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  1. audioguru2

    LED Resistor Question

    Hi Stingray, Welcome to our forum. ;D Nobody makes an LED that draws a whopping 20A nor 5A. The absolute max continuous current for a normal (not the new extremely bright ones that come mounted on metal or ceramic) is only 30mA. Your 5V and 3V LEDs are in series so need 8V to operate. A brand...
  2. audioguru2

    IC output help

    Your problem with the circuit is caused by sensing the load current by pin 3. An incandescent lamp draws at least 10 times its normal operating current when cold. A motor draws a huge current when started and when loaded. At first I thought of just connecting a fixed voltage of about 2.5V to...
  3. audioguru2

    Audioguru FM Tx

    Hi Alun, I don't have a scanner nor digi-cam to post the circuit's Veroboard layout. My son lost or sold his digi-cam and I don't think a pic from my cell phone would be clear enough. Hey, there's a digi-cam in the pile of "unrepairable" electronic stuff my son brought home. I fixed a portable...
  4. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Helder, Welcome to our forum. ;D There is nothing in the circuit that would break if the circuit was powered without the ICs installed. You can check Q3 by shorting its base to its emitter. If the LED turns off then the transistor is OK. Did you use high-supply-voltage rated opamps as...
  5. audioguru2

    pulse generator

    Then don't change the variable resistor as much. Don't you have the 1M resistor in series with the variable resistor? The variable resistor adjusts the time between pulses a little. If the resistance is too low then both transistors will be turned-on all the time and the 2N2222 and 50 ohms will...
  6. audioguru2

    BJT biasing formulas

    I have experience but I am not a genius. The hFE (DC) is 100, 230 and about 400. The hfe (AC) is less and is shown on Fairchild's datasheet. The 1st thing was to choose a voltage gain of 10. I made a small mistake with it so leave the collector resistor as 10k. Correct. I didn't use a reverse...
  7. audioguru2

    Audioguru FM Tx

    Hi Walid, There isn't any text. It isn't even a project. Someone posted a very simple FM  transmitter circuit and said it didn't work. I looked at it and saw that its audio amplifier transistor was incorrectly biased so that it worked only when the battery was from 7V to 8V. I also explained...
  8. audioguru2

    opto coupler triac

    I don't think a diode gives enough voltage as a photodetector to turn-on a Mosfet. IR make some opto-coupled Mosfets with some kind of photo-voltaic cell as the detector. The Mosfets are tiny and can't drive much current for an ordinary relay.
  9. audioguru2

    PNP and NPN replacements

    The impedance of an antenna depends on its length and its percentage of the wavelength of the signal, doesn't it? I think it has a perfect resistance at a quarter and at a half of a wavelength and one is low and the other is high. In between, the impedance is capacitive or inductive.
  10. audioguru2

    opto coupler triac

    You should use an opto coupled transistor maybe driving another transistor for enough current to drive the DC relay. Don't forget about adding an anti-spike diode across the relay's coil.
  11. audioguru2

    My laptop the firebomb

    Hee, hee. ;D It says to store extremely flamable lithium in gasoline! (petrol for some blokes) ;D If there's any air inside the container and you shake it, then ... Kaboom![move] ;D ;D ;D
  12. audioguru2

    IC output help

    Hi MrHeckles, Your lamp will have a very low resistance when cold and prematurely limit the output due to the current sensing at pin 3. Therefore I don't think that this current-sensing circuit will work with an incandescent lamp as its load. :'(
  13. audioguru2

    IC output help

    Hi MrHeckles, An N-channel Mosfet needs its gate 10V more positive than its source to fully turn-on. Therefore since your light bulb the source's load then it gets only a couple of volts max. If you rewire the circuit so the light bulb is the drain's load, then the Mosfet will work correctly.
  14. audioguru2

    pulse generator

    Hi Streets, Welcome to our forum. ;D The 2N2222 shouldn't get hot in that circuit. It would if its collector and emitter wires were reversed. Look-up its datasheet's pic of it at www.datasheetarchives.com . Your car's ECU could be damaged if your circuit feeds too much voltage to it. The ECU...
  15. audioguru2

    CMOS 555 BURNS???

    Hi Kain, I'm glad to have helped you fix it. ;D Without a supply bypass cap, the supply voltage came up so fast that the TLC555 became a turned-on SCR across the supply. A regular 555 needs a supply bypass cap because its high-current 200mA+ output transistors are both conducting when they...
  16. audioguru2

    CMOS 555 BURNS???

    1) Every single one of the applications circuits in National's datasheet for their LMC555 Cmos IC has a 0.1uF supply bypass capacitor. 2) Cmos ICs are known to "latch-up" across the supply like an SCR under certain conditions. 3) SCRs have a dv/dt limit of the rate of rise of their supply...
  17. audioguru2

    BJT biasing formulas

    Yes. Yes. Attached is a graph comparing the impedance of a 2.5k resistor with the collector of a BC547 transistor operating over the same voltage range. The collector has an impedance that is 23 times the resistor. You want max voltage swing at the collector. When the transistor is saturated...
  18. audioguru2

    CMOS 555 BURNS???

    Hi Kain, I suspect that the supply voltage is too high because with only a 12V supply, the LED would look dim with only 1mA or less. Did you exceed the absolute max supply voltage of only 15V for National's or 18V for TI's Cmos IC? Is a relay or something connected to its output? D1 is used to...
  19. audioguru2

    0-30 Vdc Stabilized Power Supply

    What is a "schokky"? This project doesn't use nor need a high-speed, high-leakage Shottky diode for D9. It is an ordinary 1N4148 diode. Use the same kind of opamp with a high supply voltage rating as U3. Can't you see the PNG schematic I posted? Download and save the pic and open it in a viewer...
  20. audioguru2

    Getting a high pitch with my device to record phone conversation.

    Hi LegendBreath, Turn off the TV next time you record. I hear lotsa stuff going-on on your recording. I can identify the sounds from most things, but I wonder where the flute playing comes from. Audio equipment needs shielded audio cables to avoid interference like you have, and the transformer...
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