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  1. audioguru2

    LM317 Variable power supply

    Hi Um...Me, A 24V transformer will allow this LM317 project to produce up to 28V. About 1.5A will be available at high voltage settings, but at lower voltages the IC cuts its max current down to only about 200mA to protect itself. Therefore consider using a 24V center-tapped transformer...
  2. audioguru2

    ElCheapo PSU

    Great! Typo. It is 2200uF
  3. audioguru2

    Electronic Stethoscope

    Hi Xoy, 1) Your transistor is connected to ground instead of to the signal. 2) You are trying to use the transistor as a gate, but it doesn't isolate the timer from the signal. When the 555 timer circuit has a logic high output then a high current flows beween the signal and the output of the...
  4. audioguru2

    PC speakers amp with TEA2025

  5. audioguru2

    cuckoo sound generator

    Hi Phil, Welcome to our forum. ;D The project is here: http://www.electronics-lab.com/projects/misc/011/index.html Q1 is fine. Its base-emitter junction is connected backwards so that it has avalanche breakdown like a zener diode. When it has avalanche breakdown then it makes a lot of white...
  6. audioguru2

    Electronic Stethoscope

    Hi Aaron, It is great to hear that you got it working. ;D ;D But it is too bad that it passes friction noises. In my test setup, I used a soft, thick rubber grommet around my electret microphone to isolate it from friction and handling noise conducted from the stethoscope head. I used a very...
  7. audioguru2

    ElCheapo PSU

    Use very short spacing between the IC's 0V pin and the 0V of the main filter cap and the load's 0V connection. Solder a heavy wire on the stripboard trace. Use very short spacing between the IC's output pin and the connection for the load. Solder a heavy wire on the stripboard trace. The IC has...
  8. audioguru2

    Electret microphones characteristics

    Ohm's Law says that 1.5V/500uA is 3k ohms, 4.5V/500uA is 9k ohms and 6V/500uA is 12k ohms. I injected a 100mV sine-wave through a variable resistor in series with a capacitor to the junction of the electret mic and its load/supply resistor. I measured the voltage at the junction and changed the...
  9. audioguru2

    PC speakers amp with TEA2025

    Let's call your circuit's "power neutral" its ground. Earth is an earthed ground that your computer has through its mains cord. Since your amp makes hum when it doesn't have an input then its input wires and parts are unshielded antennas for mains pickup. Maybe your power transformer is too...
  10. audioguru2

    ElCheapo PSU

    Hi Autir, You shouldn't use a breadboard when tesing a power supply circuit. The resistance of its wires and contacts messes-up the voltages. The 0V point at the IC should be soldered to its 0V pin and a heavy copper trace on its pcb should be a short distance from the main filter cap and to the...
  11. audioguru2

    Electronic Stethoscope

    Hi Xoy, You don't need a relay. A simple logic gate or transistor can cutoff the counter. It would be best to latch the display driver (a high at the latch pin of a CD4511) when the time has elapsed then reset the counter and let it continue counting for the next update. A 1 minute update on a...
  12. audioguru2

    supplying power to 12v 1.4a, 3v 3a with a diy power supply

    Hi, your maths are correct. ;D Why use an expensive transformer that has a continuous power rating of 60VA and many voltages up to 24V when you will be using only 9VA for a few seconds at a time at only a few volts? Why use a voltage regulator for your electric motors when their speed and...
  13. audioguru2

    Watts , amps?

    Electrical power that is being used is measured in Watts. A 100V/1A lightbulb or heater uses 100 Watts. A 1V/100A lightbulb or heater uses 100 Watts. A 10V/10A lightbulb or heater uses 100 Watts. They all produce about the same amount of light or heat even though their voltage and current has...
  14. audioguru2

    supplying power to 12v 1.4a, 3v 3a with a diy power supply

    Your multiple output voltages transformer is overbuilt and probably not suitable for your requirements. Its secondary current is rated for only 2A max probably due to the small size of its secondary wire. At 6.3V it can pass only 12.6VA. If you rectify and filter its 6.3V then the peak voltage...
  15. audioguru2

    "Line In" requirements

    About 10k ohms. 100mV to 300mV RMS averaged but peaks could be as high as 11V p-p or more. Yes, they are all different, there isn't a standard. The circuit probably has adjustable gain or an adjustable attenuator. ;D
  16. audioguru2

    Electret microphones characteristics

    Hi Autir, I think the circuit's R1 should be adjusted to match the supply voltage. The FET inside an electret mic draws about 500uA, so in order to have half the supply voltage across it then for a 3V supply, R1 should be about 3k ohms, for a 9V supply R1 should be about 9k ohms and for a 12V...
  17. audioguru2

    Electronic Stethoscope

    Hi Xoy, The Digital Stopwatch project you posted shows how to use 4511 ICs to drive common-cathode displays. But it counts seconds, not events. You need a counter circuit to count heartbeats and is gated and latched every 6 or 60 seconds. So you need a circuit like the 4018 and 4511s part of the...
  18. audioguru2

    supplying power to 12v 1.4a, 3v 3a with a diy power supply

    Power doesn't work that way. The max current of the output of the adapter and the 3V regulator is 1A. A linear 3V regulator would waste 9W leaving 3W for 1 motor. Use a 5V/3A adapter and regulate its output down to 3V/3A.
  19. audioguru2

    veroboard pen: minor cuts and failure :'(

    Glue a drill bit into a piece of wood or plastic.
  20. audioguru2

    trafic signal

    Hi Shahriar, A black IR photodetector reduces its sensitivity to all light including sunlight. Sunlight also has a high amount of IR that can't be changed. Many 3-pin IR receiver ICs such as the TSOP series, have an automatic gain control system that reduces their sensitivity if there is...
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