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  1. audioguru2

    telephone related question

    Hi Walid, Two of the diodes are forward-biased all the time that the phone is active, so rectification of the audio doesn't happen. The audio passes through these diodes like they are a low-value resistor.
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Firefly, Your 25V/5A transformer would allow the modified project to provide 25V or 26VDC at 3A. With only 18VAC, many resistor values must be changed to make it work. You cannot parallel regulated supplies easily without using isolating resistors that ruin the voltage regulation. You will...
  3. audioguru2

    tachometer

    It is probably a violation of Silicon Chip magazine's copyright to post the entire project here, without their permission. Therefore it is best for people to get access to it in Google like I did. It is strange. If I click on MP's link, I get the 1st page of the project and a request for...
  4. audioguru2

    Keys finder circuit

    Hi Lapsap, N5 N6 R8 R9 C5 are a 4kHz oscillator and drive T2 which drives the piezo to make sound. When you ground the base of T1 then its collector is open-circuit which allows the oscillator to work. C5 is 1.5nF which is 0.0015uF. R10 is 4700 ohms.
  5. audioguru2

    tachometer

    Today, MP's link wants me to pay to see the project, but I got it for free from Google. The schematic was posted as a blurry Jpeg so some things are hard to see. Do you also need the parts list? It is also on Google.
  6. audioguru2

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

    Hi Kain, It looks very nice. ;D A 30V transformer, 1k for R4 and a low-current BZX79C5V6 zener diode for D8 would make the output voltage a little over 30V. 
  7. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Electrofreak, Your positive unregulated voltage is probably about 41V (across C1) and your negative supply is about 5.2V (across D7). It is strange that the TL081 opamp survives with the resulting total voltage of more than 46V across it since its absolute max rating is only 36V! :o I don't...
  8. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Electrofreak, U2's max output current is about only 30mA. With 30mA through a 100 ohm resistor it dissipates only 90mW. Didn't you use an OPA445 high power supply voltage opamp for U2? 
  9. audioguru2

    LIGHTENING STRIKES

    A neon bulb and a very high-value resistor will show you the polarity of static charges fairly safely. I think its negative internal post will light with a negative polarity on it, and it will breakdown at about 90V and prevent any higher voltage from occuring. ;D
  10. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Elecrofreak, If you used the original value of 1k for R15, it would smoke with about 16V across it. Maybe the pins of Q2 are incorrect, or maybe Q2's collector isn't connected. About the only thing that would kill D11 is if it was shorted or connected backwards, and the current was set high. ;D
  11. audioguru2

    Light bulb dimmer

    I don't know if our project was designed with a neon bulb instead of a Diac because either a neon bulb was on hand, or because the Diac wasn't invented yet. ;D
  12. audioguru2

    tachometer

    Hi Guys, Today, like the other day, I searched Google for Siliconchip Tachometer and copied the link into Notepad. It is exactly the same link as MP posted. Clicking on my Google link allowed me to see the entire project. Then I tried clicking on MP's link again and it also allowed me to see the...
  13. audioguru2

    LOAD RESISTOR IN A MOSFET AMPLIFIER

    You need a power amplifier circuit or IC.
  14. audioguru2

    tachometer

    On MP's link, Silicon Chip asks you to pay them to see the remainder of the project. On a Google search, you get a link to the entire project for free. ;D
  15. audioguru2

    Light bulb dimmer

    Hi Kevin, welcome back. ;D The 120V AC light bulb dimmer circuit in our projects section might work, but nowadays, a Diac is used instead of its neon light bulb for triggering the Triac. http://www.electronics-lab.com/projects/motor_light/029/
  16. audioguru2

    tachometer

    Hi Source, In a search on Google ( www.google.com ) I entered siliconchip tachometer and the very 1st link was the entire project with schematic, parts list, pcb layout and tips on how to make it.
  17. audioguru2

    What are the test condition for power Transistors?

    Hi Shariar, If your TIP122 transistor gets hot when it dissipates only 6.5W then either your heatsink is too small, you didn't use thermal grease between it and the heatsink or you used an insulating washer between it and the heatsink. All power transistors have their absolute maximum power...
  18. audioguru2

    Cellular Phone Repeater for home use

    To avoid oscillation you don't want any gain. Why use an amplifier?
  19. audioguru2

    What does 12V - 4.5Ah means?

    Hi Prateek, Of course a rechargable battery should include time in its ratings. It is its capacity, or how long its charge will last for a certain load. I think all batteries, especially disposable ones should state their A/hr rating. Instead of "super heavy duty", whatever that means. ;D 
  20. audioguru2

    Cellular Phone Repeater for home use

    Hi Ets, Welcome to our forum. ;D Save yourself 500 bucks. If the signal is good outside, put an antenna there and wire it with RG-6 satellite coax cable to another antenna inside. If the antennae are proper for the RF frequencies and the cable isn't too long, I think it will work. ;D
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