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  1. audioguru2

    replacement CA3237

    Hi Newelco, Welcome to our forum. The CA3237 was probably made by RCA, who sold their IC making to Harris. Harris sold their IC making to Fairchild or Texas Instruments who don't make that one anymore. Here's its datasheet: http://www.datasheetarchive.com/semiconductors/download.php?Datasheet=512017
  2. audioguru2

    Bug detector

    Hi Pakguy, Welcome to our forum. ;D We have many projects in our Projects section. Its button is at the top of this page. One is an Electronic Eavesdropping Detector that I fixed its schematic so that it can detect RF transmitters over a wide range of frequencies. It is quiet without detecting...
  3. audioguru2

    motion detector, N.C COM

    Won't 12V applied to the input of a ToothPIC blow it up? Connect the detector's COM to the ToothPIC's ground. Connect the relay's contact and a 10k pullup resistor (from the ToothPIC's supply) to the input of the ToothPIC. The normally-closed relay contact will apply a logic low to the ToothPIC...
  4. audioguru2

    Resistance wattage in series

    What did Ante say about resistors in series? Each resistor dissipates 0.5W. If two series resistors have the same value then each one dissipates half as much as if you used a single resistor that has twice the resistance of each one, because they share the power. Just like they are in parallel...
  5. audioguru2

    Switching idea

    A -5V negative supply severely restricts the range of input and reference voltages. Use -12V. The 741 opamp has a limited input common-mode voltage range so it should also have a negative supply. My analysis shows that it will work fine. Isn't its operation backwards? Merry Christmas in a few...
  6. audioguru2

    Switching idea

    You are right. The 1st opamp must have a negative supply. Philips had a little stereo power amplifier that was like two LM386's in one. Since its inputs could have a negative voltage, it could do what you want without a negative supply. EDIT: My text wiped out a resistor. It is re-installed.
  7. audioguru2

    Input signal for LM3915. need help.

    BTW, with LEDs being driven, the low voltage at the outputs of the LM3915 are not a valid logic low voltage. The go only one LED voltage drop (2V?) below the positive supply.
  8. audioguru2

    Input signal for LM3915. need help.

    Hi Ryeeson, Farnell in America is called Newarkinone, and an MC33171N costs only $.68US. They have only 30 in stock. 50dB is a low sound level. If your project uses the peak detector then it will cause an alarm when people walk on a bare floor or if a book is dropped. Maybe you should make the...
  9. audioguru2

    Switching idea

    Hi Mr. Heckles, I was incorrect about the 2nd diode. It is needed to prevent the input of the 1st opamp from going negative. I added it but removed a few parts from your schematic to see its operation clearer. Your Schmitt trigger has the outputs of two opamps shorted together. Which one will...
  10. audioguru2

    9v to 6v DC/DC Converter

    The Stethoscope project will work fine with positive and negative 5V or 6V supplies. A 9V battery's voltage will drop to 6V over its life. It drops to about 7.2V fairly quickly, then slowly drops to 6V when it is considered to be dead.
  11. audioguru2

    Clock/timer

    Hi Steve, There are some digital stopwatches in our Projects section: http://www.electronics-lab.com/projects/oscillators_timers/014/index.html http://www.electronics-lab.com/projects/oscillators_timers/015/index.html
  12. audioguru2

    digital elec-stetho..

    Hi Xoy, I don't know what you are doing. Do you know what you are doing?
  13. audioguru2

    pramplifier circuit

    Is the microphone or opamp making hiss? Much more expensive microphones and audio opamps are available with a much lower noise level. A gain of 214 is very high. my cutoff frequency is 3.5 KHZ i dont know whether this preamplifier can use for this frequency. Are you using a lowpass filter for a...
  14. audioguru2

    Input signal for LM3915. need help.

    They should be the same, but different manufacturers. I am building this mic preamp/detector for my project:
  15. audioguru2

    Switching idea

    I think the 1st opamp should have the diode across it removed to allow its output to protect its input from going too negative. Then your absolute value circuit will do what you want. You made some good thinking. ;D Except: 1) The LED won't light because the CTRL input of the Cmos doesn't use...
  16. audioguru2

    Alarm sound detector schematic

    An LM567 or CD4046 Phase-locked-Loop circuit can be used to detect a certain frequency and give a high output. But your alarm is audio. Many sounds contain 3kHz and 4Khz frequencies, including noise. A 1kHz square-wave contains plenty of 3kHz. A frequency detector would give an output when a...
  17. audioguru2

    Switching idea

    A absolute value circuit is a full-wave rectifier that uses two opamps. Usually one of the opamps needs negative and positive supplies.
  18. audioguru2

    LED amperage question

    I don't know how many wires are in a printer's parallel cable. Just because it has a 25 pin connector doesn't mean it has 25 wires.
  19. audioguru2

    LED amperage question

    Ohm's Law determines the value of the LED's current limiting resistor and its current.
  20. audioguru2

    Switching idea

    An inverting opamp with only a positive supply will have a positive output voltage with a negative input voltage and its output will be close to ground with a positive input voltage.
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