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  1. poor mystic

    Op amp problem ua741

    Hi I just wanted to suggest the LM318, which is capable of replacing a 741 on pretty well any circuit board but has way better specs and can deal with rail-to-rail input voltages. The data sheet: http://vakits.com/lm318-smt-high-speed-op-amp-ic
  2. poor mystic

    Omnidirectional Ultrasonic transmitter

    I've had a further day to think... If you use back-to-back frisbees instead of LP records, you'll get a much better acoustic match between the transducer and the atmosphere, because of the rounded edge of the frisbees. If you're interested there are tricks to use to help get the match perfect...
  3. poor mystic

    Omnidirectional Ultrasonic transmitter

  4. poor mystic

    Omnidirectional Ultrasonic transmitter

    I think it's pretty easy to engineer this waveguide. It really will work using a couple of LP records! All you need is to fit your transducer to the hole in the middle of the top LP, block up the hole in the bottom LP, and put in a few small spacer blocks to keep the 2 discs the right distance...
  5. poor mystic

    Omnidirectional Ultrasonic transmitter

    Hi I think that you need a waveguide. It is difficult to design a waveguide with true omnidirectionality, but easy enough if all you really need is 360° on a plane. Here's an idea how to engineer an anisotropic planar wavefield given a point source transmitter. Imagine you have 2 discs, like LP...
  6. poor mystic

    Triac Testing

    :) Usually you'd expect to find a diode, testing across the main terminal of a triac.
  7. poor mystic

    ribbon controller

    , :-) well, there's this: http://www.paia.com/ProdArticles/dual-ribbon-howto.htm I think we'd like to know how you get on. :-)
  8. poor mystic

    Help with signal leaking to power input

    Perhaps if the Darlington fails again you might try replacing it with a higher specification unit, and/or a heatsink.
  9. poor mystic

    Effect of humidity on MOSFET over time

    What did you observe? :-)
  10. poor mystic

    Effect of humidity on MOSFET over time

    :) Isn't there some evidence that small scale channels (in IC's) tend to change in a similar way to the ways that the flow of water changes the shape of rivers?
  11. poor mystic

    Lm386 Audio amplifier

    Hi :-) Most designs use at least one more stage of amplification, depending on how much power is wanted at the output. I personally like DC amplifiers with long-tailed pair inputs and FET output transistors, but perhaps they're out of fashion by now...
  12. poor mystic

    How can we Improve EP in 2017?

    Hi Ian and members :) I say that the forum is as good as its members are helpful to one another. Kindness and service to others might be good things to reward, both for the sake of the rewarded individual and for the sake of the community. Mark
  13. poor mystic

    12V relay with 9v battery_not working

    :) Hi and hope y're happy The tick sound is made when a metallic switch moves inside the "relay" block. When you press your button, electric current flows through a coil, which makes a magnetic field around the relay (which you could detect with a compass). The magnetic field causes a metallic...
  14. poor mystic

    Interfacing with old phone mic/speaker.

    :) Hi Mitch I'd "suck and see" with the speaker question, and if there wasn't enough oomph in the result I'd think about amplification. I'd be very careful with bringing the microphone into the sound card though.There could easily be an inconvenient DC voltage in a telephone. I hope you can...
  15. poor mystic

    Repairing old stereo

    I've been for a look myself, and although I did find, and download, a manual there wasn't any description of the electronics included. It might not be possible to operate either board without the other; in other words you might need both boards. I think myself that it would not be in Samsung's...
  16. poor mystic

    Repairing old stereo

    Hi :) to find out whether your job is possible, we need to gather information. @shrtnd is quite good at that sort of thing, give him a chance!
  17. poor mystic

    CNC machine, Shapeoko 2 or 3, or XCarve Kit

    https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjejM3Oy-3NAhUDi5QKHW1sCbQQFggmMAE&url=http%3A%2F%2F3dtek.xyz%2Fblogs%2Ftechnical-docs%2F19171599-shapeoko-vs-x-carve-vs-heavy-mill-choosing-a-cnc-router&usg=AFQjCNFCKWb39pz_zZ9KKa9nFh7-irws1g&sig2=Eg30A_C...
  18. poor mystic

    How to test a capacitor

    Hi :) See if there's current going in, see if the right voltage is coming out, try and burn your finger or otherwise see if the chip is hot. PS the chip ought be hot
  19. poor mystic

    How to test a capacitor

    Hi :) Internal leakage in electrolytics, at rated voltage or below, can cause problems. These problems often appear in the circuit as noise.
  20. poor mystic

    Transformer Help!!

    Hi and wow! What is this voltage to be used for, please? I'm sure that'll be a question of interest to the moderators... :)
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