2/1/12 - 3/1/12

Description: Initially, the thermistor (temperature-sensitive resistor) R1 has a resistance of 10 kilo-ohms at room temperature. As the temperature increases, its resistance decreases. When the resistance of R1 falls below the combined resistance of R2 and the potentiometer (POT), the comparator outputs a high signal, activating Q1 and the relay. The preset temperature can be adjusted by modifying the potentiometer. For example, to set the control to activate at 50 degrees Celsius, R1 should be exposed to the temperature, and the potentiometer should be adjusted until the relay activates. At night, the light-dependent resistor (LDR) has a high resistance, keeping the circuit off. Conversely, during the day, the relay is energized. The potentiometer POT1 adjusts the circuit's sensitivity to light intensity. Increasing the resistance of POT1 makes the circuit trigger even in low-light conditions, while decreasing the resistance reduces sensitivity. The circuit employs transistors configured in a high-gain Darlington pair. When the plate is wet, transistors Q1 and Q2 activate the relay. This simple lamp circuit is constructed from minimal components and utilizes high-intensity white LEDs. The circuit is current-regulated, protecting the LED even with variable supply voltages. Its operation closely resembles that of an LED driver using an LM317 regulator. The current is controlled by resistor R1 using the formula: Current = 1.2V/R1. When no light is present, the LDR has a very high resistance, several mega-ohms. In illuminated conditions, the LDR’s resistance drops to several kilo-ohms, activating transistor Q1. When Q1 is on, the musical UM66T IC is activated, generating sounds through the speaker via transistor Q2. A 3V to 3.6V battery can be used as the power supply. Additionally, a simple water detector circuit can be constructed using the NAND gate in the 4093B IC. This circuit operates similarly to a rain alarm, activating the relay when the sensor is wet. The relay can be employed to drive motors or other devices. Pin 1 is the "GRND" pin, pin 2 is the "IN" pin, and pin 3 is the "OUT" pin. It is important to note that these pin assignments differ from those of the 78xx IC series, as the "IN" and "GRND" pins are interchanged.

The described circuit integrates various components to create a multifunctional device capable of responding to both temperature and light conditions. The thermistor R1 serves as the primary temperature sensor, allowing for temperature-based control of the relay. The comparator circuit, which compares the resistance of R1 with the combined resistance of R2 and POT, ensures that the relay is activated only when a specific temperature threshold is reached. The adjustment of the potentiometer allows for user-defined sensitivity, making the circuit versatile for different applications.

The inclusion of the LDR adds another layer of functionality, enabling the circuit to operate differently during day and night. The use of a Darlington pair configuration for transistors Q1 and Q2 provides a high gain, making the circuit responsive even with low input signals. This is particularly useful in applications where moisture detection is critical, such as in automatic watering systems or rain alarms.

The current regulation aspect of the circuit, achieved through R1, ensures that the high-intensity white LEDs operate safely within their specified current ratings, thereby enhancing the longevity of the LEDs. This feature is particularly advantageous in battery-operated devices where variable supply voltages may be encountered.

The musical feature provided by the UM66T IC adds an auditory signal to the visual indication of the relay activation, making the circuit suitable for alarm applications. The power supply range of 3V to 3.6V allows for flexibility in powering the circuit, accommodating various battery types.

Finally, the water detector circuit utilizing the 4093B NAND gate IC is a straightforward implementation that can be adapted for various sensing applications. The specific pin configuration of the 4093B must be adhered to, ensuring correct operation within the intended design. Overall, this circuit design exemplifies a practical approach to creating an intelligent sensing and control system using basic electronic components.Initially, thermistor (temperature sensitive resistor) R1 has 10 kilo ohms resistance at room temperature. As the temperature rises, its resistance drops. When the resistance of R1 is lower than the combined resistance of R2 and POT, comparator will output high and activates Q1 and the relay.

You can adjust the preset temperature by just adjusting the potentiometer. Example if you want to preset the control to activate when 50 deg centigrade is reached. Expose or place R1 to temperature and adjust the potentiometer until the relay activates. During night time, LDR (light dependent resistor) resistance is high, making the circuit off. On theother hand, during day time, the relay is energized. Potentiometer POT1 controls thesensitivityof the circuit to lightintensity. Increasing the resistance of POT1 helps the circuit trigger even in less lighted environment, whiledecreasingthe potentiometer resistance decreases the sensitivity. The circuit uses transistors formed in a high gain (Darlington pair) configuration. When the plate is wet, transistors Q1 and Q2 turn on and activate the relay. This simple lamp circuit ismadeof very few materials. It uses high intensity white LEDs. The circuit is current regulated thus the LED is protected even the supply voltage is variable. The operation of the circuit is very similar to LED driver using LM317 regulator. The current is controlled by resistor R1 with the formula:Current = 1. 2V/R1 Whenthereis no light, the light dependent resistor or LDR have a very high resistance, several Mega-ohms.

When there is illumination in thesurrounding, the LDRresistancedrops to several kilo-ohms, this time it will activate transistor Q1. When Q1 is on, the musical UM66T IC will turn on and will generate sounds to the speaker via transistor Q2.

You can use 3V to 3. 6V battery as a power supply. Another simple water detector circuit using Nand in 4093b IC. The idea of the circuit is similar to rain alarm circuit that when the sensor is wet, it will activate the relay. You can use the relay to drive motors or any device. Pin 1 is the "GRND" pin, pin 2 is the "IN" and pin 3 is the "OUT" pin. Take note that these pins are different from the pins of 78xx IC series since "IN" and "GRND" pins are interchanged.