Search results

  1. audioguru2

    Proximity alarm for camping

    If it is a big bear ot alligator coming then I think you would hear them and smell them before they eat you.  ;D
  2. audioguru2

    white led

    A 100k resistor will nearly fully discharge 30uF in 15 seconds. It will use only 1.2mA and dissipate only 137mW with the power connected. Use a 1/2W resistor for its high voltage rating.
  3. audioguru2

    white led

    Yes. I can't remember how many volts is across the capacitor that bites you.
  4. audioguru2

    Electronic Eavesdropping Devices Detector

    hi Eplanet, The original AM detector circuit is odd. R9 and R10 are not needed with the opamp that is used. The inverting mode of the opamp is a low impedance to the detector. My modified circuit is a "normal' high impedance AM detector circuit and should work better with the opamp that is used.
  5. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pawel, 1) Use "normal" modern opamps. 2) Find out why D10 gets hot when it should not have any current in it.
  6. audioguru2

    Automatic heat detector

    Hi Walid, Can you still get old AC188 germanium transistors in Palestine? The last one I saw was in about 1964.
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pawel, The old OP07 should not  be used in this project: 1) It has a different input offset voltage adjustment curcuit requirement. Try it with RV1 removed. 2) Its max output bandwidth is only to about 2.5kHz. The TL081 is 100kHz. 3) It has diodes across its inputs. Hi AN920, The TIL31A is...
  8. audioguru2

    Automatic heat detector

    Hi Walid, That is an extremely old circuit. A reversed-biased silicon diode increases its leakage current as the temperature rises. A silicon transistor amplifies its own leakage current and can also be used as a temperature sensor. Usually a diode or transistor feeds a comparator IC to switch...
  9. audioguru2

    Crystal examiner

    Hi Walid, The 'scope pic of the oscillator's output shows severe distortion that is cleaned up with the 3rd-order lowpass filter.
  10. audioguru2

    Electronic Eavesdropping Devices Detector

    You could use the same pcb if you use only the highpass filter. Replace R7 with the coil and change the values of C4 and C5 like this:
  11. audioguru2

    white led

    Yes, but I can't remember the voltage across it and the capacitance value to calculate the resistor value and power rating.
  12. audioguru2

    Sound Level Indicator

    They say how to connect the Mode pin 9 of the first LM3915 to pin 1 of the second LM3915 and a resistor across LED #9 for Dot mode. For Bar mode then leave both pins 9 disconnected. They show a reference voltage of 10V so the LM3915s should have a 12V supply. But then a power resistor would be...
  13. audioguru2

    Sound Level Indicator

    Hi Jon, The datasheet for the LM3915 shows how to cascade two of them for an extended range. Then the most sensitive one will have an input DC voltage of only a few milli-volts so an offset voltage adjustment should be made to cancel the input offset voltage of the most sensitive LM3915 and the...
  14. audioguru2

    Sound Level Indicator

    Hi Jon, You said that it was too sensitive. Did you try changing R5 to 10k to reduce the sensitivity 20dB? You said the voltages at the pins of the LM3915 without a signal were 0.04V for pin 5 and 0.5V for pin 6. Pin 6 is correct but pin 5 is a little high that would make the LEDs #1 and #2...
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    D10 is supposed to be reversed biased with about 1.4V across it and no current flowing. Therefore it should not be hot. Check its wiring in the circuit.
  16. audioguru2

    Sound Level Indicator

    I built my project according to my Veroboard layout and it works perfectly. What is the problem with yours?
  17. audioguru2

    Your next lawn mover!

    Hi Jbarnaby, I am retired. All my time is free time. Every day is a weekend.
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Pawel, Welcome to our forum. ;D The BD139 is a good substitute for the little 2N2219. It should have a heatsink. The project will be easy to fix if you measure and post some of its voltages without a load. Put the negative lead from your voltmeter on the 0V output of the project: 1) Pin 7 of...
  19. audioguru2

    Electronic Eavesdropping Devices Detector

    Hi Eplanet, The input of the circuit needs the highpass filter shown by AN920 so it has reduced sensitivity to cpmputers, monitors, AM radio stations and other interference. The rectifier/detector circuit looks strange. Did you try my modification? If there is a sound output when the...
  20. audioguru2

    Sound Level Indicator

    R17 charges my 7.2V rechargable battery when the AC adapter is plugged into the adapter jack. The arrow on the adapter jack shows which way its built-in switch moves when the adapter's plug pushes it. Then the battery is charged through R17 and the circuit gets +9V from the AC adapter. When the...
Top