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.
Led is usually used as lighting indicator and display. This electronic device emits light when electricity is flowing across it. Aside from the conventional use, LED can be used also as light detector. The simple circuit below is a schematic of the detector.
schematic diagram
741 pinouts
Part List:
LED - ordinary green LED (see LED pinout for more info)
IC - LM741 or any similar op-amps
VM - volt meter
R - 3.3 Mega ohms resistor 1/4W
Bat - two pcs 9V battery
This project is a simple mobile cellphone detector circuit. As the phone receives or sends massage or call, it sends off signal. The emitted signal will be detected by the circuit and will cause the LED to light up and the buzzer to sound. You can use this circuit as decoration to your cellphone or use this as a detector to unauthorized use of cellphone in prohibited area. Any cellphone activities like sending or receiving SMS, sending videos or any form of data transmission can be detected by this simple circuit. R5 and C7 set the duration of the buzz and ON time of the LED for 1 sec (you can modify it using the 555 timer calculator in monostable mode). Click diagram to enlarge.
phone detector circuit
Part List:
R1, R2 - 2.2 Mega ohms 1/4W
R3, R6 - 1.2 kilo ohms 1/4W
R4, R5 - 10 kilo ohms 1/4W
R7 - 100 kilo ohms 1/4W
C1, C2 - 22pF ceramic capacitor
C3, C7 - 47uF electrolytic capacitor rated 16V
C4 - 220nF
C5 - 33pF ceramic capacitor
C6 - 4.7uF electrolytic capacitor rated 16V
C8 - 100nF
ANT - just a piece of conductor less than 1ft
Q1 - 2N2222 or similar NPN transistor
LED - red led (see LED pinout in case you forgot)
Buz - 12V buzzer 555 - LM555 or similar timer IC
IC - CA3130 or similar
Bat - 9V to 12V battery
According to some sources, when a person is telling a lie, he can’t look at your eyes directly; changes or diverting the topic; and behaves with some unexpected physical gestures and reactions. Another interesting thing about the person who is lying is his body usually perspires rapidly (normal when frightened or over excited). When body perspires, your body or skin resistance drops.
The circuit illustrated below is a simple lie detector that measures changes in body resistance of the person who is under lie detection test. When the person is lying, the meter needle will move. To use, attach the pads 1 to 2 inches apart in the palm. Adjust the potentiometer R3 until the reading of the meter M is zero.
lie detector circuit
2N2222 pins
Part List:
R1 - 100 kilo ohms 1/4W
R2 - 120 ohms 1/4W
R3 - 2 kilo ohms potentiometer
R4 - 1 kilo ohms 1/4
R5, R6 - 4.7 kilo ohms 1/4W
Q1 - 2N2222 or similar NPN transistor
M - Analog or digital ammeter (10mA)
Bat - 9V battery
Pads - any conducting pads
Note: The circuit is for educational purposes only. Though the circuit is working, it does not guaranty its accuracy. Keep in mind also that there are many factors that can affect to the sudden drop or change of body resistance.
This a very simple detector of electricity in our surroundings. The detector will demonstrate on how sensitive is the three transistor connected the same way as the diagram below. The LED will light when electricity is detected.
very simple electricity detector
With this transistor configuration, the current amplification through the LED is the product of the gains of the three transistors. Example if each transistor has a gain of 150, the total current amplification is around 150 X 150 X 150 or 3.375 million times. You can use this circuit to detect static electricity, current carrying wires, human body or any thing that has electricity. Part list:
Q1,Q2,Q3 - 2N2222, BC547, 9013 or similar NPN transistor
LED - red , yellow or orange
R1 - 270 ohms 1/4W
R2 - 2 kilo-ohms 1/4W
plate - piece of metal or just ordinary wire conductor
Have you tried wasting your time troubleshooting your equipment and to find out its just a blown fuse? Well this simple circuit indicator might help you not to experience that again. Two versions are shown below.
simple blown fuse schematic
The two LEDs above will light up when fuse is broken. Circuit below is an improved fuse indicator, which at normal operation LED2 is on and LED1 is off. When the fuse is broken, LED1 is on and LED2 is off.
