The operating systems like Archlinux ARM, OpenELEC, Pidora, Raspbmc, RISC OS and the Raspbian and also Ubuntu versions are available for the Raspberrypi board. Linux operating systems especially Ubuntu is preferred for all kind of programming and development. The immediate advantage of having an Operating System like Ubuntu running on an embedded system device is multitasking. The Raspberrypi is a board actually designed for helping computer education for remote schools but it is a nice platform for programmers especially beginners to explore various coding techniques. In a multi-tasking system several processes will be running at a time. The Operating System can control a process by sending signals to it. A user can sometimes initiate a signal sending and the processes can also send signals to each other. This project demonstrates how a process can receive the signal called SIGALRM from the OS and use it. 

Many a time it happens we forget to switch off the gas, electric oven, stove or motor while watching TV or taking on the phone or while talking to a friend in your neighborhood. To solve this problem we have described a circuit below which alarms you after the preset time interval. It will give a loud musical alarm and reminds you that you to off your machine or gas. It uses NE555 which is a well known multi-vibrator IC.Here 555 timer IC is wired as an a-stable oscillator which provide a clock pulse to CD4017 IC. CD4017 which is a medium speed Johnson Counter that works at 10MHz and has 10 decoded outputs. CD4017 ICs are widely used in frequency dividers, binary counters, and divide by N counters and register design applications. 

This small alarm circuit protects your valuables from thefts by engaging the alarm when somebody attempts to pick up your suitcase.It can be operated with the [[wysiwyg_imageupload::]]help of 3V therefore power consumption is also very less.It uses very less components that why it can be easily fit on the suitcase. Due to its small size you can easily carry this small alarm while you are travelling.The circuit is build around IC LM358 which is a low power transducer amplifier. The important component of this circuit is piezo sensor. Piezo sensor converts vibration or pressure into electrical signal. This same piezo element can be found inside the buzzer or you can purchase the same from market. Its working is somewhat similar to capacitors. Piezo element holds the charge when potential applied, until it is mechanically disturbed or some vibration will be there.

The circuit is built around two IC namely CD4060 and UM66 with few more components. IC CD4060 is 14 stage ripple carry binary counter, divider and an oscillator. Its built in oscillator is main feature of this IC that’s why it can be used in numerous application like flasher, clock generator in timer circuits. UM66…

This switch, when hidden under the floor mat, triggers an alarm when the person walks over it. Mat switch can be used as a security measure in a restricted area. [[wysiwyg_imageupload::]]Just put the switches beneath the mat after regular intervals so that when anybody who puts his feet on switch will engage the alarm.This circuit is built around the CMOS UM3561 IC which is mostly used in toys and alarms because of its low cost and power saving ability.One of the advantages of this switch is that the circuit does not consume the battery current in standby mode therefore lead to longer battery life.  Also, you can also stabilize 9V DC mains adaptor in place of the battery. Read more to find out how the circuit is designed and how it works.

While travelling in public transport such as buses or trains, people usually carry expensive belongings and are quite insecure about their safety. Even though after [[wysiwyg_imageupload::]]locking the luggage thoroughly, there is always a worry about it.To solve this problem here is a simple circuit based on NAND gate. When somebody tries to steal the luggage, the circuit will give a warning alarm. An audio visual indication can also be provided by connecting it to the relay.This project circuit can also be used in home to prevent the attempt of burglary as when somebody tries to open the door, the loop breaks and the alarm. The project is built around CD4011 with components like LDR, variable resistor, capacitor, transistor and relay.. It generates a warning beep when somebody attempts to open the locker.

The project presented can be used as a smart circuit for the cash box that thwarts any theft attempt by activating an emergency alarm. This can also be used to [[wysiwyg_imageupload::]]trigger any external burglar alarm by connecting a relay to the output of the circuit. The circuit is built around a NAND gate IC in which all gates are used as an inverter. The circuit is based on the concept of Light Dependant Register (LDR) whose resistance varies with the intensity of light falling on it. This small circuit can also be installed in a locker system where if somebody tries to open the locker, the light will fall on the LDR and the circuit will start sounding with the help of buzzer connected to the relay. A switch is also provided so that the circuit can be switched off when not in use to save the battery power.

It is very essential to keep the door of fridge closed all the time. The refrigerator will not work efficiently if the door is left open. To avoid such situations, this [[wysiwyg_imageupload::]]project presents an interesting circuit that will sound an alarm if the door is not properly closed This alarm circuit will not  buzz till the door is opened and closed between the predefined times but if it crosses the predefined time it will start buzzing. NAND Gate is created by applying NOT operation to an AND gate. Hence, the outputs of this gate are opposite to that of AND gate when the inputs are kept same. This simple circuit project is based around transistor, switches and NAND gates. In the standby mode, the switch is closed and the current flowing through R1 is grounded through the switch.

The circuit gives an audio visual alarm when somebody enters from a door. This project can also be used in locker and almirah door.  This circuit is based on [[wysiwyg_imageupload::]]operational amplifier LM741 and LDR. An op-amp produces an output voltage that is hundreds of thousands times larger than the voltage difference between its input terminals. The circuit comprises of Operational amplifier A741 which is used as sensitive voltage comparator, LDR and Preset VR1. The preset provides reference voltage to the non-inverting terminal pin 3 and LDR. R2 is connected to inverting pin 2 of IC1. How does the alarm sense someone entering? How is the circuit constructed? What is the role of op-amp in its working? Continue reading to find out how answers to these questions and more. 

This project presents another application of RF (radio frequency) communication. The capability of fire alarm circuit can be improved by incorporating an RF [[wysiwyg_imageupload::]]module. This way the temperature sensor and buzzer for alarm can be placed away from each other. This provides flexibility in installing various sensors at different locations in a building and thus overheating at a place (due to fire) would signal the buzzer to go on. This project about fire alarm circuit can be divided into four parts, namely, temperature sensor, comparator, transceiver part (RF module) and the output. In this circuit a temperature sensor (LM35) is placed at a certain place and its output is given to the negative end of a comparator. LM324 has been provided in the circuit for comparator.  The positive end of comparator is connected to a preset, to set the reference temperature. As long as the output of temperature sensor is below the set reference, the output of comparator stays high.

This project extends the functionality of intruder alarm to alert a user at a distant location. The intrusion can be detected at a faraway place by making use of RF [[wysiwyg_imageupload::]]communication. For this purpose, an RF module can be used as has been explained here. This project about intruder alarm circuit can be divided into three parts, namely, IR circuit, transceiver part and the output. The IR circuit is used as a sensor to detect an intrusion in its proximity. RF module works as the transceiver here. For more details, refer wireless RF remote. The transceiver transmits the signal generated by IR sensor. It provides this signal to the data pin of decoder IC. The output part consists of a NOT gate IC 74LS04 (to invert the low signal) and a buzzer to alert the user. Read more to find out how the circuit is constructed and how it works.