Intelligent Presence Simulator

However effective a domestic alarm system may be, it’s invariably better if it never goes off, and the best way to ensure this is to make potential burglars think the premises are occupied. Indeed, unless you own old masters or objects of great value likely to attract ‘professional’ burglars, it has to be acknowledged that the majority of burglaries are committed by ‘petty’ thieves who are going to be looking more than anything else for simplicity and will prefer to break into homes whose occupants are away.

Rather than simply not going on holiday – which is also one solution to the problem (!) – we’re going to suggest building this intelligent presence simulator which ought to put potential burglars off, even if your home is subjected to close scrutiny. Like all its counterparts, the proposed circuit turns one or more lights on and off when the ambient light falls, but while many devices are content to generate fixed timings, this one works using randomly variable durations.

Circuit diagram:

 

Intelligent Presence Simulator Circuit Diagram

So while other devices are very soon caught out simply by daily observation (often from a car) because of their too-perfect regularity, this one is much more credible due to the fact that its operating times are irregular. The circuit is very simple, as we have employed a microcontroller – a ‘little’ 12C508 from Microchip, which is more than adequate for such an application. It is mains powered and uses rudimentary voltage regulation by a zener diode.

A relay is used to control the light(s); though this is less elegant than a triac solution, it does avoid any interference from the mains reaching the microcontroller, for example, during thunderstorms. We mustn’t forget this project needs to work very reliably during our absence, whatever happens. The ambient light level is measured by a conventional LDR (light dependent resistor), and the lighting switching threshold is adjustable via P1 to suit the characteristics and positioning of the LDR.

Note that input GP4 of the PIC12C508 is not analogue, but its logic switching threshold is very suitable for this kind of use. The LED connected to GP1 indicates the circuit’s operating mode, selected by grounding or not of GP2 or GP3 via override switch S1. So there are three possible states: permanently off, permanently on, and automatic mode, which is the one normally used. Given the software programmed into the 12C508 (‘firmware’) and the need to generate very long delays so as to arrive at lighting times or an hour or more, it has been necessary to make the MCU operate at a vastly reduced clock frequency.

PCB Layout:

PCB Layout Of Intelligent Presence Simulator

In that case, a crystal-controlled clock is no longer suitable, so the R-C network R5/C3 is used instead. For sure, such a clock source is less stable than a crystal, but then in an application like this, that may well be what we’re after as a degree of randomness is a design target instead of a disadvantage. Our suggested PCB shown here takes all the components for this project except of course for S1, S2, and the LDR, which will need to be positioned on the front panel of the case in order to sense the ambient light intensity.

The PCB has been designed for a Finder relay capable of switching 10 A, which ought to prove adequate for lighting your home, unless you live in a replica of the Palace of Versailles. The program to be loaded into the 12C508 is available for free download from the Elektor website as file number 080231-11.zip or from the author’s own website: www.tavernier-c.com. On completion of the solder work the circuit should work immediately and can be checked by switching to manual mode.

The relay should be released in the ‘off’ position and energized in the ‘on’ position. Then all that remains is to adjust the day/night threshold by adjusting potentiometer P1. To do this, you can either use a lot of patience, or else use a voltmeter – digital or analogue, but the latter will need to be electronic so as to be high impedance – connected between GP4 and ground. When the light level below which you want the lighting to be allowed to come on is reached, adjust P1 to read approximately 1.4 V on the voltmeter.

If this value cannot be achieved, owing to the characteristics of your LDR, reduce or increase R8 if necessary to achieve it (LDRs are known to have rather wide production tolerances). Equipped with this inexpensive accessory, your home of course hasn’t become an impregnable fortress, but at least it ought to appear less attractive to burglars than houses that are plunged into darkness for long periods of time, especially in the middle of summer. (www.tavernier-c.com)

