A handy tester suitable for universal AC and DC supplies

When measuring voltages around the home, in the lab, or out in the field, some kind of voltmeter – either a traditional moving coil type, or a digital “multimeter” version – is usually indispensable. However, there are many instances where a basic “go/no go” indication is more than sufficient. For example, when tracing a fault in a car electrical system, or when checking a mains circuit to see whether it is “live”, a simple “yes” or “no” visual indication can be the easiest and quickest way of checking for a healthy voltage supply.

In this respect, an l.e.d. (light emitting diode) provides an ideal solution. Unlike an incandescent filament bulb, the l.e.d. does not require much power, and it can operate at very low voltages where traditional neon indicators have not got a chance. However, using an l.e.d. to indicate the presence of a voltage ranging from less than 3V to more than 200V – both d.c. and a.c. – requires something more than just a resistor and a suitable l.e.d.

Housed in a small plastic case, the Volts Checker is a handy, pocket-sized instrument that can be used to check an a.c. or d.c. voltage as low as 3V or as high as 240V r.m.s. (root-mean-square). Using the unit could not be easier – just connect the two leads to the circuit under test and the l.e.d. will illuminate if there is a healthy voltage present.

Furthermore, there is no need to worry about which node is positive and which is negative, the unit automatically senses any d.c. voltage regardless of polarity. Alternating voltages, such as those produced by step-down transformers in consumer equipment or high-voltage mains domestic circuits, are dealt with just as easily.