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  1. audioguru2

    High Power LED Mood Lamp

    Hi Nefelodemon, I am sorry that it is confusing. If the base resistors for the BC337 transistors are 680 ohms instead of 10k ohms then any BC337 transistor will saturate well and cause the max LED current to depend on the value of the current-limiting resistor, the power supply voltage, the LED...
  2. audioguru2

    4 watt fm transmitter

    Hi Point, Attach the schematic and parts list of the transmitter you are talking about for us to see if it is good or bad.
  3. audioguru2

    How do I draw a truth table for this!???!

    It is not difficult to make a chart of the sequences of the LEDs in the circuit. A CD4017 steps forward one step each time its input goes positive. It makes one output go positive during a step. Start the chart by resetting all the CD4017's so that each one has its "0" output high and that LED...
  4. audioguru2

    Automated plant watering

    I am using many of the Plants Watering Watcher-2 devices and discovered that different types of soil and water have a different resistance. Distilled water (rain?) is an insulator while my tap water conducts the same as salt water. Perilite is also an insulator but soil with some fertilizer...
  5. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    The MC34072 is a dual opamp. The project needs single opamps like the MC34071 which might be in stock. Lots of online electronic supply stores have Motorola (now ON Semi) and Texas Instruments opamps that are rated for 44V.
  6. audioguru2

    230V/1000W AC dimmer

    Your link doesn't work so I cannot see the circuit.
  7. audioguru2

    Body Resistance help

    The resistance of your skin is lower if you are sweating (even just a little), if you press harder on the probes and if a lot of area of the probes is touching your skin.
  8. audioguru2

    Cutoff frequency and 3dB points

    Hi Cabwood, Good summary of the "chosen" -3dB cutoff point. ;D You forgot another "convenient" attribute of -3dB: It is a small drop in level that can be noticed by most people. Picture Bell cutting a speaker's power in half with a switch in his meeting, "Hear the small difference guys?".
  9. audioguru2

    Convert 0-30V 3A PSU to 5A or more

    The 24VAC will be about 25.5VAC without a load. Then the peak voltage will be 36V and the unregulated voltage will be 34.7VDC. Most of the opamps use the positive unregulated voltage plus the negative 5.6V supply for a total of 40.3VDC. The absolute max supply voltage for a TL081 opamp is only...
  10. audioguru2

    a low value wattage resistance

    Hi Walid, I never use resistors at their power rating. Look at their datasheet, the temperature is hundreds of degrees C at the rated power. Their power rating is "the absolute max do not ever exceed" amount. Power resistors are big and take time to heat up. So they can pass pulses of current...
  11. audioguru2

    High Power LED Mood Lamp

    Thanks, Mixos. The BC337 transistor has a very wide range of current gain. With 680 ohm base resistors then the base current is 6.3mA which is well within the amount that a PIC can safely supply (25mA max) and is enough for any BC337 transistor to saturate properly for high brightness. The mood...
  12. audioguru2

    a low value wattage resistance

    Hi Walid, Power resistors are much smaller and cost much less than 0.5 ohm or 1 ohm of long wire. Copper wire increases its resistance with heat, most power resistors don't.
  13. audioguru2

    request for walkie talkie circuit

    I just looked in www.google.com and got links to 254,000 walkie talkie circuits. Some are old and use vacuum tubes, some are cheap toys for kids and some are pretty good. Take your pick. Also look in Google's Images for pics of the circuit boards used in walkie talkies.
  14. audioguru2

    230V/1000W AC dimmer

    Hi Buddi, Welcomr to our forum. ;D A triac is made for AC. They are used in light dimmers to quickly switch the power on and off and they dim by changing the duty-cycle. Because they quickly switch, they don't get hot. The quick switching is bad for an electro magnetic load. IGBT's and Mosfets...
  15. audioguru2

    Radio Circuit Analysis

    It isn't a receiver. It is a tuned circuit followed by an AM detector that doesn't have a proper DC load nor filter, then an improperly biased transistor as an audio amplifier. It is similar to an old fashioned crystal "radio". The tuning capacitor for many AM radios is 365pF when turned to...
  16. audioguru2

    Triggering a 12VDC relay switch with 5V

    Hi Migrier, You have a driving power of 4V x 50mA= 200mW available but the relay coil needs 12V x 75mA= 900mW. So your circuit doesn't provide enough power to drive the relay. Why not use a transistor or Mosfet instead of a relay?
  17. audioguru2

    Question about FM Telephone Bug (Need reply ASAP. Tnx!)

    Hi CarHammer, Only C1 and the rectifier diodes need to have high voltage ratings. The other parts operate at the 2V of the red LED. In Canada, the telephone line is about 50VDC when not in use. A 90VAC ringing signal is applied. Therefore the peak of 90VAC is 127V and when added to the 50V...
  18. audioguru2

    High Power LED Mood Lamp

    The purpose of this thread is to show my discovery of two problems with this new project. Hopefully, the problems will be corrected so people making the project will have it work well. 1) The value of the base resistors for the transistors is much too high and stops the transistors from...
  19. audioguru2

    plz help urgently

    No, Sarma. An LM324 has four opamps, not comparators. An opamp can have negative feedback applied to have any amount of closed-loop gain required. An opamp is fairly slow. A comparator cannot have negative feedback applied so is used with its full gain of about 200,000. A comparator is fairly...
  20. audioguru2

    High Power LED Mood Lamp

    MP, you contradicted yourself. My LED Mood Lamps have been working very well with all parts operating within their spec's for about 6 years. They slowly produce millions of colours on the ceiling including every tint of white. Nothing gets hot.
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