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  1. audioguru2

    EYE SIGHT SENSOR

    Your eyes detect only red, green and blue with some overlap. Your brain determines colours in between and can be fooled. As example, the colour Yellow emits a wavelength between red and green. If you look at a red object and a green object that are close together, like a red/green LED, your...
  2. audioguru2

    Electronic Eavesdropping Devices Detector

    Hi Maroela, Maybe the circuit isn't sensitive enough to detect the low power of an FM bug. Try to detect a cell phone. Maybe the kitmaker supplied 2N2222 transistors with a plastic case. To be certain that you have installed them correctly, compare the pins of the metal case on the kit's layout...
  3. audioguru2

    car battery charger

    I am also sorry, the old LM301A is still being produced but also doesn't work with a supply voltage less than 10V. ::)
  4. audioguru2

    Use a speaker as a microphone while useing it as a speaker

    Hi Alun, A speaker sounds lousy when used as a microphone due to its very strong resonances. Cheap intercoms at gas (petrol?) stations use them. They perform not too bad as a speaker because the extremely low output impedance of an amplifier damps the resonances. Try it with any speaker: tap the...
  5. audioguru2

    Electronic Eavesdropping Devices Detector

    Hi Maroela, Welcome to our forum. ;D Does the speaker make a sound when you turn-up the sensitivity? What radio transmission are you trying to detect? Please measure the voltages at the outputs of the opamps and the collector of  TR1 and post them here.
  6. audioguru2

    0-30 Vdc Stabilized Power Supply

    A 17% difference in power capability won't make much difference. As long as it doesn't get hot. It is funny that the numbers don't agree with each other. ;D
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Thomas, When you use the project with both windings, the average transformer current is: 1) 30VAC X 1.414 = 42.4VDC peak. 2) With a 3ADC load, the total power used is 42.4V X 3A = 127.2W. 3) The average transformer current is 127.2W/30VAC = 4.24A, plus a little for its negative supply. ;D
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Yeah, before you added a winding, the voltage changed 3V and with the new winding the voltage changed only 2V. You must have used that newfangled wire that has negative resistance! ;D
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Thomas, It is good that your transformer has enough extra power capability to stay cool. I used to test power with heater wire strung between bolts on a board. It made a strong burning smell and heated up the joint. It looked cool too when glowing red-hot! ;D I suppose the transformer's...
  10. audioguru2

    TRANSMISSION LINES

    Every voltage source has a source impedance. Even a brand new little 9V alkaline battery might burn you to death if you short it and place it near a vital organ in your pocket. The short won't get hot but the battery certainly will. The opposite will occur with a powerful car battery. A short...
  11. audioguru2

    audio expansion circuit with split power supply

    Hi Xtp, There must be ways for you to get stuff sent to you. A relative who moved to over here? Check with local embassies of modern nations or join an international or travellers club. Many sports groups are also international. When you find a way to get stuff you can start a business for...
  12. audioguru2

    TRANSMISSION LINES

    Years ago, I had a house with aluminum wiring that was approved by the loonies in my country's government. Big thick wires that didn't fit the screws on receptacles, a maze of loose wires joined by the biggest twist-on wire connector that I've ever seen and burnt-off insulation at every joint...
  13. audioguru2

    Universal Active Filter IC

    Why do you want its schematic? It has 4 opamps so probably contains hundreds of transistors. If you could make one, it would take you many years.
  14. audioguru2

    DC MOTOR SPEED CONTROLLER

    Hi Alun, Good point! ;D Duh, since the Mosfets are common-source voltage amplifiers, don't they amplify the supply voltage? He, he. ;D ;D
  15. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Thomas, It seems to have poor regulation. Is it rated for the required 106VA? Does it get hot with the project at full load? Your additional windings will load its primary even more. It is a good thing not to use opamps with their supply rated at only 36V or 44V. Thanks for the tip. I...
  16. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    Hi Maksar, Welcome to our forum. ;D Of course you can connect two regulated power supplies in series, but only if they have separate transformer windings or transformers. Also, the one with the lowest output current setting determines the load's current. If you parallel them, they will fight...
  17. audioguru2

    Duplicate threads and circuit requests.

    I'm getting many personal messages because the students don't want their teachers to see where the answers are coming from. They have been told not to post questions on internet forums. I think it is important for members to attempt to find things themselves on Google or Datasheetarchives...
  18. audioguru2

    TRANSMISSION LINES

    There are also limits for PA levels being distributed in open ceiling spaces without conduit. In Canada in schools it is 25VRMS, offices 70.7V but ordinary telephones use 90V for ringing. In Japan the PA voltage limit is 100V. I found an intermittert PA problem one time by turning off the lights...
  19. audioguru2

    Time out circuit

    hi Prateek, The same problem of an extremely high resistor value (900M!) and a low-leakage capacitor, plus more current from the 555's input messing-up the timing. The max recommended value of the timing resistor for a 555 is only 20M. A 20M timing resistor would need a 45uF extremely...
  20. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Thomas, It's great that your modified power supply project works so well! ;D Did you add the 8.5V winding so it is in series with your original 26V winding? It makes the voltage much higher than the 30V required. No wonder your voltage across C1 is so high. Thanks for the tips about R2...
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