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  1. audioguru2

    Why doesn't my inductor give more kick.

    Mosfets have a built-in zener diode from drain to source. If you use an IRF540 Mosfet then the zener clamp voltage is about only 100V. The rapidly rising voltage at the drain feeds back through the Mosfet's internal capacitance to the gate, trying to turn the Mosfet back on and slowing down the...
  2. audioguru2

    Photosensing circuit problem

    Your circuit shows and is designed for a photo-transistor. You will need to change the input resistors to 100k or 1M (try both) for photo-diodes. Then the photo-diodes need to have their anodes to ground so that they are reverse-biased. What is a LDA? An LDR is different from a photo-transistor...
  3. audioguru2

    Constant current source for high brightness LEDs

  4. audioguru2

    motor driver L298 help

    MP. In his 1st post he said he needed PWM and asked for an explanation about how it works. I explained, but you told him it isn't needed, then you continued arguing about it.
  5. audioguru2

    Light management system

    These problems with your idea were discussed on another forum: 1) A person leaves at the same time as another person arrives. 2) A person blocks a sensor when another person arrives or leaves. 3) A tall person is counted as two shorter people. 4) Short people aren't counted. 5) A few people are...
  6. audioguru2

    PSU WITH LCD VOLTMETER--TROUBLE!!

    The - measuring input of the voltmeter circuit is not the same as its - power supply terminal. The voltmeter circuit probably needs a negative supply which can be made with a Cmos hex inverter package. Then maybe its positive supply voltage should be reduced.
  7. audioguru2

    Photosensing circuit problem

    The photo-transistor turns on when it sees strong IR light relected off white floor or a white line on dark floor. Then the opamp's output goes high and the LED turns off. Both the IR LEDs and the photo-transistors should be mounted on the bottom, shining on the floor and be shielded so that IR...
  8. audioguru2

    my radio is changing stations by itself!

    Rvar1 is fine as 62k. It could be any value higher than 33k. 1nF is fine for the varactor coupling cap if it is a ceramic disc with short wires. Anything more than about 200pF is fine. Did you use low capacitance 2N3904 or higher capacitance 2N4401 transistors as varactors? Did the circuit tune...
  9. audioguru2

    50Hz when you touch Oscilloscope probe

    Your body is an antenna for picking up 50Hz mains radiation. Same thing happens if you touch an amplifier's input, it produces a loud 50Hz. That is why the scope's cable and audio cables are shielded. If your heart fibrillates at 50Hz instead of 50 bpm, then you are having a heart attack.
  10. audioguru2

    need help for cfl lighting

    Of course. It takes power to make light. Less current from the battery is less power so is less the amount of light.
  11. audioguru2

    Choice of op.amp. model

    Your circuit is from their datasheet so should work if it is correct. Maybe a parts value of yours is wrong, the diode is reversed or the IC is bad.
  12. audioguru2

    Constant current source for high brightness LEDs

    I was nearly finished calculating things for the constant current sink when Microsoft told me, "Paint encountered a problem and needs to close. Tell us about it.", so it's gone. Use 82 ohms for the upper resistor. It supplies base current to the upper transistor (use a TIP31) to turn it on. The...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Roujhan, U3 measures the voltage across R7 which is caused by load current, and subtracts the offset voltage provided by P2.
  14. audioguru2

    my radio is changing stations by itself!

    Hi MStechca with a new name, how are you? Please post your circuit again so we can see why the varactor doesn't work properly.
  15. audioguru2

    RC-(remote controlled) Car

    Those "all-in-one" radio ICs are not very good. I have a similar one in my cheap clock radio and the Sony one is in my inexpensive Sony AM-FM Walkman. My stereo and car radio tuners are much better. Those cheap radios are "stable" because they have AFC (automatic frequency control) to coverup...
  16. audioguru2

    Mini project (Help me)

    Then make a highpass filter circuit with a cutoff frequency of 200Hz, followed by (cascaded) a lowpass filter with a cutoff frequency of 20kHz. Make the circuits with BJT's, old 741 opamps or both.
  17. audioguru2

    RC-(remote controlled) Car

    Hi Faizan, If you use a crystal oscillator then you won't be able to frequency modulate it. You can't get crystals with a high enough frequency anyway. Old FM transmitters used an 11MHz crystal oscillator that was frequency modulated a little then it was followed by many frequency multiplying...
  18. audioguru2

    Constant current source for high brightness LEDs

  19. audioguru2

    Need help identifying part

    That's nice. An electronic component that stores time. I wonder if it is time that has past or if it is time in the future. If I connect a bunch in parallel then I could see which horse will win in a horse race and I could bet on it in advance and win!
  20. audioguru2

    project help with toy IC boards

    It is a Korean copy of Motorola's MC34119 that is used in telephones. It can't provide much power but is better (?) than an LM386 if you only have a 3V supply, and it doesn't need the pretty big output capacitor. I used one in my son's alarm clock. With a 3V supply and an 8 ohm speaker, the...
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