK

    'headphone' mixer

    With all the volume controls you want, an active circuit would be best. I would use a headphone amplifier that works like an op amp (most do) and use the summing configuration. Each input would go through a pot to control the level, and the feedback resistor would be the master volume. The...
  13. BobK

    Impedance Increaser

    Okay. You could also use an opamp voltage follower to get input impedance of 10s of Megohms. Bob
  14. BobK

    Charging & Powering at the same time.

    So you are admitting you lost the bet? Your new battery has 12 * 7.2 = 86.4 Watt Hours of energy. Calculate the Watt hours needed by each device by multiplying the current by the voltage by the hours of operation. For example, say the phones charge at 5V and 1A for 3 Hours, which I think...
  15. BobK

    Charging & Powering at the same time.

    Tell me the current draw of the LEDs and the amplifier, then we can talk :) Edit: Oh, and how long they must be powered. If you say a few seconds, you probably win. Bob
  16. BobK

    Impedance Increaser

    Look up FET preamp. What are you expecting to happen when you have "super high impedance?" It should not be needed for a microphone. Bob
  17. BobK

    Charging & Powering at the same time.

    Without knowing the current draw of the chargers, the LEDs and the speaker amp, I cannot say whether you would win or not, but my gut feel would be to bet on your son. 10 AA cells is barely enough to give a full charge to two mobile phones. Bob
  18. BobK

    Impedance Increaser

    That would be called a preamp. A FET preamp should do the trick. Bob
  19. BobK

    Stepper control using PC

    If you have a GPIO board, all you need is an H-bridge for each stepper motor winding, and of course software. Bob
  20. BobK

    circuit calculation

    I mentioned it in the last paragraph of my post. A buck converter. You can get these on Ebay for a couple of bucks. Bob
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