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  1. BobK

    Can I drive an LED via audio line out?

    Did you look at the circuit? He has a 3 volt battery and a couple of resistors with the headphone out going across one of the resistors. So the the voltage is adding or subtracting from the voltage seen by the LED, with most of the voltage supplied by the battery. Bob
  2. BobK

    Coupled inductor SEPIC is wrong?

    That paragraph is self-expanatory. A SEPIC converter has non-coupled inductors, if you couple them, it is no longer the same design. Bob
  3. BobK

    555 timer using a transistor to drive a 12 v. 30 amp relay

    You need 300ma for the relay coil. The TIP3055 has a gain of 20, so you need 15ma of base current. Actually calculate for 20ma to make sure the transistor is saturated. So the base resistors is calculate to drop the voltage from Vin (the voltage driving to the base) to 0.7V (the typical Vbe...
  4. BobK

    nimh charger

    NiMH batteries are the most difficult type to charge correctly. A good charger will detect charging is complete by either detecting a rise in temperature or a drop in voltage. An overchange will cause the battery to vent and damage it. I have made one that charges at a constant current of 1C...
  5. BobK

    protection for short circuit

    I am having trouble understanding what you are asking. It sounds like you are trying to prevent damage when a battery is hooked up backwards, but then you keep talking a short circuit. These are two different things. A diode would be all you need to prevent the first problem. If it is really...
  6. BobK

    Variable power supply

    If it is rated as 20W at 6.3V it will not use 20W at 4V, it will use something less, which is why it would be less bright! It will certainly draw less current at 4V than it does at 6.3V. But, as I tried to explain the relationship is not linear as it would be for a resistor. If a resistor...
  7. BobK

    Variable power supply

    The 20W rating of the bulb is at some specific voltage. At that voltage, V, it will draw 20/V Amps. At a lower voltage it will draw less current, but not linearly, because the resistance of the filament is temparature dependent. It will therefore draw more than half the rated current as half...
  8. BobK

    Model train railway project w/o pic

    Actaully, they can, but the circuit I suggested would not do that. You are right, I did not think about the fact that it must move slowly. A servo will position anywere in between two extremes, proportional to the pulse with. So to move it slowly you would have to slowly increase or descrease...
  9. BobK

    Model train railway project w/o pic

    The standard pulse width for servos is 1.0 to 2.0 ms pulses repeated every 20ms. Whatever pulse width you are sending, it will go to that angle, so, the answer to your question is yes. Edit: Removed part about sending no pulses. The servo will just shut off if you do that. Bob
  10. BobK

    GPS Transmitter

    A GPS module is a receiver only. You need a transmitter as well. A GSM module is a cell-phone transmitter, which is capable, under control of a microprocessor, to send text messages. So the system looks like this: The GPS module constantly (about every second) provides position data to...
  11. BobK

    Step down voltage from 36V to 12V for EV

    Look up buck converter. Your circuit is way over complicated. There are buck converter controller chips that will do this quite well. All you need to add is an external MOSFET, inductor and a few passive compoents. Bob
  12. BobK

    Model train railway project w/o pic

    A servo will hold a particular angle depending on the length of pulses that are sent to it. You would need to send one pulse length for the up position and another for the down position. A single 555 timer could be used, to provide these two pulse widths by switching in a different resitor to...
  13. BobK

    LED Lighting project

    Yep. Power does add that way. Bob
  14. BobK

    LED Lighting project

    2.88 Watts at 12V is 240ma. An AA size NiMH is likely around 2000maH. So you would get about 8 hours out of a battery made up of 10 cells in series to get your 12V. The charge them in 12 hours you would need a charge rate of 2000/12 or 166ma ideally, but there are losses, so more like 200ma...
  15. BobK

    Amplifier antenna question

    Dieter, Read Kris's post that you quoted again. He said "Frequecies in this range do not travel through the air". When you connect your amp to your speaker the signal goes through the wires, not through the air. Same with the 60Hz power. Why do you think you have to plug your amp into the...
  16. BobK

    Model train railway project w/o pic

    A servo and a '555 with a switch to switch between two duty cycles. Bob
  17. BobK

    GPS Transmitter

    You would need a GPS module, a GSM module and a microcontroller to do this. If you don't know what these are, you are in for a long learning period. Bob
  18. BobK

    connecing a PICkit 2 => PIC24EP128GP

    You can use any of the PGC PGD pairs for programming. You can then set configuration bits to determine which pair is used for debugging. Bob
  19. BobK

    Building a device from a schematic (Yet another work in progress)

    Hi All, I volunteered to do a production board based on this design. Here is the thread I have started for this. I will be posting as I finish each step. https://www.electronicspoint.com/projectlogs/build-a-device-from-a-schematic-production-pc-board.26/ And I decided to also do a DIY pc...
  20. BobK

    Trying to use a Morse Key as a lamp switch

    Coca Cola has given you the solution, why are you asking again? I would add that a solid state relay would be the right thing to use, since you probably don't want it to click when tunrned on and off. Bob
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