In manual flush systems, the userpresses a button, which opens aflush valve allowing mains-pressurewater to flow into the bowl, orsometimes the user presses directlya flush lever (a handle connected toa flushometer). The valve contains apneumatic mechanism that closes itafter a preset time.Today, manual flush system hasbeen replaced with a sensor-operatedsystem that automatically flushes thefixture when the user departs.The microcontroller-based automaticflush system presented here usesan infrared sensor to detect a user approachingthe fixture, then it waits un- K.S. SankA rSUNIL KUMARtil the user departs. A solenoid is usedto actuate the flush from a 6V powersupply with battery backup inside theunit that also powers the sensor circuit.This flush system is fully controlled bya microcontroller. It also flushes beforethe person departs if the person ispresent for more than the preset time(5 minutes).Installation of this microcontrollerbasedautomatic flush system is shownin Fig. 1. The IR transmitter LED andthe IR receiver modules are mountedside by side such that when the userapproaches the mechanism, the IRreceiver module receives the IR signalreflected off the person. A solenoidoperatedwater valve is used in thesystem.
Circuit description
Fig. 2 shows the circuit of the microcontroller-based flush control system.It is built around Atmel 89C2051 microcontrollerthat controls the processof automatically flushing the toilet.The AT89C2051 is an 8-bit microcontrollerwith 2 kB of flash-basedprogram memory, 128 bytes of RAM,15 input/output lines, two 16-bittimers/counters, on-chip oscillatorand clock circuitry. A 6MHz crystalis used for providing clock. Portpins P1.0 through P1.4 of the microcontrollerare connected to buffers N1through N5 of CD4050 via 10-kilo-ohmpull-up resistors, respectively.All the input/output (I/O) pinsare reset to ‘1’ as soon as RST (pin9) goes high on pressing switch S3.Holding the RST pin high for twomachine cycles while the oscillator isrunning resets the device. Power-onresetis achieved by capacitor C2 andresistor R9.

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