Telephone in use light

R1,R2 1 Meg


R3 10 K

R4 1 K

R5 4.7 K

R6 470 ohm

C1 .005 uF

CR1-3 1N914 diode

LED1 any old led

Q1 2N2222 or 2N3904

U1 LM339 quad comparator (be sure to connect power and ground)

--> <-- are connected (jump)

^ or v cathode of diode

+ connection

9VDC any old 9VDC wall transformer works nicely


Circuit description

R1 and R2 form a voltage divider, insuring that the phone line sees a high impedance load and that high voltages (such as the ring voltage) are easily dissipated by the protective diodes (CR1 and CR2). Also (obviously) they serve to divide all incoming voltages by two. Capacitor C1 filters out some of the audio signals that might otherwise make the LED flicker with speech.
The voltage across a busy line is generally 5-10 volts, whereas a free line sits at more like 48 volts, and a dead line (definitely not in use!) sits at 0. This circuit uses two comparators (sections of U1) to detect when the voltage is either too high or too low. Normally Q1 is kept turned on by pullup resistor R5, keeping LED1 illuminated. If either comparator detects incorrect voltage, its open-collector output goes into saturation and forces Q1 (and thus the LED) off.
The top comparator section has its negative input connected to the +9V supply, so it will force the LED off if the voltage at its positive pin should exceed 9V. Remember that we are dividing by two, so the phone line voltage would have to exceed 18V in order for this comparator to force the LED off. This would normally happen when the phone is not in use (48V, remember?).
The bottom comparator section has its positive input connected to the anode of a forward biased silicon diode, so it is sitting at 0.6V. If its negaive pin is ever lower than 0.6V, this comparator's output will go into saturation and force the LED off. Remember, again, that we are dividing the phone line voltage by two, so the phone line voltage would have to drop below 1.2V in order for this comparator to turn off the LED. This is clearly a dead line.
Serving Suggestion: Install the circuit in an out-of-the-way place, then connect the collector pin of Q1 and the +9VDC to unused (yellow or black) conductors in your home or office phone wiring. Then you can place additional LEDs (with current limiting resistors like R6) at each phone. I once used a power transistor for Q1 and peppered our electronic repair shop with LEDs at every workstation.

If you have any difficulty understanding my ascii art, the circuit theory, or anything about this posting, please feel free to contact me.
 
 
from  dthomas@bbx.basis.com (Dave Thomas)

White LED Flashlight

I took my car to a mechanic recently and while inspecting the seal around the oil pan, he pulled out a small penlight that put out what appeared to be "white" light. When he showed it to me I realized the light was coming from a single, white LED.

Later that afternoon, I opened my latest copy of Electronic Design Magazine and turned to the Pease Porridge column. Lo and behold, Bob had written an article about a low dropout current source for a white LED flashlight. I have taken his hand-drawn schematic and reproduced it below.

D1 is the white LED from Chicago Miniature. They can be ordered from DigiKey for $3.00 each. U1, the LM334 current source provides negative feedback to Q1 to maintain a constant current of 40mA through the diode. If you want less light but longer battery life, you can increase R1 to 3.3 ohms. An LM334 in a TO92 package can be acquired from DigiKey for about $2.10.

When operating at 40mA, the AAA batteries should provide about 28 hours of operation. If the current is reduces to 20mA, 57 hours of operation should be possible.


from  http://web-ee.com

7 Segment LED Counter

This simple counter can be used to count pulses, as the basis for a customer counter (like you see at the doors of some stores), or for anything else that may be counted. The circuit accepts any TTL compatible logic signal, and can be expanded easily (see Notes).




Parts

Part           TotalQty.            Description                                                   Substitutions

R1-R7        7                        470 Ohm 1/4 Watt Resistor

U1              1                        74LS90 TTL BCD Counter                        IC 7490,74HC90

U2              1                       74LS47 TTL Seven Segment Display Driver IC 7447,74HC47

DISP1        1                       Common Anode 7 Segment LED Display

MISC         1                        Board, Sockets For ICs, Wire
 
 
Notes


1.All pulses to be counted are to be TTL compatible. They should not exeed 5V and not fall below ground.

2.You can add more digits by building a second (or third, or fourth, etc...) circuit and connecting the pin 11-6 junction of the 74LS90 and 74LS47 to pin 14 of the 74LS90 in the other circuit. You can keep expanding this way to as many digits as you want.

from  http://www.aaroncake.net

2 Transistor LED Flasher

This is a classic 2 transistor astable multivibrator. Many other NPN small signal or switching transistors can be used, including 2N4401, PN2222 or 2N2222 using the circuit on the left. The circuit can also be inverted using PNP transistors such as 2N3906, 2N4403, PN2907, or 2N2907 as shown to the right.




