Hardware Reference
In-Depth Information
Figure 9.29
Temperature threshold detector based on an AD590
semiconductor temperature sensor
Figure 9.30
Interface circuit to permit AC sensing
cycle. The circuit requires an input of greater than 10 mV for frequencies up to
10 kHz and greater than 100 mV for frequencies up to 100 kHz.
The obvious application the arrangement shown in Figure 9.28 is the detection
of audio frequency signals but, with its input derived from the low voltage
secondary of a mains transformer (via a 10:1 potential divider), it can also
function as a mains failure detector.
Output devices
Having dealt at some length with input sensors, we shall now focus our attention
on output devices and the methods used for interfacing them. PC-based systems
can readily be configured to work with a variety of different output transducers
including actuators, alarms, heaters, lamps, motors, and relays. Ready-built
output drivers are available for several types of load including relays and stepper
motors. Many applications will, however, require custom-built circuitry in order
to interface the necessary output devices.
Status and warning indications
Indicators based on light-emitting diodes (LEDs) are inherently more reliable
than small filament lamps and also consume considerably less power. They are
