The operation of the Arduino Ohmmeter is based around the concept of the voltage divider. Two resistors are connected in series, and the reading is taken from where the two resistors join. The voltage measured at that point is the ratio of R2/(R1+R2) multiplied by the voltage in. For example, if R2 is 10K and R1 is 10K, then the ratio is 1/2; multiplying that by 5 volts returns 2.5 volts.
The Arduino Ohmmeter uses that relationship between voltage and resistance slightly differently. It knows that it started with 5 volts from the VCC pin. It also knows that the reference R1 has a value of 1K ohms. It then reads the divided voltage in at analog pin 0. Using those numbers, it is relatively easy to calculate the value of the object at R2.
A Fritzing electronic circuit schematic diagram of the Ohmmeter is shown in Figure 13-4. The Arduino Ohmmeter block diagram showing the connecting electronic components is shown in Figure 13-5. As a reminder, circuit schematic diagrams use electrical symbols for electronic components and are abbreviated drawings of Fritzing diagrams.
Figure 13-4. An Arduino Ohmmeter circuit schematic diagram
Figure 13-5. An Arduino Ohmmeter circuit block diagram
ELECTRICAL SAFETY TIP
Under no circumstance should the Ohmmeter be used to test powered electrical/electronic devices. For your safety and the protection of the Arduino and MakerShield, do not use the Ohmmeter to test any powered electrical/electronic devices!
Leave a Reply