COMPONENTS LIST Resistors
R1 = 1k 500mW
R2 = 4k7
R3 = 560R
R4,R6 = 10k
R5 = 7k5
R 7 = LDR
R8 = 470k to 1 M
P1 = 470k potentiometer
Capacitors
C1 = 470µF 25V
C2 = 10µF 25V
C3 = 1nF5
C4 = 10nF
Semiconductors
D1,D2 = 1N4004
D3 = diode zener 4V7 400 mW
LED1 = LED, red
D4 = 1N4148
T1 = BC547
IC1 = PIC12C508, programmed, see Downloads
Miscellaneous
RE1 = relay, 10A contact
S1 = 1-pole 3-way rotary switch
F1 = fuse 100 mA
TR1 = Mains transformer 2x9 V, 1.2 -3 VA
4 PCB terminal blocks, 5 mm lead pitch
5 solder pins 

www.ecircuitslab.com

On Demand WC Fan Using 555

In most WCs with an extractor the fan is connected to the lighting circuit and is switched on and off either in sympathy with the light or with a short delay. Since toilets are sometimes used for washing the hands or just for a quick look in the mirror, it is not always necessary to change the air in the smallest room in the house. The following circuit automatically determines whether there really is any need to run the fan and reacts appropriately. No odour sensor is needed: we just employ a small contact that detects when and for how long the toilet seat lid is lifted.

If the seat lid is left up for at least some presettable minimum time t1, the fan is set running for another presettable time t2. In the example shown the contact is made using a small magnet on the lid and a reed switch mounted on the cistern. The rest is straightforward: IC2, the familiar 555, forms a timer whose period can be adjusted up to approximately 10 to 12 minutes using P2. This determines the fan running time. There are three CMOS NAND gates (type 4093) between the reed switch and the timer input which generate the required trigger signal. When the lid is in the ‘up’ position the reed switch is closed.

Capacitor C1 charges through P1 until it reaches the point where the output of IC1a switches from logic 1 to logic 0. The output of IC1b then goes to logic 1. The edge of the 0-1 transition, passed through the RC network formed by C2 and R2, results in the output of IC1c going to logic 0 for a second. This is taken to the trigger input on pin 2 of timer IC2, which in turn switches on the relay which causes the fan to run for the period of time determined by P2. The circuit is powered from a small transformer with a secondary winding delivering between approximately 8 V and 10 V. Do not forget to include a suitable fuse on the primary side.

The circuit around IC1b and IC1c ensures that the fan does not run continuously if the toilet seat lid is left up for an extended period. The time constant of P1 and C1 is set so that the fan does not run as a result of lavatorial transactions of a more minor nature, where the lid is opened and then closed shortly afterwards, before C1 has a chance to charge sufficiently to trigger the circuit.

Circuit Source: DIY Electronics Projects

Battery Discharger Using Discrete Components

The battery discharger published in this website may be improved by adding a Schottky diode (D3). This ensures that a NiCd cell is discharged not to 0.6–0.7 V, but to just under 1 V as recommended by the manufacturers. An additional effect is then that light-emitting diode D2 flashes when the battery connected to the terminals is flat. The circuit in the diagram is based on an astable multivibrator operating at a frequency of about 25 kHz. When transistor T2 conducts, a current flows through inductor L1, whereupon energy is stored in the resulting electromagnetic field. When T2 is cut off, the field collapses, whereupon a counter-emf is produced at a level that exceeds the forward voltage (about 1.6 V) of D2.

A current then flows through the diode so that this lights. Diode D1 prevents the current flowing through R4 and C2. This process is halted only when the battery voltage no longer provides a sufficient base potential for the transistors. In the original circuit, this happened at about 0.65 V. The addition of the forward bias of D3 (about 0.3 V), the final discharge voltage of the battery is raised to 0.9–1.0 V. Additional resistors R5 and R6 ensure that sufficient current flows through D3. When the battery is discharged to the recommended level, it must be removed from the discharger since, in contrast to the original circuit, a small current continues to flow through D3, R2-R3, and R5-R6 until the battery is totally discharged.

The flashing of D2 when the battery is nearing recommended discharge is caused by the increasing internal resistance of the battery lowering the terminal voltage to below the threshold level. If no current flows, the internal resistance is of no consequence since the terminal voltage rises to the threshold voltage by taking some energy from the battery. When the discharge is complete to the recommended level, the LED goes out. It should therefore be noted that the battery is discharged sufficiently when the LED begins to flash.