improved blown fuse indicator
Part List:(improved fuse indicator)
D - 1N4007 or similar diode
LED1- yellow or any LED with higher forward voltage than LED1
LED2- red or any LED with much lower forward voltage than LED2
This circuit will monitor if your input DC supply is delivering current to your battery or load. This is very simple and very easy to build since uses only minimal parts.
current flow indicator
We have two working versions, one is using a NPN and other is PNP type of transistor.If your input DC supply is delivering current to your load, LED will light up while it stays off when no current flow or no load is connected. LED brightness is dependent on the magnitude of current, the larger the current the brighter the LED. You can use this circuit also to monitor if your charger is delivering current to your battery.
Part List:
LED - Red or any low current LEDs
R1- 1.2 kilo-ohms 1/2W
NPN - 2N2222 or similar NPN transistor
PNP - 9012, 2N3906 or similar PNP transistor
R2 - value is dependent on the expected maximum current flowing in the load. See table below.
R2 vs expected current
Note: This current flow indicator is for DC supply use only and maximum input voltage is limited to 25V.
This water level indicator is very easy to build and does not require any good background in electrical engineering. It is very similar to 555 IC based water level indicator, but much simpler to construct.
Water level indicator schematic
Part list:
R - 390 ohms (4pcs)
Rb - 22k ohms (4pcs)
Q - 2N2222 or any general purpose NPN transistor (4pcs)
LED - red, green, yellow, orange or similar (but not a high intensity or power LED) (4pcs)
9V battery
piezo buzzer 6V (optional)
220 resistor (optional)
Operation:
water vs air resistance in 1 inch gap
Lets look at the diagram above. Assuming that the resistance of air is around 10^8 to 10^9 ohms-meters and water resistance is around 182 kilo ohms-meters. For 1 inch plate gap, air resistance is around 3Meg while water is around 4.62k. It is clear that the transistor and LED is turn on only when the plate is wet. Just place the plate 1 at the lower part of the water vessel or tank and plate 4 at the top most level. You can add a buzzer in parallel to any indicator to alarm you on the water level. See diagram below.
This project is a simple electronic doorbell circuit powered by a battery source ranging from 6 volts to 12 volts. This doorbell circuit is powered by a 555 timer IC operated in monostable mode. The use of the timer IC is to set the time delay for the doorbell to ring. The 100K resistor and 33uF capacitor sets the time delay about 3.6 seconds of continuous ringing. Increasing the value of resistor and capacitor increases the time delay about the product of resistor-capacitor combination times 1.1 (1.1RC).
The switch S1 is a push button that will activate the electronic doorbell. The 10K resistor across the S1 and supply voltage provides protection of false triggering of 555 timer.
The buzzer to be used must be self oscillated type or having a built in oscillator for this doorbell circuit to function well.
For persons with some problem in hearing, you can modify the door bell circuit by replacing the buzzer to LED and 150 ohm resistor (see diagram below), or you can put this LED and resistor in parallel to buzzer for better functionality
The LED is preferably blinker type, but an ordinary one is just okay.
schematic diagram of simple electronic doorbell circuit for deaf
Another version of simple electronic doorbell is shown bellow. This type of electronic doorbell uses the same 555 timer IC but it is operated in astable operation a generating an audible sound of 2880 Hz. Another difference of this doorbell circuit is the buzzer is replaced by a speaker. The sound frequency is set by the resistors 1K, and 2K, and 100nF capacitor. Increasing their value lowers the pitch of the doorbell sound.
The same with the electronic doorbell above, you can replace the speaker with an LED as an indicator. Advantage of this type of electronic doorbell is you can use a buzzer or speaker while the version above can’t. Disadvantage of this version is it requires more parts and you are going to push the button (S1) all the time for the doorbell to sound.
This simple project uses 555 timer IC in mono-stable mode. Initially the trigger is connected to the source via 10k resistor, and when the water level reaches the desired level, the trigger is partially connected to the ground thus making the output high. You can replace the LED with any circuit like relay to drive greater load like motors. You can build also a multiple stage water level indicator using transistor if you don't have any 555 at hand.
