Search results

Search Forums New Posts
  1. Audioguru

    LED strips underwater

    Water corrodes many metals. If the LED strip has exposed metal that can corrode, then corrosion will ruin it.
  2. Audioguru

    How can one regulates DC voltage automatically to the voltage required by an appliance using micro-c

    An inverter needs Pulse-Width-Modulation and a voltage sensor for voltage regulation. Then when the sensor shows the output voltage dropping, the PWM circuit increases the pulse widths that raises the voltage. When the output voltage rises then the opposite occurs and the pulse widths become less.
  3. Audioguru

    LED strips underwater

    Several days is nothing. Several months will cause severe corrosion especially if the water is not distilled. Tap water has all kinds of nasty things in it.
  4. Audioguru

    How to turn Smoke alarm into Ultrasonic Dog Repeller

    A piezo transducer is made to produce audible beeps, not ultrasonics.
  5. Audioguru

    I want to modify my car radio

    When most stupid drivers see an emergency vehicle behind them, they stop and block the path instead of getting out of the way. Hearing the siren will alert them before it is too late.
  6. Audioguru

    Adjusting voltage

    It looks like the 555 uses Pulse Width Modulation to vary the speed of a DC motor by adjusting the pot. The output voltage of an555 has a voltage loss depending on its load current. Then the 555 should drive a switching transistor or logic level Mosfet to switch the load to +5V and 0V.
  7. Audioguru

    Electret microphone is giving unsual resistance

    To disable means to prevent an unused opamp from oscillating which causes an interference input to the other opamp. Disable it by connecting its (+) input to 0V and connecting its (-) input to its output. Then its output will always be close to 0V.
  8. Audioguru

    Electret microphone is giving unsual resistance

    An LM358 dual opamp might work if you disable its second opamp.
  9. Audioguru

    Electret microphone is giving unsual resistance

    A TLE2141CP opamp works fine when its supply has dropped down to 4V and sells today for $1.92US at Digikey for the 8DIP package.
  10. Audioguru

    Electret microphone is giving unsual resistance

    I calculated 26k ohms for the mic. Most electret draw double the current of yours resulting in a resistance measurement of about 10k ohms. Its resistance changes a tiny amount with sounds. The 3.3k resistor R1 should be between 7.5k to 10k. The very old 741 opamp was designed to use only a 30V...
  11. Audioguru

    A few questions on small dual battery solar

    In winter, the car oil is thick then cranking the engine takes 200A to 300A. The engine might not start immediately so you crank it at hundreds of Amps for many seconds. Lookup the hundreds of "cold cranking Amps" of a car battery. 3A or 4A is nothing to a half-decent car battery. Yours are old...
  12. Audioguru

    VU meter

    The TDA2009 has two amplifiers in it but you said you use only one 4 ohm speaker. Are you using the 4 ohm speaker on the "bridge amplifier circuit" shown in the datasheet? The VU meter probably has one input at 0V but the speaker of the bridge amplifier does not have a speaker wire at 0V. Use...
  13. Audioguru

    VU meter

    The signal voltage across the speaker depends on its impedance and the power supply voltage of the TDA2009, both we do not know. Also we do not know the input sensitivity of your VU meter, it might be made to show a line level (amplifier input) or a speaker level(amplifier output).
  14. Audioguru

    A few questions on small dual battery solar

    Your charge controller or your batteries is/are defective.
  15. Audioguru

    AC Measurement Question

    Your 250 ohms resistor value is too high for some LM317 regulators, it should be 120 ohms then the 1k adjusting pot value should be reduced to 500 ohms for an output from 1.25V to 6.5V. The datasheet shows 240 ohms for the more expensive LM117 but the notes say that the LM317 needs less.
  16. Audioguru

    Small low-power light sensor

    Why not use a solar garden light that costs only $1.00? It has a solar panel, a 300mAh AAA Ni-MH battery cell, a circuit that switches from charging in the light or boosting the battery voltage to power the LED in darkness. It uses the solar panel to detect light or darkness. Get one with a...
  17. Audioguru

    analyse this circuits please

    The base of Q2 has no DC bias voltage then its output will be rectified and very distorted. The collector of Q2 is floating with no load resistor to the positive supply then the base of Q3 has no DC bias voltage. The base of Q5 has no DC bias voltage. Q5 is an RF oscillator then what frequency...
  18. Audioguru

    Hi, center tap transformer, how to calculate?

    The tuning capacitor is parallel with both inductances in series. The parallel LC resonates with a high impedance. Since the LC resonates with a high impedance then the reactance of each coil is much less that the impedances in the circuit.
  19. Audioguru

    Hi, center tap transformer, how to calculate?

    I never designed and built the IF transformer or discriminator for a radio, instead I simply bought an old one or took one from an old radio. Two inductances in series have a total inductance that is their inductances added. You do not know the amount of wiring or stray capacitance which...
  20. Audioguru

    Hi, center tap transformer, how to calculate?

    "n" would be nH nano-Henries.
Top