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  1. audioguru2

    Help Needed Calculating Resistance

    I think the series diode stops damage to the LEDs if the power to the circuit is connected backwards. Then I suggest using a higher input voltage or fewer LEDs in series so the current-limiting resistor has more voltage across it and the LEDs operate more with a constant current if their...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Rubick, Try connecting 0.1uF capacitors directly across the inputs of your very sensitive meters. Their power source is usually batteries and should be completely separate from what they are measuring. Hi Logitec, If you build the modified project, its transformer should be 30VAC/4.3A which...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    The tolerance of the current-setting pot is probably 20%. It should have a trimpot in series with it to reduce its max to exactly 3.0A. Or simply temporarily use anothe pot in series to adjust the max current and replace it with a resistor of the same value. The voltage-setting pot is the same...
  4. audioguru2

    Question about Ground Loops

    Hi Walid, Here in Canada, my TV and my video cassette recorder/player aren't grounded so there isn't a ground loop. If I see hum in my picture then I use a better-shielded cable connecting them. I don't think you can measure AC mV low enough to identify a very low level of hum. You also can't...
  5. audioguru2

    Help Needed Calculating Resistance

    Hi Demon, Welcome to our forum. ;D Your LEDs have a huge range of voltage rating and your current-limiting resistor has a low voltage across it with 3 LEDs in series. I assume that the 1.1V diode is in series with the array reducing the voltage to 10.9V. If the LEDs are 3V, then their current is...
  6. audioguru2

    motion detector, N.C COM

    You can make a 10 seconds timer from a 555 IC. Its details are in our Articles section and in its datasheet: http://www.datasheetarchive.com/semiconductors/pdfdatasheet.php?Datasheet=1136921
  7. audioguru2

    My first project

    Hi Ed, I like LEDs and have and had lots of projects with them blinking: 1) I made fifteen "Flash Lights" with a single ultra-bright blue, green or white LED blinking 5 times in half a second then a half-second pause. The circuit crams 90mA into the LED and at one time I had all 12 blinking on...
  8. audioguru2

    My first project

    A 6V battery will drop to 4V near the end of its life. A 7805 regulator won't work from a 6V battery anyway. It needs a minimum input of about 7V. A low-dropout regulator like an LM2931A-5.0 needs a minimum input of 5.5V to regulate well. Its Z package is like a little transistor and I use it...
  9. audioguru2

    Variable DC Power Supply

    Believe it or not, an ordinary silicon transistor makes a pretty good zener diode. A silicon transistor has avalanche breakdown of its reverse-biased emitter-base junction at about 6.6V. It has a slightly positive temperature response. If you add in series the transistor's forward-biased...
  10. audioguru2

    finding the capacity of NiCd or NiMH cells?

    It is not accurate to calculate the discharge capacity of a recharable battery by its charging time because charging is not efficient. Energizer use a discharge current of 0.2 of its rated capacity and stop the timer when the loaded battery voltage drops to 1V per cell. The cells are 1.25V over...
  11. audioguru2

    motion detector, N.C COM

    You said that the output of the detector is a normally-closed relay contact. The relay will open its contact when it detects motion. The 10k pull-up resistor to +5V allows the input to the ToothPIC to go to +5V, not less than 1V. Maybe that is the normal operation of the motion detector.
  12. audioguru2

    Alarm sound detector schematic

    The bandpass filter circuit biases the non-inverting inputs (pin 3) of the opamps to half the supply voltage so they work with opamps usually needing a dual supply. The MFBP circuit doesn't have a high Q nor high gain and any kind of bandpass filter needs an opamp with a wide bandwidth for low...
  13. audioguru2

    Dual Polarity Power Supply

    Hi Shaiq, Your opamp mic preamp with LM380 power amp project doesn't need a dual-polarity supply and doesn't need a variable voltage supply. Just use an AC to 12VDC/0.5A adapter to power it.
  14. audioguru2

    Variable DC Power Supply

    Hi Shaiq, All other regulated power supply circuits I've seen have a voltage reference like a zener diode. This circuit doesn't have one so I don't think its voltage regulation will be very good. Your opamp mic preamp and LM380 power amp project doesn't need a regulated supply and doesn't need...
  15. audioguru2

    Need help for 4009b hex inv buffer

    Who are you going to believe? My Cmos Cookbook says, "The 4009 should not be used for new designs. Use 4049 instead. It will self-destruct if the supplies are applied in the wrong sequence or if the voltage on pin 1 is higher than on pin 16". ST Micro says, "The 4009 is a preferred replacement...
  16. audioguru2

    finding the capacity of NiCd or NiMH cells?

    It is difficult to measure how much charge remains in Ni0Cad or Ni-MH cells, but you can measure their capacity with a discharge resistor and a timer circuit.
  17. audioguru2

    finding the capacity of NiCd or NiMH cells?

    Some manufacturers don't make Ni-Cads anymore, only Ni-MH now.
  18. audioguru2

    voltage regulators

    I don't know how or why you are trying to add the current of a 5V regulator with the current of an 18V regulator. Surely then the combined output isn't regulated. If you need an 18V regulator with higher output current then use a regulator or booster transistor with it that will handle higher...
  19. audioguru2

    finding the capacity of NiCd or NiMH cells?

    Hi Sukhbinder, You don't need to know the capacity of the original battery cells. Just use the biggest cells you can find that fit. I think half-D size is common for models so try a hobby shop. Modern cells have a higher capacity than older cells so change both at the same time. ;D
  20. audioguru2

    Alarm sound detector schematic

    Hi Pramono, I don't think a 4kHz filter with only a 5% bandwidth is practical. Its amplitude and frequency will drift and also probably the alarm's frequency. There are T-filter circuits on the web that narrow their bandwidth by injecting feedback to a point in the filter that is normally...
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