0 Temperature Controlled Relay

This circuit is a simple temperature controlled relay. The relay activates when the preset temperature is reached.
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.

Temperature activated circuit

Part List:
R1 - 10 kilo ohms thermistor (NTC 10K ohm 1% RAD)
R2 - 1.2 kilo ohms 1/4W
R3, R4, R5 - 10 kilo ohms 1/4W
POT - 10 kilo ohms potentiometer
D1 - 1N4001 or similar diode
Q1 - 9013, 2N2222 or similar NPN transistor
RLY - 12v relay
IC - LM393 or any comparator IC

Click image to enlarge:

9013 and 2N2222 pins

LM393 pins

thermistor

2 AC Light Dimmer (isolated control)

Another AC light dimmer, but its main difference is its control circuit is isolated to AC line that much safer to use. You can use circuit on both 120V and 220V AC lines.

Part List:

R1, R2 - 120 ohms 1/4W

R3 - 1.2 kilo ohms 1/4W

R4 - 120 ohms 1/2W

Pot1 - 10 kilo ohms potentiometer

Pot2 - 50 kilo ohms potentiometer

LED - any high brightness LED ( if  you forgot pinouts, see LED pinout)

LDR  - any light dependent resistor (LDR)

Q1 - 2N2222, 9013 or similar NPN transistor

C1 - 47nF mylar or ceramic capacitor rated 600V or higher

C2, C3 - 100nF mylar or ceramic capacitor rated 600V or higher

Diac - HT32 or similar Diac

Triac - BT136, BT139 or similar

Fuse - dependent on the load 

LAMP - filament or incandescent lamp (220V or 120V)

AC - 120v or 220V AC ( 50Hz or 60Hz)

DC - 6V DC or battery

Similar circuits:
Simple Dimmer circuit - very simple version
Modified 220V dimmer - similar with to the dimmer circuit above

Note: Voltages involve are considered high and can electrocute, thus do not assemble if you don't have experience construction similar circuits. LDR and LED must be enclosed in a box or container that no other light except from the LED.

3 Modified 220V Dimmer Circuit

The use of this circuit is similar to simple dimmer but this one is much improve and much safer to use. You can use this to control the brightness of the incandescent lamp and other devices powered by 220V AC.

dimmer schematic

Triac Pinout

Part List:
R1, R2 - 1.2 kilo ohms 1W
R3 - 120 ohms 1/2W
POT - 100 kilo potentiometer
C1 - 47nF capacitor mylar or poly rated 1000V
C2, C3 - 100nF capacitor mylar or poly rated 1000V
Diac - HT32 or similar Diac
Triac - BT136 or similar Triac (BT139 for above 1000W load)
LOAD - filament lamp or similar Load
Fuse - dependent on the load (for protection)

Note: Do not build or use this if you don't have any idea in electrical or electronics. This project is not safe for beginners and voltage involve is dangerous and can cause electrocution. Do not exceed the load to more than 600W (220VAC).

1 DC Motor Regulator Project

Simple DC motor regulator circuit based on LM1014IC. What this IC does is it maintains the motor speed on both loaded and unloaded by simply sensing the current drawn by the motor. As the motor is loaded, it draws more current; in that case the IC will supply higher voltage to maintain its speed. Closing switch SW stops the motor.

motor speed regulator circuit

TIP42C pinout

Part List:
R1 - 220 ohms 1/4W
R2 - 0.47 ohms 1W
R3 - 15 kilo ohms
POT - 2 kilo ohms potentiometer
C1 - 3.3uF electrolytic capacitor rated 10V
C2 - 470nF
Q1 - TIP42C or similar PNP transistor
M - small DC motor
SW - any small switch

1 Sound controlled circuit

The idea of this circuit is when there is sound the circuit will activate or trigger some other circuit. From the circuit below, the sound is picked up by the microphone. This sound is amplified and causes the transistor Q2 and Q3 to turn on and off. You can connect any load across point a and b in transistor Q3.

simple sound activated circuit

Part List:
R1 - 1.2 kilo ohms 1/4W
R2 - 1 Mega ohms 1/4W
R3 - 5.6 kilo ohms 1/4W
R4 - 1.2 kilo ohms 1/4W
C - 100nF capacitor
Q1, Q2 - 2N2222, 9013, or any similar NPN transistor
Q3 - 2N2907, 2N4403, 9012, or any similar PNP transistor
Mic - electret microphone
Bat - 4.5V to 6V battery
LOAD - LED, motor, bulb or any load (see possible loads below)

Part List jpg: Click to enlarge

electret microphone

2N2222 or 9013 pinouts

2N2907, 2N4403 or 9012 pinouts

Possible loads
You can replace the LOAD marked a and b in circuit above by the following circuits below.

