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Auto ranging ohmmeter using arduino

This article is about a simple auto ranging ohmmeter using arduino. The measured resistance is displayed using a 16×2 LCD display. The circuit is sufficiently accurate and uses minimum number of external components possible. Before going into the details of this project, lets have a look at the basic resistance measurement method.
Resistance measurement.
The figure above shows the circuit diagram of a simple resistance measurement scheme. Rx is the resistance to be measured. R1 is the input resistance. i is the current passing through the loop and 5V is the supply voltage. To find the unknown resistance Rx, the voltage across Rx is measured first. let the voltage across R1 be VR1. Then VR1=5-Vx. The current i=VR1/R1=(5-Vx)/R1. Since R1 and Rx are connected in series, the current through them will be equal. So the unknown resistance Rx= Vx/i. The voltage across the unknown resistance is measured using the ADC of the arduino. To be precise, analog channel A5.
Anyway this method have a …