Light Flasher

This circuits uses 555 Ic for flashing... The Flashing speed is also controllable using the trimpot..

555 IC Pin config :

Knight Rider Scanner Circuit

This in not the exact circuit for the knight rider circuit. Just make some modifications.. You can make the light flash in any sequence. I have installed this circuit in my car..

Line Follower ROBOT

Award winner from VingPeaw Competition 2543, the robot built with 2051, L293D, and four IR sensors. Simple circuit and platform, quick tracking and easy-understand program using C language.

This Robot use two motors control rear wheels and the single front wheel is free. It has 4-infrared sensors on the bottom for detect black tracking tape, when the sensors detected black color, output of comparator, LM324 is low logic and the other the output is high.
Microcontrollor AT89C2051 and H-Bridge driver L293D were used to control direction and speed of motor.



Circuit diagram Robot.



Circuit diagram of Infrared sensors and comparators.


Position of sensors, left hand side is side view and right hand side is top view.
Software
Software for write to AT89C2051 is robot1.hex ,which was written by C-language ,the source code is robot1.ccompiled by using MC51 in TINY model with my start up code robot.asm .

Automatic Load Sensing Power Switch

Part- Total Qty.- Description
C1, C3 -2- 10uF 35V Electrolytic Capacitor
C2 -1- 1uF 35V Electrolytic Capacitor
R1 -1- 0.1 Ohm 10W Resistor
R2 -1- 27K 1/2W Resistor
R3, R4 -1- 1K 1/4W Resistor
R5 -1- 470K 1/4W Resistor
R6 -1- 4.7K 1/2W Resistor
R7 -1- 10K 1/4W Resistor
D1, D2, D4 -3- 1N4004 Rectifier Diode
D3 -1- 1N4744 15V 1 Watt Zener Diode
U1 -1- LM358N Dual Op Amp IC
Q1 -1- 2N3904 NPN Transistor
K1 -1- Relay, 12VDC Coil, 120VAC 10A Contacts
S1 -1- SPST Switch 120AVC, 10A
MISC -1- Board, Wire, Socket For U1, Case, Mains Plug, Socket

Notes



This circuit is designed for 120V operation. For 240V operation, resistors R2 and R6 will need to be changed.

A maximum of 5A can be used as the master unless the wattage of R1 is increased

S1 provides a manual bypass switch.

THis circuit is not isolated from the mains supply. Because of this, you must exercise extreme caution when working around the circuit if it is plugged in.

Source: aaroncake.net

AC Motor Speed Controller

Part-Total Qty.
R1 -1- 27K 1W Resistor
R2 -1 -10K 1/4W Resistor
R3 -1- 100K 1/4W Resistor
R4 -1 -33K 1/4W Resistor
R5 -1- 2.2K 1/4W Resistor
R6 -1- 1K 1/4W Resistor
R7 -1- 60K Ohm 1/4W Resistor
R8 -1- 3K Linear Taper Trim Pot
R9 -1- 5K Linear Taper Pot
R10 -1- 4.7K Linear Taper Trim Pot
R11 -1- 3.3K 1/4W Resistor
R12 -1- 100 Ohm 1/4W Resistor
R13 -1- 47 Ohm 1W Resistor (See Notes)
C1, C3 -2- 0.1uF Ceramic Disc Capacitor
C2 -1- 100uF 50V Electrolytic Capacitor
D1 -1- 6V Zener Diode
Q1 -1- 2N2222 NPN Transistor 2N3904
SCR1 -1- ECG5400
TR1 -1- TRIAC (See Notes)
U1 -1- DIAC Opto-Isolator (See Notes)
BR1, BR2 -2- 5A 50V Bridge Rectifier
T1 -1- Transformer (See Notes)
MISC -1- PC Board, Case, Line Cord, Socket For U1, Heatsinks

Notes

TR1 must be chosen to match the requirements of the load. Most generic TRIACs with ratings to support your load will work fine in this circuit. If you find a TRIAC that works well, feel free to leave a comment.

U1 must be chosen to match the ratings of TR1. Most generic DIAC based opto-isolators will work fine. If you have success with a specific part, feel free to leave a comment.

