Hardware Reference
In-Depth Information
Figure 9.22
Optically isolated digital input for bipolar DC signals
Figure 9.23
Optically isolated digital input for AC signals
typical arrangement (the value of series resistance is the same as that required
for the circuit of Figure 9.21).
The optically-isolated input stage can be extended for monitoring AC voltages
as shown in Figure 9.23. This arrangement is suitable for AC inputs of up to
240 V 50 Hz and may be used to sense the presence or absence of a mains supply.
Input voltage (V)
Series resistor (R)
Diode (D)
range (RMS AC)
(0.25 W unless stated)
9to12
1k
1N4001
12 to 15
1.5 k
1N4001
2.7 k
15 to 24
1N4001
24 to 35
3.9 k
1N4002
50
6.8 k
0.5 W
1N4003
110
18 k
1 W
1N4004
220
39 k
2.5 W
1N4007
Sensors with analogue outputs
Having dealt with a number of common sensors which provide digital outputs,
we shall now turn our attention to a range of transducers which provide analogue
outputs. These outputs may manifest themselves as changes in e.m.f, resistance,
or current and, in the latter cases it will usually be necessary to incorporate
additional signal conditioning circuitry so that an analogue input voltage can
be provided for use with a standard PC analogue I/O card.
