Investigating LED Stability for Applications in Automated Resistance Measurement Systems

We explore the potential use of LEDs for an automated resistance measurement system. Our system utilizes an LED in combination with a CdS cell to serve as a voltage-controlled resistor (VCR), which forms one arm of a Wheatstone bridge. The viability of this LED based method is shown through tests of the stability, range and accuracy of the resulting resistance measurements. Preliminary testing found that although the system performed well, long term drift in the LED input voltage was observed which would require frequent recalibration of the system to maintain measurement accuracy.