(Note: below the "About the Authors" is a reader's comment, and the response of one of the authors.)
Receiving infrared (IR) signals while conserving system power is difficult, and typically requires the inclusion of complex power-management routines in the firmware. You can avoid that problem by disconnecting power to the microcontroller when IR is not present, Figure 1.
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Figure 1: This circuit withholds power from the attached microcontroller until it detects an IR transmission. While in standby mode, its quiescent current is under 2 μA.
U1 holds the attached microcontroller in an ultra-low power-down state until the phototransistor (Q1) detects an IR signal.
Upon detecting an IR signal and after a suitable delay (300 ms in this case), the circuit connects power to the microcontroller and applies a reset signal to it, Figure 2.
(Click to Enlarge Image)
Figure 2: When the Figure 1 circuit detects an IR signal, it powers and resets the microcontroller. After the IR transmission ends, the microcontroller suspends itself by releasing the Hold line.
After power-up, the microcontroller must assert its Hold line to prevent the circuit from returning to standby mode when the IR transmission ends. U2 buffers and inverts the IR transmissions. When the microcontroller has completed its tasks and no more IR transmissions are present, it returns the circuit to standby mode by de-asserting the Hold line.
The circuit draws less than 2 μA of supply current while in standby mode, and approximately 40 μA when active. The combined battery monitor and microprocessor supervisor (U1) comes in several versions, offering multiple voltage thresholds for the microcontroller power, and multiple RESET delays. Thus, you should choose the part-number option according to your application. The maximum data rate (determined by Q1) exceeds 10 kbps.
About the authors
David Lees and Donald Schelle were Members of the Technical Staff with Maxim Integrated Products, Sunnyvale, CA when they wrote this item.
A reader's comment:
I really do hope the 3.6V battery is pretty beefy! Or that people
realize that the circuit has a, probably fatal, flaw. Sadly unless the
receiver is actually part of an optocoupler (i.e. completely screened
from external light) the poor thing will spend about 60% of its time on
in summer and probably much the same in winter unless the user has
compact fluorescent lighting.
Sad but oh well.... If they HAD made it the receiving end of an
optocoupler link then all would have been splendid..
And the response of one of the authors:
The battery voltage is 3.3V, not 3.6V. I assume that this was a typo.
I'm also assuming that you are implying that daylight will activate the
circuit, thus draining the battery unnecessarily. The part stated in
the design-idea is a Fairchild's QSE113, as noted on the schematic.
The QSE113 datasheet indicates that the phototransistor features a
"Daylight Filter". I should also state that this circuit was built and
tested; however, I must confess that I only tested it in the lab
(fluorescent lighting) and not outside. A collegue of mine tested the
QSE113 under daylight conditions and confirmed that the transistor would
indeed saturate during daylight hours. You are correct.
What I had in mind at the time of design was a low cost indoor-only
You also wanted to use this circuit with an optocoupler instead of the
default phototransistor. Configuring the circuit to use an optocoupler
requires only the substitution of the phototransistor with the receiving
element of the optocoupler. Though I haven't bench-tested it, I'm
fairly sure that it will work. Make sure to adjust the pull-down
resistor (R3) value to generate a suitable logic-high voltage, given the
saturation current of the optocoupler transistor.
I hope that this answers your questions. Thanks for writing in.