100 WATT INVERTER CIRCUIT

1. Here is a 100 Watt inverter circuit using minimum number of components.I think it is quite difficult to make a decent one like this with further less components.Here we use CD 4047 IC from Texas Instruments for generating the 100 Hz  pulses  and four 2N3055 transistors for driving the load
2. The IC1 Cd4047 wired as an astable multivibrator produces two 180 degree out of phase 100 Hz pulse trains.
3. These pulse trains are  preamplifed by the two TIP122 transistors.The out puts of the TIP 122 transistors are amplified by four 2N 3055 transistors (two transistors for each half cycle) to drive the inverter transformer.
4. The 220V AC will be available at the secondary of the transformer.Nothing complex just the elementary inverter principle and the circuit works great for small loads like a few bulbs or fans.If you need just a low cost inverter in the region of 100 W,then this is the best.

     NOTES:

• A 12 V car battery can be used as the 12V source.
• Use the POT R1 to set the output frequency to50Hz.
• For the transformer get a 9-0-9 V , 10A step down transformer.But here the 9-0-9 V winding will be the primary and 220V winding will be the secondary.
• If you could not get a 10A rated transformer , don’t worry a 5A one will be just enough. But the allowed out put power will be reduced to 60W.
• Use a 10 A fuse in series with the battery as shown in circuit.
• Mount the IC on an IC holder.
• Remember,this circuit is nothing when compared to advanced PWM inverters.This is a low cost circuit meant for low scale applications.

     DESING TIPS:

• The maximum allowed output power of an inverter depends on two factors.The maximum current rating of the transformer primary and the current rating of the driving transistors.
• For example ,to get a 100 Watt output using 12 V car battery the primary current will be ~8A ,(100/12) because P=VxI.So the primary of transformer must be rated above 8A.
• Also here ,each final driver transistors must be rated above 4A. Here two will be conducting parallel in each half cycle, so I=8/2 = 4A .
   
  
  

  
  
   

TELEPHONE IN USE INDICATOR

1. Here is a simple circuit that can be used as a telephone status indicator. When the telephone is in use (off hook) the transistor Q1 switches ON making the red LED D2 glow.
2. When the telephone is not in use (on hook) the Q1 turns OFF and Q2 turns ON. 
3. This makes the red LED D2 off and green LED D3 ON.
4. The circuit is powered from the phone line itself and no external power supply is required.
   
   
   
   
   
   
   NOTES:
   

   • The circuit can be assembled on a general purpose PCB.
   • IF 2A ampere bridge is not available, make one using diodes like 1N4007.
   • Note that some countries prohibit people from connecting other devices to the phone line.

AIR CRAFT WARNING LIGHT CIRCUIT

1. Here is low cost circuit that can be used for implementing a warning light on the top of tall structures as a warning for low flying aircrafts.
2. Usually such lights are just stay glow type .Here our light is a flashing type, and surely this will draw more attention and of course add more safety.
3. When the AC mains is switched on the bulb will get supply and it will glow.
4. When the bulb glows the LDR adjacent to it gets illuminated and it’s resistance drops.This will increase the voltage drop at the base of transistor Q1 and it goes on.When Q1 is on the relay is activated and trips the contacts to make the bulb off.Now the LDR resistance increases and the voltage drop across base of Q1 decreases to make it off.
5. The relay will be de-energized and the bulb glows.This cycle repeats to produce a continuous flashing of the bulb.
6. Since the capacitor C1 is connected across the relay the relay will remain activated for some more time even after the transistor Q1 is OFF,making the bulb to stay off for some more time.

     NOTES:

• The LDR should be mounted at some place near to the bulb so that when bulb glows the light falls on the LDR.
• Set up the circuit as said above and power up.Then adjust the POT R2 so that the bulb starts flashing.Done!The circuit is ready.
• Some parts of the circuit are live with potential shock hazard.Be careful!.
• Bulb of any Watts can be used as load provided that a relay with suitable power rating is used.
• All capacitors are electrolytic and must be rated 25Volts.

BATTERY ELIMINATOR CIRCUITS

1. Here is the circuit diagram of a battery eliminator circuit that can be used as a replacement for 9V PP3 batteries.
2. The circuit given here can be used to power any device that operates from a 9V battery.
3. The transformer T1 steps down the mains voltage and bridge D1 performs the job of rectification.
4. Capacitor C1 is a filter. IC LM317T is the regulator here.
5.  The value of R1, R2 and R3 are so selected that the output voltage of IC1 will be steady 9 volts.
   

      NOTES:

• Assemble the circuit on a good quality PCB.
• Transformer T1 can be a 230V primary, 9V secondary, 1.5A step down transformer.
• If 1A Bridge is not available, then make one using four 1N 4007 diodes.
• Do not connect loads that consume more than 1.5A to this circuit.
• A heat sink is recommended for IC1.

CONTECT LESS TELEPHONE RINGER CIRCUIT

1. The contact less telephone ringer circuit can produce a ring as well as a visual indication when a call comes.
2. The main advantage is that since there is no direct contact between the phone line and the circuit there is no chance for a loading or disturbance in the telephone line.
3. When the telephone rings 60 Hz AC signal is generated which produces a proportional magnetic field around the telephone lines.
4.  These magnetic field will be picked up by the coil L1 due to electromagnetic induction.
5.  A proportional voltage is developed across L1 and it will bias transistor Q1 to ON.
6. This results in the conduction of transistors Q2,Q3 andQ4.The buzzer will ring and the LED will glow.
7. The switch S1 acts as an ON/OFF switch.

   
   

   
   

   
   

   
   

   NOTES:

   • For L1 make 50 close turns of 28 SWG enameled copper wire on any of the two telephone wires.Connect one end of the coil to base of Q1 and leave other end free.
   • If the circuit not works by try by changing the end of the L1 connected to base of Q1.
   • A 9V transistor radio battery can be used as the power source.
   • Assemble the circuit on a good quality PCB or common board.
   • Use of this type or any other devices other than the allowed telephones and devices with the telephone line may be a law violation in some nations.Check it properly before trying.

   
   
   
   

   
   
    

VHF FIELD STRENGTH METER

1. This is a simple and low cost wide band VHF field strength meter.
2. The field strength is measured by converting the radio signal to DC and measuring it.
3.  The RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal.
   
4. he meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal.
5. This circuit is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters( ideal for theoretical demonstrations).

     NOTES:

• The circuit can be assembled on a general purpose PCB.
• Use a 9V PP3 battery for powering the circuit.
• Use a 250uA FSD current meter for M1.Using a lower FSD meter will improve sensitivity.
• The coil L1 can be made by making 6 turns of 20 SWG enameled copper wire on a ¼ inch plastic former.
• The antenna can be a telescopic whip antenna.