APPLIED ELECTRONIC CIRCUIT

Low Cost Fire Alarm Using Thermistor

noreply@blogger.com (Go2Media) — Sat, 30 Apr 2011 17:20:00 +0000

The following is a fire alarm circuit that works by detecting heat changes due to temperature rise due to fire. For heat-detection sensors use a Thermistor. Resistance value of thermistor (TH1) in conditions of normal temperature is about 10K ohms.

The resistance value will decrease a few ohms with a temperature rise above 100 degrees Celsius. This fire alarm circuit is very easy to be built with many components available in the market.

How It Works

Timer IC NE555 (IC1) is connected as an astable multivibrator oscillating in the audio frequency band. Switching transistors Q1 and Q2 drive multivibrator IC1. The output of IC1 is connected NPN transistor Q3, the speaker (SPKR) to generate audio discs.

The frequency of IC1 depends on the values of resistors R6, R7 and capacitor C2. If TH1 thermistor gets hot, it offers a low resistance path to the positive voltage to expand the base of transistor Q1 through diode D2 and resistor R3. The capacitor C1 to the positive voltage and increases the 'on ' time for the alarm.

The higher the value of capacitor C1, the more forward voltage at the base of transistor Q1. Since the collector of transistor Q1 is connected to the base of transistor Q2, transistor Q2 provides a positive voltage to reset pin 4 of IC1. R5 is used so that IC1 is inactive in the absence of positive voltage. D2 stops discharging capacitor C1 when the

Thermistor is connected to the positive supply voltage and cooling provides high resistance (10k) path. It also stops the conduction of Q1. To prevent melting of the thermistor, wrapped in tape mica. The circuit operates from a 6V-12V power supply. D1 is used that power to the circuit is on it.
Source: Fire Alarm Using Thermistor.

Fire Alarm Parts List

R1 = 470R
R2 = 470R
R3 = 33K
R5 = 560R
R4 = 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

Frost Detector Temperature Sensor Circuit

noreply@blogger.com (Go2Media) — Mon, 13 Jul 2009 06:09:00 +0000

To know whether it is freezing you only need to measure the temperature. This has to be done accurately, of course, and therefore we need to choose a temperature sensor that we have some confidence in. The choice has again been made for a type that we have already used in many previous Elektor circuits, the LM35CZ (-40 to 110 °C). This sensor is not expensive and generates an output voltage that is proportional to the temperature in degrees Celsius (10 mV/°C).

Sensor
An LM35 is normally powered from a single-ended power supply and 0 °C corresponds to an output voltage of 0 V. It is therefore not possible to measure negative temperatures with an LM35 in the standard application circuit. It is however possible to measure negative temperatures if its output is connected to a negative supply voltage via a resistor. There needs to be a current of 50 μA through this resistor (R2 in the schematic).

We only need to detect the freezing point with this circuit. That is why there is a comparator after the temperature sensor, which turns an LED on if the temperature has dropped below 0 °C during the course of the night. To ensure that the comparator operates properly it is necessary that the measurement value can become slightly more negative with respect to the input. To solve this problem, a diode (D1) has been connected in series with the ground connection of the LM35. The voltage drop across D1 (because of the small current through the LM35 this is only 0.47 V) acts as 'negative' power supply. Since the non-inverting input of comparatorIC2 is connected via R3 to the anode of D1 it functions as the 0°C-reference level for the comparator.

Comparator
The comparator is a standard opamp type TLC271, which we configured for minimal current consumption by
connecting the bias-select input (pin 8) to the power supply voltage. There is no need for the detector to be fast and it will therefore work well with the opamp operating in its most economical mode.

LED D3 provides the frost indication. It is the intention that the LED stays on once the temperature in the room drops below freezing or when it has been below freezing. To realise this, an asymmetric hysteresis is created with the aid of R3, R4 and D2. The instant that the output goes high, the non-inverting input goes more positive via D2 and R4, and the output therefore stays high. The temperature would now have to increase to more than about 30° before the LED will go out by itself. In practice this probably means that it is summer and that it is not likely to freeze anyway. If need be, the hysteresis can be increased by increasing the value of R3.