The 470 ohm resistors determine the LED brightness. Lower resistance means higher current, and more light. LEDs that require more current or have a higher operating voltage (such as green and yellow) may work better with 300 ohms.



The RC time constant of the 39K ohms resistor and the 10uF capacitor determines the on time for each side. (The two sides do not need to match - vary the RC time constant for one side to get a lower or a higher duty cycle). With the values shown, the flash rate is about 1 cycle per second at 50% duty cycle.


from  http://www.reprise.com

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Safety Guard- Voltage Spikes Protector

Protect your home appliances from voltage spikes with this simple time delay circuit. Whenever power to the appliances is switched on or resumes after mains failure, the oscillator starts oscillating and D5 blinks. This continues for three minutes. After that, Q14 output of IC CD4060 goes high to trigger the gate of the SCR through D4. At this moment, the voltage is available at the cathode of the SCR, which energizes the relay coil to activate the appliance and D6 glows. Switch SW1 is used for quick start without waiting for delay.

Parts:

R1 = 1M
R2 = 470R
R3 = 820R
R4 = 56K
R5 = 470R
R6 = 1K
R7 = 10K
C1 = 1kuF-25V
C2 = 100nF-63V
C3 = 0.02uF-63V
C4 = 10uF-25V
C5 = 10uF-25V
D1 = 1N4007
D2 = 1N4007
D3 = 1N4007
D4 = 1N4148
D5 = Red LEDs
D6 = Red LEDs
RL1 = 12V Relay
IC1 = AN7809
IC2 = CD4060
SW1 = Switch
T1 = 24V-AC Centre Tapped Transformer

Circuit Operation:

At the heart of the circuit is IC CD4060, which consists of two inverter gates for clock generation and a 14-bit binary ripple counter. Here the clock oscillations are governed by resistor R1 and capacitor C1. In this circuit, only two outputs of the IC (Q5 and Q14) have been used. Q5 is connected to an LED (D5) and Q14 is used to trigger the gate of the SCR through D4 as well as reset the counter. The anode of the SCR is connected to +9V and the cathode is connected to the relay coil. The other pin of the relay coil is connected to the negative supply, while its contacts are used for switching on the appliances.


from extremecircuits.blogspot

Simple Cell Phone Jammer

Designer & Author:Laszlo Kirschner

Description

A “Cell Jammer” is just way of saying “Dirty Transmitter” which happens to transmit within the Cellular Phone Bands. Reality is, the dirtier the better.

The 555 timer [8 pin] IC simply makes a noise. It’s coupled via C4 [electrolytic] to modulate the MRF transistor oscillator. With C1 set at roughly 1/3rd, you will be close to 900 MHz. By sweeping the C1 trimmer capacitor, you can swing the output frequency from 800 MHz to 2 GHz with the transistor and values shown.

You could replace the 555 chip with an electret microphone and listen to yourself talk on a scanner, so the unit could easily couple as a UHF Bug.

Instead of a single Tapped Coil, I’ve used two molded inductors for ease of construction.Values for C1,C2,L1,L2 are critical for the frequency range.

You might want to build the unit into a metal box, add an on/off switch in the batteries + line, and maybe even add a LED. Connect an old 800 MHz cell phone antenna to C5.

Would you believe the whole thing can be built on top of the 555 IC itself when using surface mount components, and the lot will fit onto a nine volt battery clip. Output is reasonably good, although the current drain is a bit high, so a new 9 Volt battery will only run about an hour, [if you are lucky].

The “Cell Kill Distance” is around 10 – 15 feet, ample for most purposes.

from  http://www.circuit-projects.com

5 to 30 Minute Timer project

Circuit : Andy Collinson

Description
A switched timer for intervals of 5 to 30 minutes incremented in 5 minute steps.

Notes:
Simple to build, simple to make, nothing too complicated here. However you must use the CMOS type 555 timer designated the 7555, a normal 555 timer will not work here due to the resistor values. Also a low leakage type capacitor must be used for C1, and I would strongly suggest a Tantalum Bead type. Switch 3 adds an extra resistor in series to the timing chain with each rotation, the timing period us defined as :-

Timing = 1.1 C1 x R1

Note that R1 has a value of 8.2M with S3 at position "a" and 49.2M at position "f". This equates to just short of 300 seconds for each position of S3. C1 and R1 through R6 may be changed for different timing periods. The output current from Pin 3 of the timer, is amplified by Q1 and used to drive a relay.

