data transfer cable

Discussion in 'The Projects Forum' started by frdfreak, Oct 5, 2008.

  1. frdfreak

    Thread Starter Member

    Sep 19, 2008
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    please help me Im trying to duplicate this cable but I know nothing about electronics can I run all the grounds through the same 1uf cap and how many volts is this cap? thanks Frankie
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    Last edited: Oct 5, 2008
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is no picture or anything else in this post.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    No, you can't use the same 1uF cap for all ground capacitors. They must be individual caps.

    I suggest a minimum 16v rating.
    You can replace the ZETEX ZMR500F with a 78L05. You could also use an LM317L, but you'd need to use two resistors to set it up to output 5v exactly. For the LM317L (or even a standard LM317T) a 120 Ohm resistor between the output and ADJ terminals, and a 360 Ohm resistor from the ADJ terminal to ground should do it.
    You can replace the MXST3904 with a PN3904 or 2N3904.
    You can use 1N4148 or 1N914 diodes instead of the RLS4148 diodes.
    The opamp should be the same one as specified.
     
    Last edited: Oct 5, 2008
  4. frdfreak

    Thread Starter Member

    Sep 19, 2008
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    thanks for the quick response just thought i would ask concerning the capacitor since they all go to ground directly
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, one side of each capacitor IS connected to ground. However, the signals on the other side of each capacitor is quite different.


    Note that the capacitor connected to pin 4 of the opamp is upside-down. This means that pin 4 is more negative than ground. The diode to the left of it is connected to RTS (pin 7 on a female DB9 connector). Notice that the anode is towards the cap. If the signal on RTS is a fixed low level or alternates between high and low levels, the most negative voltage will be accumulated in that capacitor.

    There are also capacitors on either side of the voltage regulator. This is very typical. The capacitor on the input side (from pin 4/DTR on the female DB9 connector via a diode) accumulates a positive charge, providing both the opamp and the voltage regulator with a relatively stable input voltage. The capacitor on the output of the regulator helps a great deal to smooth out transients (brief instantaneous current demands). Voltage regulators are fairly quick, but they do take some time to respond to changes in loads.
     
  6. frdfreak

    Thread Starter Member

    Sep 19, 2008
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    Ok, thanks so much. You made things a lot clearer for me. The only other issue I am having is finding a part number for the diode and what diode I should use. The part numbers on my schematic as well as the ones you had previously suggested I am unable to locate.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Radio Shack carries at least one version of everything I mentioned, except for the opamp.

    Not sure why they're using an opamp there offhand, but it's late and I'm tired.
     
  8. frdfreak

    Thread Starter Member

    Sep 19, 2008
    10
    0
    good enough thanks again for your time i have alot of mechanical skills but no experience with electronics im really impressed at the knowledge onthis forum and the speed of responces much appriciated.
     
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