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  1. BobK

    Aux on portable radio

    Okay. But you cannot get an output from the input jack! The only way to do this would be to wire into the switch that selects AUX as input on the radio. That may or may not be easy. Also, are you taking about a Bluetooth transmitter or receiver? I would guess receiver, which is plugged into...
  2. BobK

    Aux on portable radio

    It is not at all clear what you are asking. Aux usually refers to an input and portable radios seldom have an aux input. Are you talking about the headphone output jack? And what is it you want to happen when a signal is seen on this jack. Switch on a Bluetooth transmitter perhaps? Bob
  3. BobK

    Amplifier for function generator output

    A bipolar power supply ±55V. Complementary pair of Darlingtons, direct coupled to output. Op amp as input stage with the feedback taken from the output stage. Bob
  4. BobK

    Sketch question

    I think what you want is this: You can press button 1 at any time and the first relay will stay energized for 1 second. You can also press button 2 at any time and the second relay will stay energized for 5 seconds. In order to do that the loop has to be structured very differently. The...
  5. BobK

    Issue in BLDC motor

    There might be a simpler answer. Have you checked the motor terminal voltage with your driver and the working drivers? Is it possible your MOSFETS are not turning on fully and the voltage is reduced? Are you, by any chance using N channel MOSFETS in the upper half of the bridge without a...
  6. BobK

    Help identifying this?

    +1 it's a power bank. Type USB A connector for power out. Plug a cable from here to your cell phone, and push the burtton to power / charge the phone. Type USB micro B connector for power in. Plug a cable from a USB charger to here to charge the power bank. Bob
  7. BobK

    Magnifying lens help needed pls.

    Then I would suggest a jeweler's loupe, and preferably lighted. Bob
  8. BobK

    Sub Bass

    That is not really an oscillator, it is a frequency divider to get derive sub-harmonics from another oscillator. Bob
  9. BobK

    Magnifying lens help needed pls.

    Depends on what you want it for. For close inspection I bought a very inexpensive ($15?) jewelers loupe with 2 lenses (30x and 60x) and an LED light. This is way to much magnification for use in soldering, but to inspect the final result or to read the code on a 0604 resistor, it is great...
  10. BobK

    trigget 12V relay from 1.8V

    You would use two comparators to determine if the signal was 1.8V. One would signal true if the signal was greater than 1.4V and the other set to true if the signal is less than 2.2V. These points chosen to be halfway between the surrounding values. Then if both are true, the signal must be...
  11. BobK

    Building a LCD 7 segment display watch from scratch

    Just driving that kind of display is a non-trivial project. Bare LCD displays, like the one you have selected, require an alternating voltage on the segment pins. There are PIC microcontrollers that have LCD display drivers built in. To do with software on a microcontroller that does not have...
  12. BobK

    555 timer smd

    Ah, so it was someone else's error. bummer. Bob
  13. BobK

    what size load capacitor for crystal oscillator?

    Yes. Changing the temperature would have more effect than the capacitors being off by a little bit. Bob
  14. BobK

    what size load capacitor for crystal oscillator?

    The capacitance is not critical. Use 27 or 33pF. Bob
  15. BobK

    TDA8932 BT audio amp board power up

    I didn't say there was no bluetooth, just thst bluetooth does not use a cable. I am guessing he plugged it in to a USB port for power, and 5V is not enoigh since itrequires 10. Bob
  16. BobK

    555 timer smd

    What an odd request. Why would you think an SMD part would have the same footprint as the throughhole part? Bob
  17. BobK

    Who gets there first!

    That is an odd kind of contest. A stationary bike, (at least the ones I have tried) do not have that much inertia. The time to reach top speed would likely be no more than a few seconds, maybe even less than a second. Bob
  18. BobK

    Using An Oscilloscope

    The isolation comes from the power transformer in the scope. Post transformer, nothing will be connected to the neutral. Bob
  19. BobK

    RF Circuit Battery Efficiency

    On average. The typical buck converter topology has all the output current coming from the source during the on phase and none during the off phase. So the source would be outputting 100mA when the switch is on and 0 when the switch is off, for an average of 50mA. Bob
  20. BobK

    LED strips for vanity/accent lighting?

    I looked at the ultrabright LED strips on you link. They are 519 lm / ft. 100' of these would be 51900 lm or about the equivalent of 35 100W incandescent bulbs. You could grow an awsome crop of your favorite indoor plants with that, but it might be a little obnoxious for accent lighting. Bob
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