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  1. BobK

    Relay output

    That circuit will put a lot of power through the resistors. If 10mA is needed for the optocoupler, that would be 2.3W each. Bob
  2. BobK

    Chinese amp with dual positive rail!?

    Audio power amps often work with a positive and negative voltage supply with a common ground. These two supplies produce the power for the positive and negative parts of the audio signal. Bob
  3. BobK

    IRF5305S Power MOSFET, is switching voltages of 3V possible?

    The 3-20V spec for that module is the voltage to drive the LED in the optocoupler, not the gate drive for the MOSFET. The input must be through a resistor that will allow 5mA of current. Bob
  4. BobK

    dimming LED indicator lights

    Exactly. The beauty of using PWM like this is that the brightness will be the same no matter how many LEDs are on. Bob
  5. BobK

    Non contact AC voltage tester

    Typically, you need a 100nF ceramic cap near each pair of power pins. Bob
  6. BobK

    What the latch?

    You still have a radio shack? An SCR works like this: It is off until a positive pulse is seen on the gate. After that it acts like a diode and remains on as long as there is current through it. Your PNP NPN circuit does essentially the same thing. Bob
  7. BobK

    What the latch?

    A SCR does the same thing as your 2 transistor circuit with a single component. Bob
  8. BobK

    Chinese amp with dual positive rail!?

    That is a center tapped transformer. It is probably used to create a bipolar ±12V supply. Bob
  9. BobK

    dimming LED indicator lights

    What you need is a PWM circuit between the common of all the indicators and ground. PWM is the switching on and off method that you menton in you post. Bob
  10. BobK

    Testing A Capacitor

    Yep, unless it is like a 1F supercap. For a 100nF definitely bad. Bob
  11. BobK

    Testing A Capacitor

    It will read infinite. On a large one it will resd low and increase over time. Bob
  12. BobK

    DC motor, higher voltage just on start...

    I don't see a mechanism for a motor to lose torque without failing completely, so what is probably happening is the mechanical load has increased due to wear on the pump. Is it possible to replace the pump without replacing the motor? Bob
  13. BobK

    solid state transformer

    Do you mean DC to DC converter? Bob
  14. BobK

    Opamp for High Frequency Output - Need Help

    The datasheet shows ±7.5V with ±15V supplies. It is not capable of 30Vpp Bob
  15. BobK

    struggling to learn basics - 555 timer led flasher

    This is a misconception. Pin 3 always supplies an output voltage. It might be 0, but that is not the same as no voltage. This should help you understand how the two LEDs alternate. When pin 3 is 0 which LED(s) light? When it is at 3V the which LED(s) light? By the way, 3V is too low, that...
  16. BobK

    Physics Project Timer

    More advanced considerations. Braking might cause skidding, which will increase the stopping distance. You would get minimum stopping distance by pulsing the brakes line anti-lock brakes on a car. Bob
  17. BobK

    Physics Project Timer

    if (distance_to_wall <= stopping_distance(current_speed)) { brake(); } 1. You will want to experiment to find how far it takes to stop at any given speed. 2. You will have to know the speed. 3. You will have to know the distance to the wall. 4. When the distance to the wall equals the...
  18. BobK

    Help with diode OR gate

    I could make an assumption about what circuit you are talking about, but if I am wrong, my response would only confuse you, Bob
  19. BobK

    How does a GPS receiver/transmitter (transceiver) work on a circuit board?

    It is the cpu. Bob
  20. BobK

    New Product Prototype

    Discharge rate refers to how much current you can draw safely as a ratio of the capacity. A discharge rate of 1 is typical and it means you can draw enough current to fully use up the energy in the battery in one hour. A discharge rate of 20, like the one you linked, can be used up in 3...
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