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E84 Lab 1: Design of a Multimeter

The schematic diagram of a multimeter is shown in the figure below: MultimeterA2.gif


Following these steps:

How to find the polarity of a diode? (not necessarily trivial!)

When the voltage at the anode (labeled by a triangle) of a diode is higher than that of the cathode, the diode has a very low resistance (close to a short circuit, called forward biased). If the polarity is reversed, the resistance of the diode becomes very high (close to an open circuit, called reverse biased). The polarity of the diode can therefore be found by checking its resistance using a multimeter.

However, we need to know which lead of the multimeter (when used as an ohmmeter) is positive and which is negative. In most analog multimeters, such as the one you are building, the positive lead (marked by +) is connected to the negative end of the internal battery, while the other lead (marked by -, or COM for common) is connected to positive end of the battery. So if the measured resistance of the diode is low, the end connected to the COM lead of the multimeter is the anode (triangle).

However, the polarities of digital multimeters may be the opposite, i.e., the lead marked by + may be connected to the positive end of the internal battery. In this case, the polarity of the diode can be determined in the opposite way compared to the method above using an analog multimeter.

Moreover, some digital multimeters have a particular position for diode measurement.

Read this page for more detailed discussions.

How to solder?

If you have never done soldering before, you should find this and this useful.

next up previous
Next: About this document ... Up: lab1 Previous: lab1
Ruye Wang 2014-01-18