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  1. audioguru2

    Question on the Plants Watering Watcher circuit

    Kiew, Sorry for the delay. I am finishing typing the modified circuit as a new project. It will be posted very soon. I have made many circuits and they all work the same and very well.
  2. audioguru2

    Pulse Width Modulation

    Thanks, Ante, That CMOS 555 chip looks like it will control PWM much better than an analog triangle generator or simple inverters, due to its well-defined thresholds and speed. I can use it for the electric model airplane that I won. With a simple NPN-PNP transistor buffer, like the complicated...
  3. audioguru2

    ELM - White LED Head Lamp

    Wellington, It not only controls the output current, but it also steps-up the voltage with a DC to DC converter.
  4. audioguru2

    Boosting Regulator Current/ATX power supply

    Hi Coder, If your battery is a fully-charged lead-acid at 13.2V, and your 7805 regulator has its minimum voltage of 4.75V, then the transistor has 8.45V across it. With your total current of 1.3A, minus the 70mA through the 7805, the current through the PN2955 is 1.23A. Therefore the power (V X...
  5. audioguru2

    Passive audio filters

    Vainajala, I have some concern about your choice of a passive 12dB/octave Butterworth crossover filter and low-value Zobel networks: 1) If the woofer and tweeter are wired with the same polarity, then the system acts like a notch filter at the crossover frequency. If one driver has its wires...
  6. audioguru2

    Device to scare mosquitoes..

    Hi Kasamiko, I don't know of any electronic device to scare mosquitoes away. The ultrasonic gadgets don't work. Over here, we use a lotion with a chemical called Deet. It works well. We also have a device with propane gas that makes a big "cloud" of carbon-dioxide (like what you exhale when...
  7. audioguru2

    Pulse Width Modulation

    MP, You didn't read my link? This stuff ain't simple. It has a pretty-good PWM motor controller, but it is limited to only 90 percent of max motor speed, and becomes an expensive smoke generator (that can be fixed) when regererative braking down a steep hill or when being towed. The sub-link to...
  8. audioguru2

    help me about AM transmitter circuit

    Hi Usama, Welcome to our forum. Since your radio seems to be receiving something (probably unmodulated carrier, which sounds quiet), then the circuit is transmitting but is not modulated. The circuit specifies a 3-wire electret microphone but you used a 2-wire mic from an old radio. Old radios...
  9. audioguru2

    Pulse Width Modulation

    MP, That circuit is good for controlling the speed of small DC motors. However, for a wheelchair, its low 400Hz switching frequency may sound annoying and cause vibration. The circuit's old, slow opamp isn't capable of a higher frequency and its slew-rate is so slow that the MOSFET heats...
  10. audioguru2

    Electric Motor

    Quantum, Since a capacitor takes on, holds and releases a charge, the voltage across it cannot change quickly, thererfore it filters-out high frequencies. Usually a higher capacitor value has better filtering, except at radio/TV frequencies where a large capacitor is actually an inductor due to...
  11. audioguru2

    Problems with opamp circuit

    Wellington, I'm glad to help you. Pin 8 is an important part of the LM386's input stage. It is used only to increase the gain (and distortion and noise) with a capacitor to pin 1. Your 1st circuit must have a "freak" IC with its pin 8 internally disconnected.
  12. audioguru2

    Problems with opamp circuit

    Hi Wellington, Don't ground pin 8, just leave it disconnected from anything. ;D
  13. audioguru2

    Electric Motor

    Quantum, A simple DC electric motor has brushes to contact the rotating armature, which causes radio-interference. The capacitors filter the interference so that it is not radiated to the receiver, and so that power supply interference is also reduced.
  14. audioguru2

    Great Free Book -

    Wellington, Thanks, that's a good one.
  15. audioguru2

    Our "DC Motors" article

    It is obvious that adding batteries in parallel to existing ones will not increase the torque of an electric motor, especially with the voltage remaining the same, as they say. It is also obvious that adding a gear-train to reduce the motor's work-load will result in the vehicle moving slower...
  16. audioguru2

    How to increase reactance in a coil of few turns?

    Thrival, I can see now that your "oscillator" is actually an emitter-driven half-wave 60Hz pulser. You won't get much 14KHz out of individual flyback pulses of 60Hz, unless something resonates at 14KHz. That's a cool application for electrolysis of water. I like the picture of the...
  17. audioguru2

    Led display Digital Voltmeter question

    Greg, If you are building our "0-30V, 0.002-3A Power Supply", instead of adding a current meter with shunt in series with the load, which spoils the voltage regulation, why not monitor the voltage across its R7, which is already in series with the load and is outside the voltage-regulation loop...
  18. audioguru2

    Our "DC Motors" article

    Ante, MP, If you re-read the article very carefully: 1) "On the other hand, if you need more torque, you can add more batteries in parallel with the existing ones, and your batteries will provide more torque at the same voltage. This is the way to go if your batteries are already supplying the...
  19. audioguru2

    Our "DC Motors" article

    But the article is just plain Wrong with those two errors.
  20. audioguru2

    Dual Lab Power Supply

    Ante, That's a nice one. In summer, I wouldn't want to be near it if it is supplying 5A at a low output voltage! Hot stuff.
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