wiring and diagram

The AC mains line that we get in our household electric socket outlets, may at times be full of dangerous fluctuations. These may either be in the form of a sudden high voltage or a low voltage. Both the situations can be very “fatal” to our sophisticated electronic equipments like TVs, DVD players, refrigerators, computers etc to name a few.

A simple electronic part such as an LED can play an important role in displaying the condition of this AC mains voltage and warn us of a possible electrical hazard.

Yeah, we will exactly learn how to make ac voltage indicator from led through a construction of a little electronic circuit.

You will need the following mentioned parts for the project:

TRANSISTORS T1, 2, 3, 4, 5 = BC547

ZENER DIODE Z1----Z5 = 3 VOLTS / 400mW

RESISTORS R 1—R10 = 1 K ¼ WATT, CFR.

CAPACITOR C1 = 1000uF/25v,

DIODE D1 = 1N4007

LED 1, 2, 3, 4, 5 = RED 5mm DIFFUSED

PRESET P1, 2, 3, 4, 5 = 47K LINEAR

GENERAL PURPOSE BOARD = 6” BY 2”

TRANSFORMER = O – 6 VOLTS/ 500mA

  It is completed through the following few easy steps:

 In the procured general purpose board, with the help of the circuit schematic start inserting the transistors first in a straight line and solder their leads.

Similarly insert and solder the resistors, zener diodes, LEDs, capacitors, presets etc. in an organized manner and solder them with reference to the circuit diagram.

The following testing details will furthermore help you to understand exactly how to make ac voltage indicator from led:

For testing the completed circuit board you will require a transformer with multiple voltage outputs.

Connect the transformer to the AC mains; also connect the common secondary output of the transformer to the negative point of the circuit.

Make an alligator clip/ wire assembly. Solder the wire end of the clip to 1N4007 diode input.

Now bite the clip to the 3 volt output of the transformer, adjust P1 so that the first LED just starts glowing.

As above go on connecting the clip to 6, 7.5, 9 and 12 volts of the transformer and adjust the presets P2, P3, P4 andP5 so that the relevant LEDs just start to glow at the respective voltages.

This completes the testing and the setting of the circuit.

Finally join the 6 volt transformer to the circuit and switch ON the power. You will find that LED 1, 2 and 3 are glowing brightly, LED no.4 is glowing with less brightness while the last LED is completely OFF, indicating a safe level of AC mains voltage.

Now in case the voltage exceeds a high level (above 260 volts) the last LED will start glowing brightly indicating a dangerous situation.

If the voltage drops to a dangerous level (below 160 V) LED 3 and may be LED 2 may cease to glow, again indicating a bad low voltage.

The explained circuit can be easily made at home by any school kid and used for displaying in his science fair exhibition. The circuit is a simple cell phone charger that may be operated in conjunction with any DC source, from a car or a motorcycle battery or from any ordinary 12 V AC DC adapter.

Nowadays we find most of the vehicles have their in built cell phone battery charger units which surely becomes very handy for travelers who mostly remain outdoors travelling in their vehicle. 

The proposed cell phone charger circuit is as good as the conventional chargers which come fitted inside the cars and bikes.

Moreover the circuit can be simply integrated to ones own vehicle if the feature is not originally available in the vehicle.

Alternatively one may think of manufacturing the present unit and selling them in the market as an automobile cell phone charger and earn some hard bucks.

Circuit Description

Cell phones as we all know are highly sophisticated gadgets by nature and when it comes to charging cell phones the parameters no doubt also needs to be of very high standards.

The AC/DC cell phone chargers which come with the cell phones are all SMPS based and are extremely good with their outputs and that’s why the cell phone gets so efficiently charged by them.

However if we try to make our own version, it may fail altogether and the cell phones may just not respond to the current and display a “not charging” on the screen.

Cell phone battery cannot just be charged by supplying DC 4 volts, unless the current is optimally dimensioned the charging won’t initiate.

Using voltage regulator IC for making a DC to DC charger, which I myself have discussed in one of my earlier article is a good approach, but the IC tends to become too hot while charging the cell phone battery and therefore requires adequate heatsinking for remaining cool and operative.

This makes the unit a bit bulkier and moreover some significant amount of power is wasted in the form of heat, so the design cannot be considered very efficient.

The present PWM controlled DC to DC cell phone charger circuit is outstanding in its respect because, the involvement of PWM pulses helps to keep the output very suitable to the cell phone circuitry and also the concept involves no heating of the output device, making the entire circuit truly efficient.

Looking at the circuit we find that again the work horse IC 555 comes to our rescue and performs the important function of generating the required PWM pulses.

The input to the circuit is supplied through some standard DC source, ideally from an automobile battery.

The voltage powers the IC which instantly starts generating the PWM pulses and feeds it to the components connected at its output pin #3.

At the output the power transistor is used for switching the DC voltage at its collector directly to the cell phone.

However only the average DC voltage is finally fed to the cell phone due to the presence of the 100uF capacitor, which effectively filters the pulsating current and provides a stable, standard 4 volts to the cell phone.

After the circuit is built, the two pots will need to be optimized perfectly so that a well dimensioned voltage  is produced at the output which may be ideally suited for charging the cell phone.   

Parts List

R1, R2, R3 = 1K,

P1, P2 = 47K,

C2 = 1n,

C3, C1 = 100uF/25V

IC1 = 555

D1, D2, D3 = 1N4007
T1 = TIP127