Search results

  1. audioguru2

    IR Headphones

    An FM radio has LC tuned circuits for 100MHz and 10.7MHz. An FM modulated IR headphones system needs only about 100kHz and 200kHz so is much different. Use the VCO from a CD4046 IC for the transmitter and use the Phase-Locked-Loop from a CD4046 IC for the receiver's FM demodulator.  The signal...
  2. audioguru2

    IR Headphones

    I don't know if the music IC biases the transistor, it probably does. The red LED will create distortion. It is an AM system like the other one and will pickup interference from mains lights.
  3. audioguru2

    Unbalanced to blanced

    Hi Alvin, Welcome to our forum. ;D Opamps don't need a negative supply. They just need to have their inputs biased to about half the single supply voltage, which is ground when there is a negative supply. Capacitor-couple the input, output and feedback resistor and any opamp works with a single...
  4. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    R7 biases the inverter IC2A into the linear region so it acts like a high gain linear amplifier. Google has the equations. The gain is the ratio of the feedback resistors.
  5. audioguru2

    5 volt to 3.3 volt

    Kevin, Manufactures make registered (1Nxxxx) zener diodes with exactly the same spec's. A 1N5226 3.3V zener diode from Fairchild has the same specs as one from Motorola (now ON Semi). The way a zener is made (doped?) determines its voltage. Its voltage also indicates if it increases or decreases...
  6. audioguru2

    IR Headphones

    The amplitude of the IR beam is modulated with the sound signal. Incandescent light bulbs and fluorescent lamps flicker at double the mains frequency. The AM receiver will pick up the interference. M modulates the frequency of a high frequency carrier so that flickering lights won't cause...
  7. audioguru2

    Phototransistor Information

    The difference in the response times is the amount of volts the output needs to slew. It takes a long time for the output to swing 30V. With only 5V for its supply then the output goes high pretty quick. It goes low even quicker. It depends on how strong is the signal from the photo-diode. The...
  8. audioguru2

    IR Headphones

    Hi Ramji, It is a very old and crude circuit. It is mono, not stereo. It doesn't transmit data, its IR beam is AM modulated so its receiver is sensitive to interference. I think it will be very distorted because the T1 transistor doesn't have any bias current and therefore it will rectify the...
  9. audioguru2

    Phototransistor Information

    Hi Salvatore, The Mosfet isn't needed. Connect the input of the comparator directly to the photodiode. I don't know how much is the output signal from the photodiode. If it is a strong signal then the circuit will work. But if the signal is weak then the LM311 is too slow. The sales sheet of...
  10. audioguru2

    Portable Power

    It sounds like you are making an MP3 player with a hard drive. I fixed one from four that were found in the garbage at a stereo store. It is about 3 years old, it is huge and heavy and its four AA Ni-MH battery cells last about 2 hours. It uses the 8GB hard drive from a laptop computer. Look at...
  11. audioguru2

    Automatic Light System

    Hi Azza, Welcome to our forum. ;D The lights in my home have on-off switches. I use them so I don't waste electricity. My street has street lights so I don't use the lights outside my home very often. My lights are almost all low power compact fluorescent bulbs or fluorescent tubes.
  12. audioguru2

    IC 555 instead of IC 50240

    Hi, I am sorry to bring up details: I think you should quickly connect three or four 555 oscillators to a simple mixer circuit and amplifier to see how awful and out-of-tune they sound. See if they stay in tune after you adjust each one. See if each oscillator affects the others. See if a...
  13. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    The sensor coil develops a small voltage across it when it picks up a signal. The inputs of a differential amplifier are opposites. A signal between them is differential and is amplified. The voltage from the sensor coil is between the inputs. The same common-mode signal (interference) to both...
  14. audioguru2

    Phototransistor Information

    A phototransistor produces about 60 times more current than a photodiode. The transistor part amplifies the small leakage current through its collector-base diode. A photodiode can also be used as a small signal voltage source since it can act like a tiny solar cell.
  15. audioguru2

    Phototransistor Information

    Hi Salvatore, The rise time of a phototransistor is the time it takes for its current to rise from 10% to 90% after continuous light shines on it. The fall time is the time it takes for the current to drop from 90% to 10% after the light is turned off. So the highest modulation frequency is...
  16. audioguru2

    5 volt to 3.3 volt

    The 3.3V zener diode has only 7.3mA of current so its 24.1mW of power dissipation won't heat it much. I was talking about an increase in the ambient temperature causing the zener's voltage to drop. Heat from dissipation is the same as heat from the ambient. Here is a graph showing that the...
  17. audioguru2

    5 volt to 3.3 volt

    A 3.3V zener diode doesn't regulate very well. A 6.8V zener diode regulates 11.5 times better. The  diode in series with a zener diode reduces the amount of regulation. A 3.3V zener diode's voltage decreases as it heats, the same as the diode in series with it. So the total voltage changes...
  18. audioguru2

    decibel meter 90Db

    Hi Elec, Welcome to our forum. ;D 90dB is a very wide range. A sound pressure of 30dB is extremely low and background sounds and noise from the electret microphone and its preamp are higher. Then add 90dB to the 30dB and you have 120dB which is extremely loud and will overload the electret...
  19. audioguru2

    IC 555 instead of IC 50240

    Hi, A 555 oscillator makes a buzz-sounding square-wave output. The resistors and capacitors determine its frequency, they are not a filter. To make a chord with 3 frequencies, you need three 555 oscillator circuits. Then you need a simple circuit to mix them together. A filter circuit and an...
  20. audioguru2

    Crystal examiner

    In Google's search box enter Colpitts Crystal Oscillator and there will be about 32,000 articles.
Top