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  1. audioguru2

    help on soil moisture probe

    Hi Smooth, Welcome to our forum. ;D Our Plants Watering Watcher-2 project blinks its LED to save battery power. It blinks brighter as the soil gets drier. When the soil is damp then it is very dim. http://www.electronics-lab.com/projects/science/018/index.html
  2. audioguru2

    Got a couple questions regarding this fm transmitter

    20Hz - 15kHz (flatness +/- 1.5dB) is pretty good. The curves for the Micromitter show that 15kHz is down more than that because of the 19kHz filter's action. It is worse in North America due to our increased pre-emphasis.
  3. audioguru2

    Got a couple questions regarding this fm transmitter

    The EDN transmitter might be good. It is expensive. Is it manufactured or is it a kit? The spec for frequency response doesn't say plus or minus how many decibels. The equalization is in Rohm's BH1415 and BH1417 chips so it should sound just as good as a Micromitter. The Micromitter kit is from...
  4. audioguru2

    Got a couple questions regarding this fm transmitter

    Hi Dot-com, Use the bandpass filter in the Micromitter but don't use its attenuator. I live beside Toronto where there are more than 80 FM stations. So using a 1W RF amplifier would cause radio and TV interference and would cause complaints. It would be very illegal. So I am sorry that I don't...
  5. audioguru2

    Got a couple questions regarding this fm transmitter

    Hi Dot-com, You found a very old RF amplifier circuit. I looked in Digikey and the diode and all the transistors you listed are not available anymore.
  6. audioguru2

    Got a couple questions regarding this fm transmitter

    Hi Dot-com, Welcome to our forum. ;D The Micromitter is intended to transmit an MP3 player to a car radio with a range of only about ten feet. If you remove the attenuator at its antenna, use a strong 12V supply (8 AA cells at least), use an 31 inch long antenna wire and a very good FM receiver...
  7. audioguru2

    Adjustable precision shunt regulators, TL431

    Hi Walid, The TL431 is a shunt regulator like a zener diode. You have its two resistors setting its voltage to 14.97V. I didn't notice that your input voltage is only 12V so it won't work.
  8. audioguru2

    Adjustable precision shunt regulators, TL431

    Hi walid, For the inexpensive TL431C, the datasheet lists the Vref as minimum 2.44V, typical 2.495V and max 2.55V. So in your example the Vout is typically 14.97V.
  9. audioguru2

    Transistor Protection

    Then my fixed circuit is fine since it has only 24mA load current. This circuit has a 24mA load current. Smaller resistor values are needed for a 1A load current. A short circuit protection circuit is complicated: 1) a small value resistor senses the load current. 2) A comparator amplifies the...
  10. audioguru2

    Total voltage drop in series circuit

    The voltage dropped on the Nokia charger because it is a constant current source or because it was overloaded or because it has lousy voltage regulation.
  11. audioguru2

    Simple Unipolar Stepper Driver

    Your original circuit fed 6V to each coil and wasted 18V in the resistors. You can use 12V safely if you reduce the width of the pulses to half to avoid too much heat. The coils are inductors that build current slowly. Therefore at high speeds they have less average current so increasing the...
  12. audioguru2

    Simple Unipolar Stepper Driver

    Hi Adam, The original circuit used power resistors as an inefficient way to use a 5.4V stepper motor on a 24V supply. The coils are 1.5A, not 3A. Your new current source is good for low currents where a small transistor can be used that has a high current gain. In your circuit with 3A (it...
  13. audioguru2

    Transistor Protection

    Hi Monster, Don't short the output, turn off the input instead. The input needs the added current limiting 1.8k ohm resistor anyway to stop the base of the BD135 from being blown up. Why does the BD135 have such a high current in R1? The current in the BD136 is a max of only 24mA so its base...
  14. audioguru2

    Total voltage drop in series circuit

    Please tell us what are your voltage measurements. Measure the battery voltage with it powering the LED when its voltage is reduced by the current.
  15. audioguru2

    Single Supply Op-Amp with Negative Ouput

    The opamp can oscillate and drive a "charge pump" made with a couple of diodes and a couple of capacitors. Then the negative DC output will be about -3.6V if the load current is low. Use an ICL7660 charge pump IC to create a negative DC supply voltage for the opamp. The output will be -5.0V if...
  16. audioguru2

    Sound-activated circuit

    Hi Mt, Any sound at the frequency you need to detect will activate a filter circuit unless it is louder than other similar sounds. A high-Q bandpass filter circuit is needed. A filter is not perfect, it reduces the levels of unwanted frequencies, it doesn't eliminate them.
  17. audioguru2

    transistor saturation

    No, it will break. You must not exceed any "max" rating. The max collector current is 200mA. It performs poorly above 100mA. Use a power transistor like a TIP31 if you need a collector current of 1.5A. Its max collector current is 3A.
  18. audioguru2

    PROFILE PA2120

    $49.95 for a cheap Chinese amp that is imported by two companies. They might get them for only $19.95 then make a big profit. 120W max (peak?) power? Is it 60W RMS as the total of both channels? Then its output is only 30W per channel with no distortion spec (10%?) making square waves.
  19. audioguru2

    satellite speaker problem

    I couldn't find spec's for the Sony satellite speaker system in Google, but I suspect that it uses a separate amplifier for its sub-woofer with a lowpass filter, and a stereo amplifier for the satellite speakers with a highpass filter that uses small capacitor values. Then the satellite speakers...
  20. audioguru2

    satellite speaker problem

    Hi John, I wish you continued on the other thread instead of making this new thread. I reviewed the other thread and it talked about our "22W" amplifier project. With a 12V supply each 6 ohm speaker will get 6.5W but they are small so bass might break them. You need a crossover circuit and a...
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