T.K. Hareendran writes:
All items stored in a deep freezer will thaw out if, for some reason, the temperature inside the freezer rises to the thaw point. However, a freezer monitor alarm can warn you of the rising temperature before the thaw point is reached.
This simple circuit is powered by regulated 9V and built around a few discrete components that are readily available in the market. Current consumption of the circuit is only a few milliamperes in idle state. So you can also use a 9V 6F22/PP3 type compact battery for powering the circuit.
Freezer Monitor Alarm - [Link]
At the heart of this circuit is a precision integrated temperature sensor, LM35 (IC1), which provides an accurate linear and directly proportional output in mV, from 0 to +155 degrees C. Designed to draw a minimal current of its own, the LM35 has very low self heating in still air. Here the output of the LM35 is applied to the non-inverting input of a comparator wired around a CA3130 opamp (IC2). A voltage divider network R3-P1 sets the threshold voltage, at the inverting input of the opamp. The threshold voltage determines the adjustable temperature trip level at which the circuit is activated.
When the measured temperature exceeds the user-defined level, the comparator pulls its output High to approx. 2.2 V causing transistor T1 to be forward biased instantly. T2 is also switched on, supplying the oscillator circuit around IC3 with sufficient voltage to start working. The 555 set up in astable mode directly drives active piezoelectric buzzer Bz1 to raise a loud alert. Components R7, R8 and C4 determine the on/off rhythm of the buzzer.
Overheat Detector Alarm - [Link]
Boris Landoni writes:
It’s small but packed with features. The GSM alarm we present today, sports a PIR motion sensor, can be battery operated and it’s capable to communicate via GSM. It can transmit alarm conditions and receive commands from remote. It’s also capable to indicate problems such as is insufficient voltage supply or tampering.
It’s not so conventional for antitheft system: to integrate a movement sensor, a PIR motion sensor and a temperature probe in a single appliance: all this accompanied by an SMS sending GSM / GPRS module. This circuit was born as a very versatile, ready to use, built-in alarm system: no installation is required, you can just drop it and it’s ready to work. It’s not by chance that is designed to be battery operated: it also features a battery state control to check the power.
GSM Multifuction Alarm with SIM900 - [Link]
The STD32 offers the user the possibility to remotely switch ON or OFF electronic devices and to receive alarm messages via (SMS). You can switch devices either with an SMS or using a simple voicecall. Alarm messages (SMS) can be received with any mobile phone supporting SMS functionality.
With the new generation of the STD32 you now also have the possibility to receive alarm messages via e-mail. With the help of the digital camera which is available as an accessory, pictures can be taken and sent via e-mail triggered by an alarm.
The STD32 has an integrated webserver which allows direct access to the device via the internet and a standard webbrowser (e.g. Internet Explorer or Firefox) from a computer or a mobile phone with web functionality. Thus it is very simple to switch electrical devices remotely and to change the configuration of the STD32 from anywhere.
Simple GSM control
- New! Fixed IP address (in-built server)
- New! Camera interface (sends still images via email)
- Two alarm inputs, e.g. for movement, vibration, temperature or moisture sensors
- Two relay outputs, potential-free max. 6A/250V
- Alarms via text message
- Remote setting of parameters (on times, etc.) possible
- Five alarm addresses
- Basic functions can be activated by telephone with no call charge
- Online configuration via the internet
- Camera and built-in box available as accessories
- Supplemented with SIM cards
STD32IP Remote Controlling /Alarm for GSM Network - [Link]
Well, basically break beam sensor consists of two parts: transmitter and receiver. Transmitter emits light (it could be, for example, an LED or a laser) and that light goes to receiver. If that light beam between transmitter and receiver is broken by some obstacle, and receiver detects no incoming light even for a brief moment – it triggers an alarm (or any load you want). For example you can count people that entering some room, or you can use it as an alarm system, yeah, just like in movies!
First thing that comes to mind is to connect LED or laser to DC power supply on transmitter side, and use phototransistor with an amplifier on receiver side. But that is not gonna work with changing ambient light level. For example you calibrated your amplifier to work on a cloudy day, and then bright sun shined at it and in this case it won’t trigger an alarm because it already has sufficient level of incoming light.
Break-Beam Sensor - [Link]
Professor Mark Csele writes:
Presented is a simple temperature alarm which uses a PIC16C84 microcontroller and a 2-line LCD display. The alarm displays current temperature in both Celsius and Fahrenheit degrees and features a 3-key keypad which allows the user to set independent high and low temperature alarm points. The alarm also records the minimum and maximum temperatures encountered.
A PIC-Based Temperature Alarm - [Link]
I thought it would be fun to build an alarm clock that looks just like the type of bomb that we always see in Hollywood movies. I certainly don’t know anything about how a real bomb might look, but in the movies they always have sticks of dynamite strapped together, a red digital readout, and a bunch of curly wires. Instead of just building an ordinary clock, I thought it should have a detonation sequence with a scary countdown just like in the movies. And why not make it “defusable” so I can try to stop the countdown by cutting the correct wire?
Defusable Alarm Clock is Dy-No-Mite - [Link]