Brigadoon - An Occasional Corner on the Internet
Build Ground Temperature Sensor
Designed by Mark Little
Each Ground Temperature Sensor consists of three components:
The prototype temperature sensor was constructed using the multiturn potentiometer as the carrier for the LM335 and the 1.8k Ohm resistor, using "dead bug" construction technique. This allows the construction of each sensor to be kept as small as possible making it easier to feed them down the pipe that holds the temperature sensors in the ground. Once the components are wired, a dab of an glue is added to hold the components in place. Care must be taken to leave clear points for connecting the three wires that must be attached to the sensor when placing it in the array wiring.

Although an epoxy glue like Araldite™ is suitable for holding the components in place, I find that it can be messy and I often mix too much glue for the job for these small jobs. I recently received an AtmosFlare™ 3D drawing Pen to play with, while recovering from an operation. After discovering that I have absolutely no artistic talent, I have taken to using the liquid plastic as a substitute for glue, and it works a treat for this sort of task.
LM335Z Temperature Sensor.
10k Ohm Multiturn Cermet Trimpot
1.8k Ohm Metal Film Resistor
Although attaching the temperature sensor to the trimpot may increase its thermal mass, this is not really important as the expected rate of temperature change in ground is rather slow and the sensor should be able to easily track the rate of temperature change.