Showing posts with label alarm. Show all posts
Showing posts with label alarm. Show all posts
Wednesday, November 12, 2014
indicator alarm for Water level circuit with explanation
This electronic circuit is a simple water level indicator alarm that is based on few transistors . The circuit is very simple and it has a very low current consumption , so you can use a 9 volts battery to powering this water level indicator alarm . This water level indicator alarm electronic circuit can be used even for rain alarm or short circuit alarm , a resistance with a value from 0 to about 1 M ohm will trigger it . The Q1 transistor acts as a switch which applies current to the unijunction relaxation oscillator Q2 . The signal frequency of the alarm circuit is give by the values and ratios of the C1 / R2 .
If you don’t have the transistors marked on the schematic diagram you can replace them almost with any similar types . As you can see in the schematic diagram , between probes is mounted a switch ( you can use a push-button) for testing the circuit , but it can be removed .
The speaker used in this project must have a impedance between 15 and 90 ohms .
Wednesday, November 5, 2014
Best Automatic Car Alarm
Even the best car alarm is useless if you forget to set it upon leaving your car, whence this circuit. The relay has a make and a break contact: the former is necessary to delay the switching in of the alarm after you have got out of your car, and the latter serves to switch on the car alarm proper. Immediately on re-entering your car, you must press the hidden switch, Si. This causes silicon-controlled rectifier Thi to conduct so that the relay is energized. At the same time, the green LED lights to indicate that the alarm is switched off.
Best Automatic Car Alarm Circuit Diagram
As soon as the ignition is switched off, T, is off, T2 is on, and the buzzer sounds. At the same time, monostable IC1 is triggered, which causes T3 to conduct and the red LED to light. The silicon- controlled rectifier is then off, and D4 is reverse biased, but the relay remains energized via its make contact for a short time, preset by Pi As soon as this time has lapsed, the relay returns to its quiescent state, and the alarm is set via the break contact. The delay time can be set to a maximum of about 1 minute.
Tuesday, November 4, 2014
Fire Alarm Using Thermistor
Small and simple unit, Can be used for Home-Security purpose. In this fire alarm circuit, a Thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the Thermistor (TH1) is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature increases beyond 100 C. The circuit uses readily available components and can be easily constructed on any general-purpose PCB.
Fire Alarm Using Thermistor Circuit diagram:
| Parts | Description |
| R1 | 470R |
| R2 | 470R |
| R3 | 33K |
| R4 | 560R |
| R5 | 470R |
| R6 | 47K |
| R7 | 2.2K |
| R8 | 470R |
| C1 | 10uF-16V |
| C2 | 0.04uF-63V |
| C3 | 0.01uF-63V |
| Q1 | BC548 |
| Q2 | BC558 |
| Q3 | SL100B |
| D1 | Red Led |
| D2 | 1N4001 |
| IC1 | NE555 |
| SPKR | 1W-8R |
| TH1 | Thermistor-10K |
Circuit Operation:
Timer IC NE555 (IC1) is wired as an astable multivibrator oscillating in audio frequency band. Switching transistors Q1 and Q2 drive multivibrator IC1. The output of IC1 is connected to NPN transistor Q3, which drives the loudspeaker (SPKR) to generate sound. The frequency of IC1 depends on the values of resistors R6, R7 and capacitor C2. When Thermistor TH1 becomes hot, it provides a low-resistance path to extend positive voltage to the base of transistor Q1 via diode D2 and resistor R3. Capacitor C1 charges up to the positive voltage and increases the ‘on’ time of alarm.
The higher the value of capacitor C1, the higher the forward voltage applied to the base of transistor Q1. Since the collector of transistor Q1 is connected to the base of transistor Q2, transistor Q2 provides positive voltage to reset pin 4 of IC1. R5 is used such that IC1 remains inactive in the absence of positive voltage. D2 stops discharging of capacitor C1 when the Thermistor connected to the positive supply cools down and provides a high-resistance (10k) path. It also stops the conduction of Q1. To prevent the Thermistor from melting, wrap it up in mica tape. The circuit works off a 6V-12V regulated power supply. D1 is used to indicate that power to the circuit is switched on.
Friday, September 5, 2014
Build a Photo Alarm Wiring diagram Schematic
Build a Photo Alarm Circuit Diagram. This schema is an application for an alarm. The alarm rings, you can see the your photos, family, lover, friends. This schema use LDR1, a cadmium sulphide (CDS) photo resistive cell is used as the lower leg of a voltage divider between Vcc and ground. The timer terminals 2 and 6 are connected to the junction of the photocell and SENSITIVITY control Rl.
