timer ic NE 555 and LM555

ldr is a light dependent resistor. it has high resistance at night or at dark and it has low resistance at bright ir day.. it is also called light sensor. it can be used in any electronics projects like light sensor, automatic street light, line following robot etc. if you are interented in making such project please watch my posts. thank you for watching

circuitsnepal: bc547 npn transistor

circuitsnepal: bc547 npn transistor

World's most simple automatic street light using only one transistor.

A transistor is an electronic device which has three terminals and can be used as electronic switch and signal amplification.Here is an example of transistor as a switch which is designed by me. AUTOMATIC STREET LIGHT Automatic street light is the automatic switching device which glows at night automatically and turns off automatically at day. The following diagram shows the schematics of automatic street light. PART LIST Transistor -- BC547 light dependent resistor resistors--330R, 1k led 6/9 volt battery EXPLANATION The automatic street light functions as switch. To understand this let us view the following diagrams. During day time, the the ldr or light dependent resistor has minimum resistance and a little current flows through it. it results the biasing of transistor bc547 and the current flows through it due to the sufficient charge carrier at base. so the potential drop across the transistor is zero and at that time light doesn't glow. so at day time light turns off. during night time, the resistance of the ldr is very high so that the current doesn't flow through it and the transistor doesn't get base biasing. so the current doesn't flow through transistor bc547 and the voltage across it is maximum.so the current flows through led and the led glows. so at night the light glows. click the link below to know about ldr http://www.google.com.np/imgres?imgurl=http://tutorial.cytron.com.my/wp-content/uploads/2011/08/LDR1.jpg&imgrefurl=http://tutorial.cytron.com.my/2011/08/10/project-9-%25E2%2580%2593-analog-sensor-light-detection-using-ldr/&h=301&w=555&sz=16&tbnid=rncu010iSzWXsM:&tbnh=72&tbnw=133&zoom=1&usg=__HZucrbooALGMs_rbKLcvBoKVAqo=&docid=w7xVeq0pXp9kcM&sa=X&ei=QBEsUqbmHMuTrgfNy4CoDw&ved=0CDEQ9QEwAQ&dur=3209 In this way the automatic street light designed by me works. so please try it and enjoy the project. if you have any question about this post you can ask to me by writing the comments or my mailing me on the email sangit.niroula@gmail.com.... thank you so much for watching....please like and share knowledge and technology.. ckick this link for bc 547 npn transistor information

bc547 npn transistor

breathanalyser circuit

Breathalyzer circuit using 8051 ADMIN JUNE - 5 - 20134 COMMENTS 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 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.

alcohol meter using 8051 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.

diode story

The Story of PN Junction Diode JOJO AUGUST - 13 - 20137 COMMENTS I am really excited by the amazing comments & responses I got for my two articles on PN Junction. If you have not read them yet, here they are – 1) Understanding the PN Juction and 2) PN Junction Diode Characteristics. In those 2 articles, I have tried to demystify PN Juction and explain it in very simple words. From those good responses, I assume my attempt has been successful to some extent. In this article, my objective is to take you through the “invention story” of PN Junction diode. We are going to see how a pn juction diode came into existence. The Story begins! So lets begin!

semiconductor diode

a diode is an semiconductor device which is used in various types of electronics instruments. It has two terminals positive and negative. the main feature which made the diode to be very useful is that it can allow the flow of current through it in only one direction called forward bias and it doesn't allow the flow of current through it in another direction. It consists of two type of semiconductor known as p-type and n-type. when they are fused together the nearer + and - fuses to form a depletion layer. so to cross the depletion layer by electrons some energy is needed.the following diagrams illustrate the introduction and characteristics of diode

electronics introduction

Electronics ------------- electronics is the branch of engineering which deals with the behavior of electrons in a material and application in our necessary field. the current and electricity is due to the movement of electrons in a conductor. the materials and devices made from the useful behavior of electron motion are called electronics devices. for example resistor, capacitor, inductor, diode, transistor, intigrated circuits and micro controller. the instruments which use these component to carry out some tasks are called electronic appliances. so the field of electronics engineer is to design electronics device and appliance. computer, television, radio, dvd, mobile and all other appliances conducting from electricity are electronics appliances.