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  1. audioguru2

    STK465 Stereo Amp

    Hi Roby, The pcb has connection terminals near the inputs for the input grounds. I don't see connection terminals for the power supply ground nor do I see terminals for the speaker grounds. I think a very heavy wire should connect the power supply ground to the pcb then the speakers should have...
  2. audioguru2

    resonate at 100 Hz

    Quartz crystals and ceramic resonators operate at high frequencies. You make a high frequency oscillator with one then use a counter IC to divide the frequency down to 100Hz. A CD4060 IC is an oscillator with a counter that can divide up to 16,384.
  3. audioguru2

    Problems with my 555 circuit

    An LED need to have a current-limiting resistor in series with it. Without a current-limiting resistor then the LED shorts the output of the 555 which might blow up the LED, the 555, the battery or all of them. Maybe the 555 kept trying to drive a very high current into the LED and got so hot...
  4. audioguru2

    High Power LED Mood Lamp

    The microcontroller does whatever it is programmed to do. It does not do what it is not programmed to do.
  5. audioguru2

    Problems with my 555 circuit

    On the other chat site it looks like you didn't know that electrolytic capacitors have polarity and must not be installed backwards.
  6. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Steven, I couldn't find a datasheet for those transistors to see their ratings. They appear to be made in the 21st week of 1993. Jaycar don't say the inverter is 140W. They rate it at only 30W.
  7. audioguru2

    Problems with my 555 circuit

    You can use a variable resistor to adjust the frequency of a 555 oscillator if its value isn't too high so that it cannot supply enough current for the leakage current of the capacitor. But changing the variable resistor's value will also change the duty-cycle of the 555's output.
  8. audioguru2

    a very simple FM Tx

    Hi Walid, A filter capacitor needs time to charge or discharge in order for its voltage to change. At 100MHz its value makes a good filter so its voltage doesn't change. At 7.5kHz and lower audio frequencies then the value of the capacitor makes a very poor filter so its voltage can change to...
  9. audioguru2

    Led display Digital Voltmeter question

    Don't you have the datasheet for the ICL7107 that is used in this project? It says that the inputs don't work near ground (outside the input common-mode range) unless it has a negative supply, and a few other problems must be solved.
  10. audioguru2

    Led display Digital Voltmeter question

    It is best to make a +5V with a 7805 and make -12V from a 555 then regulate it with a 7905 to get -5V. The datasheet shows the ground of the meter connected to its negative input lead. The same ground as the negative terminal of the car battery.
  11. audioguru2

    Is there a way to make DRL gates oscillate?

    An oscillator needs to have a gain more than 1. A resistor and some diodes don't have any gain so they won't oscillate. Transistors and opamps have gain so make good oscillators. Two or more Cmos inverters can be biased or even be self-biased to be linear and make a good oscillator. An...
  12. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Steven, My first comment about the kit was about the first line in its instructions, "max 120 watts input, output power max. 60...70 watts". The circuit's output cannot provide anywhere near 140W. So I calculated that its input power is about 105W and its output power about 62W. Depending on...
  13. audioguru2

    sony trinitron

    I found the service manual of my Sony TV for free in Google by entering its model number. I also found forums of guys talking about the same problem that my TV had and a secret notice to authorized dealers about repacing some capacitors that might have caused my TV's problem.
  14. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    Hi Bob, Your DRL gate in reply #6 has a very low value for its resistor that needs way more current than a Cmos output can provide with a 5V supply. I looked at a Cmos datasheet and saw that its max logic low output voltage is 0.4V when it has a load current of 0.5mA. So the output voltage of...
  15. audioguru2

    Problems with my 555 circuit

    The capacitor needs to charge to 2/3 of the supply voltage, then the LED will turn off. If the capacitor has a high leakage current then the value of the resistor charging it needs to be reduced or the capacitor will never charge and the LED will not turn off. Big capacitors have a higher...
  16. audioguru2

    Could some one please explain to me how a DRL...? Wait! one more thing!

    Yes and No. The CD4081 is made with complimentary Mosfets, not ordinary NPN transistors and diodes like the older logic families. Their logic family is called Cmos: 1) Cmos has no input current. Old TTL had massive input current. The other old families also had high input current. 2) Cmos...
  17. audioguru2

    220 volts Versus 120 volts

    You forgot in your calculation that countries with 220V mains charge much more for electricity and all other forms of power (gasoline, for example) than the very cheap power in Canada and the US.
  18. audioguru2

    a very simple FM Tx

    The transistor needs a change of base to emitter current to be an amplifier and to oscillate. If the base voltage is not secured with a capacitor to ground then it will also have its voltage changed when the positive feedback changes the emitter voltage, then there is no change in base to...
  19. audioguru2

    Inverter Circuit 12V DC to 230VAC Sine Wave

    Hi Guys, I found the schematic of Steven's super-simple inverter kit and I have figured out why it wastes half of its supply power and has an output power of only 60W to 70W: 1) The BD234 PNP driver transistors are in a multivibrator like I thought. They have avalanche breakdown since their...
  20. audioguru2

    Binary clock :)! Any one familiar with binary counters?

    Hi Bob, In "the good old days", chips for making a clock were available. Now a clock is so cheap that the chips aren't sold anymore. I also couldn't find a 6-bit binary Cmos counter IC. Ripple counters with many stages are available but cannot have their outputs gated together for decoding like...
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