Photo Alarm Circuit Diagram
The resistance of the photo resistive cell varies inversely as the light intensity; resistance is high when the illumination level is low; low in bright light. (The Radio Shack CDS cell 276-116 has a typically wide resistance range€”about 3 megohms in darkness and 100 ohms in bright light.) When the light is interrupted or falls below a level set by SENSITIVITY control Rl, the rise in LDRls resistance causes the voltage on pins 2 and 6 to rise. If the control is set so the voltage rises above 2A Vcc, the relay pulls in.
The relay drops out when the light level increases and the drop across the photocell Ms below lA Vcc.(The schema can be modified by placing relay K1 and diodeD1 between pin 3 and ground. In this case, the relay drops out when the voltage on pins 2 and 6 rises above V% Vcc, and pulls in when it falls below Vi Vcc. This modification is valuable when the relay has single-throw contacts.) Opening and dosing of the relay contacts occurs at different illumination levels. This J/3 Vcc hysteresis is an advantage that prevents the schema from hunting and the relay from chattering when there are very small changes in illumination.
Thursday, December 26, 2013
Pc Temperature Alarm
If your PC overheats, it could damage its expensive components. Here’s a circuit that warns you of your PC getting heated. Today’s computers contain most of the circuitry on just a few chips and reduced power consumption is a byproduct of this LSI and VSLI approach. Some PCs still have power supplies that are capable of supplying around 200W, but few PCs actually consume power to this extent.
On the other hand, apart from some portable and small desktop computers that use the latest micro-power components, most PCs still consume significant amount of power and generate certain amount of heat. The temperature inside the aver-age PC starts to rise well above the ambient temperature soon after it is switched on. Some of the larger integrated circuits become quite hot and if the temperature inside the PC rises too high, these devices may not be able to dissipate heat fast enough. This, in turn, could lead to failure of devices and eventually of the PC. Various means to combat overheating are available, ranging from simple temperature alarms to devices like temperature-activated fans to keep the microprocessor cool.
Here is a temperature alarm that activates an audio ‘beeper’ if the temperature inside the PC exceeds a preset threshold. This temperature is user-adjustable and can be anywhere between 0°C and 100°C. The unit is in the form of a small PC expansion card, which you simply need to plug into any avail-able slot of the host PC. It is powered from the PC and consumes only about 12 mA. The sensor (LM35) used here pro-vides a substantial amount of on-chip signal conditioning, including amplification, level shifting and phase in-version. As a result, it provides an out-put of 10 mV per degree centigrade rise in temperature. It caters to a temperature measurement range of 0°C to 100°C, which corresponds to 0V to 1V of voltage.
Pc Temperature Alarm Circuit Diagram
Fig. 1 shows the circuit of the PC temperature alarm and Fig. 2 shows the pin configuration of sensor LM35. IC LM35 (IC1) is an easy-to-use temperature sensor. It is basically a three-terminal device (two supply leads plus the output) that operates over a wide supply range of 4 to 20V. It consumes only 56 µA at 5V and generates insignificant heat.
IC2 is an operational amplifier used here as a voltage comparator. VR1 pro- vides a reference voltage that can be set anywhere from 0V to approximately 1V, which matches the output voltage range of IC1. This reference voltage is applied to the inverting in- put of IC2 and the output of IC1 is coupled to the non-inverting input. Consequently, the output of IC2 is low if the output of IC1 is below the reference voltage, or high if the output of IC1 exceeds the reference voltage.
Pin details of LM35
The low-frequency oscillator IC3 is a standard 555 astable multivibrator circuit. It is gated via the reset input at pin 4, which holds output pin 3 low when IC3 is gated ‘off’ (when the out-put of IC2 is low). This prevents IC4 from oscillating. IC4 is another 555 astable multivibrator circuit, gated via its reset input. It has an operating frequency of approximately 2.5 kHz. When IC3 is activated, its output pro-vides a square wave of 1 Hz. This is used to trigger IC4, which gives an audio output of 2.5 kHz in bursts. It is connected to loudspeaker LS1 to generate alarm.
The alarm circuit can be fitted into any spare expansion slot of the PC, but be careful to fit it the right way round. Before setting VR1 to a suitable thresh-old temperature, decide what that temperature should be. The technical specification in your computer’s manual might be of help here. If we assume that the room temperature will not normally exceed 25oC, the temperature of the interior of the computer would be up to 35oC. Unless you have good reason to use a different threshold temperature, VR1 should be set for a wiper potential of 350 mV.