Capacitor C2 is added to make sure that the LED remains off (the circuit is reset) when the power supply is connected. The non-inverting input of the opamp is briefly connected to ground and the output is therefore low. R1 and S1 are only required if the circuit needs to be reset when the battery is connected. Instead of S1 you could also use a power supply switch or even just simply disconnect the battery for a moment.

Thrifty Power supply
Since the circuit is assumed to be powered from a battery there was a conscious effort to minimise the power consumption. The current consumption of the prototype, at a power supply voltage ranging from 6 to 9 V, was less than 120 μA. When the LED is on, the current consumption rises to only 1 mA at 6V and 1.8 mA at 9V, because a low current LED is used. In our prototype we used a green, low-current LED.

If four AA penlight batteries (with a capacity of about 2 Ah) are used, then the circuit will run for about two years in standby mode. When the LED is on this is considerably shorter, of course (about two months, this is easily long enough to run through a severe winter period). A standard 9-V battery will also last a single winter, provided you frequently check whether the LED is on.

Finally, a comment about the TLC-271CP used here. The version with the C-suffix is specified for an operating range from 0 to 70 °C, but will continue to work at lower temperatures, particularly considering that the IC is not used in a linear application. If in doubt you can always try to get your hands on a version with the I-suffix (that is, TLC271IP: –40 to 125°C). But that is only necessary if you expect it to be real cold in the monitored room...

Quick assembly
The circuit contains very few parts and can therefore be easily built on a small piece of prototyping board. There is no need to calibrate anything, once built it is ready to go. Author: Ton Giesberts, Elektor Magazine, 2008.

5 Zone Alarm Circuit

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 18:33:00 +0000

Each zone alarm uses a normally closed contact. These can be micro switches or standard alarm contacts (usually reed switches). Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppresser. The key switch acts as the Set/Unset and Reset switch.

For good security this should be the metal type with a key. At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1.

To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Source

Light-Sensitive-Alarm

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 18:27:00 +0000

The Alarm circuit detects a sudden shadow falling on the light-sensor and sounds the bleeper when this happens. The circuit will not respond to gradual changes in brightness to avoid false alarms. The bleeper sounds for only a short time to prevent the battery running flat. Normal lighting can be used, but the circuit will work best if a beam of light is arranged to fall on the light-sensor. Breaking this beam will then cause the bleeper to sound. The light sensor is an LDR (light-dependant resistor), this has a low resistance in bright light and a high resistance in dim light.

- The light-sensitivity of the circuit can be adjusted by varying the 100k preset.
- The length of bleep can be varied from 0.5 to 10 seconds using the 1M preset.

Using the 7555 low-power timer ensures that the circuit draws very little current (about 0.5mA) except for the short times when the bleeper is sounding (this uses about 7mA). If the circuit is switched on continuously an alkaline PP3 9V battery should last about a month, but for longer life (about 6 months) you can use a pack of 6 AA alkaline batteries.

Source

Sun-Up Alarm

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 18:24:00 +0000

The Sun-Up Alarm circuit can be used to provide a audible alarm for when the sun comes up or it can be used in a dark area and detect when a light comes on. It can also be used to detect a light beam, headlights etc. The circuit works as follows.

The phototransistor is very sensitive to light. (Any phototransistor will work fine) The sun shining on this device will provide a high to one of the NAND gates. This will cause another NAND gate to oscillate which will drive another gate to output a 100hz tone. The transistor provides drive for the speaker.

Source

Touch Switch Circuit

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 18:19:00 +0000

This electronic circuit uses a 555 timer as the bases of the touch switch. You can learn more about 555 timers in the Learning section on my site. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.

Source: http://www.free-electronic-circuits.com/circuits/touch-switch.html

Proximity Detector Using CS209

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 15:02:00 +0000

This is a simple proximity detector using IC CS209. The CS209A is a bipolar monolithic integrated circuit for use in metal detection/proximity sensing applications.The CS209A contains an oscillator set up by an external parallel resonant tank and a feedback resistor connected between pin 2 & 3.

The internal oscillator operates close to the resonant frequency of the tank circuit.As a metal object is brought close to the inductor, the amplitude of the voltage across the tank gradually begins to drop. When the envelope of the oscillation reaches a certain level, the IC causes the outputs to toggle states.potentiometer connected between pin 1 & 8 is adjusted to achieve a certain detection distance range. The larger the resistance the greater the trip-point distance.

