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  1. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, My schematic looks lousy on this page, click on it to open it and it is clear. I used Microsoft Paint to copy, paste and add to the block diagram in the datasheet. Didn't you use my circuit for your test? It should work fine with a 10k collector resistor and any little NPN...
  2. audioguru2

    Infrared Activated Switch

    We were both wrong. The receiver's output is active low, when it receives IR. It will be pulled high by an 80k resistor when the beam is blocked. You certainly can connect the base directly to the reciever's output. The output is already an 80k  current-limiting resistor. Your 2nd transistor is...
  3. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, What are the transistors for? They both invert, so the output might be the same as the input, except: 1) The output of the receiver has a very high value pull-up resistor. So R1 isn't necessary
  4. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, I wouldn't use an old BFY51 transistor to drive 850mA. It is shown in my 1968 Philips databook! :o It doesn't have much DC current gain, a minimum of only 15 at 1A. Also, it doesn't saturate very well at its max current, its max saturation voltage is 1.6V at 1A even with a huge...
  5. audioguru2

    Infrared Activated Switch

    That is the "it won't time-out when the beam is blocked" problem I mentioned. Buy a transistor rated for 1A to 3A. Since the transistor has a minimum gain of 25, supply it with at least 850/25 X 1.3 = 44mA of base current to be certain that it saturates fairly well. ;D
  6. audioguru2

    Electronic Stethoscope

    Hi Xoy, Silicon Chip magazine has a heartrate monitor project. They use a sensor that detects blood motion in the skin with an LED and optosensor. They use a PIC to do the counting and drive to a 3-digit LED display. You can see the entire project for free if you enter into a Google search...
  7. audioguru2

    solder

    Hi Cody, 60/40 solder is alright. 63/37 solder was designed to work better. They cost the same so why not use the better one?
  8. audioguru2

    headphone motor project

    Hi Andy, Welcome to our forum. ;D The very small power that headphones require is much too low to drive a motor. Since the motor requires a high current, it will appear as a dead short to the circuit driving the headphones, possibly damaging it. Since an AC motor won't work with the wide...
  9. audioguru2

    Infrared Activated Switch

    An electrolytic capacitor provides poor filtering at the high frequency of the switching edge of the supply current spike caused by a 555. The 0.1uF ceramic disc capacitor is an excellent filter for medium-high frequencies due to its low inductance. At radio frequencies much smaller-values of...
  10. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, Since you don't care if the 555 doesn't time-out on schedule when the IR beam remains blocked, just connect the output of the IR receiver directly to the trigger pin 2 of the 555. The pull-up resistor in the output of the IR receiver will set pin 2 to +5V when it sees the beam...
  11. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal, Now your circuit certainly doesn't have a -12V supply. It has +12V and ground, or 0V. I am sorry you don't understand, I think explained my comments simply. What don't you understand? The end of the 10 seconds time period from the 555 is its "time-out". The datasheet for the...
  12. audioguru2

    C_B transistor impedance matching

    Hi Walid, I did a search for Common Base on Google and got links to 7,900,000 articles that all say that the input is the emitter and the output is the collector. Some articles say that the impedance at the emitter is simply hIE/hFE, but don't allow for the emitter resistor being in parallel. ...
  13. audioguru2

    telephone related question #4

    Hi Walid, A telephone feeds part of the mic signal to its earphone. A speakerphone needs to eliminate the mic signal from its speaker to avoid local acousical feedback howling. The transmitted mic signal is reflected back to its speaker at the telephone line, so frequently negative feedback is...
  14. audioguru2

    Infrared Activated Switch

    Hi Hamoodyjamal Genius! ;D Don't use a -12V supply with the IR receiver, it will blow up! :o Your circuit will work fine without the transistor, relay and -12V supply: 1) Use a well-filtered +12V supply for the 555 because it causes a huge current spike in the supply when its output switches...
  15. audioguru2

    transistor voltage regulator

    Hi Kevin, A linear voltage regulator has a reference voltage generated by a temperature-stable zener diode or band-gap device that is amplified and buffered from its load by a high input resistance opamp. The opamp drives a series pass power transistor that is in series with the load and...
  16. audioguru2

    VCR HEAD

    Hi Ante, I think Source shows the motor's slip ring contacts that connected to the spinning head. I think he wants to mount a circuit on the other side and needs a way to connect the circuit's power supply to the slip rings. Are the contacts for the slip rings in the small ribbon cable shown...
  17. audioguru2

    telephone related question #4

    Hi Walid, If its collector load has the correct polarity, then it conducts, creating a low voltage between its collector and emitter. A PNP transistor's collector has a negative supply to its load, and an NPN transistor a positive one. A PNP's collector pulls up and an NPN pulls down in a...
  18. audioguru2

    Keys finder circuit

    Hi Alun, The project's author is unknown, like me. ;D I keep my name a secret because sometimes I reveal bad things about my previous employers and manufacturers. I talked about the big skunk under my porch and I don't want more to find out where I live. It dug another hole under there again...
  19. audioguru2

    Hi,friends look at this

    It looks like a nice stereo FM transmitter, but does it work? ??? ???
  20. audioguru2

    telephone related question #4

    Hi Walid, I can't find a datasheet so I don't know if the mute pin has a PNP transistor's collector, an NPN one , a P-channel Mosfet's drain or an N-channel one. "Open collector" is just the bare collector of a transistor without a resistor load. When it is turned-off it floats, so the circuit...
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