[time-nuts] Temperature weirdness with Thunderbolt & Lady Heather 5

Pete Stephenson pete at heypete.com
Sat Dec 17 13:56:21 EST 2016

On 12/15/2016 3:05 AM, Pete Stephenson wrote:
> Hi all,
> I have a Thunderbolt and am running Lady Heather 5. I've been seeing
> odd drops of ~0.7 degrees Celsius that slowly recover over around 10
> minutes or so. This has happened 19 times in the last 36 hours.


Hi all,

I'm pleased -- but a little frustrated -- to report that I've been
unable to reproduce the issue after a few days of trying. A screenshot
of the happy Thunderbolt as shown by Lady Heather is attached.

At first, I thought the issue might have been a dodgy USB-to-serial
dongle, so I connected the Tbolt directly to the computer's hardware
serial port (which normally is connected to another device). The issue
immediately cleared up.

However, when I later reconnected the Tbolt to the same USB-to-serial
adapter (which uses a genuine FTDI chip) the problem did not recur.

The power supply is a used, Cisco power supply provided by the Chinese
eBay vendor that sold me the Thunderbolt. My digital multimeter showed
that the voltages provided were, while not dead-on -12V, +12V, and +5V,
were within the specs required by the Thunderbolt's manual.

Additionally, I probed the power pins with my oscilloscope both while
the Thunderbolt was powered off and also when I disconnected the power
connector. Visually, the traces appeared smooth, with no visible ripple
or spikes. The FFT function on the scope showed no spikes or anything
unusual between DC and 5 MHz (I didn't bother checking beyond that).

Since the Thunderbolt had been turned off for a few months to save
electricity, I thought that perhaps the issue only occurred when the
unit was started after being cold. I unplugged it and let it cool
overnight, then started it again. Again, nothing unusual. It's working fine.

The only other thing I can think that might have caused an issue is I
had recently connected another USB device (an Arduino Pro Micro
programmed as an EDtracker: http://www.edtracker.org.uk/) that had been
previously setup to use the same COM port number as the FTDI adapter.
Although Windows should prevent (or at least warn about) such conflicts,
it did not. It's possible that the output of the EDtracker was getting
mixed in with the serial data from the Thunderbolt and causing
corruption that Lady Heather interpreted as temperature and DAC excursions.

Unfortunately, I can't seem to replicate the issue, so I'm out of ideas.

In short: everything I can think to check seems to be ok.

Thanks to all for the help and suggestions, but I think this issue is
resolved for the time being.

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