Using the RE46C140 integrated circuit you can design smoke detector alarm using few external electronic components . The RE46C140 IC is a low power CMOS photoelectric type smoke detector IC that will provide all the required features for a photoelectric type smoke detector project .
This smoke detector alarm design incorporates a gain selectable photo amplifier for use with an infrared emitter detector pair.
An internal oscillator strobes power to the smoke detection circuitry for 100us every 10 seconds to keep standby current to a minimum. If smoke is sensed the detection rate is increased to verify an alarm condition.
An interconnect pin allows multiple detectors to be connected such that when one units alarms, all units will sound.
An internal 10 minute timer can be used for a reduced sensitivity mode. In standby the LED is pulsed on for 10mS every 43 seconds . In a local alarm condition or the push to test alarm the LED pulse frequency is increased to once every .5 seconds. In the case of a remote alarm the LED not active. In the timer mode of operation the LED is pulsed on for 10mS every 10 seconds.
A comparator compares the photo amp output to an internal reference voltage. If the required number of consecutive smoke conditions is met the device will go into local alarm and the horn will be active.
The bidirectional IO pin allows interconnection of multiple detectors. In a local alarm condition this pin is driven high immediately through a constant current source. Shorting this output to ground will not cause excessive current. The IO is ignored as an input during a local alarm.
This smoke detector circuit must be powered from a 9 volt DC power supply .
A very simple low cost water level indicator circuit is presented in this schematic circuit . This water level indicator is based on a simple CMOS IC CD4066 and indicates the amount of water present in the overhead tank and also gives an alarm when the tank is full.
As you can see in the circuit diagram the circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs.
When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the + supply are shorted by water. This closes the switch S1 and turns the LED1 ON. As the water continues to fill the tank, the LEDs2 , 3 and 4 light up gradually.
The no. of levels of indication can be increased to 8 if 2 CD4066 ICs are used in a similar fashion.
When the water is full, the base of the transistor BC148 is pulled high by the water and this saturates the transistor, turning the buzzer ON. The SPST switch has to be opened to turn the buzzer OFF.
As you can see this electronic liquid sensor circuit require very few external components and need to be powered from a 6 volts DC power supply .
A very simple ultrasonic proximity detector circuit can be constructed using few external electronic components . As you can see in the circuit diagram shown here, this proximity detector circuit require some external components and is very easy to build. The R4 ( 100k ohms potentiometer ) sets the current fed to the buzzer ( sounder) . The potentiometer must be adjusted to a sounder point where the buzzer begins to sound .