 | Author | Message | | | eric | | Posted: Thu Oct 05, 2006 2:29 am Post subject: Infra-red sensor/monitor | | | | Site Admin Joined: 01 Jan 1970 Posts: 311 | A Maxim Application 047
The sensor/monitor shown in the diagram ‘wakes up’ the host system
on detection of infra-red (IR) signals. It draws so little supply
current that it can remain on continuously in a notebook computer
or PDA device. Its ultra-low current drain (4 μA maximum, 2.5 μA
typical) is primarily that of the comparator/reference device, IC1.
The circuit is intended for the non-carrier systems common in
infra-red Data Association (IrDA) applications. It also operates
with carrier protocols such as those of TV remote controllers and
Newton/Sharp ASK (an amplitude shift keying protocol developed
by Sharp and used in the Apple Newton). The range for 115,000-
baud IrDA is limited to about 6 in (15 cm), but for 2400-baud
IrDA, it improves to more than 12 in (30 cm).
Immunity to ambient light is very good, although bright flashes
usually cause false triggers. To handle such triggers, the system simply
looks for IR activity after waking and then returns to sleep
mode if none is present.
The sensor shown, D1, a relatively large-area photodiode packaged
in an IR-filter material, produces about 60 μA when
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