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  1. Audioguru

    Need help with this circuit.

    Since you are simply copying a circuit that might not even work, then I guess you are not learning how to design an electronic circuit. Then are you simply learning how to ask on a forum where to gather parts and solder them together?
  2. Audioguru

    Home stereo compatible with 12v campervan?

    If you are thinking about using a rechargeable battery then Ni-MH cells are modern and a charge lasts for 1 year on newer ones. Ni-cads had many problems. Today, Ni-MH cells are sold everywhere but almost nobody sells Ni-Cad cells today. Lithium-Ion or Li-Po cells are even newer but have risks...
  3. Audioguru

    Help with Li-po

    An ordinary lithium rechargeable cell must never be allowed to discharge below 3.0V but 3.2V is safer or it will be destroyed and might catch on fire if it is charged later.
  4. Audioguru

    Help with Li-po

    The output power is 2.5A x 5.1V= 12.75A. A good voltage booster is 80% efficient so the total power needed is16W. Then the 3.7V battery must provide 16W/3.7V4.32A. Then a charge will power the circuit for 6A/4.32A= 1.4 hours. A battery power bank can charge from USB 5V and give an output of 5V.
  5. Audioguru

    NPN Transistor Amp not working!!?!?!

    Don't you have a multimeter that can measure DC voltage? On your original single transistor circuit, without the speaker, measure the voltage at the collector output. Is it 4.3V? Then connect the 8 ohm speaker and measure the DC voltage again. Is it 0.022V? Can a transistor work if its collector...
  6. Audioguru

    simple radio amplification

    The circuit is a very simple poor quality FM radio transmitter with low output power. The schematic is wrong because R5 should connect to ground and C4 should be parallel with it. The value of C3 is also wrong because it is much too small and will pass only high pitched squeaks. It will not work...
  7. Audioguru

    Home stereo compatible with 12v campervan?

    1) It is not "hifi" because it does not produce low audio frequencies. 2) It is not stereo because its speakers are too close together. Do any of its "effects" sound natural?
  8. Audioguru

    IR tx & Rx

    I think the seller knows nothing about electronics. It is the receiver with a dark case that must block visible light so it gives an output only with infrared. The transmitter is an LED that can have a clear case because its output is already only infrared. I go to the major electronics parts...
  9. Audioguru

    Building an EKG analog front end circuit

    No huge current. The input current of the TL084 opamp is very low because it has Jfet inputs. Its error with the 1M resistors in the circuit is only 0.4mV which is nothing. The MCP6004 has even lower input current that makes a difference if the resistors are 500M or more. Your problems are the...
  10. Audioguru

    IR tx & Rx

    You do not know what you have (IR? Rx? Tx? Ordinary Light Rx?) and we do not know what you have. When we buy IR Rx and Tx then they have part numbers and detailed datasheets that tell all about them.
  11. Audioguru

    Ring Doorbell

    The doorbell might use a high power motor to spin a hammer that strikes the gong as it rotates. Then maybe the motor draws a very high current when it starts and the resistor limits the current?
  12. Audioguru

    Calculation of a Potentiometer

    A pot is used to control a speed control circuit then the circuit drives the fan. Your fan has a resistance of 12V/0.25A= 48 ohms. If you put a 48 ohms resistor in series with the fan it probably will not start running but if you spin it with your fingers to get it going it might run at half...
  13. Audioguru

    NiMH battery charging with a phone charger

    Your photo is not a schematic and it does not show what is connected to what. I assume that you have two groups of 4 battery cells in series? Then you are feeding the 5V to both groups in parallel? Then if the cells are good they will never reach a full charge because each cell should be 1.4V to...
  14. Audioguru

    BAT. Holder

    You forgot to say the chemistry of your battery D cells (antique carbon-zinc?) and if they are new or have been sitting on a store shelf for 10 years. I use Energizer Name-Brand AA size alkaline cells. They are stamped "best before 12-2026" and are guaranteed for 10 years so they were made this...
  15. Audioguru

    741 circuit amp wont turn on

    I suspect that he wants the light bulb to light up when there is a low level AC signal at the input. Then a properly biased amplifying opamp van drive a rectifier/filter circuit that drives the light bulb. The datasheet for a 48 years old 741 opamp says that its non-inverting input pin3 will...
  16. Audioguru

    Increasing battery life of smart lock

    You need to measure or calculate the current needed then buy an adapter that provides that much current or more. Cheap Chinese "super heavy duty" battery cells might be a few years old and power your lock with a few mA for 5 days. Fresh Name Brand Alkaline battery cells can supply hundreds of mA...
  17. Audioguru

    LED Specs

    An LED is supposed to be fed a limited current, not just a voltage. Post a video of your LED instantly burning out when you connect 3.4V to it.
  18. Audioguru

    BAT. Holder

    What chemistry are the Bats? Many D size Ni-Cad and Ni-MH rechargeable Bats have a little AA or C cell inside because nobody uses D size Bats anymore.
  19. Audioguru

    Battery Pack Conversion Project

    Lithium is extremely reactive and will explode or catch on fire if a Lithium rechargeable battery is charged or discharged wrong (too much voltage or too much current). Those power supplies are not a proper charger. Learn about it.
  20. Audioguru

    Battery Pack Conversion Project

    I have never seen AA Li-Ion cells because they are not supposed to be able to fit into the battery holder for AA alkaline, Ni-Cad or Ni-MH cells. They are usually a larger 18650 size (18mm diameter by 650mm long). The "power adapter" has an expensive switch (that will usually be in the wrong...
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