Search results

  1. audioguru2

    design n develop electronic stethoscope

    There is an extremely simple electronic stethoscope in our projects section: http://www.electronics-lab.com/projects/science/003/index.html It is used in 3rd-world countries that don't have modern devices. I tried it and heard my heart beats. It has a modification to increase the cutoff...
  2. audioguru2

    LED project. :(

    RadioShack doesn't know anything about electronics and doesn't know if the cheap Chinese power supply has a regulated output voltage or not. The over-priced switch and jack are also probably cheap Chinese junk. Guess why RadioShack is gone from Canada?
  3. audioguru2

    LED project. :(

    Your selected power supply has an output of 4.5V when it has a 1600mA load. Its voltage is probably not regulated. When its load is only 600mA then its voltage might be 6V then each LED will have a current of 55mA and they will all burn out. Also the 47 ohm resistors will heat with more than...
  4. audioguru2

    LED project. :(

    If you want to connect lights in parallel then use incandescent light bulbs. Their voltage is accurate because they are electrical and mechanical. LEDs all have a different voltage even if they have the same part number. If you connect them in parallel then the ones with the lowest voltage hog...
  5. audioguru2

    0-30V Stabilized Power Supply

    A transistor can be tested with a new digital multimeter. In the low voltage ohm-meter function that supplies only 200mV so the juctions do not conduct, the collector to emitter should not conduct and the reverse-biased base-emitter and base-collector diodes should not conduct. In the...
  6. audioguru2

    0-30V Stabilized Power Supply

    Philip, You forgot to say which version you made. The original version has the opamps operating at a supply voltage that is above their max allowed voltage. The power transformer, the rectifiers, Q2 and Q4 are overloaded. Some of the resistors get too hot. Any of them could fail at any time.
  7. audioguru2

    AM Radio Activated Switch

    The fundamental strongest signal might be 30kHz, 200kHz or any frequency that divides correctly. A special radio tester (a spectrum analyser) can identify its frequency and the harmonics.
  8. audioguru2

    AM Radio Activated Switch

    Hi Daisy, The guy on the other website said that the fundamental frequency is 30kHz where the output is the strongest. If the waveform has distortion then it is not a pure sine-wave and has harmonics. If the output is a square-wave then harmonics of 30kHz are at 90kHz, 150kHz, 210kHz, 270kHz...
  9. audioguru2

    Too many SPAMMERS here

    Why does this site allow a new member (a SPAMMER) to post many threads or many replies to old threads? This morning I received e-mail notices of many replies to very old threads. They were all from one new SPAMMER who deleted all his replies. The Most Recent Topics index is jammed full of SPAM...
  10. audioguru2

    AM Radio Activated Switch

    Since you have an AM radio that gives some kind of output when it nears the transmitter's wire then use the radio's output to trigger your switch. Is your AM radio receiving the fundamental frequency or a harmonic from the transmitter?
  11. audioguru2

    Transistor biasing help

    A transistor is rarely used for current gain. It is almost always used for voltage gain. Without an emitter resistor a common-emitter transistor is a thermometer that is saturated when hot, when it has a high current gain and when its Vbe is low. It is cutoff when the conditions are the...
  12. audioguru2

    Transistor biasing help

    I drew load lines 47 years ago when I was in university. Never again. Pick an operating voltage for the collector so that the output will be symmetrical at full output, use an emitter resistor value that is 1/10th to 1/20th the collector resistor and use a divider current that is 10 times the...
  13. audioguru2

    Transistor biasing help

    The datasheet for a 2N3904 transistor says that its current gain can be anywhere from 100 to 300 when its callector current is 10mA and its temperature is 25 degrees C. Many 2N3904 transistors have different current gains and it changes with collector current changes and with temperature...
  14. audioguru2

    My own PSU-PCB (30 VDC / 0.002-3 A PSU REV2) [WIP]

    Thanks for attaching your schematic here. The widened tracks on the pcb are good. It is too bad that you changed many of the parts identification numbers since the original Q3 is your T1. I notice that you have the collector and emitter of your transistor T1 connected backwards.
  15. audioguru2

    power amplifier- pls help me

    But the power opamp is a push pull amplifier with a lot of loss (a Mosfet H-bridge should be used instead).
  16. audioguru2

    power amplifier- pls help me

    The 20k is the best one to change. But changing the 1k resistor also changes the gain. The formula for the voltage gain of a non-inverting opamp is the ratio of the feedback resistors plus 1. so the ratio of 20k and 1k is 20 plus 1= a gain of 21. It limits the max current to typically 3A to 4A...
  17. audioguru2

    My own PSU-PCB (30 VDC / 0.002-3 A PSU REV2) [WIP]

    Hi Leech, I think a pcb track of only 1mm is much too small for 3A at low loss. It should be 3mm to 5mm. Your narrow tracks probably will not burn out but their resistance will probably cause poor voltage regulation. Please attach your files here to your replies. ImageShack takes all day to...
  18. audioguru2

    0-30V Stabilized Power Supply

    The pcb traces will add a lot of unknown resistance and will destroy the accuracy of the current setting. 3A in only 0.0075 ohms produces a voltage drop of only 22.5mV which is fairly close to the input offset voltage of U3 so some ICs will read the current as being much too low and other ICs...
  19. audioguru2

    Question about CMOS ICs, specifically 4516B - presettable up/down counter.

    I get datasheets from www.datasheetarchive.com where I can select a datasheet from many manufacturers. I usually look at the datasheet of the manufacturer who invented the IC because their datasheet has the most details. RCA invented Cmos. Then Harris bought RCA's Cmos division then Texas...
  20. audioguru2

    0-30V Stabilized Power Supply

    The BD139 is in a very old case so its thermal resistance is high (it is difficult to cool). The 2N3055 output transistors have a lot of power to dissipate. It is easy for you to calculate the max power of a transistor, look up its max allowed temperature, decide how high you want the max temp...
Top