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  1. Audioguru

    Questions lithium polymer battery

    The charging circuit for a Lithium battery is supposed to do many things. Some do and some don't. If the circuit is cheap and simple then it wrecks the battery soon so that you must replace it and they make lots of profit. Store your battery at 2 bars, then charge it before using it.
  2. Audioguru

    Questions lithium polymer battery

    A lithium battery charger circuit is supposed to charge to 4.20V and when the charging current drops to 5% the charger is supposed to turn off. Then the battery is at a full charge and its life is shortened if it stays there for one month or more.
  3. Audioguru

    Questions lithium polymer battery

    Rechargeable batteries are measured in Volts, not in Bars.
  4. Audioguru

    Headset mic not working

    The earphones are dynamic and are 32 ohms each. The microphone has no spec's. The Frequency Response Range is absolutely useless since it does not say the plus and minus level deviation. Plus and minus 2dB is good but plus and minus 30dB is horrible. A pc sound card mic input should already...
  5. Audioguru

    Questions lithium polymer battery

    Just guessing: 1) Leave it at 2 bars for most of the time. 2) Charge it to 3 bars before using it. 3) If it ever shows 1 bar then charge it to 2 bars if you do not use it soon.
  6. Audioguru

    Questions lithium polymer battery

    The 3 bars do not show the details that are needed about charging: 1) Less than 3V per battery cell reduces its life. 2) Continuously 4.2V per battery cell reduces its life. 3) Between 70% to 100% of a full charge the cell's voltage is 4.2V. 4) 3.7V to about 3.8V per cell is a good storage...
  7. Audioguru

    Amp driving LED project issue

    3dB is double or half the power that sounds only a little louder or a little less loud. The first comparator in an LM3915 turns on its LED at a certain loudness that you set then the second turns on at a loudness a little more, then the third at a little more..... all the way up to the tenth...
  8. Audioguru

    Headset mic not working

    Most electret mics have 2 terminals, the output that is powered with 0.5mA by the preamp, and the ground which connects to its metal case and to the cable's shield which connects to the preamp's ground. But electret mics are also available with 3 wires that you cannot use. The original aviation...
  9. Audioguru

    Headset mic not working

    Your pc uses an electret mic that has an infinite resistance. When it is properly powered then it has an impedance that is 1k to 5k ohms. An aviation mic might be an old fashioned carbon particles mic with a varying resistance or it might be a dynamic mic with a coil and magnet like an earphone...
  10. Audioguru

    Amp driving LED project issue

    You are too late. The LM3915 was an IC with 10 comparators in a logarithmic arrangement of level detectors. It made a simple but useful VU meter. it could make a bar of light or a dot of light move up and down with the level. It ain't made anymore. I have one in my living room with a microphone...
  11. Audioguru

    Where to add dimmer in ac led bulb?

    There are three identical circuits on the circuit board. The IC is made by SI of China.The datasheet for the IC shows a circuit and the IC has two pins and three resistors that are not explained. A dimmer is not shown.
  12. Audioguru

    convert 3v to 12v?

    A string of LED "fairy lights" is sold at The Dollar Store and uses one AA cell and lights about 20 LEDs. I have two that have 10 LEDs that can be switched on or switched to flashing and they are powered from one rechargeable AAA cell and are charged from a little solar panel. The LEDs are all...
  13. Audioguru

    Capacitor Knowledge Wanted

    Electrolytic capacitors in the good old days had a plus sign. Not anymore, now they have a minus (negative?) sign.
  14. Audioguru

    Capacitor Knowledge Wanted

    If you can rad the letters and numbers on the audio power amplifier ICs shown in your photo then its datasheet will have the schematic of the power amplifier.
  15. Audioguru

    Questions lithium polymer battery

    www.batteryuniversity.com answers most of your questions about a lithium rechargeable battery but they don't know the product's charger or anything in the product (a clock?) that is draining the battery for 3 months. They say that if a Lithium cell's voltage has stayed long at a full charge...
  16. Audioguru

    Questions lithium polymer battery

    Nobody knows what the bars mean. Nobody knows why they say to recharge every 3 months.
  17. Audioguru

    DIY Metal detector

    I found a few of the same metal detector circuit in Google that are demo'd in You tube. (They might be from the same guy from "over there" who can barely speeky zee Engrish). They also use a 555 circuit that has an LC series circuit in it. Some of them wrongly say the 555 is a monostable but...
  18. Audioguru

    DIY Metal detector

    Pin3 provides positive feedback so the circuit can oscillate. When pin2 goes low it causes pin3 to go high which slowly charges the capacitor at pin2 and pin6. When the voltage on pin6 gets high enough then it causes pin3 to go low which causes the capacitor at pin2 to discharge until its...
  19. Audioguru

    Transistor base-emitter voltage pulled down

    I edited my previous post. I think C1 charges more only for very loud sounds. Each positive-going half-wave from the mic that has R1 pulling the capacitor up, C1 charges more because the base-emitter diode of the transistor does not allow the base end of C1 to go up, resulting in C1 charging...
  20. Audioguru

    Transistor base-emitter voltage pulled down

    With no sounds, C1 has about +4V at the microphone end and about 0.6V at the base of Q1. Sounds cause the voltage at the microphone to wave up and down. The base-emitter diode of Q1 does not allow the base end of C1 to go up so it is charged more by the mic's resistor R1.. When the microphone...
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