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  1. audioguru2

    What happen when downloading the previous stage?

    Hi Walid, Yes, the 1V signal is attenuated to only 0.1V. I don't say downloaded. I say the signal is loaded down. When you put too much load on a donkey (or a camel) then it goes slower or it stops because it is loaded down. Overloaded would be a better word but it sounds bad. An attenuator is...
  2. audioguru2

    infrared help

    The IR beam is pulsed with a square-wave at about 40kHz. A logic high has the pulsed beam turned on and a logic low has the beam turned off. The IR receiver has a narrow bandpass filter tuned to about 40kHz so continuous IR radiation or IR that is pulsed at a different frequency doesn't cause...
  3. audioguru2

    BJT biasing formulas

    1) When the load requires a higher current. 2) When the output capacitance of the transistor and stray capacitance combines with the collector resistor's value to form a lowpass filter. A lower value of the resistor would require a higher collector current for a higher frequency response.
  4. audioguru2

    Two PCBs off of one power source

    Hi Bruce, Since an earbud still works then the power amplifier IC in the FRS radio is not blown. One earphone wire has signal and the other earphone wire is not grounded and should not be grounded because it has a DC voltage. You need to connect the signal wire to the capacitor input of the...
  5. audioguru2

    What happen when downloading the previous stage?

    The impedances form a voltage divider and reduce the level of the signal.
  6. audioguru2

    do inverters work how i think they work?

    Nope. Not in simple square-wave inverters. There is no rectifier. A rectifier converts AC to DC. The big battery is already DC. There is no amplifier. The transformer steps-up the voltage. An oscillator (also called a multivibrator) with very high input and output currents has two opposite...
  7. audioguru2

    Help!! My Door Alarm is not work?

    Our projects section has a problem printing Greek letters on schematics. Look at the original project: http://www.redcircuits.com/Page54.htm 2u2 is 2.2uF.
  8. audioguru2

    Two PCBs off of one power source

    AAA cells will produce exactly the same current to your circuit as AA cells except they are smaller and won't last as long. Lithium keeps the voltage higher, longer than alkaline. One wire from the earbuds is the signal and the other wire (pin 3 of its power amplifier) has a DC voltage that must...
  9. audioguru2

    Cut Phone Line Detector

    Good, you fixed it. The capacitor filters strong radio and TV transmissions from messing up the circuit. It also keeps the circuit from buzzing if you are dialing with an old rotary dial phone. 1) Try removing the capacitor. 2) Try a capacitor with less capacitance like 100pF. You want to hear...
  10. audioguru2

    Duty Cycle control for square wave inverter

    Hi AN920, That is nice. ;D Maybe a FET or some other voltage controlled resistance can act as a voltage regulator to replace the R2 pot to keep the average output voltage up as the inverter is loaded down, and to keep the average voltage down if the load is removed.
  11. audioguru2

    Two PCBs off of one power source

    R107 is 3.3 ohms, not 3.3 thousand ohms. It and the capacitor connected to it keeps the power amplifier IC from oscillating. The 3.3 ohms resistor and the output for the headphones (and for your MC34119 power amplifier) is at the power amplifier IC pin 1. The jack had a built-in switch that...
  12. audioguru2

    Two PCBs off of one power source

    Yes, or 4.7k or 5.6k or 6.8k or many other values above 3.3k and below about 100k and they are the same.
  13. audioguru2

    Two PCBs off of one power source

    The value of the resistors for the MC34119 power amplifier don't matter much if they are all the same. Use 10k and it will be fine. The same for the capacitors. The 0.1uF can be 0.1uF to 10uF. The 1uF can be 0.1uF to 10uF. The 5uF can be 0.1uF to 22uf. The 100uF can be 10uF to 1000uF.
  14. audioguru2

    white led

    The LM317 with a 3.9 ohm current-regulating resistor will have a current of about 324mA. 324mA across 25 ohms is a voltage of 8.1V. The power in the 25 ohms resistor is 324mA squared x 25= 2.6W. The LM317 needs to have an additional 1.25V across its 3.9 ohms resistor and an additional 2.5V at...
  15. audioguru2

    Two PCBs off of one power source

    Their speaker outputs have completely different circuits and have completely different DC voltages. A high current will flow between them. The batteries and the amplifier circuits will suffer. Shielded audio cable is used to connect together all audio equipment. It is not hacked, it is simply...
  16. audioguru2

    white led

    The LM317 with one resistor is a regulated current source, not a regulated voltage source. Its output voltage will adjust to whatever voltage is needed to produce its programmed current in the load.
  17. audioguru2

    Two PCBs off of one power source

    Hi Bruce, Of course one or both amplifiers will fry if you connect them to the same speaker and the same battery. Their output DC voltages are completely different and all the battery current will flow between them. I have sketched how to connect to the units with shielded audio cable and how...
  18. audioguru2

    infrared help

    A modern IR remote control uses a high current in one or two IR LEDs and modulates the beam at about 40kHz. The IR receiver is an infrared detector IC with a photo-diode and a high gain amplifier tuned to the 40kHz. The photo-diode has a visible light blocking cover that looks black but passes...
  19. audioguru2

    0-30 Vdc Stabilized Power Supply

    The schematic shows where RV1 is connected and you were told where it is connected. The datasheets for the opamps also show where it is connected.
  20. audioguru2

    Cut Phone Line Detector

    Since the buzzer does not turn off with a 9V battery connected to the input of the circuit then the circuit has a problem. Did you use the correct transistors? Did you check the pins of the transistors from their pic in their datasheets so that the pins are not mixed up?
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