Hardware Details

Electronics 

The detailed circuit diagram, and corresponding derivations, are available here: Circuit Diagram and Voltage to Temperature Derivations

Thermistors:

235-1625-ND: FP 07 FAST TIP PROBE, 150 Kohm, at 25C

AAS-920-267D-Thermometrics-NTC-TypeFP07-041216-web.pdf

self-heating is 1C per 50 uW of power dissipation. Resistance is 150K at room temperature. Still-air thermal time constant is 100 msec. 

plot of temperature increase vs. applied voltage across thermistor:

The problem with self-heating is that we are increasingly sensitive to local windspeed rather than temperature. We definitely don't want to exceed one volt across one thermistor, or 2 volts across both of them. 

Paper on thermal time constant measurements in still and moving air: [15200426 - Journal of Atmospheric and Oceanic Technology] Time Constant Estimates for Radiosonde Temperature Sensors.pdf

Reference Resistors: 

• Replace thermistors in test lines 
• All are 5% 150 kOhm resistors 

Wiring:

Note: for the two reference lines (thermistor + resistor and resistor + resistor), a resistor might replace a thermistor in the description below.  The wiring scheme is the same for all 5 lines, whether thermistor/thermistor, resistor/thermistor, or resistor/resistor. 

• All lines are twisted pair, shielded wires
• For main line (that which includes both thermistors):
  • low wire (black wire) is connected to low end of power supply (which can be ground)
  • high wire (red wire) is connected to high end of power supply
  • Top thermistor in voltage divider configuration is soldered directly into high (red) wire
  • Bottom thermistor in voltage divider connects high and low (red and black) wires 
  • Shield is connected to ground (unattached at the end with the bottom thermistor)
• For the sample line (running off of midpoint of voltage dividers) 
  • High (red) wire is soldered to the middle side of the top thermistor (side between thermistor pair) 
  • Low (black) wire is shorted to shield
  • Low (black) wire and shield are connected to ground on measurement end of array, unconnected on end connecting to thermistor

ADU Board 

Jim's Arduino-based hardware

Arduino Model: MKRZERO

To use on Linux, install Arduino IDE. Next go to Tools > Board: <some-model-name> > Boards Manager...

In the Boards Manager, filter by MKRZERO, and install the Arduino SAMD Board drivers. Change the board model to MKZERO via Tools > Arduino SAMD ... Boards > Arduino MKRZERO.

Next, ensure your user is part of the `uucp` and `dialout` groups via

sudo usermod -a -G dialout -G uucp <user>

If you are unsure what the pointer to the device is, run

sudo dmesg --follow -T

and unplug/plug the device. You should see output with information about the device. You are looking for something like

/dev/ttyACM0

Finally, whenever you plug/unplug the device and get `Permission Denied` errors, add rw permissions to the file

sudo chmod a+rw /dev/ttyACM0

Now you can ingest the serial stream using Python, or in the Arduino IDE via Tools > Serial Monitor.