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  1. audioguru2

    again, microphone input high school project

    Kevin, you won't have a triangle wave if your filter cap is big enough. It is filtering audio, not rotations of the moon. You will just have nice smooth DC with hardly any ripple. Hey, the cap barely has any load current (25nA input current of the LM3915) so stores its charge for a long time.
  2. audioguru2

    Question on resistors?

    Hi Randy, Sure you can make a 1M resistor with two 500K ones in series, but they aren't made as 500K. A 330K and a 680K will make a 1.01M resistor, which is close enough. Get a resistor selection package from any electronic parts distributor, even Radio Shack but you might need to order it. The...
  3. audioguru2

    again, microphone input high school project

    Hi Kevin, Of course you will get DC out of the rectifier and its filter capacitor when it is being fed many volts of signal from the mic preamp. That is what a rectifier is for. Also, of course the changing level of the signal will also change the level of the DC, but the rectifier can be...
  4. audioguru2

    again, microphone input high school project

    Hi Zgnoh, 1) You only need to rectify the AC audio into smoothed DC. A single diode will do it with a filter capacitor. 2) A single rectifier diode needs at least 130 times the voltage from a microphone to turn-on, so of course the microphone's signal must be amplified by a preamp before being...
  5. audioguru2

    What oscillator/clock should I use

    Have you seen a time-of-day clock now-a-days that uses an analog timing reference? Yeah, the 200 parts per million frequency drift of a MAX038 looks impressive, but is more than an ordinary 555 (150) and isn't its max. Its 600ppm max drift works out to a timing error of almost 1 minute per day...
  6. audioguru2

    Electronic Stethoscope 2

    Hi Con, That's a nice PCB. Please make a circuit and tell us how it works. Where did you find a logarithmic (audio taper) trimpot for R11? All trimpots I've seen are linear.
  7. audioguru2

    True RMS

    Hi Kevin, Check the frequency response of your meter with sine-waves on each voltage range of it. You will probably find that the response drops-off above only a few hundred Hz, especially at high voltage ranges. The frequency response of my premium true-RMS-reading DMM is down 3dB (0.707 of the...
  8. audioguru2

    switching circuit

    No, Kevin: Batteries charge with current, not voltage. You could charge a battery from 1 million volts if you limit the current to the recommended value, and stop the current at full-charge. 1) A battery doesn't deliver a steady voltage. Its voltage drops as the battery is discharged. 2) Also...
  9. audioguru2

    What oscillator/clock should I use

    In the good old days I made an extremely accurate clock with an 8-pin, $2.00 MM5369AA Cmos IC, and a very accurate $1.50 colour TV 3.58MHz crystal. The output was exactly 60Hz but 50Hz and 100Hz versions were also available. Since nobody makes their own clocks anymore, it was discontinued in...
  10. audioguru2

    Very basic question from a newb

    Hi Adverse, I'm a Canuck too, eh! Sorry, I think of NNE as being in the Ukraine. Don't get a 0.05A transformer, 500mA is what is needed and it's 0.5A. Radio Shack doesn't have a 10V but has a 12V DC/500mA regulated adapter that gives exactly 12V with both your fans connected to it in parallel...
  11. audioguru2

    Very basic question from a newb

    Hi Adverse, I wouldn't use that adapter. It is not just an ordinary one: 1) Its input voltage range is very wide, from only 100V to 240V. An ordinary adapter is rated at only one input voltage. 2) Its output is rated at 4.56W. But its input is rated at 18W to 43.2W. 38.64W makes a lot of heat...
  12. audioguru2

    6V Ultra-Bright Chaser

    Hi Guys, Look up at the moon! It is flashing blue because my latest ultra-bright chaser is shining on it. ;D ;D Yeah, I've finished my 10th and final ultra-bright chaser, all with Veroboard (I could make one quicker than you could etch and drill a PCB). I've also re-built 6 of them to have the...
  13. audioguru2

    What oscillator/clock should I use

    The frequency of a 555 oscillator isn't nearly stable enough for a clock. You need a crystal oscillator with divider, or sync with the mains frequency.
  14. audioguru2

    again, microphone input high school project

    Just one little bug: The microphone needs a preamp. The output voltage of a microphone is about only 20mV if you shout closely. The voltage requirement of the rectifier bridge is at least 1.3V. A big difference of 65 times. If you talk normally at a normal distance from the mic, the difference...
  15. audioguru2

    I am not receiving topic notification.

    Hi Dazza, Look at the "properties" of your notification e-mail. It shows times and dates of its routing. It will probably show that your ISP received them long ago, but forwarded them to you just recently. My ISP recently added virus-scanning software for e-mails. When they catch a virus, they...
  16. audioguru2

    Designing feedback amplifier

    Hi Vishu, A transistor amplifier? Why not use an opamp? If Av1 = 2 and Av2 = 2 and you want the total gain to be 4, you don't want and can't use any negative feedback! The total gain will be a little less than 4 without feedback because the 2nd transistor circuit loads-down and reduces the gain...
  17. audioguru2

    LED

    Hi Bryen, Welcome to our forum. I've tried it. A LED makes a very inefficient photodetector. With an extremely bright light up close or light from a similar LED up close, they produce a little more than 1 volt with hardly any current. They also conduct hardly any current. Why not use an...
  18. audioguru2

    Very basic question from a newb

    Hi Adverse, What are you going to use the fan for? If it is not near a radio, TV or not inside a computer, its ground wire doesn't have to be connected. It is good that its voltage requirement is marked. Just connect it to 12V, with the red wire as positive and the black to negative. If it runs...
  19. audioguru2

    Very basic question from a newb

    Hi Adverse, Welcome to our forum. According to the info you provided and Evercool's datasheet http://www.evercool.com/kor/product_list.htm# the fan is designed for 5V. I don't know how much smoke it would make if you applied 12V or more. Usually a 12V AC adapter produces 16V or more when not...
  20. audioguru2

    in search of a FM STEREO transmitter

    Hi Ras, Please don't underline your shortcut or it doesn't link. If you enter Minimitter in a Google search, the project's link is on the 1st page and you can get the whole article for free! As you can see by its spec's, this project also has high distortion that might be more when it transmits...
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