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  1. BobK

    TDA8932 BT audio amp board power up

    I presume you mean USB cable; Bluetooth is wireless! I found that board on Ebay, it requires 10 to 18V power. It is not surprising it does not work on. 5V USB port. Bob
  2. BobK

    Why does this lamp need a transformer?

    The "transformer" is probably a ballast, a large inductor used to limit the current to the bulb. Bob
  3. BobK

    Dither for PWM circuit driving a proportional solenoid

    You don't need to combine two signals, you just need to periodically change the duty cycle. If programming at low level instead of using Arduino primitives this should be simple. On a low-end 8-bit PIC, just for kicks I, I output a 1MHz PWM signal (yes, they go that high), changing the duty...
  4. BobK

    First ever help

    Q1. It switches the current for the relay coil. The port pin cannot switch that much current by itself, so you use a transistor as a switch. Bob
  5. BobK

    Silly regulator question

    Assuming the source can provide 1A, you can, but you might need too add or increase to the heat sinking. What is the input voltage? This will determine how much power is dissipated. Bob
  6. BobK

    64 to 6 decoder

    http://www.ti.com/lit/ds/symlink/sn74ls348.pdf Bob
  7. BobK

    LED stripe resistor

    I'll tell you what. Buy one of the PWM LED or motor controllers off Ebay and then look at what it outputs. You will see a square wave with varying duty cycle. Then buy an LED driver or switch mode power supply and you will see a constant current or voltage produced. They are not the same...
  8. BobK

    LED stripe resistor

    Nobody suggested a constant current power supply. The original post recommending PWM post #2. You are confusing a PWM controller with a switch mode power supply. Yes, a PWM controller does output a fixed voltage and variable duty cycle waveform. A PWM controller feeding an inductor and...
  9. BobK

    RF Circuit Battery Efficiency

    Uh, yes. It is a switch mode regulator and the inductor is a critical part of the circuit. It is a fixed regulator, wire it exactly as in the datasheet, and you will get 3.3V. Bob
  10. BobK

    What is this?

    An invisible pink unicorn? Bob
  11. BobK

    LED stripe resistor

    Sorry, but wrong again. You apparently do not understand what PWM is. PWM still drives the strip with 12V. It reduces the brightness by turning it on and off rapidly. If it is on 0% of the time, it is off, if it is on 50% of the time it is half-brightness, if it is one 100% of the time it is...
  12. BobK

    LED stripe resistor

    Yep, I am everyone's uncle! Bob
  13. BobK

    LED stripe resistor

    Ignore this, this is wrong. They absolutely can be used with a PWM controller. Bob
  14. BobK

    Hall effect switching info needed

    I applaud your effort to get back the last few % of power that current high-efficiency motors waste. Bob
  15. BobK

    Cable length using r1 and r2

    I thought you were trying to calculate voltage drop. If you already know the resistance and the current, why do you need the length? Anyway, calculating the length is elenentary scool arithmetic. Divide the resistace of the cable by the resistance per meter of the cable, which you can get...
  16. BobK

    Cable length using r1 and r2

    Calculate it from what? Bob
  17. BobK

    Current limit for 5V @ 120mA

    Please explain further what you are trying to do. If you intend to hook up a device that requires 120mA at 5V, you can connect it directly to a 5v, 500mA supply. It will use only the current it needs. The rule for power supplies is that they must provide the correct voltage and at least the...
  18. BobK

    First ever help

    Welcome to the forum! 1. Take the schematic and check each wire, crossing it off when it is found to be connected correctly. 2. No, the port pin probably cannot drive the relay directly. You need the transistor to supply enough current to the relay coil. 3. Changing the sensor will...
  19. BobK

    Cable length using r1 and r2

    Voltage does not go through a cable, current goes through a cable. So, first calculate the current: If it is 100W at 24V the current is 100 / 24 = 4.16A. Next calculate the resistance: For the given size of wire, you can find the resistance / length. For example, 22AWG wire has 0.053 Ohms /...
  20. BobK

    Analog to 1-Bit Digital Signal at a Threshold

    All signals switch over some period of time, and are therefore actually analog signals. In most cases, the rise time is not critical. Comparators (not opamps) are designed to switch quickly. Just use a comparator. Use positive feedback to avoid multiple triggering at the threshold. Bob
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