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  1. Audioguru

    LM358 to make FM Audio Receiver

    C3 grounds the base of Q2 at RF frequencies so that it can be a common base amplifier that oscillates. Calculate the reactance of the 0.01μF capacitor C3 at 100Mhz: 0.01 ohm. Is C3 part of a lowpass filter that cuts audio high frequencies? Simply calculate the cutoff frequency: Yes, 3200Hz...
  2. Audioguru

    Brake light flasher (555 - based) circuit works on breadboard, but not PCB

    The transistor has nothing to turn it off, especially if the power was removed then turned on again. Fix it by connecting a 22k resistor from the base of the transistor to ground.
  3. Audioguru

    Brake light flasher (555 - based) circuit works on breadboard, but not PCB

    The schematic should work fine if the polarity of C2 is correct, its polarity is not shown so maybe it is installed backwards.
  4. Audioguru

    LM358 to make FM Audio Receiver

    Sorry, I make design and build circuits, not simulations. I have never stepped a capacitance in an RF circuit when the RF is a sweep, and I think 100M is not 100 Megahertz, I think 100m should be used.
  5. Audioguru

    Brake light flasher (555 - based) circuit works on breadboard, but not PCB

    Why didn't you show a schematic so we can see what might be wrong? The video showing the dark side of the circuit board is useless.
  6. Audioguru

    Darlington pair false triggering.....

    How much current is needed for the relay coil? You say you used a 12V/1A AC adapter which is wrong. You need a 12VDC adapter. TIP122 darlingtons made by a good company do not turn on when they have no base current. Maybe they are fakes from ebay?
  7. Audioguru

    Light therapy device

    The very cheap IR light with hundreds of LEDs has no detailed spec's. Some might produce a much higher output power than others or they all might produce only a tiny amount of output power. But it is Cheeeep!
  8. Audioguru

    LM358 to make FM Audio Receiver

    There is no "modulator". The mic preamp modulates the current in the RF oscillator transistor which produces a little AM that an FM radio ignores. The changing current in the oscillator transistor also changes its capacitance which varies the frequency of the oscillator producing FM.
  9. Audioguru

    LM358 to make FM Audio Receiver

    You must reduce the timebase to see audio at your locations 2 or 3. Use tran 0 100ms 95ms 1ms. It is impossible to see an audio signal at the antenna.
  10. Audioguru

    LM358 to make FM Audio Receiver

    What do you expect to see in your simulation? The timebase is set to see the carrier AM modulation but the oscillator is very overloaded by your 300mV audio signal that is 30 times higher than a mic signal and the value of C4 is almost nothing. I think you should first get your oscillator...
  11. Audioguru

    XR2206 FUNCTION GENERATOR

    Phase shift from a coupling capacitor usually causes a squarewave to have tilt. Your schematic from the datasheet does not show an output coupling capacitor so maybe your oscilloscope is set for AC then its input has a coupling capacitor.
  12. Audioguru

    Light therapy device

    Thermal runaway occurs only when LEDs are operated near their maximum allowed current. If your supply voltage is fairly constant (a wall-wart power supply might not be) then a resistor can be used to limit the current for each string. Calculate the resistor smartly (not with a stupid wizard)...
  13. Audioguru

    LM358 to make FM Audio Receiver

    You were told before that the very high stray capacitance between the rows of contacts and the wires all over the place on a solderless breadboard cause a radio circuit not to work. Also the long wires have inductance that the circuit does not want. Also your parts are too far apart. Also your...
  14. Audioguru

    Light therapy device

    I assume your 9V batteries are alkaline type that have 6 cells that are 1.5V each, not Ni-MH rechargeable type that have 7 cells that are 1.3V each. Both types of batteries drop their voltage as they run down and you might need to replace or charge them when they become only 6V. Two 9V...
  15. Audioguru

    LM358 to make FM Audio Receiver

    Xyq, it seems that you did not read my descriptions of the parts and that you know almost nothing about simple electronic circuits. Don't you have a teacher and a text book? 1) Is a resistor that powers the junction field effect transistor inside the electret mic and a capacitor that couples...
  16. Audioguru

    2 questions about speakers

    Speakers used electromagnets about 100 years ago. They have used powerful permanent magnets ever since. Bolts are made in many different metals. A brass bolt will not work in an electromagnet. If you need a speaker then why not buy a speaker? Cheap ones sound awful but a speaker selling at a...
  17. Audioguru

    Light therapy device

    I did not see the datasheet for your Radio Shack LEDs. (OH, IT IS SPELLED WITH A VERY FAINT BLUE FONT) Since Radio Shack knows nothing about electronics usually their datasheet for an electronic part lists only the size and weight. This datasheet is the Chinese one translated very well. How...
  18. Audioguru

    transistors, and capacitors

    I wonder why all transistor datasheets do not mention transconductance but show current gain instead?
  19. Audioguru

    transistors, and capacitors

    The hFE is shown in all transistor datasheets to be the current gain. A transistor with an hFE of 100 when its collector current is 50mA will have a base current of only 50mA/100= 0.5mA when it is active and is not saturated. The hFE varies with the collector current as shown in a graph in the...
  20. Audioguru

    Light therapy device

    Your Radio Shack LEDs also have a range of forward voltage. Some might be 1.2V. If their forward voltages are a little higher then they will not work from the 21V supply. If their forward voltages are a little lower then they will burn out. Your wizard is stupid. You must calculate the lowest...
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