The latch-up alarm described here is based on single IC NE555, configured as an astable multivibrator. The timing components are selected such that the oscillation frequency of the multivibrator lies within the audio range. Instead of a flip-flop stage, an opto-coupler (MCT2E) is used for latching of the alarm.  Under normal condition, pin 4 of IC1 is pulled to ground via resistor R2, and its output at pin 3 is held  ‘low’.

Circuit Diagram:



When switch S1 is pressed momentarily, transistor T1 conducts to bring reset pin 4 of 555 to logic  ‘high’. As a result, IC1 is activated and the alarm starts to sound. Simultaneously, the LED inside opto-coupler glows and the phototransistor conducts. As a result, trigger transistor T1 gets base bias via phototransistor and resistor R6. The alarm sounds continuously until reset switch S2 is pressed. When switch S2 is pressed, transistor T1 is switched  ‘off’ to bring pin 4 of IC1 to logic ‘low’ and the alarm is disabled.

This simple  road ice alarm electronic circuit schematic use a LM3900 quad operational amplifier. As a temperature sensor this road ice alarm circuit use a thermistor. When the temperature is around  36 degrees Fahrenheit (2.2 celsius degrees)  the LED connected on pin 4 at the LM3900 op amp will flashes at once about each one second.

Simple Road Ice Alarm Schematic:



When the temperature is going down to 32 degrees Fahrenheit (0 degrees Celsius) the led remains on. Before you use this road ice alarm electronic circuit you need to calibrate it. To calibrate the circuit you need to put the thermistor in a mixture of a crushed ice and water and adjust the variable resistor R2 until the LED is remaining on.

The road ice alarm circuit needs to be powered from a 12 volts DC power supply circuit ( If you use it for car the car battery can be used for powering the circuit ).

Low-cost Gated Alarm Circuit Project build very easily and simple. The circuit shown here employs just four components and a piezo sounder and is unlikely to be out-done for simplicity. While it does not offer the most powerful output, it is likely to be adequate for many applications.

Circuit Diagram:



Circuit Details:

A dual C.M.O.S timer IC type 7556 is used for the purpose; with each of its two halves being wired as a simple as a standard 556 IC will not work in this circuit, or will two standard 555’s. Note that the “CMOS7556” is supplied by many different manufacturers, each using their own type code prefix and suffix. The relevant Texas Instruments product, for instance, will be marked ‘TLC556CN’.

The circuit configuration used here is seldom seen, due probably to the inability of this oscillator to be more than lightly loaded without disturbing the timing. However, it is particularly useful for high impedance logic inputs, since it provides a simple means of obtaining a square wave with 1:1 mark-space ratio, which the ‘orthodox’ configuration does not so easily provide.

IC1.A is a slow oscillator which is enabled when reset pin 4 is taken High, and inhibited when it is taken Low. Out-put pin 5 of IC1.A pulses audio oscillator IC1.B, which is similarly enabled when reset pin 10 is taken High, and inhibited when it is taken Low.

A 12 Volt power suppiled designed for Ron's Modular Burglar Alarm. However, being a popular supply voltage this circuit will have many other uses as well.

Circuit Diagram:



Notes
This Power Supply is suitable for the Modular Burglar Alarm. However, it has other applications. It is designed to provide an output of 12-volts, with a current of up to 1-amp. In the event of mains failure, the back-up battery takes over automatically. When the mains is restored, the battery recharges. Use a genuine alarm type back-up battery. They are maintenance-free, and their terminals can be held at 13v8 for many years, with no ill effects.

A smaller or larger capacity battery may be used, without circuit modification. Use the 2-amp version of the 7805. It needs the larger heatsink because it has to dissipate a lot of energy, especially when called upon to recharge a flat battery. This heatsink is at 9v1, and must NOT be connected to ground. The 7812 never has to dissipate more than 2-watts, so its heatsink can be smaller.

Many of the components, which are shown lying flat on the board, are actually mounted upright. The links are bare copper wire on the component side. The heatsinks are folded strips of aluminium, about 2mm thick. Use a well-insulated panel mounted fuse holder for the mains supply to the transformer, and fit it with a 1-amp fuse.

The Alarm Power Supply Support Material provides a complete circuit description.

This is a Bar Display With Alarm Flasher Schematic Project. Hello Freinds ! Here designed SIMPLE BAR DISPLAY WITH ALARM FLASHER . Schematic: Return to Display Circuits. By using two switching transistors and two LEDs, this circuit can distinguish low-level ac and dc signals. If the red LED illuminates, the signal is positive dc. If the yellow LED lights, the signal is negative dc. If the signal is ac, both LEDs will light.

Bar Display With Alarm Flasher Circuit Schematic Diagram: 

Alarm Power Supply is Simple Alarm Power Supply Circuit.
A 12 Volt power supplied designed for Ron's Modular Burglar Alarm. In-addition, being a popular supply voltage circuit will have many other uses as well as.

Alarm Power Supply Circuit Structure:





The 7812 never has to dissipate more than 2-watts, so its heat sink can be smaller.Many of the components, which are shown lying flat on the board, are actually mounted upright. The links are bare copper wire on the component side. The heat-sinks are folded strips of aluminum, about 2mm thick. Use a well-insulated panel mounted fuse holder for the mains supply to the transformer, and fit it with a 1-amp fuse.