50 Watts Inverter Circuit

A 50 watt inverter might look quite trivial, but it can serve some useful purposes to you. When outdoors, this small power house can be used for operating small electronic gadgets, soldering iron, table top radios, incandescent lights, fans etc.

Let’s learn how to build this homemade 50 watt inverter unit, beginning with a brief description regarding the circuit diagram and its functioning:

 

Circuit Description

The circuit may be understood with the following points:

Referring to the figure, transistors T1 and T2 along with the other R1, R2, R3 R4, C1 and C2 together form a simple astable multivibrator (AMV) circuit. A multivibrator circuit basically is composed of two symmetrical half stages, here its formed by the left and the right hand side transistor stages which conduct in tandem or in simple words the left and the right stages conduct alternately in a kind of a perpetual “motion”, generating a continuous flip flop action.

The above action is responsible of creating the required oscillations for our inverter circuit. The frequency of the oscillation is directly proportional to the values of the capacitors or/and the resistors at the base of each transistor.

Lowering the values of the capacitors increases the frequency while increasing the values of the resistors decreases the frequency and vice versa. Here the values are chosen so as to produce a stable frequency of 50 Hz.

Readers, who wish to alter the frequency to 60 Hz, may easily do it by just changing the capacitor values appropriately.

Transistors T2 and T3 are placed at the two output arms of the AMV circuit. These are high gain; high current Darlington paired transistors, used as the output devices for the present configuration.

The frequency from the AMV is fed to the base of T2 and T3 alternately which in turn switch the transformer secondary winding, dumping the entire battery power in the transformer winding.

This results in a fast magnetic induction switching across the transformer windings, resulting the required the mains voltage at the output of the transformer.

Parts Required

You will require the following components for making this 50 watt homemade inverter circuit:

R1, R2 = 100K,

R3, R4 = 330 Ohms,

R5, R6 = 470 Ohms, 2 Watt,
R7, R8 = 22 Ohms, 5 Watt

C1, C2 = 0.22 uF, Ceramic Disc,
D1, D2 = 1N5402 or 1N5408

T1, T2 = 8050,

T3, T4 = BC316,
T5, T6 = 2N3055 (TO-220)

General purpose PCB = cut into the desired size, approximately 5 by 4 inches should suffice.

Battery: 12 volts, Current not less than 10 AH.

Transformer = 9 – 0 – 9 volts, 5 Amps, Output winding may be 220 V or 120 volts as per your country specifications

Sundries: Metallic box, fuse holder, connecting cords, sockets etc

 

Testing and Setting Up the Circuit

After you finish making the above explained inverter circuit, you may do the testing of the unit in the following manner:

Initially do not connect the transformer or battery to the circuit.

Using a small DC power supply power the circuit.

If everything is done rightly, the circuit should start oscillating at the rated frequency of 50 Hz.

You can check this by connecting the prods of a frequency meter across T3’s or T4’s collector and the ground. The positive of the prod should go to the collector of the transistor.

If you don’t own a frequency meter, never mind, you do a rough checking by connecting a headphone pin across the above explained terminals of the circuit. If you hear a loud humming sound, will prove that your circuit is generating the required frequency output.

Now it’s time to integrate the battery and the transformer to the above circuit.

Connect everything as shown in the figure.

Connect a 40 watt incandescent lamp  at the output of the transformer. And switch ON the battery to the circuit.

The bulb will immediately come ON brightly…..your homemade 50 watt inverrer is ready and may be used as desired by for powering many small appliances whenever required.

Breathalyzer circuit using 8051

Alcohol Breathalyzer circuit using 8051 microcontroller (AT89S51).

This article is about a breathalyzer circuit using 8051 microcontroller which outputs the blood alcohol content (BAC) from the breath. The BAC is displayed in percentage on a 3 digit seven segment display. The microcontroller used if AT89S51 which belongs to the 8051 family and the alcohol sensor is MQ135 gas sensor from Futurelec.

MQ135 gas sensor.

MQ135 is a stable and sensitive gas sensor which can detect  ammonia, carbon dioxide, alcohol, smoke, nitrogen dioxide etc. The sensor consists of a tin dioxide sensitive layer inside aluminium oxide micro tubes, measuring electrode and a heating element inside a tubular aluminium casing. The front end of the sensor is covered using a stainless steel net and  the rear side holds the connection terminals.

The ethyl alcohol present in the breath is oxidized into acetic acid while passing over the heating element. This ethyl alcohol falls on the  tin dioxide sensing layer and as a result its resistance decreases. This resistance variation  is converted into a suitable voltage variation using an external load resistor. The typical connection arrangement of an MQ135 alcohol sensor is shown below.

MQ135 alcohol sensor

MQ135 has different resistance values at different temperature and different concentration of gases. The manufacturer recommends to calibrate the sensor at 100ppm of ammonia or 50ppm of alcohol. The recommended value of the load resistor is between 10K to 47K.

Circuit diagram.

Breathalyzer using 8051

The voltage output of the alcohol sensor is converted into a digital format using the ADC0804 (IC1). The Vref/2 pin of the ADC is held at 1.28V using the voltage divider network made of R14 and R15. Vref/2 =1.28V means the step size of the ADC will be 10mV and the output of the ADC will increment by one bit for every 10mV increment in the analog input. Refer the datasheet of ADC0804 for a better grasp. Digital out of the ADC (D0 to D7)  is interfaced to Port1 of the microcontroller. Control signals CS, RD, WR, INTR are obtained from the microcontrollers P3.7, P3.6, P3.5, P3.4 pins respectively. R9 and C1 are associated with the clock circuitry of the ADC0804.