Parts List:
Relay 9 volt coil with c/o contact (1)
S1: On/Off (1)
S2: Start (1)
S3: Range (1)
IC1: 7555 (1)
B1: 9V (1)
C1: 33uF CAP (1)
Q1: BC109C NPN (1)
D1: 1N4004 DIODE (1)
C2: 100n CAP (1)
R6,R5,R4,R3,R2,R1: 8.2M RESISTOR (6)
R8: 100k RESISTOR (1)
R7: 4.7k RESISTOR (1)


from  http://www.zen22142.zen.co.uk

Electronic Siren

Circuit : Andy Collinson

Description
An electronic siren made from discrete components. A push button switch is used to create the sound, which rises in pitch when the switch is pressed, and falls in pitch when the switch is released.

Notes
The sound produced imitates the rise and fall of an American police siren. When first switched on the 10u capacitors is discharged and both transistors are off. When the push button switch is pressed to 10u capacitor will charge via the 22k resistor. This voltage is applied to the base of the BC108B which will turn on slowly. When the switch is released the capacitor will discharge via the 100k and 47k base resistors and the transistor will slowly turn off. The change in voltage alters the frequency of the siren.

Oscillator action is as follows. As the BC108B transistor switches on its collector voltage falls and so the 2N3702 transistor is switched on. This happens very quickly ( less than 1us). The 22n capacitor will charge very quickly as well. As this capacitor is connected between the collector of the 2N3702 and the base of the BC108B, it soon reaches almost full supply voltage. The charging current for the capacitor is then much reduced and the collector emitter voltage of the 2N3072 is therefore increased; the collector potential will fall. This change in voltage is passed through the 22n capacitor to the base of the BC108B causing it to come out of saturation slightly. As this happens its collector voltage will rise and turn off the 2N3072 transistor more. This continues until both transistors are off. The 22n capacitor will then discharge via the 100k, 22k resistor, the closed push button switch, 9V battery, the speaker and 56 ohm resistor. The discharge time takes around 5-6msec. As soon as the 22n capacitor is discharged, the BC108B transistor will switch on again and the cycle repeats. The difference in voltage at the collector of the BC108B (caused by the charging 10u capacitor) causes the tone of the siren to change. As the 10u capacitor is charged, the tone of the siren will rise, and as it is discharged, it will fall. A 64 ohm loudspeaker may be used in place of the 8 ohm and 56 resistor, and the values of components may be altered to produce different sound effects.

Current drain is fairly high in this circuit so a suitable power supply is required. The duration the tone takes to rise and fall is determined by the 10u and 22k resistor. These values may be varied for different effects.

from  http://www.zen22142.zen.co.uk

Electronic Canary

Circuit : Andy Collinson
Description
An electronic version of a chirping canary. May be used as an alarm, a sound effects generator or perhaps a replacement doorbell.

 

Circuit Notes
This circuit is a modified hartley oscillator with a couple of extra components included. The transformer is a small audio transformer, type LT700. The primary is center tapped with an impedance of 1Kohms at 1KHz . The secondary has an impedance of 8 ohms. The inclusion of R1 and C1 give this oscillator its characteristic "chirp". As the 100u capacitor charges via the 4.7K resistor, R1 the bias for the transistor is cut off. This causes the oscillation to stop, the capacitor discharges through the base emitter circuit of the transistor and oscillations start again. Altering these components alters the frequency of the chirp. The chirp is also voltage dependent. When the push button switch is operated the 100u capacitor is charged. When its released, the oscillation decays and the chirp becomes faster.

from:  http://www.zen22142.zen.co.uk

Sound Operated Switch

Circuit :Andy Collinson
A sound operated switch with a relay driver.

Notes
This sensitive sound operated switch can be used with a dynamic microphone insert as above, or be used with an electret (ECM) microphone. If an ECM is used then R1 (shown dotted) will need to be included. A suitable value would be between 2.2k and 10kohms.

The two BC109C transistors form an audio preamp, the gain of which is controlled by the 10k preset. The output is further amplified by a BC182B transistor. To prevent instability the preamp is decoupled with a 100u capacitor and 1k resistor. The audio voltage at the collector of the BC182B is rectified by the two 1N4148 diodes and 4.7u capacitor. This dc voltage will directly drive the BC212B transistor and operate the relay and LED. It should be noted that this circuit does not "latch". The relay and LED operate momentarily in response to audio peaks.

