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  1. audioguru2

    Mobile Robot Power Consumption

    On the other web forum you said you did not use a new name-brand alkaline 9V battery. It is dead. Even a good new 9V alkaline battery doesn't have enough power for your application. There are tiny and weak AAAA cells inside a little 9V battery. Use a real battery. Six AAA alkaline cells have...
  2. audioguru2

    help with a school project

    You saved your schematic as a fuzzy JPG file type instead of a very clear GIF or PNG file type. Pin 7 is the output of an adjustable voltage reference. Pin 8 is its adjustment terminal. The two resistors are calculated similar to the LM317 adjustable voltage regulator. You are forcing a voltage...
  3. audioguru2

    0-30 Vdc Stabilized Power Supply

    It is bigger than is needed but it will work fine. The 30VAC transformer will be about 31.5VAC without a load. Then its peak voltage is 44.5VDC and the rectifier bridge will charge C1 to +43.1V which is the positive supply for the opamps. The negative supply should be close to -5.6VDC. If...
  4. audioguru2

    AMPLIFIERS..OUTS..SPKRS..OHMS = DAMAGE?

    You are correct. Connecting two 8 ohm speakers in parallel makes a 4 ohms load. If the amplifier is not designed to drive 4 ohms then the twice as high current might destroy it. Since it has two output jacks per channel then it is likely that it can drive 4 ohms. Look up its spec's.
  5. audioguru2

    TV Signal Amplifier ?

    Look at the datasheet for a 741 opamp. With 100% negative feedback it has no gain because its output level is the same as its input level up to about 9kHz. Then at higher frequencies its max output level drops because of "slew-rate-limiting" where the output becomes a triangle-wave and it can't...
  6. audioguru2

    AC adaptor help!

    A "travel adapter" is made to reduce the power to electrical hair dryers, not transformers. The LED lamp might also be burned out. Your transformer has a rated output of 12VAC, 1667mA. Get one with a primary winding to match the mains voltage in the UK (230VAC?) and a 12VAC, 2A secondary.
  7. audioguru2

    500W sine wave inverter design

    A car battery works poorly when it is cold but it has the ability to deliver hundreds of Amps to a starter motor when the oil in an engine is very thick due to the cold. When it is at room temperature a fully charged car battery can supply 50A easily for about 1 hour. Maybe car batteries are...
  8. audioguru2

    white led

    Hi Pier, Since you have a full-wave bridge rectifier and 60uF of smoothing capacitors then the DC is without much ripple and is pure DC. You measured the current (calculated with Ohm's Law by the voltage across the 22 ohms resistor) at two voltages so just multiply the voltage times the current...
  9. audioguru2

    12V Car outlet

    The load determines how much current it takes if the power supply can supply that much current. A load that draws 25mA will draw 25mA from a little 12V battery and draw only 25ma from a huge 12V car battery. An ordinary LED with a current-limiting resistor draws only about 25mA. The cigarette...
  10. audioguru2

    12V Car outlet

    A car outlet? You mean a cigarette lighter socket? It must have a fuse that will blow if wires get shorted in a crash. Then the wiring won't catch on fire. The fuse might be about 20A. A car battery can supply hundreds of Amps to the starter motor when the engine oil and mechanics are cold in...
  11. audioguru2

    help with a school project

    Hi Telephone Man, Are all the LEDs lighted all the time? Look at a tutorial about how the 555 works and you will see that the voltage on the capacitor will go from 1/3rd of the supply (4.0V) to 2/3rd of the supply (8.0V). Look at the datasheet or at a tutorial about the LM3915 and you will see...
  12. audioguru2

    0-30 Vdc Stabilized Power Supply

    U2 needs to be a single high voltage opamp because it has input offset voltage adjustment pins for RV1. Then the value of RV1 and R10 must be adjusted to match different opamps. Some opamps need RV1 to connect to the positive supply instead of the negative supply.
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    There are a few opamps rated at 44V: TLE2141 and MC34071. Why are your prices nearly double the price in the US?
  14. audioguru2

    0-30 Vdc Stabilized Power Supply

    Yes, the opamps have a supply voltage that is higher than their max allowed voltage. They will fail. Some of the parts get too hot. They will also fail. That is why I recommend using OPA445AP high voltage opamps, then the transfomer's voltage can be increased to 30VAC so the project's output...
  15. audioguru2

    TV Signal Amplifier ?

    Opamps don't work at VHF and UHF. A 741 opamp has a voltage gain of 200,000 at DC but no voltage gain above 1MHz and its output can't swing above 1MHz anyway. You need a high frequency RF amplifier if all TV signals are very weak.
  16. audioguru2

    The caps surrounding the LM7812 regulator?

    The load current doesn't affect the voltage regulator circuit. It works perfectly with zero current up to max current. It also works perfectly with minimum input voltage up to its max input voltage.
  17. audioguru2

    dancing leds with counter

    You can replace the CD4017 sequencing counter IC with the digital counter and displays from our project that counts and displays the distance that you walk: http://www.electronics-lab.com/projects/misc/007/index.html The displays might be a blur if the Dancing LEDs input is counting high music...
  18. audioguru2

    dancing leds with counter

    Are you talking about the Dancing LEDs project that is in our projects section? http://www.electronics-lab.com/projects/motor_light/021/index.html It has a counter so it sequences the LEDs with each sound. What is wrong with yours?
  19. audioguru2

    Turning a 7805 on/off with a Push to Make Switch

    You could connect a Mosfet in series between the output of the 12V supply and the input to the 5V supply. It could be turned on and off with a momentary button that controls this "alternate action" circuit:
  20. audioguru2

    Simulating input bias current

    Hi fredrick, It is easy to calculate the effect of input bias current with an input resistor for an opamp. The typical input bias current for an old LM358 is 45nA and the max is 250nA. The inputs are PNP transistors so a resistor to ground will have the bias current in it causing the input...
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