Is the shield explicitly powered? It may be being phantom powered from
the control lines when connected to the PC which are not present when
connected to the Thunderbolt.
David McGaw N1HAC
On 6/3/15 12:38 AM, Dan Quigley 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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