T1 is any small transformer with a 1:10 turns ratio. The circuit is designed to run on 120V so a 120V to 12V transformer will work. Alternately, you can wind T1 on a transformer core using a primary of 25 turns, a secondary of 200 turns, and 26 gauge magnet wire.

R9 is used to adjust motor speed. R10 is a trim pot used to fine tune the governing action of the circuit. R8 fine tunes the feedback circuit to adjust for proper voltage at the gate of SCR1. It should be adjusted to just past the minimum point at which the circuit begins to operate.

R13 must be chosen to match the load. Generally, larger loads will require a smaller value.

Since this circuit is not isolated from mains, it must be built in an insulated case.

Source - Aaroncake.net

Temperature-controlled Fan

Parts:
P1_____________22K Linear Potentiometer (See Notes)

R1_____________15K @ 20°C n.t.c. Thermistor (See Notes)
R2____________100K 1/4W Resistor
R3,R6__________10K 1/4W Resistors
R4,R5__________22K 1/4W Resistors
R7____________100R 1/4W Resistor
R8____________470R 1/4W Resistor
R9_____________33K 4W Resistor

C1_____________10nF 63V Polyester Capacitor

D1________BZX79C18 18V 500mW Zener Diode
D2_________TIC106D 400V 5A SCR
D3-D6_______1N4007 1000V 1A Diodes

Q1,Q2________BC327 45V 800mA PNP Transistors
Q3___________BC337 45V 800mA NPN Transistor

SK1__________Female Mains socket

PL1__________Male Mains plug & cable

Device purpose:
This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain.

Circuit operation:
R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generate a fixed two-thirds-supply "reference" voltage, P1-R1 generate a temperature-sensitive "variable" voltage, and Q1 is used as a bridge balance detector.
P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.
This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.

Device purpose:
This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain.

Circuit operation:
R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generate a fixed two-thirds-supply "reference" voltage, P1-R1 generate a temperature-sensitive "variable" voltage, and Q1 is used as a bridge balance detector.
P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.
This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.

Notes:
The circuit is designed for 230Vac operation. If your ac mains is rated at about 115V, you can change R9 value to 15K 2W. No other changes are required.
Circuit operation can be reversed, i.e. the fan increases its speed as temperature decreases, by simply transposing R1 and P1 positions. This mode of operation is useful in controlling a hot air flux, e.g. using heaters.
Thermistor value is not critical: I tried also 10K and 22K with good results.
In this circuit, if R1 and Q1 are not mounted in the same environment, the precise trigger points are subject to slight variation with changes in Q1 temperature, due to the temperature dependence of its Base-Emitter junction characteristics. This circuit is thus not suitable for use in precision applications, unless Q1 and R1 operate at equal temperatures.
The temperature / speed-increase ratio can be varied changing C1 value. The lower the C1 value the steeper the temperature / speed-increase ratio curve and vice-versa.
Warning! The circuit is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Source- Redcircuits
The circuit is designed for 230Vac operation. If your ac mains is rated at about 115V, you can change R9 value to 15K 2W. No other changes are required.
Circuit operation can be reversed, i.e. the fan increases its speed as temperature decreases, by simply transposing R1 and P1 positions. This mode of operation is useful in controlling a hot air flux, e.g. using heaters.
Thermistor value is not critical: I tried also 10K and 22K with good results.
In this circuit, if R1 and Q1 are not mounted in the same environment, the precise trigger points are subject to slight variation with changes in Q1 temperature, due to the temperature dependence of its Base-Emitter junction characteristics. This circuit is thus not suitable for use in precision applications, unless Q1 and R1 operate at equal temperatures.
The temperature / speed-increase ratio can be varied changing C1 value. The lower the C1 value the steeper the temperature / speed-increase ratio curve and vice-versa.
Warning! The circuit is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Plant Moisture Meter

Stick the metal probes into a freshly watered plant and adjust R5 for a mid-scale meter deflection. The meter will monitor the soil wetness and the meter will indicate whether it is to moist or to dry. This circuit uses a dual power supply which could be created by two 9 volt batteries.