 

 

Streampowers

RGB Solar Lamp

This deluxe solar-powered light  uses a battery and solar cells salvaged from a solar lamp with a four-cell battery (4.8 V nominal terminal  voltage).

Circuit diagram :

RGB Solar Lamp Circuit Diagram

The circuit can operate from any  DC voltage around this value and  its current consumption, at 20 mA,  is low. This means that the battery  can give up to five days of operation. The circuit consists of an Atmel  ATtiny microcontroller which drives  a red, a green and a blue LED directly  from three port pins. Series resistors are of course included to limit  the LED current. The microcontroller  drives the LEDs in sequence to produce an  RGB running light effect. The microcontroller  is also responsible for ensuring that the light automatically switches on when it gets dark  and off when it is light. The light sensor is  made from one of the solar cells from a bro-ken solar lamp (it is more common  for the battery to fail rather than  the solar cells). 

The power output of this cell is not  important, as the microcontroller  only measures its output voltage  using its internal A/D converter  connected to pin PB4. The project is  ideal for beginners, as a ready-programmed microcontroller is avail-able from the Elektor Shop (order  code 100581-41). 

Source by : Streampowers

The National Semiconductor LMV225 is a linear RF power meter IC in an SMD package. It can be used over the frequency range of 450 MHz to 2000 MHz and requires only four external components. The input coupling capacitor isolates the DC voltage of the IC from the input signal. The 10-k? resistor enables or disables the IC according to the DC voltage present at the input pin. If it is higher than 1.8 V, the detector is enabled and draws a current of around 5–8 mA. If the voltage on pin A1 is less than 0.8 V, the IC enters the shutdown mode and draws a current of only a few microampères. The LMV225 can be switched between the active and shutdown states using a logic-level signal if the signal is connected to the signal via the 10-kR resistor.

Circuit diagram:

 Linear RF Power Meter Circuit Diagram

 

The supply voltage, which can lie between +2.7 V und +5.5 V, is filtered by a 100nF capacitor that diverts residual RF signals to ground. Finally, there is an output capacitor that forms a low-pass filter in combination with the internal circuitry of the LMV225. If this capacitor has a value of 1 nF, the corner frequency of this low-pass filter is approximately 8 kHz. The corner frequency can be calculated using the formula fc = 1 ÷ (2 p COUT Ro) where Ro is the internal output impedance (19.8 k?). The output low-pass filter determines which AM modulation components are passed by the detector.

 

The output, which has a relatively high impedance, provides an output voltage that is proportional to the signal power, with a slope of 40 mV/dB. The output is 2.0 V at 9 dBm and 0.4 V at –40 dBm. A level of 0 dBm corresponds to a power of 1 mW in 50 R. For a sinusoidal wave-form, this is equivalent to an effective voltage of 224 mV. For modulated signals, the relationship between power and voltage is generally different. The table shows several examples of power levels and voltages for sinusoidal signals. The input impedance of the LMV225 detector is around 50 R to provide a good match to the characteristic impedance commonly used in RF circuits.

The data sheet for the LMV225 shows how the 40-dB measurement range can be shifted to a higher power level using a series input resistor. The LMV225 was originally designed for use in mobile telephones, so it comes in a tiny SMD package with dimensions of only around 1 × 1 mm with four solder bumps (similar to a ball-grid array package). The connections are labelled A1, A2, B1 and B1, like the elements of a matrix. The corner next to A1 is bevelled.

 

 

 

http://streampowers.blogspot.com/2012/06/linear-rf-power-meter-circuit.html 

Heat Detector Alarm using UM3561

A very simple heat detector alarm electronic project can be designed using the UM3561 sound generator circuit and some other common electronic parts . This heat detector electronic circuit project uses a complementary pair comprising npn and pnp transistor to detect heat Collector of T1 transistor is connected to the base of the T2 transistor , while the collector of T2 transistor is connected to RL1 relay T3 and T4 transistors connected in darlington configuration are used to amplify the audio signal from the UM3561 ic.

