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  1. Audioguru

    Light therapy device

    Who says the forward voltage of each LED is 1.55V? Did you measure all of them? The datasheet shows a range of voltages from minimum to maximum[/b] because they cannot make them all the same like a simple incandescent light bulb. You must use the maximum forward voltage in the calculation, plus...
  2. Audioguru

    Zener diodes not working

    Doesn't your multimeter have a "low battery" indication before its calibration fails?
  3. Audioguru

    LM358 to make FM Audio Receiver

    I guess you have not seen the datasheet for the 2N3904 transistor. It show it working well up to 300MHz. You can use any transistor that works well up to 300MHz but Asian transistors, European transistors and American transistors all have different pinouts.
  4. Audioguru

    LM358 to make FM Audio Receiver

    What does R1 do? It applies a current to the electret microphone. Why? Look up Electret Microphone in Google to see that it is a condenser microphone that has 48V permanently embedded in its electret material so that when its membrane vibrates with sounds then it is a variable capacitance...
  5. Audioguru

    Light therapy device

    When LEDs are in series then they are all using the same 50mA of current. When all 15 LEDs are in parallel then their total current is 750mA. You must limit the current with a resistor or a current source. If you use a resistor then you will see the LEDs slowly dimming as the battery runs down.
  6. Audioguru

    Please Please Help Me Understand This ...

    Your do-it-yourself battery will produce very low power unless it is HUGE.
  7. Audioguru

    Segment counter with IC 555 & IC 4026

    Before it is destroyed by too much current melting the output transistors you should read the "Maximum Ratings (absolute-values)" on the datasheet of the CD4026. 500mW for the entire IC which is 500/7= 71mW for each output when all 7 are turned on. The datasheet from Texas instruments has graphs...
  8. Audioguru

    Ceramic Disc Confusion

    A capacitor marked 104 is 10 followed by four zeros in pF which is 100,000pF which is 100nF or 0.1μF. 222 is 2.2nF or 0.0022μF. Many ceramic capacitors have a wide range. A 0.1μF could be 0.05μf to 0.2μF They change their value when the voltage changes so they cause low frequency distortion if...
  9. Audioguru

    Segment counter with IC 555 & IC 4026

    Pin 5 on a 555 needs decoupling if the supply jumps up ands down caused by another 555, and the supply is not decoupled.
  10. Audioguru

    Zener diodes not working

    9V/10k= 0.9mA, a very low current for a power zener diode. A 1N5349B 12V/5W zener diode is tested at 100mA. It might be 11.5V at 5mA.
  11. Audioguru

    Segment counter with IC 555 & IC 4026

    The circuit is also missing a very important supply bypass capacitor mentioned on the datasheet of the 555. The datasheet of a ICM7555 Cmos 555 explains that an ordinary 555 causes a current shoot-through of 400mA (!) each time the output switches that causes the 9V battery voltage to crash and...
  12. Audioguru

    Zener diodes not working

    Were the zener diodes very cheap and were sold on ebay? Was your voltmeter very cheap and was sold on ebay?
  13. Audioguru

    LM358 to make FM Audio Receiver

    Why didn't your teacher teach you about the basic transistor circuits? Don't you have a text book about transistor circuits?
  14. Audioguru

    Power Supply for Car Radio

    You might find a 13.8VDC/10A power supply. I notice that it has an old cassette tape player that I have not used for about 25 years and it won't play CDs or MP3s.
  15. Audioguru

    Li Ion batt. pack

    A 2-cells Lithium battery is balance charged so the battery and charger have 3 wires. One wire connects between the two cells. Ternigy is an extremely cheap and poor quality battery from HobbyKing in China. Much better ones are available buy they cost more.
  16. Audioguru

    Building a drone from scratch. What motors do I get?

    Will you use Wi-Fi or Bluetooth? Will the range be far enough? The model drones at the park have GPS and the flight plan is programmed into the model's memory. They have video transmitted back to the pilot watching through video goggles. A few model drones flew away and the pilots do not know...
  17. Audioguru

    Need A 5v Or 12v Audio Amplifier To Get 100 Db Out Of 1 Or 2 Speakers

    The dB sound level from a speaker is determined at a certain distance (usually 1 metre, it is much louder if you hold it against your ear and it is less by -6dB per doubling of distance when no echoes), the power and the frequency. Most speakers are rated at about 86dB to 94dB at 1W, 1m...
  18. Audioguru

    Understanding A Datasheet

    These transistors have a two-resistors voltage divider at the base. The fairly low 0.15V saturated Vce is when the collector current is 10mA and the base current is 0.5mA (1/20th). The higher 0.3V is when the collector current is 5mA and the input voltage is typically 1.7V but you must calculate...
  19. Audioguru

    Adding Input to the Amplifier circuit!

    I cannot find a datasheet for the obsolete Sanyo power amp IC. It looks like pin 4 of the connector applies +12V to turn on the IC slowly to avoid a loud POP! If you connect the pin 4 to pin 1 then the amplifier will be on all the time. Do not connect pin 2 to anything. The left and right...
  20. Audioguru

    LM358 to make FM Audio Receiver

    Your receiver is hopeless because its input is shorted to its output. I biased the first transistor properly with a base resistor to its collector and put C1 and L1 as a parallel tuned circuit as its collector load, then I capacitor coupled its collector to the base of the second transistor that...
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