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  1. audioguru2

    Who is using the oldest computer?

    Hey Johnny (Wasssup), What are you doing over here? Welcome to our forum. That's a nice computer that you made. You overclocked that much without meltdown? Yeah, my download accelerator program breaks-up a download into many parts and downloads them all at the same time. During the moment that...
  2. audioguru2

    PWM using 555 timer

    Darrin, The 3.4V is the reference output voltage of the other chip which is being used to power the 555. That is a VCO circuit which varies the 555's frequency with voltage changes. It will give pulses that are "more frequent", but also narrower, so the end result isn't PWM because the...
  3. audioguru2

    Electronic Stethoscope

    Damras, You shouldn't have acoustical feedback between the mic and earphones if you use a stethoscope head (or jar lid) to surround the mic, and use enclosed earphones. CDAK's mic preamp circuit is posted ealier in this thread. He didn't use earphones but instead used external digital filters...
  4. audioguru2

    Latch triggering

    Kevin, What are the part numbers of the gate and latch? What supply voltage are you using? What is the value of your pull-down resistor? Your pull-down resistor and parallel capacitor may be overloading the gate's output, or may be drawing an out-of-spec current that another gate can't duplicate...
  5. audioguru2

    PWM using 555 timer

    Darrin, I am sorry that I am not giving you a formula for the 555's control input to produce PWM. The control input's voltage range is limited in both polarities by the common-mode input range of the comparators, which the manufacturer doesn't specify. And I can't find my slide-rule! But you can...
  6. audioguru2

    PWM using 555 timer

    In the 556 PWM circuit that I recently posted, I think that pins 2 and 3 of the LM311 should be reversed. Here's another 555 PWM circuit that uses diode steering to vary the charge/discharge of the timing capacitor. Note that its output is not the output pin of the 555:
  7. audioguru2

    PWM using 555 timer

    Hi Darrin, Here's a 556 (dual 555 chip) circuit that uses the control pin (11) of the monostable to vary its pulse width:
  8. audioguru2

    Latch triggering

    But what is causing that short-duration, unwanted pulse? If we can help you eliminate that pulse, then your problem is solved.
  9. audioguru2

    Re:how does this add YABBC tags

    Hi Oldratech, To add a picture, I just "attach" it from the file on my hard drive. The file must have the "allowed types" extension, and is limited to 3MB. Click the Browse button, navigate through your hard drive and double-click your file. Your file will be copied to the Attach window, then...
  10. audioguru2

    TV Signal Amplifier - Part II

    That's correct. Please let us know how well it works.
  11. audioguru2

    TV Signal Amplifier - Part II

    Hi Christiano, This simple TV amplifier is designed to amplify low-level antenna signals. It will probably be overloaded if there is an FM or TV station nearby. The overloading will cause severe interference on all channels. The article's text says to connect a 9V battery to terminal 2 (-) and 3...
  12. audioguru2

    Latch triggering

    Kevin, 1) Why does the gate that drives the latch's "set" input have a pulse when you don't want one? The problem is with the inputs to the gate, not a latch that is too sensitive. 2) What is the duration of the unwanted "short duration" pulses? 3) Are you trying to decode the outputs of a...
  13. audioguru2

    Levitating Globe

    Wow! How do dey do dat?
  14. audioguru2

    On/Off heater controller using triac

    Hi Darrin, If your input pulse occurs during the high-voltage "excluded-firing" time of the mains, then the triac won't turn-on. That is why zero-crossing triacs are used for bang-bang controlling, not phase control. A triac needs only one pulse to turn it on for each half-cycle of the mains...
  15. audioguru2

    Who is using the oldest computer?

    Wizard, Hi and welcome. 70 computers? Wow! I fondly remember the old 8086. Your XT is twice as old as my 486.
  16. audioguru2

    Dual Lab Power Supply

    Darrin, Nope, my rechargeable batteries have their own charger (the overnight kind) so I don't use the LM317 for charging. It is difficult to make a fast charger for NI-CADs or NI-MH because you don't know how much charge remains. There are charger chips available that detect the peak of the...
  17. audioguru2

    Dual Lab Power Supply

    Hi Darrin, Of course, the AC mains voltage will be affected a little bit when you add a load to it. The amount of voltage drop depends upon the length and quality of the wiring between the generating station and your circuit. But since the power supply is regulated, then it won't be affected. I...
  18. audioguru2

    Generating square wave of voltage levels 0-5V

    But the datasheet shows that the 2N3906's beta could be as low as only 30, at 100mA of collector current. In this circuit, beta doesn't matter since the FET supplies plenty of base current.
  19. audioguru2

    Electronic Stethoscope

    Hi Damras, Welcome to our forum. To pickup a heartbeat sound, the microphone must not touch the skin, but should be spaced a short distance away. A stethoscope head (or jar lid) provides this spacing, surrounds the skin around the listening location and blocks background sounds. It is important...
  20. audioguru2

    Generating square wave of voltage levels 0-5V

    Kevin, The collector load resistors for the PNP total 310 ohms. If 100mA was flowing through them then their voltage drop would be 31V. How can 31V be developed from a 5V supply? With the transistor fully saturated in this circuit, its collector current is 15.8mA, which is fine. Like all...
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