Description.

Here is the circuit diagram of 9 V regulator using popular 7809 IC.The 7809 is a 9 V voltage regulator IC with features such as internal current limit,safe area protection,thermal protection etc.A 16 V transformer brings down the 230V mains  , 1A bridge rectifier rectifies it and capacitor C1 filters it and 7809 regulates it to produce a steady9V DC  output.

Circuit diagram with Parts list. 

Notes. 

• If a current of 300 mA or above is required ,fit a proper heat sink to the IC 7809.
• If 1A bridge is not available,make one using four 1N 4007 diodes.

Description.

A variety of humidity tester circuits are available, but this  is a circuit which is as simple as possible.Using only a transistor ,LED and few resistors ,this circuit can be used to check the humidity level of materials like soil , paper etc.

When the humidity in a substance increases the current conducted through  it also increases .This is the working principle.If there is required humidity, the current through R3 will be sufficient to produce a voltage drop across R3 which is sufficient enough(0.7V)  to switch on the transistor and LED glows.R1 is the current limiting resistor for LED.R1 protects the transistor from accidental shorting of the probes.

Circuit diagram with Parts  list.

Notes. 

• The probes can be anything like iron nail.pin paper clip etc.
• To calibrate the circuit for particular density,insert the two probes to the required material and adjust R3 so that the LED glows.The LED will glow whenever the humidity of the testing sample becomes equal to this humidity level.
• A 3V battery can be used to power the circuit.
• Another general purpose NPN transistors like BC107,BC148,2N2222 etc can be also used for Q1.

Description.

7805 is a 5V fixed three terminal positive voltage regulator IC .The IC has features such as safe operating area protection,thermal shut down, internal current limiting which makes the IC very rugged.Out out currents up to 1A can be drawn from the IC provided that there is a proper heat sink.A 9V transformer steps down the main voltage , 1A bridge rectifies it and capacitor C1 filters it and 7805 regulates it to produce a steady 5V DC .

Circuit diagram with Parts list.

Notes.

• The bridge D1 can be also made by yourself by using four 1N 4007 diodes.
• If more than 400mA current is supposed to be taken from the circuit , fit a heat sink with to the 7805 IC.

Description.

Here is the circuit diagram of a simple stepper motor controller using only elementary parts.The circuit uses , four transistor (SL100) to drive the motor windings , two NOT gates and one XOR gate to decode the two bit control logic to drive the four windings of the motor.The diodes D1 to D4 protects the corresponding transistors from transients generated during the switching of motor windings. d0 and d1 are the control logics which determines the direction of rotation as well as speed.

Circuit diagram with Parts list.

Notes.

• The control logic for the circuit can be obtained from a 2 bit up/down counter clocked by a 555 astable multivibrator.The direction of count determines the direction of rotation and the frequency of astable multivibrator determines the speed of rotation.
• IC1a IC1b belongs to same IC 7404.
• Pin 14 and pin 7 of both IC1 and IC2 must be connected to +5 V and ground respectively,though it is not shown in circuit diagram.
• The 5V can be obtained from a 7805 based power supply circuit
• 5V power supply using IC 7805.Click Here.
• Vcc is the voltage required for the stepper motor.It varies from motor to motor.Here we can use up to 24V stepper motors.For higher operating voltages and power the SL100 transistors must be replaced with higher power transistors like 2N3055.

Truth table for clockwise rotation.