[time-nuts] Thunderbolt/Arduino RS232 Interface Issue

Paul Williamson paul at mustbeart.com
Wed Jun 3 02:05:09 EDT 2015

That sounds a lot like you have the Thunderbolt's TX pin hooked up to the
RS-232 Shield's TX pin, which is what would happen if you tried to use the
same cable that worked between the Shield and the PC or between the
Thunderbolt and the PC. To connect the Shield and the Thunderbolt you might
just need a null modem cable -- that is, one that swaps the RX and TX pins.

  -Paul KB5MU

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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