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  1. audioguru2

    Voltage Regulator LM317 to 120ohm or to 240ohm

    Hi Jhanus, The datasheet shows 240 ohms as R1 with a more expensive LM117 on its first page. The spec's in the datasheet show that an LM117 costs more than an LM317 because its operating current has a max amount of only 5mA but an LM317 has a max amount of operating current of 10mA. The...
  2. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Tinny, Welcome to our forum. ;D Your project has a few problems: 1) the 741 opamps have a positive supply of 33.8V as you measured plus a negative supply of 5.6V for a total of 39.4V. Their absolute maximum voltage allowed is only 36V so maybe they are broken. 2) Your transformer has only a...
  3. audioguru2

    icl7106 + LCD (help this amateur girl)

    Hi Zeeq, You saved your schematics as very fuzzy JPG file types which are very difficult to see. Next time, please save schematics as very clear GIF or PNG file types like this comparison:
  4. audioguru2

    Speaker selector project

    You have a stereo amplifier and one wire from each speaker is connected to ground. If you disconnect both speakers from ground with a SPST switch but leave the speaker wires connected together then the speakers will play Left minus Right which is a form of surround sound. The speakers are still...
  5. audioguru2

    Op-amp recommendation?

    Hi Ante, Farnell bought Newark in the US and they don't have any MC33172's in a DIL case. Digikey in the US also don't have any. They both have lots of surface-mount ones.
  6. audioguru2

    The caps surrounding the LM7812 regulator?

    You can buy a 7805 voltage regulator for $.60US each at Digikey. It has one power transistor, 16 small transistors, two zener diodes, two capacitors and countless resistors. It regulates well. You can also buy a cheap TIP31 power transistor in the same case for nine cents more: $.69US.
  7. audioguru2

    The caps surrounding the LM7812 regulator?

    The 7812 has a typical output voltage change of only 10mV when its input voltage changes from 14.5V to 30V. Its output voltage changes typically only 12mV when its output current changes from 5mA to 1.5A. A 7805 is even better because it has more negative feedback. Its output resistance at DC...
  8. audioguru2

    white led

    I think 0.56V across the 27 ohms resistor is fine.Then the LED current is 20.7mA. You could replace the 27 ohms resistor with 22 ohms then the current would be 25.5mA and the LEDs would be a little brighter.
  9. audioguru2

    white led

    Maybe the pins on the ST13005 transistor are also connected backwards. This is what the voltages should be:
  10. audioguru2

    Electronic Stethoscope

    Hi Subodhthok, You must design the interface circuit yourself or ask your teacher to help you. The output pulses of U5 are only plus and minus about 3V if the batteries are new, and only 2V if the batteries are old. A rectifier would reduce it to be too low to drive logic circuits. The output...
  11. audioguru2

    white led

    Hi Pier, Good, you fixed it! The LED current flows through the 27 ohms resistor. Ohm's Law says that the current is the voltage across the resistor divided by its resistance value. If the 27 ohm resistor has 0.65V across it then the current in the LEDs is 24mA. The absolute max continuous...
  12. audioguru2

    white led

    Hi Pier, The base-emitter of the ST13003 is supposed to be a forward biased diode with a max voltage of 1V. You measure 13.7V so I think you connected its base and emitter pins reversed, causing the base-emitter to be reverse-biased and acting like a 13.7V zener diode.
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    C5. C6 and C9 keep the output from oscillating.
  14. audioguru2

    Op-amp recommendation?

    Hi Mark, I use "ordinary" opamps. They aren't rail-to-rail but almost. The MC3317x and MC3407x have a supply voltage down to 3V, an output that goes down to ground and have a much wider bandwidth and much lower distortion than the old LM324 quad and LM358 dual opamps. I have some MC33172 dual...
  15. audioguru2

    Electronic Stethoscope

    Hi Subodhthok, Welcome to our forum. ;D It is good that it works perfectly. The circuit has AC signals. Digital counters use DC pulses, not AC as their input. In order to count heartbeats then the signal must be rectified into DC pulses but the polarity of the pulses might be negative instead...
  16. audioguru2

    0-30 Vdc Stabilized Power Supply

    A huge difference. The BC548 has a max current rating of only 100mA and max power rating of only 625mW. A 2N2219 has a max current rating of only 800mA and a max power rating with a clip-on heatsink of only 1.6W. The recommended TIP31A has a max current rating of 3A, a max power rating of 40W...
  17. audioguru2

    Op-amp recommendation?

    Hi Mark, Rail-to-rail, low supply voltage opamps are fairly new. New ICs are in surface-mount packages only. You don't say where in the world you are so I don't know what is available for you.
  18. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Jhanus, Others recommend adding trimpots in series with the voltage and current adjustment pots for calibration of 30.0V and 3.0A. A few pcb designs have also been posted in this thread. Here is my recommended list of parts for this project:
  19. audioguru2

    Site Accessing Trouble

    I also couldn't get into this site for a few days. I also couldn't get in a couple of hours ago. I changed my IP address and now this site loads fine.
  20. audioguru2

    white led

    Post the DC voltages at various parts of the operating circuit without electrocuting yourself. The voltage across the 27 ohm resistor should be about 0.65V then the LED current is 0.65/27= 24ma which is a little less than their max allowed continuous current of 30mA. Check which pin is which on...
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