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  1. BobK

    Calculating resistance and Base current

    For the first question. Notice that there will be no more then 0.4V on the base, so it will not conduct. What you are left with is a simple voltage divider. You should be able to compute the resistance of the LDR from that. For the second question. You know the voltage on one side of the...
  2. BobK

    Test bench power supply

    If you do find such a transformer, it will probably cost you more than buying a complete bench power supply. Bob
  3. BobK

    Combining multiple amplified outputs to feed one speaker only

    Colin: If you had read all of the thread, you would know that the output of the radio is bridged and there is therefore no common. Bob
  4. BobK

    Choice of Op-Amps

    But the real question is why you want to use a variable voltage to drive a motor? PWM is much superior and does not waste power like the solution you are proposing. Bob
  5. BobK

    Velocity/Accelerometer w/Digital OP??

    Agree, I think an accelerometer + a delayed turn off would do the trick. Bob
  6. BobK

    Test bench power supply

    It would help if you told us what the parts were, or at least linked to the article. Bob
  7. BobK

    Velocity/Accelerometer w/Digital OP??

    The laws of physics make it impossible to sense motion in the way you are asking. Moving relative to what? The car may be parked, but it is spinning around with the earth and revolving around the sun. Is it moving? That said, an accelerometer can tell you if the car has changed it velocity...
  8. BobK

    Problem with wiring project

    Yep, that looks like the right one. Bob
  9. BobK

    Problem with wiring project

    The circuit is designed for 150mA LEDs. You are using what are probably 20mA LEDs. No wonder they are burning out. And if you change the resistors to make them run at 20mA they will not put out much light. And they are narrow as opposed to wide angle. Really not suitable for this project. Bob
  10. BobK

    Power Supply Challenge

    If you disconnect the negative sides of the two bridges you will be okay, you just cannot have a common between the two supplies. I am not absolutely sure I am right about this. I hope someone else will weigh in. Bob
  11. BobK

    Power Supply Challenge

    I think there is a problem with that circuit. You cannot have the negatives of the two bridges connected together. This creates a short of two windings through a diode. Bob
  12. BobK

    Radio receiver controlled enable switch

    The RC time constant would have to be much longer than the period between pulses (which I assume is 20mS) in order to come to 2 distinguishable voltages. This means you would have a response time of maybe 20mS x 10 = 200mS. Would that be too slow? Bob
  13. BobK

    Help designing an Inductor

    If you are operating at the fastest frequency possible using a gate driver, we are talking about > 1MHz here. Why are you worried about ripple of << 1% at 1MHz for driving an LED? This would be the most egregious case of over-design I have ever come across. And let's talk about efficiency as...
  14. BobK

    Help with a capacitive touch panel

    What you need is a programmer (hardware that is, not one like yourself). I would recommend the PICKIT 2 or 3 from Microchip. The software tools are free. MPLABX is the development environment, which comes with assembler and linker. Then there are the C compilers, XC8 16, OR 32 depending on...
  15. BobK

    Help with a capacitive touch panel

    The markings of a connector with SCL, SDA, GND, and VDD indicate that it talks via the I2C serial protocol. If this is the case, there is no spot that will indicate the state of each button, these are sent as messages that must be interpreted by a microcontroller. Edit: BTW the 5 pads near...
  16. BobK

    Rechargeable A.C.

    Okay then, about 750WH. For a 12V battery this is 62.5AH. Bob
  17. BobK

    solonoid controler

    Don't go by the circuit diagram, that is just the symbol for a voltage controlled switch in LTSPICE. The parameters in the .model directive determine what is the resistance when the control signal is on and off. And they are opposite, so they are never on at the same time. Harald has used...
  18. BobK

    solonoid controler

    Look at the .model directives for the two switches. One is on when the control voltage is high and off when the control voltage is low. The other is off when the control voltage is high and on when the control voltage is low. Bob
  19. BobK

    Help designing an Inductor

    If you are needing 12mH for your inductor, you are probably using too low a switching frequency. IC switch mode controllers use frequencies in the 100s of KHz and require only 10s of microhenries for the inductor. It is much easer to find a 47uH inductor than can handle 5.5A than it is to...
  20. BobK

    Radio receiver controlled enable switch

    That is the control signal for a servo. You could use a servo to flip a switch! Bob
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