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  1. KrisBlueNZ

    Problems substituting a relay

    Paul, I'm sorry, my earlier calculations were wrong. I apologise. I clearly do not fully understand the way power is transferred through the input capacitor to the circuitry. I tried simulating the circuit in LTSpice and found that the value of the input capacitor is far too low. At values...
  2. KrisBlueNZ

    What value of resistors do I need and a sanity check

    I tend to agree about "ineffective". I got the same impression reading the Wikipedia page. It sounds like pseudoscience to me, but it's hard to be sure. That's pretty cool! I checked out the data sheet for the Littelfuse series, at http://www.littelfuse.com/data/en/Data_Sheets/272_273.pdf and...
  3. KrisBlueNZ

    What value of resistors do I need and a sanity check

    Thanks Chris :-) I obviously have much too much time on my hands. I need a job :-/ Agreed. After reading the relevant Wikipedia page I can see a few things I would do differently if I was designing the current generator, but I'm cautious about suggesting anything because of the application. If...
  4. KrisBlueNZ

    What value of resistors do I need and a sanity check

    See http://en.wikipedia.org/wiki/Transcranial_direct-current_stimulation The electrodes are prepared with saline solution and the skin at the contact area is prepared with "electrode cream".
  5. KrisBlueNZ

    What value of resistors do I need and a sanity check

    Nice one Dave, that looks just right. That's right, it's just a matter of experience and knowing what's available and how things are done. You can learn a lot from taking things apart. You're supposed to wait until the thing is broken, but when I was young I discovered a shortcut - break it in...
  6. KrisBlueNZ

    What value of resistors do I need and a sanity check

    I think his reason was that he thought you could indicate the setting of the potentiometer with the meter. But that's not possible. And the diode won't work, because the LM334's current is set by the resistance between -V and Rset and you can't have a series diode in that path.
  7. KrisBlueNZ

    New Power Supply

    Yep! It's worth doing a nice job for something you'll use often.
  8. KrisBlueNZ

    What value of resistors do I need and a sanity check

    The right side of the potentiometer needs to be connected to the same place as the other four resistors, i.e. to the left side of the fuse, and you also need a resistor in series with the potentiometer. Thanks Dave.
  9. KrisBlueNZ

    What value of resistors do I need and a sanity check

    jjanes, I want to clarify something. Connecting ANY circuit to electrodes attached to your head has certain risks. I and others on this thread have made suggestions in good faith and on the basis of the information you have given us so far. You must accept the final responsibility if you...
  10. KrisBlueNZ

    What value of resistors do I need and a sanity check

    Nice work davenn :-) I have a few corrections for you to make if you want to. The centre pin on the LM334Z is called "Rset" not "RESET". The potentiometer needs a resistor in series with it to limit the maximum current, and needs to be returned to the same place as the other resistors...
  11. KrisBlueNZ

    New Power Supply

    Looks nice alfa! One tiny point. I would put a small resistor, say 1K, between the wiper of each current limit adjustment pot and the base of the transistor. Without it, at the minimum current setting, you have the base-emitter junction of a small transistor connected straight across the...
  12. KrisBlueNZ

    What value of resistors do I need and a sanity check

    jjanes, I don't think you need to worry about being "banned from the forums" for posting a thoughtful, rational and measured comment like that. But I can tell you for sure that TELLING US ABOUT YOUR PROJECT will be a big help towards getting people "on your side". Edit: actually, your original...
  13. KrisBlueNZ

    What value of resistors do I need and a sanity check

    To summarise the comments so far and add some of my own. 1. Your schematic, and the original schematic, are drawn in a confusing way. It is normal to put the main negative rail at the bottom of the schematic (unless it uses all PNP transistors, but that's another story). That means the negative...
  14. KrisBlueNZ

    Why does speaker on output click twice on 555 timer output?

    You're welcome :-) "Charge" is not the right word. The speaker responds to current. When the 555 output goes high, current flows from the 555, through the limiting resistor and through the coil in the speaker, creating a magnetic field, which interacts with the static magnetic field created by...
  15. KrisBlueNZ

    spreading out the PWM on a PIC16F627a

    If you want really useful suggestions, you need to post a LOT more detail on what you want. Show us how the LEDs are going to be arranged, describe exactly how you want them to behave. Tell us what PIC you're considering. Don't worry, no one will steal and patent your idea before you've finished...
  16. KrisBlueNZ

    on/off light switch/controller

    Will there be an issue with ambient light falling on your receiver? It's common in these cases to modulate the transmitted light at a certain frequency, and filter the receiver output to detect that frequency, so that your circuit detects the light from the emitter and is immune to ambient...
  17. KrisBlueNZ

    Why does speaker on output click twice on 555 timer output?

    I have two answers. First, why a sudden movement in a speaker cone "sounds like" a click. Second, how a series capacitor affects the movement of the speaker. Assuming your speaker is directly connected to the output of the 555 (without a coupling capacitor) (which I hope is not the case), each...
  18. KrisBlueNZ

    Amplifier circuit for speakers

    BTW, all I'm trying to do on this thread is defend the OP's desire to (as I see it) do something practical before getting into a lot of theory. I absolutely agree that theory is essential, but I don't think he's damaging his chances of learning theory properly by doing something simple and...
  19. KrisBlueNZ

    Amplifier circuit for speakers

    I guess it depends on the nature of the distortion, but it's actually very hard to hear plain old harmonic distortion. The trend towards THDs of 0.01%, 0.001% and lower is mainly a marketing race IMO. There isn't much research but from what I can glean from a quick web search, THD becomes...
  20. KrisBlueNZ

    Amplifier circuit for speakers

    I wouldn't assume a kitset based on the STA540 will be inferior. It's a good quality IC and it and similar devices are used in commercial products. I wouldn't be surprised if the Bose amplifier was based on something similar. It's a good way to get high performance for low cost. I don't think...
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