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  1. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, The 12VAC output of a fully loaded 12V transformer has the same heating power as 12VDC. Since the AC voltage changes polarity, it frequently passes through zero volts when it provides no power. In order for the average power to be the same as with 12VDC, the AC peak voltage is...
  2. audioguru2

    Automotive 12V to +-20V converter

    It doesn't matter because the resistance and impedance of the coil L1 is very low. The current comes from the entire secondary winding, not from only half of it. Since one end of the secondary is positive and the other end is equally negative, the center-tap is at ground voltage. The...
  3. audioguru2

    Automotive 12V to +-20V converter

    Kevin, Coil L1 is just a piece of wire to ground, with a small inductance to slow-down  the fast charging current of the filter capacitors when the positive and negative loads are unbalanced. Since the center-tap is grounded, when one end of the secondary is positive, the other end is negative...
  4. audioguru2

    Automotive 12V to +-20V converter

    Of course it is a full-wave bridge rectifier and with the seconday's center-tap grounded, produces positive and negative voltage outputs. L1 connects the center-tap to ground and doesn't have any current through it when the positive and negative load currents are equal. ;D
  5. audioguru2

    i need a transistor specification

    www.datasheetcatalog.com
  6. audioguru2

    Automotive 12V to +-20V converter

    Kevin, Which circuit did you build? This project does have a center-tapped transformer.
  7. audioguru2

    Replacement of two components

    Hi Shaiq, The BB109 varicap diode is obsolete, so I couldn't find its details. It changes its capacitance when its reverse voltage is changed. There are many other more modern varicaps. I wouldn't use an LED because its max reverse voltage rating is only 5V, and its capacitance usually isn't...
  8. audioguru2

    Silly Question

    Hi Birdie, Your switch is probably a double-pole, double-throw one. Its center pin on each row connects to an end pin, then to the pin on the other end when it is switched. ;D
  9. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Tedy, Who knows how long your 44V-rated opamps will last with excessive supply voltage? ??? If you can't get the high-supply-voltage-rated OPA445AP opamps that I recommend, then the transformer should have an unloaded voltage of no more than 28V, which would be about 26V when fully loaded and...
  10. audioguru2

    frequency detection without oscilloscope

    Hi Glass-Giant, I used a smiley because I'm glad to have an accurate frequency counter in my portable Digital Multimeter. I thought everyone knows to use a frequency counter for measuring frequencies. ;D ;D Hi Cody, Your TSOP1738 is designed for data, not for continuously modulated IR. It has...
  11. audioguru2

    frequency detection without oscilloscope

    My portable Digital Multimeter has a very accurate frequency counter built-in. ;D
  12. audioguru2

    transformer

    Hi Cody, Use a 7805 regulator since most things are spec'd to operate at 5V, but many shouldn't have a supply as high as 6V. The 7805 needs a DC input voltage from your DC adapter of at least 8V to regulate properly. If your DC adapter has an 8VDC output then the ripple in it reduces the minimum...
  13. audioguru2

    0-30 Vdc Stabilized Power Supply

    Hi Tedy, It is great to hear you say that your project works well! ;D Did you build the modified version? In order for the offset voltage adjust trimpot to work with the TLE2141 opamp, the value of RV1 must be changed from 100k in the parts list to 5k, and the value of R10 must be changed from...
  14. audioguru2

    cd4541 rc timing calculation

    With a long timer project you simply adjust the time of a shorter count sequence, then multiply it by the remaining counter stages. ;D
  15. audioguru2

    telephone related question #4

    Hi Walid, In a telephone handset the mic signal is fed to the earpiece so that the user can hear himself. This is called sidetone and you can look at this definition in Google. Speakerphones usually try to cancel as much mic signal from being fed to the speaker as possible, to avoid local...
  16. audioguru2

    cd4541 rc timing calculation

    Maybe a moderator could correct this topic's erroneous spelling. A CD4511 is a 7-segment driver, not this CD4541 timer. :(
  17. audioguru2

    cd4541 rc timing calculation

    The CD4541 is perfect for this 5 minutes run time application. Just select the divider and calculate an oscillator frequency. The oscillator's frequency can be varied quite a lot with a pot, to make a variable-time timer. ;D
  18. audioguru2

    Infrared Activated Switch

    Did you measure the supply voltage? A 12VAC transformer's output might be 16V when it is not fully loaded, and rectifying and filtering it could result in 21.2V. The absolute max for an ordinary 555 is 18V and only 15V for the Cmos version. What is its load? What is regulating the 5V for the IR...
  19. audioguru2

    cd4541 rc timing calculation

    The CD4541 timer already has an oscillator and a divide by 256 to 65,536 counter built in.
  20. audioguru2

    Infrared Activated Switch

    AGC is Automatic Gain Control.
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