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  1. Audioguru

    Can anybody explain about how bjt works??

    A bjt is a bipolar junction transistor, not a Mosfet. It has 3 regions, cutoff, linear and saturated. When it is cutoff then it is turned off and does nothing. When it is linear then its output can swing up and down and it can be an amplifier. When it is saturated then it is a turned on DC switch.
  2. Audioguru

    Can an old Ni-Cd battery charger be used for Ni-MH batteries?

    I have two old Ni-Cad chargers and I have used them to charge my Ni-MH cells for years with no problems. These chargers simply limit the current and keep charging forever. I did not measure them but I suspect the current drops as the voltage of the battery rises. I have another "smart" stupid...
  3. Audioguru

    A Current Balance Circuit for LED Strings in Parallel with Polyswitch Protection

    I believe that if you buy a bunch of LEDs from an electronic distributor their forward voltage will be nearly the same either high, typical or low because they will be made about the same time and will be from the same batch. A few might be random from other older batches. An LED can burn out...
  4. Audioguru

    Battery charged by a solar panel?

    If the output voltage at the charging current is correct and the charging current is safe for the battery then the solar panel can be directly connected to the battery. But a diode in series should be used to prevent the charged battery from discharging into the solar panel at night. The forward...
  5. Audioguru

    Charge battery from speaker audio

    Do you want the LEDs to light from the battery when the music is not charging the battery or do you want the LEDs to flicker to the music or both? For the LEDs to only flicker to the music then you do not need a battery and charger. White, blue or bright green LEDs need at least 3.5V plus...
  6. Audioguru

    Please help me identify battery!!

    How do you know that the battery has failed and not the charger? The plug says [nothing[/b] about the charging circuit or the battery. The battery should say on it its voltage, its capacity in mA hours and its chemistry (Ni-cad, Ni-MH or Lithium).
  7. Audioguru

    Would variations in weather temperature shorten life of LED bulb?

    I think there is much more variation in LED light bulb designs than ordinary ambient temperature changes. An LED bulb designed "over there" to be cheaper than is possible will fail soon even if its ambient temperature does not change. An LED light bulb made by a name-brand company will be...
  8. Audioguru

    A Current Balance Circuit for LED Strings in Parallel with Polyswitch Protection

    If you pulse an LED at a high speed with a very high current but have the average current low enough that the LED does not overheat then it is not super bright, instead it looks like its average current because our vision is slow and does not see the peak brightness of the pulse. That is how PWM...
  9. Audioguru

    A Current Balance Circuit for LED Strings in Parallel with Polyswitch Protection

    I have always used LEDs that are spec'd with minimum, typical and maximum forward voltage at various currents. Cree shows only typical voltages because they expect you to use constant current with plenty of extra voltage. The Bins show different colors, not voltages. Other companies like...
  10. Audioguru

    A Current Balance Circuit for LED Strings in Parallel with Polyswitch Protection

    Cree and you do not know the range of forward voltage for the LEDs. Most might be minimum voltage or most might be maximum voltage then your tight design will not work because you cannot buy only "typical" ones. You need to design with a high enough voltage that the LEDs and the current...
  11. Audioguru

    Need help identifying this

    Why do you think the resistor should be replaced? It measures and looks OK. Did you subtract the 0.5 ohms resistance of the leads of your multimeter when measuring the 2.2 ohms? The other website shows that this toy car is HUGE! I now suspect a dead baddery.
  12. Audioguru

    Is this circuit diagram correct?

    1) The Jfet in an electret mic draws 0.5mA so the value of R1should be reduced to about 10k to prevent the Jfet from saturating. 2) The transistor has a high input impedance then the high 10μF value of C1 passes low earthquake frequencies so its value should be reduced to about 0.22μF and it...
  13. Audioguru

    RC Car Toy Modification Help !!!

    Why don't you know that Vcc is high and ground is low? Please look at the word "latched" in a dictionary: "secured, fixed and locked". It is DC, not pulsing.
  14. Audioguru

    Sound module

    If the microphone can hear the speaker then you will have acoustical feedback howling. Record it with the speaker turned off then play it back with the microphone turned off.
  15. Audioguru

    RC Car Toy Modification Help !!!

    You show two different receiver ICs. One of them has a MOD pin #9. A close look at the function of the MOD pin shows that the function is latched when the MOD pin is high or open and the function pulses when the MOD pin is low.
  16. Audioguru

    Can anyone provide me a link or book how to make a woofer at home?

    No. The impedance does not vary with the enclosure. The resistance is not made very low for high power handling ability. The impedance is high at the resonant frequency and increases at higher frequencies because it is inductive. The resistance is only a little less than its impedance because it...
  17. Audioguru

    RC Car Toy Modification Help !!!

    The receiver IC latches an output when it receives pulses with the code of that function.
  18. Audioguru

    Can anyone provide me a link or book how to make a woofer at home?

    A high quality speaker in an enclosure designed for its specs sounds good and lasts for a long time. A cheap speaker sounds bad and fails soon.
  19. Audioguru

    Can I use 12 Ohms instead of 8 Ohms speaker?

    A loudspeaker is supposed to be enclosed in an enclosure designed for its specifications for it to sound good. If too much power is fed to a speaker then it can be physically damaged (its coil smashes into its magnet structure) and/or it burns out.
  20. Audioguru

    Power consumption calculation

    Nobody makes a 5V battery. It might be 7.4V then a low dropout regulator will have a 5V output until the battery voltage drops too low.
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