Resistance

246 Hacking Electronics

Figure 11-1 Multimeter range selection

Resistance

The multimeter in Figure 11-1 has six resistance ranges, from 200MΩ down to 200Ω. If you pick a range that has a maximum resistance lower than the resistor you are measuring, then the meter will indicate this. Mine does so by displaying a “1” on its own without any further digits. This tells me I need to switch to a higher resistance range. Even better, start at the maximum range and work your way down until you get a precise reading. For the most precise reading, you need the meter to be on the range above the one that tells you it’s out of range.

When measuring highvalue resistors of 100kΩ and up, remember that you yourself are also a big resistor, so if you hold the test lead to the resistor at both ends (see Figure 11-2), you are measuring both the resistor in question and your own resistance.

Use test leads with crocodile clips, or pin the resistor to your work surface with the flat of the test leads.

Figure 11-2 How not to measure high-value resistors