Detection range can be incresed by using a high Q coil.Maximum possible range is 1 inch with a well tuned circuit.Only difficulty in making this circuit is the tuning up the circuit to a particular range.For making it easy place a metal piece at the desired distance from coil (with in 1 inch) and adjust resistance Rf to make one of the outputs ( pin4 or 5) to change state.

CS209 Datasheet

Fire Alarm Using Thermistor

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 14:48:00 +0000

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.

Timer IC NE555 (IC1) is wired as an astable multivibrator oscillating in audio frequency band. Switching transistors T1 and T2 drive multivibrator NE555 (IC1). The output of IC1 is connected to npn transistor T3, which drives the loudspeaker (LS1) to generate sound. The frequency of IC1 depends on the values of resistors R5 and R6 and capacitor C2.

When thermistor TH1 becomes hot, it provides a low-resistance path to extend positive voltage to the base of transistor T1 via diode D1 and resistor R2. 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 T1 (BC548).

Since the collector of transistor T1 is connected to the base of transistor T2, transistor T2 provides positive voltage to reset pin 4 of IC1 (NE555). Resistor R4 is used such that IC1 remains inactive in the discharging of capacitor C1 when the thermistor connected to the positive supply cools down and provides a high-resistance (10-kilo-ohm) path. It also stops the conduction of T1. To prevent the thermistor from melting, wrap it up in mica tape.

The circuit works off a 6V-12V regulated power supply. LED1 is used to indicate that power to the circuit is switched on.

Source

Fire Alarm Circuit

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 14:42:00 +0000

This electronic circuit is a simple fire alarm circuit based on a LDR and lamp pair for sensing the fire. The alarm works by sensing the smoke produced during fire.The circuit produces an audible alarm when the fire breaks out with smoke.

When there is no smoke the light from the bulb will be directly falling on the LDR.The LDR resistance will be low and so the voltage across it (below .6V).The transistor will be OFF and nothing happens.When there is sufficient smoke to mask the light from falling on LDR, the LDR resistance increases and so do the voltage across it.Now the transistor will switch to ON.This gives power to the IC1 and it outputs 5V.This powers the tone generator IC UM66 (IC2) to play a music.This music will be amplified by IC3 (TDA 2002) to drive the speaker.

The diode D1 and D2 in combination drops 1.4 V to give the rated voltage (3.5V ) to UM66 .UM 66 cannot withstand more than 4V.

Notes:

The speaker can be a 8Ω tweeter.
POT R4 can be used to adjust the sensitivity of the alarm.
POT R3 can be used for varying the volume of the alarm.
Any general purpose NPN transistor(like BC548,BC148,2N222) can be used for Q1.
The circuit can be powered from a 9V battery or a 9V DC power supply.
Instead of bulb you can use a bright LED with a 1K resistor series to it.

Source: http://www.circuitstoday.com/?p=255

Car Battery Alarm with CA3140

noreply@blogger.com (Go2Media) — Mon, 07 Jul 2008 11:07:00 +0000

This electronic circuit is for Checking battery in car. It use IC CA3140 and Transistor circuit.

click here for schematic

Source: elecfree.com

Modular Burglar Alarm

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 05:25:00 +0000

The Basic Alarm Circuit has an automatic Exit/Entry Zone - an Instant Alarm Zone that will accept both normally-closed and normally-open triggering devices - and an "Always On" 24-hour Personal Attack/Tamper Zone. By using the Expansion Modules - you can add as many extra alarm zones as you require.

Schematic Diagram

The Alarm is armed and disarmed by SW1. Before you move the switch to the "set" position - all the green LEDs should be lighting. You then have up to about a minute to leave the building. As you do so - the Buzzer will sound. It should stop sounding when you close the door behind you. This indicates that the Exit/Entry loop has been successfully restored within the time allowed.

When you re-enter the building - you have up to about a minute to move SW1 to the "off" position. If SW1 is not switched off in time - the relay will energize - and the main bell will ring. It will continue ringing for up to about 40 minutes. But it can be turned off at any time by SW1.

