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  1. BobK

    weird DMM voltage readings

    Really? And you are bothering us to determine why it is not working? The pin is not set to an output. Bob
  2. BobK

    Audio limiter to quiet loud radio commercials

    There is no ground symbol there. In your case, the ground is one of the two input lines from radio, and it will produce voltage both above and below that ground, just as the circuit you showed produces voltages both above and below the lower transformer secondary connection. The problem is...
  3. BobK

    Hight input impedance DC buffer ?

    If you really want an exact copy of the input, a rail-to-rail opamp would do the trick. Bob
  4. BobK

    Unable to find replacment potentiometer

    Agree with Harald. What markings are you reading? I cannot see them well enough in your pictures. Bob
  5. BobK

    Audio limiter to quiet loud radio commercials

    The voltage doubler is giving you a + and - output. You still get no more voltage with respect to ground. Bob
  6. BobK

    Audio limiter to quiet loud radio commercials

    I understand all of that and I am pointing out that a bridge will have higher losses than a half-wave rectifier in this case, as long as the smoothing capacitor is large enough. I tried to make a 1 JFET circuit, but saw no way to get around the fact that the JFET is switched the wrong way, I...
  7. BobK

    Piher Potentiometer?

    If you can't find any info, which seems likely, you can measure the resistance, determine whether is is linear or logarithmic by measuring the resistance at the midpoint, and the size should give a decent clue about the power rating. Bob
  8. BobK

    Audio limiter to quiet loud radio commercials

    A single diode half wave rectifier will give you a higher output than a bridge because there is only one diode drop instesad of two. Bridges are used on power circuits to reduce the capacitance needed for filtering and the power factor on the source, not to get a higher output voltage. Bob
  9. BobK

    Audio limiter to quiet loud radio commercials

    If that means what I think it does, you no longer have a bridge. This is why a single diode is used in peak detectors, you cannot connect one of the outputs to ground. It shorts across one of the diodes, and places another diode directly across the inputs. Show us you circuit if you disagree...
  10. BobK

    Analog guitar amp with digital meter

    Anyone who is not jaded by age 66 has not been paying attention. At least this was not as costly as the lesson I learned when I tried to repair the boiler used to heat my house. I was very proud of the plumbing job I did, but, after finishing I forgot to turn the water feed back on. Total...
  11. BobK

    Buck Converter with PİC16F877A

    Perhaps you should show us the circuit you tried with a P-channel MOSFET, it would be much easier to fix. Bob
  12. BobK

    Analog guitar amp with digital meter

    Okay, it looks like you are on the way to a solution. All you need to do is replace rhe meter you zapped with a resettable one. Bob
  13. BobK

    power supply rebuild

    It might work, but then you will have added additional current capability that would immediately be shut down by the current limiting. Bob
  14. BobK

    Is it wrong to leave a transformer plugged in ??

    That is not a transformer, it is a switching power supply. Switching the AC input would conserve energy. How much is anybody's guess unless you have specs for the idle current taken by the power supply. If you have a kill-a-watt you could find out. If you do put in an AC switch, make sure...
  15. BobK

    Audio limiter to quiet loud radio commercials

    You got that backwards. MOSFETS have a diode in the reverse direction so they always conduct with reverse bias. JFETs conduct or not equally in either direction. Connect the source to the ground of the signal. A negative voltage on the gate will turn then turn it off. I will try simulating...
  16. BobK

    IR trans-rec

    If you go to an actual electronic parts supplier, and not Ebay or Amazon, they will show you phototransistors when you search for phototransistors. https://www.mouser.com/Optoelectronics/Optical-Detectors-and-Sensors/_/N-6jju9?Keyword=phototransitor&FS=True Bob
  17. BobK

    IR trans-rec

    No, those are 38KHz receivers that require a lot of active electronics to use, typically a microcontroller. Stop looking for IR transmitters and receivers and look for what I suggested: IR LED and Phototransistor Bob
  18. BobK

    IR trans-rec

    Okay then, a simple IR LED and phototransistor will work then, driving either a relay or a more powerful transistor. However, ambient light is still a consideration. You may need to put the detector insude a tube looking directly toward the LED, shielding it from extraneous light. Bob
  19. BobK

    IR trans-rec

    You have not told us what you want to do with an IR transmitter and receiver. You might be talking about sending data a mile away, or you might be talking about detecting when a sheet of paper is in place in a printer. Both of these are done with IR. So what is it you expect to do, in detail...
  20. BobK

    Reflow Bga chip.

    Just to lighten things up — use an anti-gravity field. Bob
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