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  1. audioguru2

    Help With Pulse Generator Circuit

    Nope, teachers don't teach no more, no more. My kids discovered it too. When I was in school I taught my teachers a few tricks. ;D
  2. audioguru2

    high voltage photo flash capacitor charger

    Hi Steven, Photoflash capacitors have much lower internal resistance than ordinary large HV caps. If you put a bunch in parallel then they would take longer to charge but would pack more power. Then make the coil gun with thicker wire and more turns and you will have a real gun!
  3. audioguru2

    Help With Pulse Generator Circuit

    Hi Tb, Design the circuit as taught by your teacher. The biggest obstacle is the Mosfet's wide range of threshold voltage between different transistors:
  4. audioguru2

    LM317 works Bad "SOS"

    Although the 1k resistor's value is high, it is a close match to the 10k pot and 9.6V output. The 1k resistor wil have 1.25V across it and therefore 1,25mA of current. To provide the remaining 8.35V the pot's resistance must be 6.68k which is when the pot is set near halfway. If you use 240...
  5. audioguru2

    555 timing circuit

    Hi Blogbo, Welcome to our forum. ;D I assume that you are using the 555 timer in its "monostable" mode, so when it times-out it remains sounding the alarm until its timing is started again with its 'trigger" input. Use an NPN transistor to externally discharge its timing capacitor when the...
  6. audioguru2

    LM317 works Bad "SOS"

    Hi Steve, You are lucky that you didn't blow the fuse in your multimeter. Current is measured by connecting the current meter in series with the power source and the load. A current meter is like a dead short to be able to pass current without much resistance. You used your meter to...
  7. audioguru2

    LM317 works Bad "SOS"

    Hi Steve, Usually an LM317 has 120 ohms for R1,  to hold down its output voltage without a load, but your 1k is fine with your pot and your fan. Since the output voltage is correct, then obviously your fan doesn't draw more than 235mA. Therefore the LM317 will be able to drive up to 6 of your...
  8. audioguru2

    UC3843 for a motor controller?

    I didn't look at other manufacturers but Fairchild is discontinuing it soon, so I wouldn't use it.
  9. audioguru2

    Choice of op.amp. model

    All single opamps have offset null pins. Their max input offset voltage is as low as the distorted, noisy, narrow-band old 741 opamp and is only 6mV so doesn't matter in an AC circuit. All opamps work fine with a single V+ and GND. They just need to be biased correctly when using a single...
  10. audioguru2

    Choice of small signal BJTs

    Please don't send me any transistors, they distort too much. I have been using low distortion opamps for most of my audio projects. With my FM transmitter project I had a hard time getting any gain from its preamp transistor and still have inaudible distortion. I added negative feedback to a...
  11. audioguru2

    Gas turbine bike.

    Thanks Ante, That's a nice video. ;D
  12. audioguru2

    Gas turbine bike.

    Why not use a turbo system from a smashed car like the other guys?
  13. audioguru2

    Help With Pulse Generator Circuit

    Hi Tb, Welcome to our forum. ;D Depending on your resistor values and on the threshold voltages of your Mosfets, Q2 might always be saturated. It would be difficult to match the Mosfets for identical threshold voltages and select resistor values to match. Perhaps a comparator IC would work much...
  14. audioguru2

    Electronic Stethoscope

    Hi Fibrauk, Welcome to our forum. I'm glad that my modfied project works well for you. ;D The microphone holder called a "head" must be a solid material so it doesn't vibrate nor resonate. The microphone should be mounted to it in a rubber grommet to provide isolation from conducted sound. The...
  15. audioguru2

    NiCd Battery Powered LED Lamp

    So how many LEDs do you need? ??? What is their total current for enough brightness? ???
  16. audioguru2

    Electronic Stethoscope

    It has only one LM386 power amp IC which is not an opamp. The output voltages of the TL072 opamps must be zero volts since their input is zero volts. C2 is shorted or backwards, or the positive power supply pin 8 isn't connected to +ve. The schematic shows the mic feeding the opamps which feed...
  17. audioguru2

    Electronic Stethoscope

    Did you replace the dead batteries to make it work? Did you find an electret microphone? If you speak softly near the electret microphone, is your voice heard (but with muffled high frequencies) at the output? Did you measure the DC voltage at the opamps' outputs like I asked before?
  18. audioguru2

    Choice of small signal BJTs

    Then those people are making their own opamps from separate transistors. They use class-A only to warm their homes and to avoid the crossover distortion caused by a poorly designed push-pull circuit. Maybe they are the same people who still use vacuum tubes (valves) in audio amplifiers. Some...
  19. audioguru2

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

    Break down the project into blocks then search in Google for the blocks: Electret Microphone. Microphone preamplifier. Digital Logic. Cmos Logic Devices. Cmos oscillators. Analog Applications for Cmos Digital Devices. Piezo Transducer. Transistor. You can add the keyword Theory following them if...
  20. audioguru2

    Electronic Stethoscope

    Hi Dj, The project is designed for a common 2-wire electret microphone that is available at nearly every electronic parts supplier on this planet. You can steal one from a child's toy, telephone or cassette recorder. A "condensor" mic needs an external 48V supply. An electret mic has the high...
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