The "Instant" zone has no Entry Delay. The moment one of its normally-open switches is closed - the main bell will ring. Similarly - the moment one of its normally-closed switches is opened - the main bell will ring. If you don't want to use normally-open switches - leave out R8, C8 and Q2 - and fit a link between Led 3 and C7.

The 24 Hour Personal Attack and Tamper protection is provided by the SCR/Thyristor. If one of the switches in the normally-closed loop is opened - current through R11 will trigger the SCR - and the main bell will ring. In this case the bell has no time limit. To reset the PA/Tamper zone - first restore the normally-closed loop - then press SW2 momentarily. This will interrupt the current and reset the SCR.

Two-Zone Expansion Module

The basic circuit will be satisfactory in many situations. However, if you have a large building to protect - it's much easier to find a fault - when the system is divided into zones - and the control panel can "remember" which zone has caused the activation.

The expansion modules are designed to do this. Although they will work with the existing instant zone - they are intended to replace it. When a zone is triggered - its red LED will light and remain lit - to indicate that the zone has been activated.

The idea is that - once you've noted the zone in question - you then press the reset button and turn off the LED. The reset button simply turns off the LED. It doesn't reset the zone. The zone resets automatically when the trigger circuit is restored. If you're using more than one expansion module - they can all share a single reset button.

Inertia-Sensor Module

Power Supply

Source

Electronic Candle Blow Out

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 03:28:00 +0000

This electronic design was developed by request of a correspondent having made a sort of LED candle and needing to switch off the LED with a puff. This simple, easy to build gadget can be useful as a prop for Halloween and Christmas season, shows and the like. Q2 & Q3 form a self-latching pair that start operating when P1 is pushed: in this way the LED (or bulb) will illuminate steadily. When someone emits a strong puff in the vicinity of the small electret microphone, the resulting signal will be greatly amplified by Q1 and a rather long positive pulse (shaped by D1 and C2) will reset the self latching pair through the Emitter of Q2.

The very low (and unusual) value of C1 acts as a simple high-pass filter, in order to prevent that normal speech or environmental noise shut off the device. Obviously, such a simple filter cannot be very discriminating, therefore, not only a strong puff will reset the circuit but also a loud shout, blow, clap or stroke.

Parts:
R1 - 10K 1/4W Resistor
R2 - 1M 1/4W Resistor
R3 - 1K 1/4W Resistor
R4 - 4K7 1/4W Resistor (See Notes)
R5 - 10K 1/4W Resistor (See Notes)
R6 - 100R 1/4W Resistor (See Notes)
C1 - 100pF 63V Ceramic Capacitor
C2 - 10µF 25V Electrolytic Capacitor
C3 - 100nF 63V Polyester or Ceramic Capacitor
D1 - 1N4148 75V 150mA Diode
D2 - LED (Any suitable type)
Q1 - BC550C 45V 100mA Low noise High gain NPN Transistor
Q2 - BC337 45V 800mA NPN Transistor
Q3 - BC327 45V 800mA PNP Transistor
MIC1 - Miniature electret microphone
P1 - SPST Pushbutton Switch
B1- 3V Battery (2 x 1.5V AA, AAA Cells in series etc.)

Notes:

A small bulb can be used in place of the LED. In this case a 3 - 3.5V, 0.7W (200mA) incandescent bulb can be used satisfactorily. Therefore, D2, R5 and R6 must be omitted, the bulb wired in place of R5 and R4 value changed to 1K5.
Using a bulb instead of the LED, a 1.5V battery supply could also be used. A 1.5V, 0.3A incandescent bulb will work, but R4 must be replaced by a 470 Ohm Trimmer, adjusted to allow a reliable circuit operation.
Please note that the circuit will draw a small current even when the LED or bulb are off. This current is about 1.2mA for the LED version of the circuit, 1.5mA for the 3V bulb version and 1mA for the 1.5V bulb version. Therefore, in some circumstances, the addition of a power on-off switch could be necessary.

Source

Fogger Controller

noreply@blogger.com (Go2Media) — Mon, 30 Jun 2008 02:58:00 +0000

Foggers used to generate fog and smoke effects operate by heating a special fogger fluid. They consist of a heting element which is kept in the right temperature using a thermostat. When the operator want to generate smoke, he/she presses the controller button which starts the pump which pumps fog fluid to the heating element. When smoke fluid enters the heating element, in starts to evaporate and produce smoke.

