Elektronik 2 Prof. Roland Kueng The final cut - PowerPoint PPT Presentation

Elektronik 2 Prof. Roland Kueng • The final cut Zürcher Fachhochschule 1

Plant Guard for Forgetful Persons Zürcher Fachhochschule Zürcher Fachhochschule 2

Plant Guard for Forgetful Persons - Power the circuit from a 3V battery. - Two metal wires A and B driven into the soil serve as probes. + 3 V - AC driving probes prevents corrosion of electrodes. 470k 47n - IC U1 is a quad two input Schmitt NAND IC TC4093 (Toshiba). 1,2 10 1N4148 - If Toshiba not available use leaky rectifier to 3 V DC between pin 10 and 1,2 of U1a 1N4148 or a Diode between pin 3 and 5 3 5 - The sensitivity can be adjusted by varying the preset resistor R2. Zürcher Fachhochschule Zürcher Fachhochschule 3

An Electronic Candle to Blow out Zürcher Fachhochschule Zürcher Fachhochschule 4

An Electronic Candle to Blow out Alternative: App for iPhone freaks who do not love their loudspeaker http://www.youtube.com/watch?NR=1&feature=endscreen&v=18RuLED2nQM Zürcher Fachhochschule Zürcher Fachhochschule 5

Blow Out Electronic Candle Schematic On/off On/off Pulsed HP(C1, Ri) on/off/on • Power the circuit from a 3V battery. • Use Electret microphon e.g. Monacor MCE-2002 • Capacitor C1 has to be matched to Mic and Q1 selection: 100 nF to start decreasing • Q1 can also be BC 107, BC108… type, may be R2 should be lowered to 470 k • For Q2 and Q3 any equivalent NPN and PNP can be used • Instead of S1 a light dependent resistor plus serie resistor can be used. Switch on with a match! Zürcher Fachhochschule Zürcher Fachhochschule 6

Masse BC337 BC107 BC327 BC550 Zürcher Fachhochschule 7

Plant Guard for Forgetful Persons Circuit operation: IC1A and related components R1 and C1 form a 2KHz square wave oscillator feeding one gate input of IC1B through the voltage divider R2/R3 made variable by adjusting the Trimmer R2. If the resistance across the probes is low as when there is a sufficient quantity of water into the pot) C2 diverts the square wave to ground, IC1B is blocked and its output will go steady hight. IC1C inverts the high status to low, thus keeping IC1D blocked: the LED is off. When the ground in the flower-pot is becoming too dry the resistance across the probes will increase and C2 will be no longer able to divert the square wave to ground. Therefore, IC1B output begins to transfer the 2kHz signal to IC1C which, in turn, passes it to the oscillator built around IC1D. No longer disabled by a low level on its input, the IC1D oscillator slowly pulses Q1 base low causing the LED to flash, signalling the necessity to water the plant. The short low pulse driving the base of Q1 is actually a burst of 2kHz pulses and therefore the LED flickers about 2,000 times per second - appearing to the human eye as if the LED was steadily on for the entire duration of the pulse. Notes: A square wave is used to avoid problems of probes oxidization. Probes are made with two pieces of bare, stiff lighting cable of 1mm diameter and should be about 60mm long. The probes should be driven fully in the pot's ground about 30 - 50mm apart. Please note that all parameters regarding probes material, dimensions and spacing are not critical. Current consumption: LED off = 150µA; LED on = 3mA for 0.1 sec. every about 2 sec. allowing the battery to last for years. The quiescent current consumption is so low that the use of a power on/off switch was considered unnecessary. In any case, to switch the circuit completely off, you can short the probes. Zürcher Fachhochschule 8

http://www.circuit-finder.com/categories/sensor/fluid-and-humidity/263/plants-watering-watcher R1 470K 1/4W Resistor R2 3K3 1/4W Resistor R3 100K 1/2W Trimmer Cermet C1 1nF 63V Polyester Capacitor C2 47µF 25V Electrolytic Capacitor D1 1N4148 75V 150mA Diode D2 5mm. Red LED IC1 4093 Quad 2 input Schmitt NAND Gate IC P1,P2 Probes (See text) SW1 SPST Slider Switch B1 3V Battery (2 AA 1.5V Cells in series) Zürcher Fachhochschule 9