Simple Regulated Charger Circuit

Most of the battery chargers do not have current and voltage regulation provisions. The step down voltage is simply used for charging. These chargers develop internal resistance so the output voltage drops when the battery is connected to the charger. This is a design circuit for the charger circuit. This is the figure of the circuit;

0-15 1 Ampere step down transformer drops 230 volt AC into 15 volt AC which is rectified through the bridge rectifier comprising D1 through D4. The rectified DC is then made ripple free by C1 and send to the collector of the medium power NPN transistor T1 to give regulated output. Resistor R1 and Zener diode ZD are used for both voltage and current regulation. Output current from the emitter of T1 depends on the value of R1 which can be changed according to the requirement using the ohms law. 12 volt Zener diode gives constant 12 volts to the base of T1 so that output voltage remains 12 volt irrespective of the input fluctuations. Diode D5 is polarity protector that prevents short circuiting if the polarity of the battery is reversed. LED indicates the charging process.

Simple Logarithmic LED Bar Display Circuit Using AN6884 IC

This is a circuit for a logarithmic scale LED bar display driver. AN6884 accept wide range of supply voltage, ranging from 3.5V to 16V. This VU (voltage unit) bar display circuit provides only 5 levels, but will accept wide range of input level because the scale is logarithmic: -10, -5, 0, 3, and 6dB points. The output current for each LED will be constant at 15mA, suitable for most LED types. This is the figure of the circuit;

To operate at voltage higher than 6V, a current limiting resistor R should be inserted between Vcc and the LEDs anodes, and the values should be chosen as shown in the table for appropriate power supply voltage and maximum operating temperature. This circuit is suitable for monitoring audio level of your amplifier’s output. If you need only to measure DC voltage level then the 2.2uF electrolytic capacitor can be omitted. [Circuit's diagram source: Panasonic Application Notes]

Simple LDR Light Alarm Circuit

This circuit is a design for a light alarm circuit. This circuit uses Light dependent resistor (LDR). When there is no light fall on the LDR, the transistor driving the speaker is not turned on, because its resistance is high. When the LDR receives light, its resistance decreases and the collector of the second transistor falls. This is the figure of the circuit;

The first transistor turn off slightly, via the second 100n. The base of the second transistor receives additional spike from the first 100n.  It continues until the second transistor is turned on. The second transistor cannot be kept turned on because the first 100n is now nearly charged. To produce the second half of the cycle, both transistors swap conditions and The second transistor is turned off.

Simple Emergency Light Circuit

This is a design circuit for an emergency light is a battery-backed lighting device that comes on automatically when a building experiences a power outage. This is the figure of the circuit;

If AC supply is present, the alternating voltage is passed through diode D1. D1 behaves as a half wave rectifier and lets only positive voltage to pass on. When AC supply goes off, capacitor C1 discharges through R3. Due to this discharging of C1, voltage across C1 decreases gradually.

Part:
R1, R2 _____200k – 1W
R3 ________100k – 1/2W
R4 ________100k – 1/2W
D1 ________IN4004
C1 ________0.1mF – 50V
T1 ________BC148B
T2 ________SL100
Dry cell battery 1.5V
Bulb 3V

The Simple Gentle Touch Circuit

This is a circuit for gentle touch. The approach requires that a microcontroller is already available in the circuit, and a spare input port pin and a spare output port pin are required, along with a little software. When power is applied T1 initially remains turned off. When the button is pressed the gate of T1 is taken to ground and the p-channel power MOSFET conducts. The microcontroller circuit is now supplied with power. Within a short period the microcontroller must take output PB1 high. This turns on n-channel MOSFET T1 which in turn keeps T1 turned on after the push-button is released. This is the figure of the circuit;

The circuit itself draws no current in the off state, and for (rechargeable) battery-powered appliances it is therefore best to put the switch before the voltage regulator. For mains-powered devices the switch can also be fitted before the voltage regulator (after the rectifier and smoothing capacitor). Since there is no mains switch there will still be a small standby current draw in this case due to the transformer. Be careful not to exceed the maximum gate-source voltage specification for T1: the IRFD9024 device suggested can withstand up to 20 V. At lower voltages R2 can be replaced by a wire link; otherwise suitable values for the voltage divider formed by R1 and R2 must be selected.

Simple Dancing Lights Circuit

This is a design circuit for a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed. This is the figure of the circuit;

The circuit consists of two astable multi vibrators. One multi vibrator is formed by transistors T1 and T2 while the other astable multi vibrator is formed by T3 and T4. Duty cycle of each multi vibrator can be varied by changing RC time constant. This can be done through potentiometers VR1 and VR2 to produce different dancing pattern of LEDs. Total cost of this circuit is of the order of Rs 30 only. Potentiometers can be replaced by light dependent resistors so that dancing of LEDs will depend upon the surrounding light intensity. 

Muscular Bio-Stimulator Circuit

This is a circuit for muscular bio-stimulator circuit is small and portable. This circuit  provides muscles’ invigoration and stimulation but in major it could be an aid in removing cellulite. To use this bio-stimulator we just put the electrodes to the skin at both ends of the chosen muscle and then rotate P1 knob slowly until we feel a mild itching sensation. This is the figure of the circuit;

IC1 generates 150µSec. pulses at about 80Hz frequency.  As a buffer we use Q1 and to inverts the polarity of the pulses and drives the Transformer Q2. P1 is used to set the amplitude of the output pulses and the brightness of LED D1 displays the approximately . To protects Q2 against high voltage peaks generated by T1 inductance during switching this circuit uses D2. This device is forbidden to use for pregnant women and Pace-Maker bearers . Do not put the electrodes on varices, cuts, injuries or wounds. Obviously we can’t guarantee any therapeutic effectiveness for this device.