Cheap foggers usually come with only a simple one button controller. This controller is useful for smoke starting smoke effects on user request, but is not very useful if you want to keep up a constant level of fog on the room. This is where more expensive foggers come to play, because they come usually with a controller which allows you to generate fog at some slow constant adjustable rate.

If you happen to own a cheap smoke machine and happen to want this kind of functionally only found on expensive models, the circuit shown on this web page might turn to be useful to you.

Fogger controller circuit
The following circuit shows the circuit diagram of the advanced smoke machine controller I have used with my SUPERSTAR FZ-920 SMOKE MACHINE:

Circuit operation
When the power is connected to the circuit by turning on SW2, RELAY1 get energized for the time it get for it to load C3 through R1 and R3. After that the relay get de-energized, C3 gets discharged through R2 and R4. The setting of R2 determines the discharge time which can be up to 1 minute. After C3 is discharged, the releay is activated. C3 charging starts again. The charging of C3 take around 2 seconds. After that relay is de-energized and C3 discharge starts again.

Every time the relay is energised, the smoke machine is set to push out smoke. The time it puts out smoke is around 2 seconds, which was adequate to put out enough smoke fluid that the smoke machine puts out smoke for a brief amount. The iime between the smoke output is adjustable from practically constant smoke output to one minute pause between brief bursts of smoke.

Component list
R1 2.2 kohm
R2 220 kohm potentiometer
R3 4.7 kohm
R4 820 ohms
R5 470 ohms
D1 1N4007
D3 1N4148
D3 1N4007
D4 RED LED
C2 220 uF 25V
C3 470 uF 16V
C4 22 nF
IC1 LM555
RELAY1 Relay with 12V coil and 250V 4A contacts
SW1 250V 4A switch
SW2 General purpose low voltag switch, at least 1A current rating
GLIMM GLIMM lamp with internal current limiting resistor (Rx) for 230V (panel light)
CON Male 3 pin IEC mains connector

Source: Copyright Tomi Engdahl 1999

Water Level Alarm

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 19:05:00 +0000

This circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full. The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs.

When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the + supply are shorted by water. This closes the switch S1 and turns the LED1 ON. As the water continues to fill the tank, the LEDs2 , 3 and 4 light up gradually.
The no. of levels of indication can be increased to 8 if 2 CD4066 ICs are used in a similar fashion.

When the water is full, the base of the transistor BC148 is pulled high by the water and this saturates the transistor, turning the buzzer ON. The SPST switch has to be opened to turn the buzzer OFF.
Remember to turn the switch ON while pumping water otherwise the buzzer will not sound!

Wireless Antitheft Alarm

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 18:55:00 +0000

This FM radio-controlled anti- theft alarm can be used with any vehicle having 6-12 volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside.

Receiver is tuned to the transmitter’s frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energised.

When an intruder tries to drive the car and takes it a few metres away from the car porch, the radio link between the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hissing noise. Hissing AC signals are coupled to relay switching circ- uit via audio transformer. These AC signals are rectified and filtered by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2. Thus transistor T2 conducts, and it pulls the base of relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on. If, by chance, the intruder finds out about the wireless alarm and disconnects the transmitter from battery, still remote alarm remains activated because in the absence of signal, the receiver continues to produce hissing noise at its output. So the burglar alarm is fool-proof and highly reliable.

Rain Alarm

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 18:44:00 +0000

This circuit gives out an alarm when its sensor is wetted by water. A 555 astable multivibrator is used here which gives a tone of about 1kHz upon detecting water. The sensor when wetted by water completes the circuit and makes the 555 oscillate at about 1kHz.

The sensor is also shown in the circuit diagram. It has to placed making an angle of about 30 - 45 degrees to the ground. This makes the rain water to flow through it to the ground and prevents the alarm from going on due to the stored water on the sensor.

The metal used to make the sensor has to be aluminium and not copper. This is because copper forms a blue oxide on its layer on prolonged exposure to moisture and has to be cleaned regularly. The aluminium foils may be secured to the wooden / plastic board via epoxy adhesive or small screws. The contact X and Y from the sensor may be obtained by small crocodile clips or you may use screws.

