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  1. audioguru2

    New member says hi!

    Hi Cody, You are learning electronics quickly. I also notice that your spelling and grammar are much better now. ;D
  2. audioguru2

    Can Anybody explain How this Transmitter Works?

    Hi Shariar. Either it has windings capacitance that makes it self-resonant at the RF frequency, or it resonates with the 33pF coupling capacitor. The inputs on the comparator do not connect together. The non-inverting input is pulled high a little by the 10M resistor, probably to ensure that the...
  3. audioguru2

    Understanding this circuit diagram of AK-700 telephone

    Hi Walid, Welcome to our forum. ;D I think Q2 and Q3 are used to turn-off the supply voltage for Q4, for rotary dialing pulses. When PO (pulse output?) goes low for a dial pulse, then Q3 turns-off which turns-off Q2. With Q2 off then Q4 doesn't have a supply voltage and doesn't draw current...
  4. audioguru2

    Need help repairing and setting up this old computer.

    Hi Dazza, Don't feed your computer to the fish. They or someone who catches them might not like the lead in its solder. :( I was very lucky with my old 486 computer. I called the manufacturer in the USA to get an updated Bios chip so I could add a huge hard drive. They didn't have any for...
  5. audioguru2

    Current Limiting on Battery charger

    Hi Qbarkhuizen, Welcome to our forum. ;D Judging its voltage, isn't your battery a Lithium-Ion or LI-Po? They require a special charging technique to prevent them from catching on fire. You don't want to be near Lithium that burns, a fire extremely hot like magnesium. :o
  6. audioguru2

    Keys finder circuit

    Hi Lapsap, Without any sound, T1 is on and T2 is off. You can test its sound by shorting the base of T1 to ground, which N4 does when the microphone hears a sound. You can make the sound louder by increasing the supply voltage, by housing the piezo in a resonant cavity adjusted to the same...
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Shariar, R16 turns off the output transistor, and does it quickly. Without it, the project's output voltage would probably rise if it is powering a low-current load, because of the leakage current in Q2 and Q4. The leakage current is fairly high because the transistors operate hot in this...
  8. audioguru2

    What does 12V - 4.5Ah means?

    Hi Shariar, It can give 12V at 450mA for 10 hours. At 4.5A, it will waste some of its power as heat, so will last less than an hour, maybe only 45 minutes. ;D
  9. audioguru2

    Televisions and Voltage Transformers

    Hi Alun, NTSC is pretty good now. Before, each station had a different colour subcarrier phase, which caused their colours not to match. Now they are all the same. ;D
  10. audioguru2

    Televisions and Voltage Transformers

    My 'scope is black and green, displays a very clear but monochrome TV picture and its vintage is older than 1968. In those days, elevators had operators (a very boring job). I remember an operator watching the Mexico Olympics on a small portable TV and she missed lining-up her elevator with the...
  11. audioguru2

    Televisions and Voltage Transformers

    Hi Ante, Here in North America, black and white TVs used exactly 60Hz as their vertical interlaced frequency but sync'd from the transmitted pic, not the mains. When they changed to colour, the vertical frequency became 59.xxHz, and if the TV has mains hum in the picture you can see the hum-bars...
  12. audioguru2

    voice activated door locking system

    Hi Samartha, Are you allowed to cheat a little? Someone goes to the door and says, "O-pen or Un-lock". Then at the end of the day they say, "Close or Lock". Two syllables unlocks it and one syllable locks it. The circuit will recognise nearly everyone's voice and would be very simple if you...
  13. audioguru2

    MIDI synth (binary logic and basic electronics)

    Hi Dude, Welcome to our forum. ;D There is a good function generator in our Projects Section. It produces sine, square and triangle waveforms over a wide frequency range. It can be modified as per the 8038's datasheet for sweep frequencies and a sawtooth wavwform. Its obsolete LF351 opamp can be...
  14. audioguru2

    Automotive 12V to +-20V converter

    Hi Jonathan, I deleted mentioning the very high power SMPS car power supply that I posted because it wasn't fair to you and your much lower-power project. I am sorry that I mentioned it. You don't have mains beside your tabletop so you can use a simple transformer to power your amp? ??? We...
  15. audioguru2

    Light Computer

    Hi Alun, You don't need the size, power capability and expense of power Mosfets to drive 1/3A lightbulbs. The only fairly cheap little Mosfet I know, the 2N7000, isn't capable with only a 5V gate voltage. :(
  16. audioguru2

    Light Computer

    Hi Steve, Use BC368 transistors with 1k base resistors from the Eprom and 1k resistors from +12V to the LEDs. Connect the lightbulbs from the collector of each transistor to +12V. Your Eprom program should be able to turn-on all the LEDs at the same time. ;D
  17. audioguru2

    0-30 Vdc Stabilized Power Supply

    15V at 3A is 45 watts.
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    Yes, if you set the output voltage to 15V and its current to max.
  19. audioguru2

    Light Computer

    You shouldn't drive a 1/3A lightbulb with a BC547 transistor. When the filiament is cold it will draw a surge current of 3A or more. You need small power transistors. ;D
  20. audioguru2

    Speed-limit Alert PLEASE HELP!!!!!!!!

    You can slow down the response time of the original circuit by using two 10k resistors in series for R18 and adding a capacitor to ground at their junction. Try 100uF to 1000uF. ;D
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