Description.

This micro flasher circuit continuously emits flashing light with the consumption of very less power.The circuit can run for a very long time for four 1.5 V torch cells.

Here a low power CMOS IC CD4093 (IC1) is used to produce sharp pulses  of 20 ms from a red LED.The LED appears to be glowing continuously due to persistence of vision ,and lot of power is saved.The IC1 is quad NAND gate whose one gate is used for producing oscillations.The unused inputs are kept to logic 1 by connecting it to the positive.The value of R1 determines the charging current of C1.

Circuit diagram with Parts list. 

Notes. 

• All capacitors must be rated 10V.
• The circuit can be easily assembled on a common board.
• A 6V DC adapter can be also used to power the circuit.
• The component values need not be strict here. you can find them easily from your junk box.I think you may have to purchase only the IC.

Description. 

Here is a simple circuit for boosting 12 V DC to 24 V DC .The circuit is designed straight forward and uses few components.With few modifications the circuit can be used to boost any voltages.

The transistor Q1 and Q2 (D1616)  essentially drives the primary of the transformer.The diodes rectifies the output of transformer to obtain a 24V DC at the output load(here a fan).The capacitors filter away noise and harmonics away from the output.

Circuit diagram with Parts List. 

Notes. 

• The component values are not very specific here.We can use any NPN power transistors like D1616,2N 3055,C2236,SL 100 etc for Q1 and Q2.
• The transformer can be any center tapped 5A transformer with a  7:1 winding ratio.
• The diodes can be 1N 914 ones.
• In fact you can easily assemble the circuit from the components in your electronics junk box.
•  By experimenting on the tranformer winding you can get different boost ratios.
• For high current (around 5A)  games use 2N 3055 transistor or more powerful Darlington pairs for Q1 and Q2.

 Description.

Here is superb sound shifter circuit that can be used to add effects to the input sound signal.The circuit is ideal for incorporating in toys and adds great fun.The circuit can be also used in mixers and recorders.

The circuit is based on IC HT 8950 from Holtek. The IC HT8905 is a single chip CMOS sound modulator IC which produces seven steps of shift in the frequency of the given sound.This producing a dramatic change in the output.The IC produces two effects robotic and vibrato.The two effects can be selected using push buttons.An audio amplifier IC  HT82V 733 is also included in the circuit to amplify the sound out put of HT 8950 to a reasonable level.The 50 K POT can be used as a volume control.

Circuit diagram with Parts list. 

Notes. 

• The circuit can be powered from a 4.5 V DC supply.
• The desired sound effects can be selected from the push buttons.
• A 8 Ω  speaker can be used as the load.
• All capacitors must be rated 10V.

Description.

The IR to RF transmitter circuit given here can convert the IR signals from your remote to RF signals to long distances. The circuit given here is a good one for extending the range of your IR remote.Also such systems does not need a line of sight since RF signals are used.

The transmitter is based on a St-TX 01 ASK transmitter IC (IC2).The IR signals falling on IC 1 (TSOP 1738) will be converted to RF signals by IC2 and transmitted through antenna.The transmitter has a power output of 16dBm at 5V supply.

The receiver is based on a ST-RX04 ASK receiver IC (IC3).The IC3 receives the transmitted code, decodes it to the original IR code and re transmits through IR LED (D1).  The transistor Q1 is used to drive the D1 from the output of the IC3(pin2).

Circuit diagram with Parts list.

Notes.

• Use a 6V battery with a 1N 4007 series(forward biased) with its positive terminal as power supply for each circuit.
• Use  20 cm long  copper wire for each antenna.
• Ranges upto 200m are possible with matching antenna.
• The capacitor C1 must be rated 10V.

 Description.

The automatic door handle alarm circuit gives a audible alarm and glows a LED when somebody touches the handle of the door.The circuit is latching type and continues to produce sound until it is switched off.

The transistor Q1 is wired as an astable multivibrator whose output is used to bias transistor Q2 to conduction.As a result the transistor q3 and LED are in OFF state.When someone touches the handle ,the capacitance of the human body damps the the oscillations of Q1.The cuts the biasing of Q2 and it goes OFF.As a result the current flows to the base of Q3 , it conducts and LED glows.If the switch S1 is ON the transistor pairs Q4&Q4 which is wired in the latching mode is triggered and the Buzzer Z1 is activated.When the person removes his hand from door handle the LED goes OFF but the buzzer continues to beep.The only way to mute the buzzer is to open the switch S2.

Circuit diagram with Parts list.

Notes. 

•  A9V battery or 9V DC power supply can be used to power the circuit.
• All capacitors must be rated 15V.
• To make L1 wind 25 turns of 0.4 mm enameled copper wire on  resistor R2   and solder the ends of the wire to the resistor leads.This unit will stand for the R2 as well as L1 because both are parallel in the circuit .
• A readily available 10mH inductor can be used for L2 .
• Connect the point A in the circuit to the door handle using a long wire.