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The difference between sanity and being insane is an incorrectly wired capacitor — Parallax Forums

The difference between sanity and being insane is an incorrectly wired capacitor

NetHogNetHog Posts: 104
edited 2009-04-03 16:34 in General Discussion
I have, what is supposed to be a straight forward SX28 project. Port of which involves an MAX232N connected to PA0-PA3. The serial port gave me grief - I mean 2 weeks of grief.

I went through everything, checking my connections, making sure I had no shorts, making sure I had no dry joints. But all I was getting on the inputs was noise. I could not get a consistent level.

I put it down for a few days, and came back to it tonight. Pulled out the MAX232N. Verified the SX28 was reading inputs fine.·Replaced it with another MAX232N after checking for shorts, same result.

Finally took the circuit as implemented, and drew out the circuit diagram (a common test approach I use in software engineering). While doing so, I noticed one of the MAX232N capacitors (the one connected to pin 6 to be precise) was only half connected. I forgot to wire up the other terminal to ground. Doh!

Had to tell someone as I'm so glad I found the fault.
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Comments

  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2009-04-03 08:41
    So the software engineering approach taught you that you just needed a good grounding in electronics roll.gif

    *Peter*
  • stamptrolstamptrol Posts: 1,731
    edited 2009-04-03 13:09
    As an alternative, use MAX233 which has internal caps!

    Cheers,

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Tom Sisk

    http://www.siskconsult.com
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  • NetHogNetHog Posts: 104
    edited 2009-04-03 16:12
    Good one Peter [noparse]:)[/noparse] My degree was in electronics, I've just let it go by the wayside for many years, so lots of re-educating to do.

    Stamptrol: Found out about the MAX233 after I snapped up a couple of 232's. Actually next I want to look at a USB chip (per nuts&volts).
  • rjo_rjo_ Posts: 1,825
    edited 2009-04-03 16:34
    NetHog...

    I thought you might enjoy this... I learned that one of the ways of figuring out the innards of a stepper motor was to look at the various resistance values between the various lines... So, I started through my collection and came across an xy table that I wanted to bring back to life and not being able to find any documentation at all, I started looking at the resistance values and checking for continuity... I couldn't find any continuity between anything ... and the resistance values I found were in the M Ohm range. I put it aside figuring that even though I distinctly remember that this was a stepper motor driven table... maybe it was a really specialized stepper motor.

    The other day, I got it back out and took another look at it... and what I thought was a little stepper motor hidden in the shaft hole was actually just a coupler... there weren't any stepper motors attached[noparse]:)[/noparse]

    Of course, I don't have a degree in electronics... but even the school of common sense would revoke my degree[noparse]:)[/noparse]

    Regards,

    Rich
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