Source

Smoke Detector Circuit - Fire Alarm

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 11:13:00 +0000

This circuit uses a very simple approach to detecting smoke in the air. Quite simply, it uses a bulb as a light source, and an LDR (Light Dependent Resistor) as a light detector. As fire smoke comes between the bulb and LDR, the resistance of the LDR changes, which in turn trigger an alarm.

This probably isn't an ideal approach given that ambient light levels are likely to cause false alarms, however it is an interesting experiment. Just please don't set any fires while experimenting. And please don't rely on it as a replacement for a real fire alarm device.

Source: electrokits.com

Phone Line Status Indicator

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 10:12:00 +0000

This Phone Line Status Indicator circuit has been designed by Gabriele Bandini. His home is full of telephones, modems, and... kids. After a dozen of modem crashes, he decided to put an indicator LED on every phone plug to show to the family when the phone line is free.

If you have a FAX and a phone on the same line, this circuit can show you when to make a phone call without disrupting an incoming fax. If you have an internal modem, this circuit will show you when it is on hook

The whole circuit is placed inside the phone plug. The LED is visible drilling a hole on the back shell. Now I know why italian phone plugs are so large!!!

Note that this circuit is designed to work with italian telephones and that you need the written approval of your phone company prior to put something on the phone line.

Source: Gabriele Bandini

Wireless Alarm

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 10:02:00 +0000

Making yourself an alarm is both useful and interesting: but the best part is when you take the remote control out of your pocket, and switch on the alarm while saying to your friends: "I've done it in a weekend".

Making yourself an alarm gives you maximum flexibility: as this project works according to the Nutchip truth table, you can change it to suit your needs. Some people would like to have like a "panic" button, in order to sound the siren. Some other pepople need a very long time to leave the house. Or you might be looking for an alarm that keeps that special sensor on even if you are at home. Possibilites are unlimited!

Wired + wireless
This alarm is controlled by an handy radio remote control. It is compatible with a variety of sensors:

wireless* passive infrared sensors (PIR), capable to detect human body heat in a room of normal size
common wired volumetric sensors, radar or infrared
magnetic switches (reed switches), immediate or delayed, in order to sense door or windows openings
wireless* magnetic sensors

All of these sensors can be configured for either immediate or delayed alarm. Delayed alarms are required to allow some time for the legitimate user to get in an switch the alarm off. You can mix sensors of different types. Almost all alarm sensors adopt "normally closed" contacts in order to detect wire cuts.

Source: Copyright Alberto Ricci Bitti

Build Yourself a Witness Camera

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 09:55:00 +0000

The Witness Camera is an automated, self-recording surveillance camera, that uses a gigabyte-class flash card as recording media. I designed the Witnesscam because available surveillance solutions were too expensive or impractical for home use.

The system from a VGA CMOS colour camera, a passive-infrared (PIR) movement sensor, an ATmega32 processor, and a 1GB SD-card.

The prototype looks like an ordinary alarm detector. But when it detects people moving around, it silently starts recording.

A 1 GB card can store 50,000 colour frames, with a definition similar to industrial VHS-CCTV recorders (320x200), taking a new picture every 2.5 or 3 seconds. On most typical domestic environments, this translates to more than one month of images before overwriting the oldest frames.

The Witness Camera features also a high resolution mode, taking pictures at 640x480 pixels every 3.5 or 4 seconds. Thanks to embedded image compression, the same card can contain as much as 25,000 frames when high-resolution is selected.

The recording system is flexible, allowing to choose between PIR activated, timer, continuous and externally triggered recording modes. You can decide what intervals to use and how many extra frames to take after a trigger ends.

Creating new applications, like an automatic door capable of taking snapshots of persons entering a building, or using it as an in-vehicle recorder, is simply a matter of selecting the operating mode and connecting a trigger source.

Grand prize winner-Atmel AVR 2006 Design Contest
Source: Copyright Alberto Ricci Bitti

Build a DS1621 PC Thermometer

noreply@blogger.com (Go2Media) — Sun, 29 Jun 2008 09:42:00 +0000

This incredibly simple thermometer plugs on any free serial port. Does not make use of any programmable components as microcontrollers. It gives temperature readings accurate to 0.5°C with no calibration. It's cheap, so I've put one on any PC I use. And it's soooo nice to have the temperature shown on the Windows taskbar, that a million friends asked me to build one!

