Pulsed Sensor Extends Battery Life


Posted on Feb 6, 2014

The following demonstrates a power saving circuit that pulses a Sensor for 1 second every 30 minutes. Designed to monitor levels of salt The Sensor shown is an Optocoupler with an infrared-emitting Diode Designed to monitor the level of salt Crystals in a water softener, it relies on a reflection from the Crystals to gen


Pulsed Sensor Extends Battery Life
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erate a "no-alarm" level of emitter current in the Phototransistor (Q3). As the salt level drops past the sensor`s position, this current level makes When the drop across R7 equals the reference voltage in the Comparator reference device (IC2), Comparator B`s output goes high and releases the manual reset on the voltage monitor (IC3). After a minimum reset-delay interval of 140ms, Q4 turns on and sounds the buzzer. Comparator A monitors the Battery voltage via R1 and R2; at levels above 3V, it activates the IR-emitting Diode (D3) by turning on the constant-current sink consisting of Q2 and associated components. Thus, the Power for the Sensor is available only when Q1 turns on. Q1 is controlled by IC1 ”a microprocessor supervisor configured as a time-base generator. (IC1 consumes less power and has a smaller footprint than the alternative 5556 Timer or a 555 Timer with multistage Counters It also eliminates the large Capacitors otherwise IC1`s external connections cause its internal watch-dog Timer to cycle repeatedly. With C2 = 1. 5 µF as shown, the internal timeout is 3. 6 seconds, and connecting WDS high multiplies this value by 500, extending it to the desired 30 minutes. Each timeout produces a reset pulse that applies power to the remaining circuitry by




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