Using a multimeter

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Measuring a voltage

First you will need to set your Multimeter to the appropriate Mode and Range. It should be "V"= or "DC" and a range of approximately 20 Volts. See your Multimeters Instructions if you are unsure.

The black probe of the meter should always be touching a grounded point. There are a few places at ground potential on the Shruthi-1 circuit board, they are labelled "GND".

When someone asks you, for troubleshooting purposes, what is the voltage at the 3 pins of a regulator, the procedure should be the following:

  • Keep black probe on a grounded point.
  • Put red probe on the first point and note down voltage.
  • Put red probe on the second point and note down voltage.
  • Put red probe on the third point and note down voltage.

Measuring voltages between adjacent pins is meaningless - the black or "COM" probe must be on a ground point.

Cheap Multimeters are sometimes a bit dependent on the Status of the and the tend to read higher Voltages if the Battery is near its End of Life. If the readings do not make sense, it's maybe time to change the batteries!

Measuring resistance

You can use a multimeter to check the value of a resistor before soldering it to the board.

You cannot use the multimeter to check the value of the resistor while it is soldered in the circuit. A multimeter measures resistance by sending current through the probes, measuring the voltage and applying [Ohm's law]. This works well with a resistor taken separately, but if you try probing a resistor within a complex circuit, the current sent by the meter will flow everywhere in the circuit, possibly through other resistors or diodes/transistors in the network, and ultimately only a fraction of this "probe" current will flow through the resistor, yielding a lower resistance value.

If you measure a single Resistor be sure not to touch both wires simultaneously, you will then read a (lower) false value as part of the probing current will run through your body. Yes, you are also a Resistor!

Testing continuity

One essential way of using a multimeter is for continuity testing which is useful when you want to make sure things that should have contact has, and things that shouldn't have hasn't. Most digital multi meters have a "Buzz" mode that will make a sound when the probes have contact either direct or via the pcb circuitry, but if they don't you can use the resistance measurement mode where zero, or close to zero, means you have continuity. You test continuity by simply putting one probe, black or red does not matter in this case, on the component leg that should, or shouldn't, have contact with another component and leg and your done.

Continuity testing should be done with the unit powered off.