Designing Ideas

In 1971, Signetics—later Philips—introduced the NE555 timer, and manufacturers are still producing more than 1 billion of them a year. As "NE555 timer sparks low-cost voltage-to-frequency converter" shows, by adding a few components to the NE555, you can build a simple voltage-to-frequency converter for less than 50 cents.

The circuit in "Optoisolators compute watts and volt-amperes" is an elaboration on that older circuit. It uses optoisolaters in a bridge circuit to measures not only watts, but also volt-amperes and so makes possible an estimation of power factor—watts divided by volt-amperes.

"Single-supply circuit measures -48V high-side current" uses an AD629 difference amplifier and an AD8603 operational amplifier, both from Analog Devices, to measure current at -48 to -60V and operates from a single positive-power supply, reducing circuit cost and complexity.

"Three-state switch interface uses one microcontroller pin" presents a way to sense three states of an SPDT (single-pole/doublethrow) switch with a center-off state, using only a single pin of Atmel's ATmega8 microcontroller. The Design Idea even provides a simple program for the circuit.

An ac-based continuity tester, in "AC-continuity tester finds single-ended faults in cables," for front-line test-and-repair jobs provides a simple go/no-go test for localizing faults in multiconductor cables. Open circuits are more likely to occur at the connector ends. This tool helps to identify the faulty end, thereby avoiding the risk of damaging a good connector by opening it.