Trial-and-error method can be used in the absence of test equipment to enable VR1, but it would be a bit time-consuming. There is a slight complication in that the computer’s outer casing must be at least partially removed to provide access to VR1. Once VR1 has been adjusted, the outer casing must be put back into place so that the interior of the computer can warm up in the normal way. You must therefore al-low time for the temperature inside the computer to rise back to its nor-mal operating level each time VR1 is readjusted.
Source: http://www.ecircuitslab.com/2012/05/pc-temperature-alarm.html
Monday, December 23, 2013
THIEF ALARM
BURGLAR ALARM
To detect the present robber we have used LDR and a source of light.
LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has a resistance of about 1 megaohms when in total darkness,but a resistance of only about 2-5 k ohms when brightly illuminated. It responds to a large part of the light spectrum.
LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has a resistance of about 1 megaohms when in total darkness,but a resistance of only about 2-5 k ohms when brightly illuminated. It responds to a large part of the light spectrum.
The source of light and LDR is so adjusted with a reflector that light will directly fall on the LDR but when robber enters inside then it will block the beam of light and LDR will be under darkness.
1)9V battery with snap
2) LDR
3) Variable resistance 100K ohms
4) Resistance 470 ohms
5) LED
6) IC 555
7) Switch
2) LDR
3) Variable resistance 100K ohms
4) Resistance 470 ohms
5) LED
6) IC 555
7) Switch
8) BUZZER
Sunday, December 22, 2013
Build an Alarm Control Keypad Circuit Diagram
The IC is a quad 2 input “AND” gate, a CMOS 4081. These gatesonly produce a HIGH output, when BOTH the inputs are HIGH. Whenthe key wired to `E` is pressed, current through R1 and D1switches Q5 on. The relay energises; and Q5 is `latched on` byR8. Thus, the Alarm is set by pressing a single key, say one ofthe tw1o non-numeric symbols.The alarm will switch off when the 4 keys connected to“A,B,C,D” are pushed in the right order. The circuit worksbecause each gate `Stands` upon its predecessor.If any key otherthan the correct key is pushed, then gate 1 is knocked out of thestack, and the code entry fails.
Pin 1 is held high by R4. This`Enables` gate 1; and when button `A` is pressed, theoutput at pin 3 will go high. This output does tw1o jobs.It locksitself `ON` through R2 and it `Enables` gate 2, by taking pin 5,high. Now, if `B` is pressed, the output of gate 2, at pin 4will go high. This output does tw1o jobs. It locks itself `ON`through R3 and it `Enables` gate 3 by taking pin 12 high.Now, if `C` is pressed, the output of gate 3 will lock itself`ON` through R5 and, by taking pin 8 high, `Enable` gate 4.Pressing `D` causes gate 4 to do the same thing; only this timeits output, at pin 10, turns Q4 `ON`.
This takes the base of Q5to ground, switching it off and letting the relay drop out. Thisswitches the alarm off.Any keys not connected to `A B C D E` are wired to the base ofQ1. Whenever `E` or one of these other keys is pressed, pin 1 istaken low and the circuit is reset. In addition, if `C` or `D`is pressed out of sequence, then Q2 or Q3 will take pin 1 low andthe circuit will reset. Thus nothing happens until `A` ispressed. Then if any key other than `B` is pressed, the circuitwill reset.Similarly, after `B`, if any key other than `C` is pressed,the circuit will reset. The same reasoning also applies to `D`.The Keypad needs to be the kind with a common terminal and aseparate connection to each key. On a 12 key pad, look for 13terminals. The matrix type with 7 terminals will NOT do.
Wire thecommon to R1 and your chosen code to `A B C D`. Wire `E` to thekey you want to use to switch the alarm on. All the rest go tothe base of Q1.The diagram should give you a rough guide to the layout of thecomponents, if you are using a strip board. The code you choosecan include the non-numeric symbols. In fact, you do not have touse a numeric keypad at all, or you could make your own keypad.I haven`t calculated the number of combinations of codesavailable, but it should be in excess of 10 000 with a 12 keypad; and, after all, any potential intruder will be ignorant ofthe circuit`s limitations. Of Course, if you must have a moresecure code, I can think of no reason why you shouldn`t addanother 4081 and continue the process of enabling subsequentgates. Or you could simply use a bigger keypad with more “WRONG”keys.Any small audio transistors should do.
The 27k resistors couldbe replaced with values up to 100k. And the only requirementsfor the 4k7 resistors is that they protect the junctions whileproviding enough current to turn the transistors fully on.Capacitors (C1 C2 C3 C4 C5) are there to slow response timeand overcome any contact bounce. They are probably unnecessary.
Alarm Control Keypad Circuit Diagram
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