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  1. audioguru2

    i need help extending the keys finder project. can someone help me out????

    Hi Chetan, Welcome to our forum. ;D Did you build it and did it work? ??? It is supposed to beep when it hears a fizzle (?) sound. You could have a million of them and they will all beep, maybe continuously. The 2nd one would hear the 1st one beep and it would also beep, and the 3rd one...
  2. audioguru2

    Outdoor Light Status Indicator

    No thanks. The 100mA max rating is for 100us which is brief enough. With its 10% duty cycle its average temp won't be very high so I think there must be a fuse (thin bonding wire) in my low current LEDs. If I find a visible LED with a 2A max rating I'll try it. ;D
  3. audioguru2

    Switching power supply

    Hi Ante, Sorry I didn't notice that your transistors are darlingtons. They don't look like darlingtons. In a half-wave charge pump the transistors must conduct twice the load current, right? For your 2.5A load, each darlington conducts 5A and its max saturation voltage is 2V. Therefore their max...
  4. audioguru2

    Outdoor Light Status Indicator

    Hi Ante, I've seen IR LEDs with a 1A max rating, but I use blue, green and white LEDs with a 100mA max rating. I blink them very briefly at 90mA and they are extremely bright. I wouldn't dare to operate them with pulses exceeding 100mA. ;D
  5. audioguru2

    5 minute timer where a mechanical motion is required

    Hi Iceman, Welcome to our forum. ;D Your battery's voltage is much too high for 2.3V globes. If it is a little 9V "transistor radio" battery then it won't power 5 globes through voltage-reducing resistors for very long. You should use two C cells or D cells in series. Most two-cell flashlights...
  6. audioguru2

    Outdoor Light Status Indicator

    I would make a current transformer with a voltage too high for the LED and use a current-limiting resistor to protect the LED. Lightbulbs draw about 10 times their rated current when not hot. With an LED connected directly to a current transformer then the LED would conduct 10 times too much...
  7. audioguru2

    Understanding Vce & Vbe (newbie)

    Hi Andres, If you want to use an IRF640 Mosfet then look at its datasheet: http://www.semiconductors.philips.com/acrobat/datasheets/IRF640_S_1.pdf At room temperature if you apply 1V to the gate then it will do nothing. Its gate threshold voltage where it will conduct a tiny amount of current...
  8. audioguru2

    Switching power supply

    Hi Ante, That's a cool charge-pump circuit. ;D The current through the zeners is about 20mA continuously, and the transistors will drop out of saturation if the total load current exceeds about 200mA for each transistor if they are weak. Therefore the efficiency is about 95% before adding the...
  9. audioguru2

    4 Watt FM Transmitter

    Hi Cerium, You must get rid of TR4 and R2 and the rest of the mic preamp so it doesn't load down your external input. Don't you want the stereo input to be combined into mono like this?:
  10. audioguru2

    Understanding Vce & Vbe (newbie)

    Hi Andres, Transistors need a minimum amount of base current to turn on, depending on the amount of collector current and amount of saturation voltage that you desire.  A transistor also has a maximum amount of base-emitter voltage that must be provided by the base current source. Its max Vbe is...
  11. audioguru2

    need help new to electronics have idea

    Hi Ploppy, Welcome to our forum. ;D Stores anti-theft systems use a powerless tuned circuit of a printed metalic coil with some stray capacitance as a proximity detector. Their sensors near the doorways seem to be huge and their range isn't 2m. For your transmitter to be powered when close and...
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Mongseng, You want me to re-design the power supply for you? I don't even have a half-decent power supply for myself. I just use a simple LM317 adjustable power supply like in our Projects section. The LM317 can easily provide 1A, but it has a max current limiter instead of an adjustable ...
  13. audioguru2

    LED chaser/sequencer pattern generator

    Hi Another, I've sold some of my Ultra-bright LED Chasers http://www.electronics-lab.com/projects/games/004/index.html and yours would be even better. ;D The problem with them is that they serve no purpose and aren't something that many (if any) people need. :( Nice little LED pattern...
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Mongseng, Welcome to our forum. ;D To have a 12V max output voltage at up to 1A this circuit needs at least 16V to 17V DC input because of the output and driver transistors Vbe voltage drops, opamp saturation voltage and current regulator sense resistor (R7) voltage drop. A few of its...
  15. audioguru2

    4 Watt FM Transmitter

    Hi Cerium, That 4W FM transmitter doesn't have pre-emphasis (treble boost) like radio stations have, so its received audio won't have much treble. Its received audio will sound something like an AM radio or like your stereo with its treble control all the way down. :( You can mix the stereo...
  16. audioguru2

    220 to 110VAC circuit

    Hi Rhonn, I had to highlight your yellow "caterpillar" to read it! ;D You got caught!
  17. audioguru2

    The is a VIZZ in the output Sound!!!

    Hi Shahriar, I think that the VIZZ was your circuit oscillating at a very high frequency. Your hand on its ground stopped the oscillation. An oscilloscope would show the problem and what your hand is doing to it. ;D
  18. audioguru2

    need help on BC337

    Hi Alun, You can still buy metal-cased 2N2222A transistors at Digikey for $.86US each, but there is only one supplier (ST Micro). ON Semi make the best of both worlds, a P2N2222A in a plastic case!
  19. audioguru2

    Telephone Billing machine!!!

    Hi Shahriar, I don't know what the "pulses" are that you are talking about. There aren't any pulses on telephone lines in North America except rotary dialing pulses, and the pulse from the telco when the distant party has answered, and again when the distant party has hanged-up. These two pulses...
  20. audioguru2

    need help on BC337

    Hi Ante, The 2N2222A in a plastic case is $.36US each at Digikey. In my entire career I don't think I have ever seen one. ;D
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