When the temperature close to the T1 transistor is hot , the resistance to the emitter –collector goes low and it starts conducting . In same time T2 transistor conducts , because its base is connected to the collector of T1 transistor and the RL1 relay energized and switches on the siren which produce a fire engine alarm sound. This electronic circuit project must be powered from a 6 volts DC power supply , but the UM3561 IC is powered using a 3 volt zener diode , because the alarm sound require a 3 volts dc power supply. The relay used in this project must be a 6 volt / 100 ohms relay and the speaker must have a 8 ohms load and 1 watt power.

 

 

Streampowers

Description

Here is a simple and humble 2 Watts mini audio amplifier circuit suitable for small pocket radios and other portable audio gadgets.The circuit is based on Phillips Semiconductors IC TDA 7052.The amplifier can be run even from a 3V Mercury button cell.This makes it ideal for battery operated gadgets.

The IC TDA7052 is a mono output amplifier coming in a 8-lead DI package (DIP). The device is mainly designed for battery-operated portable audio circuits. The features of TDA 7052 include ,no external components needed,  no switch-on or switch-off click sounds , great overall stability ,very low power consumption(quiescent current 4mA) , low THD, no  heat sinks required and short-circuit proof.

The gain of TDA 7052 is fixed internally at 40 dB. . To compensate the reduction of output power due to low voltage supply  the TDA7052 uses the Bridge-Tied-Load principle (BTL) which can provide  an output  of around 1 to 2 W  Rms(THD = 10%) into an 8 Ohm load with a power supply of 6 V.

In the circuit the potentiometer can be used to control the volume. Capacitor C1 and C2 are meant for  filtering the supply voltage if a battery eliminator is used as supply source. For operations using a battery C1 and C2 are not necessary.

Mini Audio Amplifier Circuit Diagram with Parts List:

Notes.

• Assemble the circuit on a good quality PCB or common board .
• If you are a little expert, you can assemble the  circuit in a match box including the speaker.

10 000x With One Transistor

For a collector follower with emitter resistor, you’ll often find that the gain per stage is no more than 10 to 50 times. The gain increases when the emitter resistor is omitted. Unfortunately, the distortion also increases. With a ubiquitous transistor such as the BC547B, the gain of the transistor is roughly equal to 40 times the collector current (Ic), provided the collector current is less than a few milliamps. This value is in theory equal to the expression q/KT, where q is the charge of the electron, K is Boltzmann’s constant and T is the temperature in Kelvin.

For simplicity, and assuming room temperature, we round this value to 40. For a single stage amplifier circuit with grounded emitter it holds that the gain Uout /Uin (for AC voltage) is in theory equal to SRc. As we observed before, the slope S is about 40Ic. From this follows that the gain is approximately equal to 40I cRc. What does this mean? In the first instance this leads to a very practical rule of thumb: that gain of a grounded emitter circuit amounts to 40·I c·Rc, which is equal to 40 times the voltage across the collector resistor.

If Ub is, for example, equal to 12 V and the collector is set to 5V, then we know, irrespective of the values of the resistors that the gain will be about 40R(12–5) = 280. Notable is the fact that in this way the gain can be very high in theory, by selecting a high power supply voltage. Such a voltage could be obtained from an isolating transformer from the mains. An isolating transformer can be made by connecting the secondaries of two transformers together, which results in a galvanically isolated mains voltage.

Circuit diagram:

10,000x With One Transistor Circuit diagram

That means, that with a mains voltage of 240 Veff there will be about 340 V DC after rectification and filtering. If in the amplifier circuit the power supply voltage is now 340 V and the collector voltage is 2 V, then the gain is in theory equal to 40 x (340–2). This is more than 13,500 times! However, there are a few drawbacks in practice. This is related to the output characteristic of the transistor. In practice, it turns out that the transistor does actually have an output resistor between collector and emitter.

This output resistance exists as a transistor parameter and is called ‘hoe’. In normal designs this parameter is of no consequence because it has no noticeable effect if the collector resistor is not large. When powering the amplifier from 340 V and setting the collector current to 1 mA, the collector resistor will have a value of 338 k. Whether the ‘hoe’-parameter has any influence depends in the type of transistor. We also note that with such high gains, the base-collector capacitance in particular will start to play a role.

