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  1. audioguru2

    transistor question

    Hi Sevens plus a ten, Perfect!                        Perfect!                        Perfect!                        ;D ;D ;D                  ;D ;D ;D                  ;D ;D ;D                  ;D ;D ;D                  ;D ;D ;D                  ;D ;D ;D                  ;D ;D ;D           ...
  2. audioguru2

    TRANSISTOR ATTENUATOR?

    Hi Ante, You wouldn't need a dictionary or a brain transfusion if Kevin made a circuit that can have as much accurate gain or attenuation as he wants, like this one:
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Ta, Welcome back. I hope you had a nice vacation. Now that I am retired, every day is a holiday and sometimes I have a nice vacation too. ;D Sure, use 3 or 4 2N3055 transistors to divide the heat dissipation among them. Use a separate heatsink for each one. One member had trouble matching...
  4. audioguru2

    transistor question

    No, you have two inverting transistors driving the 2nd LED so both LEDs light at the same time. Get rid of the PNP transistor and drive the 2nd LED with just the NPN transistor for the LEDs to light opposite of one another. You don't need the PNP transistor and its resistors so concentrate on...
  5. audioguru2

    transistor question

    Hi Sevens and a ten, Welcome to our forum. ;D Nice try, but you missed a few important things. The circuit has two inverting transistors for the 2nd LED so both LEDs light at the same time. Try again. ;D
  6. audioguru2

    Electronic Stethoscope

    Hi Proton, Welcome to our forum. ;D I wrote a circuit description in the project: http://www.electronics-lab.com/projects/science/019/index.html
  7. audioguru2

    Electronic Stethoscope

    Use two LEDs connected back-to-back as shown in the schematic. New Lapan Radio have some low-noise dual opamps. Don't use their 1st copy of the TL072 because it doesn't work and they tried to recall them all. If you want the lowpass filter to have an adjustable frequency then just use a dual...
  8. audioguru2

    Digital Remote Thermometer

    Hi Kg, Welcome to our forum. ;D I guess you are talking about this project: http://www.electronics-lab.com/projects/sensors/010/index.html IC1D is unused and has its inputs connected to the positive supply to disable it. Its output pin11 doesn't connect to anything. ;D
  9. audioguru2

    Telephone Billing machine!!!

    How are you going to calculate how much to charge for long-distance calls? Detect the dialed area code and compare it to a list? Maybe your telco charges you for local calls. In Canada I can make as many local calls as I can, for any amount of time, at no extra cost. If I want to make a free not...
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Vedran, The original pcb will work for the 5A version with C1, the rectifier bridge module and R7 mounted externally. A few other resistors will be a tight fit and must be stood-off the pcb. Q2 will need its leads crossed or it can also be mounted externally. ;D
  11. audioguru2

    Lissajou patterns

    A 'scope shows a Lissajou pattern when it is set to XY mode and two different frequencies are a multiple of one from the other. You can have a 2nd frequency from a low voltage mains transformer. It makes 50Hz or 60Hz and your function generator makes 100Hz, 150Hz, 200Hz, or 120Hz, 180Hz, 240Hz ...
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Vedran, We discussed the necessary changes to make this project produce 5A in this topic: http://www.electronics-lab.com/forum/index.php?topic=196.0 It needs three 2N3055 output transistors with emitter resistors and each transistor needs its own pretty big heatsink. The project also needs a...
  13. audioguru2

    Early voltage determination

    The Early voltage is the rise in a BJT's collector current with increasing supply voltage when the base current is constant. It was discovered by a guy with the name of Early and is shown on a transistor's datasheet. The Early voltage and a transistor's distortion can be cancelled with negative...
  14. audioguru2

    Beta of the BJT

    Hi Walid, If you are designing a BJT circuit then a datasheet must be available or use another transistor that has one. Then design the circuit so that it works well with any beta that is specified in the wide range on the datasheet. ;D
  15. audioguru2

    BJT power supply

    The base or collector voltage will be at or closer to ground with a dual polarity supply.
  16. audioguru2

    BJT operating point

    You can design a transistor circuit to use any amount of battery current you want. It all depends on the resistance of its load. The amount of distortion of a single common emitter transistor depends on its load resistance and its gain. Since you don't specify a load resistance nor amount of...
  17. audioguru2

    Laser questions

    Hi Greek, I guess a laser brightness regulator would have the laser's photodiode reverse-biased and feeding an opamp. The opamp would compare the output of the photodiode with a reference voltage and drive a transistor or Mosfet to the correct current for the laser.
  18. audioguru2

    RBG LED how to?

    Hi MadThug, You will need many RGB LEDs and might have a problem having them matched for tint and brightness. Agilent sells white LEDs with your choice of tint. If you are making a digital TV screen with LEDs then each vertical column and horizontal row intersection would have the 3 colours and...
  19. audioguru2

    TRANSISTOR ATTENUATOR?

    Kevin, What are you talking about? The signal at the collector of the NPN transistor is small and is simply divided by the voltage divider of its collector resistor and the emitter resistor of the PNP transistor. The collector of the NPN is a high impedance (just the collector resistor) and the...
  20. audioguru2

    Laser questions

    One guy said that over-current in a laser diode burns it into an expensive LED in a cool-looking package. ;D The laser diode has a photodiode in it to sense its output and control the current. You didn't control the current. :(
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