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  1. BobK

    Choose the right Mosfet

    And don't be fooled by the gate threshold voltage. That voltage is what it takes for the MOSFET to pass 250μA, it will not turn the MOSFET on for a 2A load. The threshold voltage is more of an indicator of what voltage will turn the MOSFET off completely. Bob
  2. BobK

    Is this dc adapter safe to plug into my keyboard instrument

    Show us a photo of the power jack on the keyboard, and one of the adapter. Both should have a polarity indicator. It is quite possible that the polarity is backwards, and you might have damaged the keyboard if it was not designed with protection for reverse polarity. Does the keyboard still...
  3. BobK

    PWM Control with Shift Register Support for 3w White LED's

    Smallest and simplest hardware would be a 6 pin SMD microcontroller and an SMD MOSFET for each node. You will need a power resistor for the LED though, assuming 5V to drive it all. That would be 1.4V * 700mA or 1W. Since the duty cycle will be low, you need not go more than 1W and can...
  4. BobK

    Trouble getting enough power to LED strip

    A long wire is an antenna. It picks up RF noise, varying the voltage at the end of the wire. But that voltage cannot supply much current, so a low resistance at the end will knock it down. Bob
  5. BobK

    BPSK Waveform

    Yes, I actually did post that from my smartphone. Don't know how it got through. I meant to say 2 outputs. Bob
  6. BobK

    Trouble getting enough power to LED strip

    16 gauge wire is more like overkill for the current required by 9 RGB LEDs (max 1/2 A). The problem is probably the signal. Try terminating the data line at the LED strip with a 100Ω resistor to ground to make it less susceptible to interference. Bob
  7. BobK

    BPSK Waveform

    Easy to do with a micro. Get one that has a D/A capability. You only need twio bits, many PICs have a 6 bit one, or you could even use two outputs and a resistor ladder. Bob
  8. BobK

    Education: Transistor as a Switch

    It is actually the voltage applied to the base minus about 0.6V since it takes that much to tirn on. The circuit with the load between the emitter and ground is called a voltage follower since the output voltage follows the input voltage. Bob
  9. BobK

    simple led question

    The diameter of the LED has nothing to do with the resistor. What you need to know is what forward voltage and current it needs. That said, if you replace it with the same color, you can very likely get by without changing the resistor. Bob
  10. BobK

    Touch activated circuits

    Yes, you could simulate it in LTSPICE by using a PWL voltage source. Bob
  11. BobK

    Education: Transistor as a Switch

    Also, 10Ω is way too low for the base resistor. This would generally allow enough base current to destroy the transistor. You are lucky you used a weak battery. The correct value is one that would allow about 1/10 of the collector current to flow through the base, Bob
  12. BobK

    Education: Transistor as a Switch

    The thing that you are missing is that it is the difference betrween the voltage on the base and that on the emitter, known as Vbe, that turns on the transistor. Vbe must be above about 0.6 V to turn it on. In the first circuit, the emitter is at ground an the base is driven by the battery...
  13. BobK

    Understanding impedance

    Actually it is more complicated than that. Impedances are complex numbers and they cannot be represented by a scalar like a resistance can. Case in point: If you put and inductor and capacitor in series with equal scalar impedances, the resultant impedance across the two is zero. If you put...
  14. BobK

    Signal generator using 555 timer

    Perhaps what is needed is an analog mode on a DSO so beginners could start with that. Bob
  15. BobK

    Help with increasing the power of a Philips hue bulb Frankenstein "hack"

    It could be done, but not simply. I would have to know what the outputs of the hue bulb board look like, and what the driver for the other LED lamp looks like. Is the original light dimmable? Some are not. Bob
  16. BobK

    Help with increasing the power of a Philips hue bulb Frankenstein "hack"

    Oh, okay. If you can find the 3.3V signal, it will probably be able to switch the SSR. 4V is just the minimum that they guarantee will trigger it reliably. Bob
  17. BobK

    Signal generator using 555 timer

    Which is what I would recommend for a beginner. DSOs are tricky to use, though far more capable, especially for capturing one time events. Bob
  18. BobK

    Signal generator using 555 timer

    Great. You will find getting a scope is something like being blind and getting sight! Bob
  19. BobK

    New to electronics, need help with a cam activated switch

    I would be more worried that the lobe would pass the switch, the motor will not stop immediately. A momentary contact normally ON switch is what you are describing, but, (see above) I don't think it would work unless there was a lever with some length to it. Look for microswitches, theses...
  20. BobK

    Usb trigger for 12v TV backlight

    I would expect the MOSFET to get quite warm if not hot with 5V on the gate. How much current is the strip using? Bob
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