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  1. BobK

    Looking for a circuit design

    Are you saying you want to the transistor to heat up? Bob
  2. BobK

    help choosing right mosfet

    No, a flyback diode goes across the terminals of the motor, with the cathode to the + side and the anode to the - size, i.e. reversed. That way it conducts only when the motor is producing an opposite voltage as it is turned off. A normal diode that handles as much current as the motor is...
  3. BobK

    220v LED DIMMER??

    You are using the MOSFET in the linear region, so Rdson has nothing to do with it, that comes into play only when the MOSFET is fully on. Bob
  4. BobK

    Just joined today

    Welcome! This is a good forum for beginners. If you want to learn, you will get help here. Bob
  5. BobK

    DB 9 connector

    However, you can connect it to a PC with a monitor and a terminal emulator program. On a newer computer you would need an RS232 to USB converter since it will not have a serial port. Bob
  6. BobK

    whether possible for a microcontroller (in a separate pcb) to read from pen drive?

    Some PIC 16 and 32-bit microntrollers have USB host capability. Using a USB Flash Drive with an Embedded Host Bob
  7. BobK

    Wireless water meter reading system

    Wireless water meters exist, but I doubt that they use images... Bob
  8. BobK

    will this motor circuit diagram work

    Change the metal rod to a permanent magnet, and you have what is called a brushless DC motor. One of them powers my car some of the time (Prius.) Bob
  9. BobK

    Door Lock - USB key

    True, but unlike the credit card, you would not be handing this to someone. I suppose, if you put it on the your keychain and handed it all to a valet parker or auto repair shop it might be in danger. However, they would have to be specifically targetting you, since no one else would have a...
  10. BobK

    help choosing right mosfet

    Rdson is the resistance of the switch (i.e. between source and drain) when the MOSFET is completely turned on. 10mOhms = 0.01 Ohm. Vdss is max when the MOSFET is off, and it is the supply voltage. You will not likely find a MOSFET than cannot handle 6V. On the other hand, a motor can...
  11. BobK

    Non-inverting amplifier

    You haven't given us any details of the range of signals you need to handle as input. This would be all important in designing an amplifier. Bob
  12. BobK

    transfer schematic to stripboard

    I have used VeeCAD. It is cumbersome, but better than doing it completely by hand. http://veecad.com/ Bob
  13. BobK

    7 segment display. Single number

    That is what I originally started to suggest, until I realized that it would not work, so I just changed my suggestion to "logic gates". Timescope has given you the full answer. If you needed to be able to set the number that it stops at, you would have to use something like 7 SPDT switches...
  14. BobK

    help choosing right mosfet

    The first thing you need to do is reevaluate your battery choice. AA cells are designed for about 500mA max current. You may get 2.4A for a few minutes, but not for long (well under an hour). Next, you have a few misconceptions about MOSFETS. The major one is the power rating. This is the...
  15. BobK

    need help to figure out this problem boost up module

    Perhaps the OP talking about a saltwater capacitor? A variant of the Leyden jar. If so, (the capacitance would be very low) the most likely explanation for the behavior is a short. Bob
  16. BobK

    Door Lock - USB key

    How would copy protection or encryption help anyway? In order for someone to steal it, they would have to get a hold of the key (the USB flash drive). And if they have that, then, well, they have the key, no need to copy or decrypt it. Bob
  17. BobK

    7 segment display. Single number

    If I understand you correctly, you mean you want it to count 0, 1, 2 and then stop a selected number. Is the stop number fixed, or do you need to be able to change it? The way to do it would be to use logic gates connected to the segment outputs to determine if the selected number has been...
  18. BobK

    Limited Resistance Range on 500ohm Pot

    Actaully, NiMH batteries are only 1.2V so it would take 5 min, 6 to be safe. You still haven't said how much current the motor draws. That is all important in choosing a battery. Bob
  19. BobK

    Linear voltage regulator cooling

    Yeah, what am I thinking. 15V would be good though. Bob
  20. BobK

    Linear voltage regulator cooling

    Why not use a 12V transformer? It would result in about 15V DC and the power dissapation would go down to 3W instead of 11. Bob
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