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  1. audioguru2

    again, microphone input high school project

    Hi Zgnoh, The LM3915 isn't connected to the microphone, it is fed from the volume control like the left triangle in your previous diagram. The volume control is R2 of the "Half-wave peak detector" circuit in figure 1 in the datasheet. The half-wave peak detector circuit is DC-coupled from the...
  2. audioguru2

    voltage amplifier

    Hi Npatel, Thank-you for providing the extremely important details. You don't need an amplifier. you need a DC to DC voltage step-up circuit. Have you ever seen an amplifier that works without a power supply? The DC voltage step-up circuit consists of a power oscillator that drives an inductor...
  3. audioguru2

    Electronic Stethoscope

    This is only one problem of many with the original project. There is no way a 741 opamp can work in this circuit without a negative supply for its pin 4 that some builders added after hearing about it. There is also no way a 741 can provide enough current to drive an 8 ohm earphone or two...
  4. audioguru2

    Electronic Stethoscope 2

    Hi Con, You can make your 10K linear trimpot volume control similar to an audio taper one by connecting a 3.3K resistor from its slider to ground. ;D
  5. audioguru2

    Pb-free soldering

    I have heard that if PB-free solder mixes with PB solder it makes a terrible mess. In the future, how will a technician or hobbiest know which one to use?
  6. audioguru2

    Electronic Stethoscope

    Hi Singhal, Welcome to our forum. That project has errors and doesn't work. I have corrected and improved it and posted it here: http://www.electronics-lab.com/projects/science/019/index.html 1) The bi-colour LED and the opamp driving it aren't necessary, it just looks nice. The bi-colour LED...
  7. audioguru2

    Frequency Detector

    You can't count cars by their sounds, unless you funnel them into a single lane with spaces between them. Besides, the doppler shift from the cars quickly coming and going would make bandpass filters count many more frequencies. Maybe you could bounce ultrasonic waves off the cars and detect...
  8. audioguru2

    Variable digital resistor???????

    Hi ArcAngel, I didn't want you to cheat and use nitro in the engine. Just spray it on the intercooler to allow the engine to breath cool, dense compressed air. Better cooling than water. I hope your fuel pressure and flow rate is high enough to match it. You know what running lean will do. I...
  9. audioguru2

    voltage amplifier

    Hi Npatel, Welcome to our forum. Amplifiers are designed for a certain output voltage (that you told us) and a certain output current. I could design a simple amplifier for you with only 1mA of output current, then find out later that it must provide 1000 times more. A completely different...
  10. audioguru2

    Variable digital resistor???????

    Hi ArcAngel, Why doesn't your car's computer provide your required timing? Maybe "so as not to blow up the engine"? Just cross your fingers and give it a shot of nitro! I wish I could trick my car's computer so it doesn't turn off the engine when I am passing and a big truck is coming at me...
  11. audioguru2

    Variable digital resistor???????

    Hi ArcAngel, Welcome to our forum. There is a Digital Pot project in our projects section. It uses an IC that steps a linear voltage divider from one end to the other end in 64 steps. It uses an up button and a down button. Before you use it, precautions are required to protect it from...
  12. audioguru2

    question about variable resistors??

    I am also not sure which bulb you will use. If you use a 100W bulb and turn it down to half-power, the variable resistor will heat with the other half of the power, 50 Watts! You would need 100 regular 1/2W variable resistors, or a huge expensive one. That's why people use inexpensive dimmers...
  13. audioguru2

    Electronic Stethoscope 2

    Hi Aminu, Welcome to our forum and greetings to Nigeria. I am glad that your project works very well. Its maximum volume is determined by the impedance of the headphones and their quality. 8 ohm headphones draw 4 times the power of 32 ohm ones, and "rare-earth" neo.....um magnets are more...
  14. audioguru2

    Electronic Stethoscope 2

    Hi Doctor Emad, It is good to hear from you. I played with circuits like this Low-Cost Hearing Aid circuit about 42 years ago! I am sorry but I don't like it: 1) Although it operates with a nice low supply voltage of 3V so it needs only two battery cells (or just a single 3V lithium cell), it...
  15. audioguru2

    Distortion

    Thanks for the compliment, Mukhalled. I am glad that you are using 15V instead of only 12V as in our project. Your problem is that your speakers are too small to have good efficiency and bass, and 4 ohms would produce more power than 6 ohms. If it is for a car, get 6" X 9" (15cm X 23cm) 4 ohm...
  16. audioguru2

    What oscillator/clock should I use

    I found another idea in this post that is not very good, but also found a good solution. Have you seen the price of a MAX 038? More than $23US! And it won't be very accurate but is probably OK to time an irrigation system. I would use inexpensive but very accurate parts such as a through hole...
  17. audioguru2

    Power Supply Meter Problem

    Yeah, but the importers sell the junk on e-Bay. What about the counterfeit semiconductors that come from China? Remember a few years ago when Chinese (made in Taiwan, actually) faulty electrolytic capacitors caused grief to many manufacturers of equipment? Recently I bought 20 Chinese...
  18. audioguru2

    Distortion

    Hi Mukhalled, What supply voltage, speaker impedance and speaker size did you use? Philips datasheet for their TDA1554Q states that it produces typically only 12W per channel with a 13.2V supply into a 4 ohm load, with fairly low distortion. It also shows that it loses 30% of its power when the...
  19. audioguru2

    negative supply

    Hi Rehanessa, Yes, you will have a dual-polarity supply, but only if the supplies have completely separate transformers or windings. You might be able to do it with a center-tapped transformer.
  20. audioguru2

    Power Supply Meter Problem

    Hi Woody, Since when is Chinese stuff bought at e-Bay good quality? :o You aren't measuring AC at high frequencies so try 0.01uF ceramic caps across the inputs right at the meters.
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