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  1. Audioguru

    Consumption of a Led Matrix

    You measured the voltage of only one LED for each color. But they will all be different unless you are VERY lucky. If most LEDs have the minimum or maximum listed voltage on the datasheet then the resistor value for the one you tested will be wrong. You might need to measure the actual voltage...
  2. Audioguru

    9v Guitar Amp w/out LM386

    Your hearing's sensitivity to loudness is logarithmic so you can hear a pin drop but also hear something that is extremely loud. The linear potentiometer is not a logarithmic volume control. If you turn it down from max to half then the audio level will be reduced only a little, but a log...
  3. Audioguru

    Finishing touches on motion alarm

    An LED is a diode that emits light. A diode can conduct a massive current which will instantly burn out a low current LED if you apply a voltage to it so a resistor in series limits the current. The datasheets for LEDs show the voltage they use then the remaining voltage is across the...
  4. Audioguru

    Looking for variable frequency transducers or mini speakers

    In Europe, Down Under and North America, piezo transducers are sold at electronic distributors and stores. In Israel you can go online to Farnell Element 14 where they list 449 of them in different sizes and links to their datasheets.
  5. Audioguru

    ESC and Motor using Variable Power supply

    An ESC that has a 30A rating when it is powered from 30V will cause a 30V, 5A power supply to curl up and die or blow a fuse or burn out.
  6. Audioguru

    Finishing touches on motion alarm

    Why do you think an LED is a dead short? 15V in a 1k resistor produces a current of 15mA. 5V in a 330 ohm resistor produces 15.2mA. But 5V in a 2V red LED in series with a 330 ohm resistor produces only 9.1mA. The voltage across the resistor (3V) sets the current.
  7. Audioguru

    Consumption of a Led Matrix

    The datasheet for a real LED (not an ebay who-knows-who-made-it one) shows its range of forward voltage because it is not a simple light bulb, it is a semiconductor diode and they cannot make them all the same. I said that your blue LEDs might be 2.8V to 3.5V but the datasheet will say exactly...
  8. Audioguru

    Consumption of a Led Matrix

    LEDs have a range of forward voltage. You said your blue LED is 2.6V which seems too low. Most 20mA blue LEDs are 2.8V to 3.5V and you cannot order one voltage, you get whatever they have. If your blue LEDs are actually all 3.5V then three need 10.5 plus a few volts for the driver and current...
  9. Audioguru

    Transceiver Circuit

    It is an extremely simple circuit with very poor performance. It was used in a child's toy walkie-talkie.
  10. Audioguru

    Looking for variable frequency transducers or mini speakers

    You do not want a simple and cheap tweeter, instead you want a "squeaker" that will sound awful. A piezo transducer makes high audio frequencies. They have many resonances so their frequency response has many high peaks and low valleys. The graph of the frequency response of a good tweeter is a...
  11. Audioguru

    7809 not outputting 9v

    A resistor in series with the input of a voltage regulator will cause a voltage drop across the resistor which makes the input voltage to the regulator lower which might be too low for it to work properly. Usually a resistor is not used but it might be calculated properly to share heating. An...
  12. Audioguru

    Solder Sucker

    Cheap Chinese pcb's use chewing gum to adhere the copper to the board. Cheap Chinese soldering irons do not have temperature control so they are way too hot. My pcb's are made locally and my soldering iron has controlled temperature. Then my solder sucker sucks solder, not the pads.
  13. Audioguru

    current limiter for dual rail power supply.

    You never said how much current you need at plus and minus 12V. You could use a 78L12 and 79L12 that have a regulated output current up to 100mA and a peak current of 140mA. They are in a small transistor package so you need to calculate how much heating they produce so that their thermal...
  14. Audioguru

    current limiter for dual rail power supply.

    I have one very cheap Chinese adapter that gets hot even without a load. You are using a low current adapter with a high current voltage regulator. Why not use 78M12 and 79M12 that have outputs up to 500mA? Their peak output is about 800mA but it drops to about 240mA if the output is shorted.
  15. Audioguru

    Fidget Spinner Generator :)

    When you load the generator then the fidget slows down.
  16. Audioguru

    current limiter for dual rail power supply.

    A current regulator uses a low value resistor to sense the current then a transistor or opamp to be turned on by too much current in the sense resistor and a series Mosfet to reduce the output voltage until the current is at your current setting. A simple series resistor at the input of each...
  17. Audioguru

    Power inverter proteus simulation

    You are making a very simple inverter with a squarewave output, not a sinewave like electricity has. The circuit has no negative feedback so the output voltage drops when it is loaded. Many electronic products will not work when the AC is a squarewave because they rely on the much higher peak...
  18. Audioguru

    DC currents through Rd and Rs in JFET amplifier

    Electronic-tutorials.com got the schematic wrong but the text is correct. EDIT: I changed my attachment a little.
  19. Audioguru

    DC currents through Rd and Rs in JFET amplifier

    I agree that the positive biasing of the gate must not be used with a Jfet that is a depletion device. The positive biasing is used with an enhancement device like a bipolar transistor and a Mosfet.
  20. Audioguru

    Breadboards are awesome!

    I am sorry to hear that you are disabled. I am retired so I also don't go to work each day and every day is a very busy Saturday for me and my electronics hobby and family life. I was also disabled but not anymore: 1) I had a heart attack 8 years ago and nearly died. My wife rushed me to the...
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