As a consequence the input frequency may not be too high. For a higher bandwidth we will have to use a transistor with small Cbc, such as a BF494 or perhaps even an SHF transistor such as a BFR91A. We will have to adjust the value of the base resistor to the new hfe. The author has carried out measurements with a BC547B at a power supply voltage of 30 V. A value of 2 V was chosen for the collector voltage. Measurements confirm the rule of thumb. The gain was more than 1,000 times and the effects of ‘hoe’ and the base-collector capacitance were not noticeable because of the now much smaller collector resistor.

Author: Gert Baars Copyright: Elektor Electronics

Digital Step Km Counter

This circuit measures the distance covered during a walk. Hardware is located in a small box slipped in pants pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km. and its dot is always on to separate Km. from hm. The rightmost display D1 (the least significant digit) shows hundreds meters and its dot illuminates after every 50 meters of walking. A beeper (excludable), signals each count unit, occurring every two steps. A normal step was calculated to span around 78 centimeters, thus the LED signaling 50 meters illuminates after 64 steps (or 32 operations of the mercury switch), the display indicates 100 meters after 128 steps and so on.

For low battery consumption the display illuminates only on request, pushing on P2. Accidental reset of the counters is avoided because to reset the circuit both pushbuttons must be operated together. Obviously, this is not a precision meter, but its approximation degree was found good for this kind of device. In any case, the most critical thing to do is the correct placement of the mercury switch inside of the box and the setting of its sloping degree.

Circuit diagram:

Digital Step-Km Counter Circuit Diagram

Parts:
R1 = 22K 1/4W Resistor
R2 = 2.2M 1/4W Resistor
R3 = 22K 1/4W Resistor
R4 = 1M 1/4W Resistor
R5 = 4.7K 1/4W Resistor
R6 = 47R 1/4W Resistor
R7 = 4.7K 1/4W Resistor
R8 = 4.7K 1/4W Resistor
R9 = 1K 1/4W Resistor
C1 = 47nF 63V Polyester Capacitor
C2 = 100nF 63V Polyester Capacitor
C3 = 10nF 63V Polyester Capacitor
C4 = 10µF 25V Electrolytic Capacitor
D1 = Common-cathode 7-segment LED mini-display (Hundreds meters)
D2 = Common-cathode 7-segment LED mini-display (Kilometers)
Q1 = BC327 45V 800mA PNP Transistors
Q2 = BC327 45V 800mA PNP Transistors
P1 = SPST Pushbutton (Reset)
P2 = SPST Pushbutton (Display)
IC1 = 4093 Quad 2 input Schmitt NAND Gate IC
IC2 = 4024 7 stage ripple counter IC
IC3 = 4026 Decade counter with decoded 7-segment display outputs IC
IC4 = 4026 Decade counter with decoded 7-segment display outputs IC
SW1 = SPST Mercury Switch, called also Tilt Switch
SW2 = SPST Slider Switch (Sound on-off)
SW3 = SPST Slider Switch (Power on-off)
BZ = Piezo sounder
B1 = 3V Battery (2 AA 1.5V Cells in series)

Circuit operation:

IC 1A & IC 1B form a monostable multi vibrator providing some degree of freedom from excessive bouncing of the mercury switch. Therefore a clean square pulse enters IC2 that divides by 64. Q2 drives the LED dot-segment of D1 every 32 pulses counted by IC2. Either IC3 & IC4 divide by 10 and drive the displays. P1 resets the counters and P2 enables the displays. IC1C generates an audio frequency square wave that is enabled for a short time at each monostable count. Q1 drives the piezo sounder and SW2 allows disabling the beep.

Notes:

• Experiment with placement and sloping degree of mercury switch inside the box: this is very critical.
• Try to obtain a pulse every two walking steps. Listening to the beeper is extremely useful during setup.
• Trim R6 value to change beeper sound power.
• Push P1 and P2 to reset.
• This circuit is primarily intended for walking purposes. For jogging, further great care must be used with mercury switch placement to avoid undesired counts.
• When the display is disabled current consumption is negligible, therefore SW3 can be omitted.

Streampowers