Build yourself an accurate thermometer
Since I have no time to build a million pcTHERMs, I give you the plans and the software to build one on your own.
This project is easy enough for beginners, the only difficulties possibly arising from serial port hardware incompatibility from PC to PC. In the single-sensor version, you need only the sensor IC, a voltage regulator and and handful of diodes and resistors. Build it, and learn the secrets of IIC bus, how to implement IIC bus using only two resistors and a couple of zeners, how to drive it on a serial port using Visual Basic .Components involved are available on the worldwide RS-components catalogue.

Source: Alberto Ricci Bitti

LED Thermometer

noreply@blogger.com (Go2Media) — Mon, 23 Jun 2008 05:28:00 +0000

This LED thermometer is designed for in home use, to read temperatures between about 60 and 78 degrees Fahrenheit. It is based around a precision temperature sensor IC, the LM34DZ. This sensor require no calibration and can measure temperatures of between -50F and +300F. While the circuit shown here does not use the full range of that sensor, it can be modified to do so by simply changing the voltage reference to U2 at the sacrifice of precision.

Part Lists:
C1 - 1uF 25V Electrolytic Capacitor
C2 - 10uF 25V Electrolytic Capacitor
R1 - 2.2K 1/4W Resistor
R2, R5, R7 3 - 1K Trim Pot
R3 - 1K 1/4W Resistor
R4 - 1.5K 1/4W Resistor
R6 - 470 Ohm 1/4W Resistor
R8 - 100 Ohm Or 15 Ohm 1/4W Resistor (See Notes)
D1 - D10 - LED
U1 - LM34DZ Precision Fahrenheit Temperature Sensor
U2 - LM3914 Bar/Dot Graph Driver IC
MISC - Board, Wire, Socket For U1 and U2, Case

Notes:

The pinout of U1 depends on the version of the IC you purchase. These options are shown below:

You will want to build the circuit with U1 and U2 in sockets in order to be able to complete calibration (which requires removal of these ICs).
You can use any LED you want for D1 - D10, however blue LEDs have a higher voltage requirement so if you want to go blue for a modern look, they may appear more dim then red, yellow or green.
By leaving pin 9 of U2 disconnected, the graph will operate in dot mode and R8 should be 100 Ohm. If you build the circuit with pin 9 tied to 9V, the circuit will be in graph mode and R8 should be 15 Ohms.
To calibrate the circuit, you will need a voltmeter. Power the circuit up and let it sit for a few minutes for temperature to stabilize. Ground the negative lead of the meter and connect the positive lead to pins 6 and 7 of U2. Set R7 so the meter reads as close to 3.345V as possible. Now connect the positive lead of the meter to pin 4 of U2 and adjust R5 until the meter reads 2.545V. Finally, disconnect power to the circuit and remove U1 and U2 from their sockets. Measure the value of R3 with an ohmmeter and remember that value. Connect the ohmmeter across R1 and adjust R1 to a value of exactly 3 times the value of R3. Reinstall U1 and U2 and the circuit is ready for use.

Muscular Bio-Stimulator

noreply@blogger.com (Go2Media) — Sun, 15 Jun 2008 09:22:00 +0000

Particularly suitable for cellulite treatment 3V battery supply, portable set

Device purpose:
This is a small, portable set, designed for those aiming at look improvement. The Bio-Stimulator provides muscles' stimulation and invigoration but, mainly, it could be an aid in removing cellulite. Tape the electrodes to the skin at both ends of the chosen muscle and rotate P1 knob slowly until a light itch sensation is perceived. Each session should last about 30 - 40 minutes.

Circuit Diagram:
IC1 generates 150µSec. pulses at about 80Hz frequency. Q1 acts as a buffer and Q2 inverts the polarity of the pulses and drives the Transformer. The amplitude of the output pulses is set by P1 and approximately displayed by the brightness of LED D1. D2 protects Q2 against high voltage peaks generated by T1 inductance during switching.

