How accurate is an Arduino Ohmmeter?

Abstract

The Arduino platform is widely used in education of physics to perform a number of different measurements. Teachers and students can build their own instruments using various sensors, the analogue-to-digital converter of the Arduino board and code to calculate and display the result. In several cases this can mean incautious reproduction of what can be found on the Internet and an indepth understanding can be missing. Here we thoroughly analyse a frequently used resistance measurement method and show demonstration experiments as well to make it clear. Construction of the OhmmeterA wide range of experiments and solutions are shown where sensors and the Arduino platform are used to teach physics efficiently and attractively while the cost is kept very low [1][2][3][4][5]. Sensors have an output (voltage, current, resistance, capacitance, inductance) that can be handled by electronics.Since an analogue-to-digital converter (A/D converter, ADC) has voltage input, some circuitry is needed to convert the sensor's output into voltage that fits in the input range of the ADC. Like in any measurement, a reference is required. The Arduino board's ADC accepts an input voltage in the range from 0 V to VREF, where VREF is the reference voltage. Digital sensors incorporate all of these plus a digital data interface.The simplest way to measure resistance is to build a voltage divider which has an output voltage that depends on the unknown resistance, see figure 1. This is the common method applied in Arduino Ohmmeter projects published on the Internet.

Phonocardiography and Photoplethysmography With Simple Arduino Setups to Support Interdisciplinary STEM Education

“…Arduino is a very popular single-board computer platform used extensively in STEM education [10]- [13]. Many different solutions can be implemented and the students have the possibility to see and work with almost all of the components of real and virtual signal processing shown in Fig.…”

Comment on ‘Resistance of a digital voltmeter: teaching creative thinking through an inquiry-based lab’

“… The accuracy is fairly good.  It can be easily implemented on devices that have voltage inputs like Arduino [2,3].  The series resistor's value can be gradually reduced to see how the voltage measurement error caused by the input impedance decreases and gets insignificant below a threshold.…”

Comment on ‘A low-cost cryogenic temperature measurement system using Arduino microcontroller’

“…According to the above, it is hard to believe that a maximum of 2 K error can be expected from this system, the observation could only be accidental, we think. This error is even less than the resolution of the measurement, significantly smaller than the error specification of the A/D converter of the microcontroller [3] and the varying current is far from what is required for proper sensor biasing.…”

“…This is another reason why it is so surprising to observe maximum error close to 2 K. However, if the sensor is operated in such conditions what is required according to the datasheet, and the specified sensor characteristics are used to convert the forward voltage to temperature, then one can obtain good accuracy even without calibration. This is a real advantage, since calibration needs expertise, costly instruments, very carefully prepared conditions [3]. The inherently high accuracy of the DT-670 sensor will be degraded very likely if the unnecessary calibration procedure mentioned in the paper is executed.…”