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  1. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Bongo, The original project has mistakes that make it operate poorly and causes some of its parts to burn up. We have two very long threads here about it. With a 24VAC transformer its output voltage was a max of about only 23VDC at about 2.5A with a lot of ripple. A number of people have...
  2. audioguru2

    Sound Level Indicator

    Hi Napos, Welcome to our forum. ;D The electret microphone has a low output level. IC1 amplifies it, rectifies it and drives the transistors. IC1 has a 7.2V to 9V unregulated supply. Any opamp will work with a single supply if its input voltages are near half the supply voltage, and then amplify...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Bongo, For your supply project with the low voltage transformer, I think that MC34071P opamps would make it reliable. Then R10 might need to have its value reduced and connected to the negative supply. Then you should change the value of R4 to 1k so that the main voltage reference zener diode...
  4. audioguru2

    Use a speaker as a microphone while useing it as a speaker

    What is a "skype"? If you put a speaker next to a microphone and it is connected to the same thing at the other end, then they will make long distance acoustical feedback howling and very strong echoes. Here is a full-duplex intercom that uses a phase-shift network to cancel acoustical feedback...
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    The OPA445AP also has FET inputs and also might have the same polarity problem as the TL081. Your supply voltage is very low so the total of its positive and negative supplies is less than the 44V rating of MC34071P opamps, which have bipolar transistors at the inputs and don't have this...
  6. audioguru2

    rf coil

    Hi Arsal, Is this the circuit that you made? http://www.electronics-lab.com/projects/misc/010/index.html Did you use a Cmos 555 IC like it says? Did you make the coil like it says? Did you connect the pins of the transistor the correct way? Did you use a fresh 1.5V battery? It might work better...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Bongo, Your project has a very powerful transformer and lots of output current capability with four power transistors. You applied its mains voltage with its output nearly shorted. It is possible that the negative 5.6V supply is slow in reaching 5.6V, so U2 does not have a negative supply in...
  8. audioguru2

    Darlington TR

    The transistor is turned on too much so clips the bottom of the waveform at high levels. There isn't any phase-shift visible at 3kHz, and also none is seen at 300kHz. I don't know how to scale levels so I can't show the phase-shift with the emitter resistor bypassed.
  9. audioguru2

    200W kemokit-need help

    The project's parts list should say to use TDA2030A ICs because they have a high enough voltage rating. The TDA2050 will also work in that circuit, but KT transistors will fail because they are rated for only 40V.
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Without any voltage control. That is a severe error. Now two transistors are defective. Yes, and since the base of Q4 is also always at Vcc then it is also killed. I don't know what is wrong to short the transistors. Are their pins connected correctly? Is the rectifier bridge connected...
  11. audioguru2

    Digitally selected outputs for LM317

    Five binary bits will give you 32 different output levels. A bit's output is a transistor with a voltage-setting resistor in series with its collector.
  12. audioguru2

    Stepper motor H bridge

    It is your motor. I know nothing about it. Get an H-bridge IC that matches the spec's of your motor.
  13. audioguru2

    Problem in an H-Bridge

    Hi Shaiq, You don't say what is the max starting current of your motor. If it is only 1A or 2A then your circuit that uses darlington transistors should work. The datasheet for the darlington transistors shows that your circuit's 1k input resistors might not give enough current to the darlington...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Bongo, Welcome to our forum. maybe you damaged the project's negative supply when you connected the other supply. U2 doesn't draw much negative current. If it did then it would be very hot. The negative supply has only 7 parts. Check them.
  15. audioguru2

    Use a speaker as a microphone while useing it as a speaker

    In my electronics career, I worked with many intercom systems from cheap and lousy ones to excellent ones. The cheap and lousy ones used the speaker as a microphone. The resonance of the undamped speaker made speech very difficult to understand. When electret microphones were used, the sound...
  16. audioguru2

    rf coil

    Simple, isn't it? Make your own cell phone receivers. The professor further confuses things by saying it can be done with RF oscillators.
  17. audioguru2

    Darlington TR

    Your sim shows the same 1kHz frequency as before, but the phase-shift is different. Your sim is not done properly.
  18. audioguru2

    rf coil

    It gets more complicated. The detector must discriminate between two cell phones ringing simultaneousy. This is what Arsal wrote: "assign me to make a circuit that detects the incoming call, but the problem is he has made a condition if two mobile in the reach are being called simultaneously...
  19. audioguru2

    500W 12v to 220v Inverter

  20. audioguru2

    rf coil

    Why use a bandpass filter that will probably be at the wrong frequency? According to Red's Cell Detector project, when a cell phone is about to ring it transmits a very strong signal to the cell headquarters to tell them it is ready to receive a call. The detector circuit has just a simple coil...
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