Often there is a need to get away for a few days, that may adversely affect the potted flowers. The proposed system will successfully replace the home owner in this situation, from time to time including the pump or solenoid valve every night for watering houseplants.
Device description scheme
Schematic diagram of the device shown in Figure 1.
FR1 photoresistor together with resistor R1 forms a voltage divider, which is fed to the noninverting input of the operational amplifier US1A (LM358). P1 potentiometer sets the voltage, supplied to its inverting input – a typical voltage comparator circuit. Resistor R3 implements a hysteresis loop in the circuit, preventing oscillation when changing the intensity of incident light on the photoresistor. RC-circuit, consisting of C3 and R4, generates a short pulse, input to the inverting input US1B, at whose output there is a short rectangular pulse, arising under shading photoresistor. The time constant of this circuit is sufficiently large, to be insensitive to short outages. This pulse starts a chip US2 (NE555), working in his usual monostable trigger configuration. Potentiometer P2 sets the response time, for given values of elements it ranges from 0,5 s to 11 with (about). Resistor R7 limits the base current of transistor T1 (BC548), which load, included on the collector, a relay K1. diode D1 (1N4148) T1 protects against the breakdown due to the stress, appearing in off the relay coil. Fuse F1 protects the power supply from damage in the event of a short circuit, and capacitors C1 and C2 eliminates parasitic interference, which may affect the operation of the circuit. resistors R2, R5 and R6 protect sensitive circuit inputs of the leak current is too high.
Installation and adjustment device
The circuit can be assembled on single-sided circuit board size 90 mm × 60 mm (picture 2).
Installation is a typical method – from bridge, through resistors, diode, increasing the height of the elements and ending relay. For proper operation of the system requires a power supply in the range 11 … 13 AT, preferably stabilized. Power is connected to the connector J1, and the photocell to J2, which should be placed in such a place, so that it covered only by sunlight. J3 – this output, shorted relay. Running the system is reduced to the activation threshold setting potentiometer P1 and, not least, time relay circuit with potentiometer P2. Tuned system is ready for operation. it consumes a current in the standby mode about 10 mA, when the relay is turned on, it increases to about 30 mA.