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  1. BobK

    Project using a strong 12 volt motor

    PWM controller. Bob
  2. BobK

    Transistor Mosfet pairs to drive LED cube layers

    No issue except my stupidity. I thought you were driving the gate with 3.3V, but you are not. Bob
  3. BobK

    Transistor Mosfet pairs to drive LED cube layers

    Deleted, didn't read the circuit correctly. Bob
  4. BobK

    Treble-Cut Filter Circuits

    A treble-cut filter would more commonly be known as a low-pass filter. Filters basically work by using components (capacitors and inductors) that have an impedance that depends on frequency. For example, a capacitor has an impedance that goes down with higher frequencies. Combine a capacitor...
  5. BobK

    Power LED from USB

    If you want to power the LED at half power, it is easy. Just a resistor. But note that it would have to dissapate 2.5W so you would want to use a 5W resistor to be safe. The resistor would be 2.5 Ohms at 5W. If you want to drive the whole 5W into the LED you would need a DC to DC converter...
  6. BobK

    Capacitor value ?

    If it helps, I am that ancient also! Bob
  7. BobK

    Capacitor value ?

    MFD was often used in ancient times to mean microfarad. Millifarads would be mF. MF would be megafarads. Bob
  8. BobK

    Power LED from USB

    5W at 2.5V = 2A so no, you cannot power even one from a USB connector which is 500ma. Bob
  9. BobK

    Simple Phototransistor switch circuit

    Hi blink, welcome to the forum. A comparator will sense the difference between two voltages and then switch quickly when one exceeds the other. Bob
  10. BobK

    Circuit requires two voltages for supply

    Which schematic are your using? I don't see that chip needing 2 voltages anywhere, but maybe I am missing one. The input voltage can be up to 60V according to the datasheet. The second voltage listed on the schematics is the output voltage it is producing. Bob
  11. BobK

    Is there 0.01 rpm motor?

    You would want a stepper motor + gearing to go that low. Bob
  12. BobK

    7-segment display numbers not in order.

    Trivial with a micro. Bob
  13. BobK

    Transistor, AC amplification

    The two biasing resistors should be chosen such the the voltage on the collector is 1/2 the supply voltage. With the resistors you have chosen, I expect the transistor to be fully on and stay there, so the output should remain close to 0. The blocking capacitor is fine as you have it. Bob
  14. BobK

    Dual Polarity high current OF PSU computer

    The simple way is to buy a +- 12V power supply. I will not answer any more of your questions until you answer mine. Bob
  15. BobK

    Analog voltmeter question - minus DC voltage

    Reversing the leads will be okay as long as the meter has no other connection to the circuit. Bob
  16. BobK

    Transistor Mosfet pairs to drive LED cube layers

    What are the current and Rdson requirements? I have found many MOSFET that specify their on resistance at 4.5V but it only goes up by 20% at 3.0V. There should be one of these that would work without a driver. Bob
  17. BobK

    Transistor Mosfet pairs to drive LED cube layers

    Okay, I see the problem. Even logic level MOSFETS require 4.5V to saturate, and the signal is 3.3V. The thing is, at a multiplexing rate of around 100Hz, you are not going to need fast turn on and turn off times, so a simple voltage shifter with a collector resistor should be fine. I made a...
  18. BobK

    Transistor Mosfet pairs to drive LED cube layers

    What are the needed specs? Surely there is a logic level MOSFET in sot-23 that will do the job without any driver needed. Bob
  19. BobK

    Replace a pot with a ¿resistor?

    The pos is a voltage divider. If turned one way fully, the entire signal going into the amplifier is alowed through. If turned fully the other way, none of the signal goes through. Any position in between will allow some part of the the voltage through. What you need to do is replace the...
  20. BobK

    Dual Polarity high current OF PSU computer

    You could use and isolated DC-DC converter to generate -12V from the +12V or +5V. How much current are we talking about? Edited: Actually a buck-boost converter will give you a negative output without being isolated, this is even better. Bob
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