Parts:
P1 - 4K7 Linear Potentiometer

R1 - 80K 1/4W Resistor
R2 - 1K8 1/4W Resistor (see Notes)
R3 - 2K2 1/4W Resistor
R4 - 100R 1/4W Resistor
C1 - 100nF 63V Polyester Capacitor
C2 - 100µF 25V Electrolytic Capacitor
D1 - LED Red 5mm.
D2 - 1N4007 1000V 1A Diode
Q1,Q2 - BC327 45V 800mA PNP Transistors
IC1 - 7555 or TS555CN CMos Timer IC
T1 - 220V Primary, 12V Secondary 1.2VA Mains transformer (see Notes)
SW1 - SPST Switch (Ganged with P1)
B1 - 3V Battery (two 1.5V AA or AAA cells in series etc.)

Notes:

T1 is a small mains transformer 220 to 12V @ 100 or 150mA. It must be reverse connected i.e. the 12V secondary winding across Q2 Collector and negative ground, and the 220V primary winding to output electrodes.
Output voltage is about 60V positive and 150V negative but output current is so small that there is no electric-shock danger.
In any case P1 should be operated by the "patient", starting with the knob fully counter-clockwise, then rotating it slowly clockwise until the LED starts to illuminate. Stop rotating the knob when a light itch sensation is perceived.
Best knob position is usually near the center of its range.
In some cases a greater pulse duration can be more effective in cellulite treatment. Try changing R2 to 5K6 or 10K maximum: stronger pulses will be easily perceived and the LED will shine more brightly.
Electrodes can be obtained by small metal plates connected to the output of the circuit via usual electric wire and can be taped to the skin. In some cases, moistening them with little water has proven useful.
SW1 should be ganged to P1 to avoid abrupt voltage peaks on the "patient's" body at switch-on, but a stand alone SPST switch will work quite well, provided you remember to set P1 knob fully counter-clockwise at switch-on.
Current drawing of this circuit is about 1mA @ 3V DC.
Some commercial sets have four, six or eight output electrodes. To obtain this you can retain the part of the circuit comprising IC1, R1, R2, C1, C2, SW1 and B1. Other parts in the diagram (i.e. P1, R3, R4, D1, D2, Q2 & T1) can be doubled, trebled or quadrupled. Added potentiometers and R3 series resistors must be wired in parallel and all connected across Emitter of Q1 and positive supply.
Commercial sets have frequently a built-in 30 minutes timer. For this purpose you can use the Timed Beeper the Bedside Lamp Timer or the Jogging Timer circuits available on this Website, adjusting the timing components to suit your needs.

Warning:
The use of this device is forbidden to Pace-Maker bearers and pregnant women.
Do not place the electrodes on cuts, wounds, injuries or varices.
Obviously we can't claim or prove any therapeutic effectiveness for this device.

Disclaimer:
we can't claim or prove any therapeutic effectiveness for this device.

Source: http://www.redcircuits.com

Magnetic Proximity Sensors

noreply@blogger.com (Go2Media) — Fri, 13 Jun 2008 16:04:00 +0000

This electronic circuit is an interesting circuit for a magnetic proximity switch which can be used in various applications. The magnetic proximity switch circuit, in principle, consists of a reed switch at its heart. When a magnet is brought in the vicinity of the sensor (reed switch), it operates and controls the rest of the switching circuit. In place of the reed switch, one may, as well, use a general-purpose electromagnetic reed relay (by making use of the reed switch contacts) as the sensor, if required. These tiny reed relays are easily available as they are widely used in telecom products. The reed switch or relay to be used with this circuit should be the ‘normally open’ type.

When a magnet is brought/placed in the vicinity of the sensor element for a moment, the contacts of the reed switch close to trigger timer IC1 wired in monostable mode. As a consequence its output at pin 3 goes high for a short duration and supplies clock to the clock input (pin 3) of IC2 (CD4013—dual D-type flip-flop). LED D2 is used as a response indicator.

This CMOS IC2 consists of two independent flip-flops though here only one is used. Note that the flip-flop is wired in toggle mode with data input (pin 5) connected to the Q (pin 2) output. On receipt of clock pulse, the Q output changes from low to high state and due to this the relay driver transistor T1 gets forward-biased. As a result the relay RL1 is energised.

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