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  1. audioguru2

    Led display Digital Voltmeter question

    Hi Vk, A 7905 regulator isn't a generator. It takes a higher negative voltage and regulates its voltage down to -5V. It needs a negative voltage source as its input. There are a few ways of converting a positive voltage into a negative voltage. The datasheet for the ICL7107 IC in the project...
  2. audioguru2

    220 volts Versus 120 volts

    No. A device that operates with both voltages will draw the same power with either voltage, so the current is half when the voltage is doubled. Then the cost of the electrical power is the same. My toaster gets pretty hot. If its power is doubled then it would set itself and my house on fire!
  3. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    RTL and DTL logic are very old and haven't been used in new designs for many years. They have nearly the same logic low input voltage level limit as TTL, about 0.65V. So a DRL AND gate should not be used with them.
  4. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    A DRL gate is designed to feed only the zero-current input of a Cmos input. It doesn't have enough current to power an LED and to make a proper logic low or logic high voltage. You showed an LED connected to the output of a DRL to indicate if the output is a logic low or a logic high. I said...
  5. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    A DRL gate is used only for Cmos logic. Its low voltage of +0.7V is too close to the +0.8V max that is allowed by old TTL logic. Nothing needs exactly 0V for an input because some extra voltage is allowed for noise immunity. The low voltage would be about +0.3V if Schottky diodes are used...
  6. audioguru2

    How can I cascade 4017s?

    I look at the 1k resistor going to MR pin 15 of the upper 4017. It isn't needed since a piece of wire will do the same thing. But it allows you to connect the MR pin 15 to the positive supply for a moment to reset both 4017s. So maybe the circuit isn't finished and an OR gate should be...
  7. audioguru2

    How can I cascade 4017s?

    This circuit doesn't reset itself when power is applied, like the Bill Bowden circuit. Multisim has many problems with running circuits. Does it show an output from the 555? Build it instead.
  8. audioguru2

    How can I cascade 4017s?

    Without looking at the wiring details, the 4017s and the 4081 don't have a supply voltage nor a ground. Without being powered then they don't work.
  9. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    A diode has about 0.7V across it when it conducts current. In this circuit if the input voltage is 0V (ground) then the diode conducts and makes the output voltage about +0.7V. It doesn't need to be 0V at the output because a Cmos input connected to it works fine with a +0.7V input as a logic...
  10. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    The first link you posted is WRONG! No wonder you are confused. The second and third links have the diode Resistor AND gate correct. If both inputs are high then the output is high because the resistor pulls the output high.. If one or two inputs are low then a diode or two will conduct and the...
  11. audioguru2

    How can I cascade 4017s?

    They are supply bypass capacitors. One 0.1uF ceramic disc capacitor directly across the supply pins of each of the five logic ICs. J1 is the 12V supply input jack. C7 is the 100uF low frequencies supply bypass capacitor for the 555, but it should also have an additional 0.1uF ceramic disc...
  12. audioguru2

    How can I cascade 4017s?

    The French circuit steps through its 30 LEDs one after the other, blinking the LEDs but nothing more. Its LEDs are all the same and each of its current-limiting resistors have the same value. The LEDs all connect to the same common. So 29 of its resistors are not needed.
  13. audioguru2

    How can I cascade 4017s?

    The French circuit uses dozens of current-limiting resistors for the LEDs. Only a single current-limiting resistor is needed for all the LEDs if the supply voltage is high, because only a single LED lights at a time. Bill Bowden's circuit shows how. If the supply voltage is 9V or less then a...
  14. audioguru2

    How can I cascade 4017s?

    The "carry out" pin of the CD4017 cannot be used for cascading them. The CD4017 datasheet from Texas Instruments shows them cascaded using AND gates. But you need to figure out how to reset everything when the power is applied. Bill Bowden has already done the reset circuit for you and also...
  15. audioguru2

    How is virtual resistance calculated?

    Hi Electrojive, Sorry, I forgot all my RF calculations since I haven't used them since school many years ago.
  16. audioguru2

    How is virtual resistance calculated?

    Hi Electrojive, Welcome to our forum. ;D The collector of a transistor amplifier is a high impedance constant current sink. In an RF amplifier circuit its load is usually a high impedance inductor. Then LC circuits are used to match its high impedance to the low impedance of an antenna and to...
  17. audioguru2

    Electronic Stethoscope 2

    I took a thick plastic lid from a jar and drilled a hole in its center for my electret microphone. Holding it up I could hear the low frequencies clearly in my earphones when somebody spoke fairly far away. When I pressed the jar lid to my chest so that the microphone has a small air space from...
  18. audioguru2

    a very simple FM Tx

    The datasheet for the transistor that is used in your project and for most other small transistors shows the transistor's change of its capacitance with voltage change, like a varactor diode. The input audio causes the transistor to conduct more and less which changes the voltage across it and...
  19. audioguru2

    a very simple FM Tx

    Hi Walid, Maxim's VCO IC uses a varactor diode (it changes its capacitance when its voltage is changed) to frequency-modulate and to tune its carrier.
  20. audioguru2

    a very simple FM Tx

    This circuit uses a common-base amplifier. There are many other kinds of oscillator circuits. The capacitor makes the base at 0V for RF frequencies. If it is removed then the circuit probably won't oscillate.
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