[time-nuts] Thunderbolt/Arduino RS232 Interface Issue

Chris Albertson albertson.chris at gmail.com
Wed Jun 3 14:51:14 UTC 2015

In the RS-232 world devices are either DTE or DCE.  You need one of
each on each end of the line if using a normal straight cable.    To
connect two like devices you need a crossover cable (AKA "null modem")
    From the sounds of it I'm guessing the PC is a DCE and the Arduino
and Thunderbolt are both DTE.

On Tue, Jun 2, 2015 at 9:38 PM, Dan Quigley <danq at quigleys.us> wrote:
> Hello,
> I'm integrating an Arduino (Due/Mega have tried both) with a surplus Thunderbolt and need some advice.
> The Thunderbolt is a known working unit (supplies 10Mhz to my HPSDR rig) and the serial interface works fine between it and a PC.  I've read the coverage about this kind of integration (and some of the archived discussions on this board) and am employing a commercially available MAX232-based "shield" (RS232 V2) to handle the level translations.  Just three lines (RX/TX/GND) are  used.  The MAX232 circuit is working, reliably passing data between the Arduino and a PC.
> With the Thunderbolt is connected to the MAX232 no data passes.  Activity LEDs on the non-RS232 of the MAX232 circuit show no activity when the Thunderbolt is providing data, indicating the MAX232 is not performing the intended level translation.  I've scoped the RX/TX lines coming from the Thunderbolt both when connected to the Arduino and not.  There is a distinct difference. When disconnected, the pulses are about 10.3v and nice, crisp and square.  Connected, the pulses are ~50% lower in voltage (4.1v) showing an exponential rise in voltage and trace noise.
> I'm pretty much stumped at the moment and wonder if anyone can offer a suggestion or thoughts on a direction to take.
> Thanks in advance,
> Dan Quigley (N7HQ)
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Chris Albertson
Redondo Beach, California

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