Capacitor C3 connected between Vin+ and Vin- of the ADC0804 filters of noise (if any) in the sensor output. If C3 is not used the digital output of the ADC will not be stable. This filter capacitor will surely induce some lag in the ADC response but it is not very relevant in this entry level application. The microcontroller performs required manipulations on the ADC digital output in order to convert it into BAC % and displays it on the three digit seven segment display. Port0 of the microcontroller is interfaced to the multiplexed three digit seven segment display. The drive signals for the threes digits are obtained from the microcontroller’s P3.0, P3.1, P3.2 pins respectively.

Program.

ORG 00H
MOV P1,#11111111B
MOV P0,#00000000B
MOV P3,#00000000B
MOV DPTR,#LUT
MAIN: MOV R4,#250D
      CLR P3.7
      SETB P3.6
      CLR P3.5
      SETB P3.5
WAIT: JB P3.4,WAIT
      CLR P3.7
      CLR P3.6
      MOV A,P1
      MOV R5,A
      SUBB A,#86
      JC NEXT
      SETB P3.3
      CLR PSW.7
NEXT: MOV A,R5
      SUBB A,#115D
      JNC LABEL
      MOV A,#00000000B
      CLR PSW.7
LABEL: MOV B,#5D
       MUL AB
       MOV B,#8D
       DIV AB
       MOV B,#10D
       DIV AB
       MOV R6,A
       MOV R7,B
DLOOP:SETB P3.0
      MOV P0,#01000000B
      ACALL DELAY
      CLR P3.0
      SETB P3.1
      MOV A,R6
      ACALL DISPLAY
      MOV P0,A
      ACALL DELAY
      CLR P3.1
      SETB P3.2
      MOV A,R7
      ACALL DISPLAY
      MOV P0,A
      ACALL DELAY
      CLR P3.2
      DJNZ R4,DLOOP
      SJMP MAIN
DELAY: MOV R3,#255D
LABEL1: DJNZ R3,LABEL1
        RET
DISPLAY: MOVC A,@A+DPTR
         CPL A
         RET
LUT: DB 3FH
     DB 06H
     DB 5BH
     DB 4FH
     DB 66H
     DB 6DH
     DB 7DH
     DB 07H
     DB 7FH
     DB 6FH
END

Notes.

• The MQ135 gas sensor requires around 5 minutes of preheat before the first use.
• The MQ135 takes few minutes to retrace back to its normal condition after a positive test (alcohol present in the breath).
• If there is no alcohol in the breath  the sensor output will swing back to its normal condition very fast.
• Read these articles Interfacing seven segment display to 8051 microcontroller , Interfacing ADC to 8051 microcontroller  before attempting this project.
• This breathalyzer circuit is just an entry level one and is not suitable for high end applications such as law enforcement or laboratory application.
• The logic for converting the digital output of ADC into BAC percentage was obtained using approximation techniques.

What are the Different Types of LED’s available

This article is a guide for any one who is interested in knowing about the different types of LED’s available in the market. This can be considered as a general informational guide on LED and a buying guide for hobbyists as well.  One important challenge I faced while writing this guide was to incorporate consumer LED’s and professional/hobbyist LED’s into a single article. Let your comments say if I have been successful in this attempt.

Over the years semiconductor technology has advanced to bigger heights. The result is what we see around us in the form of smart gadgets. LED or Light Emitting Devices have also been a part of this revolution as any LED is a semiconductor. Now we have LED’s which give better illumination with low power consumption. These LED’s have better life span too. Certainly these advancements have lived upto influence  the shapes,sizes & even the format of circuit in which an LED can be mounted. So that’s quiet exciting!

Miniature LED’s

These are the one’s you see almost everyday in your life as indicators in mobile phones, television sets and a range of digital devices. They are usually available in market on a predefined,standard size & shape. This is to ensure its compatibility to different circuit boards. Different companies manufacture these LED’s in 5V and 12V ranges. They come in a “ready to fit” mode which can mounted on circuit boards directly. Usually they don’t need support of any additional cooling systems like a heat sink.

High Power LED

These LED’s are the result of advancements in semiconductor technology. As the name hints, these LED’s are known for its high output. They are capable of producing light output with higher luminous intensity. High power LED’s come in different shapes & sizes. A common example of high power LED in daily use is “LED strips” that are used light walls & room interiors. A picture of the same (an LED strip) is shown below. High power LED’s has very high heat dissipation. These LED’s need to mounted along with a cooling system (usually a heat sink).

A note on LED Strips

LED strips are a classic example of high power LED’s put together into a commercial product. In this product, high power LED’s are mounted onto a super flexible circuit board. They usually come with an adhesive sticker on its back that the strip can be pasted on to surfaces like walls or wood. LED strips are used for decorative purposes.

Application Specific LED (AS-LED)

These are LED’s which are manufactured for a particular application in mind. Some examples are digital billboards, public displays, bi color & tri color LED’s. There are many other examples, which I can talk about.  A picture of the LED based digital display is shown below.

A bi color LEDis two diodes mounted on a single frame. It has 2 pins in which one is common. The common can be anode or cathode. A picture of bi color LED is shown below. This LED can produce 2 colors at different times. They are mounted in such a fashion that one diode will turn on for forward bias and the other will turn on for reverse bias.

A tri color LED is similar to bi color LED. It is 2 diodes mounted on a single frame with 3 pins.Another type of LED’s in practical use are RGB (Red, Green, Blue) LED’s.