  We developed a simple, flexible, low-cost, and computer-controlled cryogenic
temperature measurement system for undergraduate instructional laboratories. An
Arduino microcontroller board measures the voltage across a silicon diode to
calculate its temperature. Resistors and a voltage regulator provide constant
current into the silicon diode. We present a graphical user interface based on
the open-source Processing language. The cost of the complete temperature
measurement system is thus only a small fraction of any highly-developed
commercial system. Our performance test shows that the system works at a
reasonable accuracy from 297.15 K (typical room temperature) down to 77 K
(liquid nitrogen temperature).