Different loads

Part List:
1. bulb - any 2.5V to 4.5V bulb rated 50mA to 200mA
2. R - 220 ohms 1/4W
    LED - red, yellow, or orange LED (3mm or 5mm)
3. motor - 3V to 6V small DC motor

0 Solar Street Light circuit

Same with the normal street light, this one automatically turns on when environment is dark (night or gloomy rainy days) and off during bright day. An advantage of this lighting system is very easy to build since uses minimal and very common electronic parts. Another advantage is it uses solar power as main source of energy, thus no more 220V supply is needed and environment friendly. It has a built in battery that is charged during the day and supplies power during the night.

Street light circuit

Part List:
R1 - any light dependent  resistor (LDR)  2k to 1Meg
R2 - 50 kilo ohms 1/4W
R3 - 120 ohms 1/4w
R4 - 1 kilo ohms 1/4W
D1 - 1N5817, 1N5818 or any diode with low voltage drop
Dz - 2.7V zener diode rated 1W
Q1 - 2N2907, 9012, or similar PNP transistor
Q2 - 2N2222, 9013, or similar NPN transistor
Lamp - 1.5V to 2.5V rated flashlight bulb 30mA to 75mA
Bat - 2 NiCd cell rated 1.2V @ 800mAh or higher
Solar cells - MPT3.6-150 Flexible Solar  or any  3.6V @ minimum 100mA cells

If you plan to use LED instead of  lamp, just follow the diagram below. The resistance is equal to 10 ohms rated 1/4W. Use only red or orange LED to make it work. Other LED like white or blue requires higher forward voltage (see LED forward voltage table for more info ) and our source is around 2.4V only.

Replacing buld with LED

White , blue and other high intensity LED requires 3V to 3.6V forward voltage. Our battery can supply only 2.4V, thus impossible for us to use these LEDs using the same circuit above. But if you want to use these LEDs, try modifying the circuit above and add the joule thief circuit.

7 Light Activated led driver (1.5V joule thief)

This is another LED driver circuit powered by joule thief circuitry using 1.5V cell. The only difference is it has light detection that automatically turns on the led when the environment is dark.

schematic diagram

Part list:
R1 – any light dependent resistor (LDR) or photoresistor
R2 - 100 kilo ohms potentiometer
R3 – 220 ohms 1/4W
R4 - 120 kilo ohms 1/4W
R5 - 2 kilo ohms 1/4W
Q1 - 9012, 2N4403, or any similar PNP transistor
Q2, Q3 - 2N2222, 9013, or any similar NPN transistor
C - 22pF to 47pF capacitor
L - any 100uH to 1mH inductor
LED - any type of LED  (see LED pinout in case you forgot)


Part list diagrams: Click to diagrams to enlarge

PNP transistor pins

NPN transistor pins

LDR

You can adjust sensitivity of the light detector by varying the value of potentiometer R2. Full value of R2 means highest sensitivity.

Note:  see Sir Acme Fixer recommendation on how to construct the joule thief in the comments section below.

6 Simple dimmer circuit (220V)

Using this simple circuit, you can adjust the brightness or light intensity of your incandescent or filament bulb.  By varying the resistance of potentiometer R2, you can adjust the bulb power consumption from maximum down to zero.

220V Dimmer circuit

Triac pinout (BT139)

Part List:

R1 - 5 kilo ohms 1W

R2 - 100 kilo ohms potentiometer
R3 - 120 kilo ohms 1/2W

C - 100nF rated 300V or higher

Bulb - filament or incandescent type

Triac - BT136, BT139 or similar triac

Note: The circuit is powered directly to 220V main, thus avoid touching any parts of the circuit if not insulated. Do not attempt to build the circuit if you have little or no background in electrical engineering. Be reminded always that this circuit can cause electrocution if not handled properly. Use incandescent bulb only.

You can modify the circuit above by adding a diac to the Triac's gate and add some filter to minimize harmonics (see modified dimmer circuit on how it is done).