Search results

Search Forums New Posts
  1. BobK

    Wiring a 9 Pin D connector for standalone Logitech sub-W

    2 and 5 would seem to be the correct input pins for the RCA connector, inner to 2, outer to 5. Bob
  2. BobK

    Issues with nulling offset voltage

    The input offset is the offset at the inputs, not the output. Without feedback, that offset will be multiplied by the gain of the op amp, typically 100,000 to 100,000,000. In your example, the small offset voltage is being multiplied by the gain and the op amp is trying to output a voltage...
  3. BobK

    Reducing variable voltage

    20 to 30 mA is right on the edge of what typical op amps can output. I would look for one that has a little more power, like 50mA if you really need 30. If the max need is actually below 20, a very common op amp like LM324 or LM358 would work. You probably want a single supply one, which...
  4. BobK

    Reducing variable voltage

    Is the output simply a signal, i.e. drawing negligible power, or it is providing power. If the latter, how much current? I would use an op amp to subtract 12V then, if more than 20mA is needed, use that voltage as a reference in a regulator circuit. Bob
  5. BobK

    Op amp LM339 help

    Did you measure each side of the 1K resistor and get 5V on one side and 2.5V on the other side? This seems improbable since the LM339 would have to be half on, which it is designed not to do. Bob
  6. BobK

    Problems with iPhone 5V car power supply

    You need a resistive voltage divider on each of the D+ and D- pins, depending on the current the charger can provide. https://www.voltaicsystems.com/blog/choosing-usb-pin-voltages-for-iphones-and-ipads/ Bob
  7. BobK

    Unable to read frequency of a tone signal with a frequency meter.

    A sensitivity of <= 80mV means 80mV is the minimum signal guaranteed to be accepted by the counter, not the maximum. Bob
  8. BobK

    Problems with iPhone 5V car power supply

    I use my iphone with lightning connector with all kinds of adapters and USB ports on computers and have never had it refuse to charge. Yes, it might be charging at 500mA or so, but it does charge. My 10 year old desktop is certainly not talking the proprietary Apple protocol. Bob
  9. BobK

    Unable to read frequency of a tone signal with a frequency meter.

    Have you connected it to both the scope and the counter to make sure the counter is not loading the signal and degrading it, or even stopping the oscillator? Bob
  10. BobK

    Problems with iPhone 5V car power supply

    Why not just use a USB cable , as is? If not, just connect them the same way. Bob
  11. BobK

    Problems with iPhone 5V car power supply

    You answered your question. You need to connect the green and white wires. Apple phones looks for specific voltage on these wires to set the charging current. Bob
  12. BobK

    MOSFET burning up but similar circuit on another board is fine

    The coil is 22-550 which means 22ga wire 550 turns. At a one inch diameter that is 550 * pi inches or 1728 inches or 144 feet. 144 feet of 22 ga wire is 2,34Ω. So your measurement of 2Ω is well within the ballpark. Within the infield even. Bob
  13. BobK

    MOSFET burning up but similar circuit on another board is fine

    From the info you gave us: Coil resistance 2 Ohms. Voltage 55 We can calculate the current 55 / 2 = 27.5A The Rdson is 0.077V so we can calculate the drain to source voltage: Vds = 0.077 * 27.5 = 2.12V The power when fully on is: 2.12 * 27.5 = 58.23 W And with on time of 100ms each...
  14. BobK

    HELP please OTL tube headphone amp (again)

    The middle pins go to the grids. Looking at the pot from the side of the shaft, with the pins down, the signal goes to the pins on the left. The other two piins go to ground. Bob
  15. BobK

    So I broke...

    WS2812B RGB LED strips are fun. You do need submicrosecond timing though, and I am not sure how good a board like that is for that. Strangely, microcontrollers, which are much slower are better for that kind of real-time operation because you can guarantee that nothing else is going on and...
  16. BobK

    Scanning of numbers and string in c

    Also, in your string example you have this declaration: char name; name is a char, not a string. It can store only a single character, and you scan statement will go out of bounds, probably crashing your program. To define a string you declare an array of char that can store 1 more than...
  17. BobK

    So I broke...

    That is not a microcontroller, it is a very small Linux based computer. Like a Raspberry PI, it is severe overkill for things that can be controlled by a microcontroller. So, it depends on what you intend to do. If you want something that has network connectivity and can program in Python...
  18. BobK

    Need to replace odd value capacitor

    What are the actual markings? A picture would help. 183 could mean 18,000 pF which is a standard value. Bob
  19. BobK

    MOSFET burning up but similar circuit on another board is fine

    Are you sure you got IRL and not IRF540? The IRL540 is logic level, IRF is not. How much current is the solenoid drawing? What is the voltage on the gate when turned on in your circuit? What current does the solenoid draw? Bob
  20. BobK

    I know nothing...

    No, you would not be able to push the pedals at all. What you need is 20 guys pedaling bicycle alternators, and they can keep your 1000W LEDs going as long as they pedal. You can pay them with the profits from your cannabis sales. Bob
Top