The gain of the circuit and sensitivity is controlled by the 10k variable resistor on the emitter of the first (left hand side) transistor. A preset may be used if gain is fixed, a potentiometer should be used to trigger at different sound levels.

The relay contacts close and then open (momentary action) in response to audio peaks, these can be used to switch other circuit. The diode across the relay is the usual back emf diode and a 1N4003 or 1N4004 will work well here, preventing damage to the transistor.

from  http://www.zen22142.zen.co.uk

Frost Alarm or Cold Activated Switch

Circuit : Andy Collinson

Description
A simple thermistor triggered switch with adjustable threshold. It triggers with cold temperatures so may be used as a frost alarm or cold temperature switch.

Circuit Notes
The thermistor used has a resistance of 15k at 25°C and 45k at 0° Celsius. A suitable bead type thermistor can be found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures.

If using a different thermistor then the control should match the new thermistor at its highest resistance, or be higher in value. The op-amp in this circuit is the ubiquitous 741. It may be catalogued as LM741, CA741 etc, all types will work. In this circuit it is used as a comparator. The non-inverting input (pin 3) is biased to half the supply voltage. The non-inverting input is connected to the junction of the thermistor and potentiometer. The control is adjusted so that the circuit is on when the thermistor is at the required temperature range. Once the thermistor is outside the temperature range its resistance alters and the op-amp output changes from near full supply to around 1 or 2 volts dc. There is insufficient voltage to turn on the transistor and the relay will not energise.

A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents rapid switching of the circuit when the temperature is near to the switching threshold.

from  http://www.zen22142.zen.co.uk

Rain sound effect Generator

Rain sound , relaxing effect, helping to fall asleep
Small portable unit, 3V battery powered

Parts:

R1,R2,R13______10K   1/4W Resistors
R3,R5__________33K   1/4W Resistors
R4,R6___________1M   1/4W Resistors
R7____________100R   1/4W Resistor
R8____________330K   1/4W Resistor
R9____________100K   1/4W Resistor
R10____________47R   1/4W Resistor
R11_____________1K   1/4W Resistor
R12____________15K   1/4W Resistor
R14____________47K   1/4W Resistor
R15____________10M   1/4W Resistor
R16_____________1M8  1/4W Resistor

C1,C4,C7______100µF   25V Electrolytic Capacitors
C2,C3,C6______100nF   63V Polyester or Ceramic Capacitors
C8,C10________100nF   63V Polyester or Ceramic Capacitors
C5_____________47µF   25V Electrolytic Capacitor
C9_____________10µF   63V Electrolytic Capacitor

D1___________1N4148   75V 150mA Diode

Q1___________2N3819   General-purpose N-Channel FET
Q2____________BC337   45V 800mA NPN Transistor
Q3____________BC327   45V 800mA PNP Transistor
Q4,Q5_________BC547   45V 100mA NPN Transistors

IC1___________TL062   Low current BIFET Dual Op-Amp
IC2____________4060   14 stage ripple counter and oscillator IC (See Notes)

SW1____________1 pole 3 ways Rotary Switch
SW2____________SPST  Slider Switch

SPKR___________8 Ohm Loudspeaker (40 to 85mm. diameter)

B1_____________3V Battery (two AA or AAA cells wired in series etc.)

Comments:

Sound effects generators trying to imitate rain sound or sea surf are well known to hobbyists from many years: their purpose is to induce relaxation and sleep or to help in concentration and study.
The sound generated is restrained to a background level and these devices are frequently kept on the night table.
Common designs use invariably Zener diodes or reverse-biased transistors base-emitter junctions as white noise generators. The main snag of these circuits is that a supply of at least 12V is required, therefore a big battery pack or (more commonly) mains supply is used as power source.
The aim of this project was to design a small, portable unit, powered by a 3V battery and capable of shutting-down after a preset delay, in order to save power.
Circuit operation:

Two BIFET Op-Amps are used as a good, low voltage supply, very low current, white noise source. A sound resembling to a rain shower is reproduced by the speaker after being amplified by Q2.
The higher part of the white noise spectrum is attenuated by C8, slowly driven into operation by means of Fet Q1 acting as a variable resistor. Therefore, a sort of automatic tone control is obtained.
IC2 provides all the timings: it auto-resets at switch-on, shutting-down the generator after one of three time-delays, chosen by means of SW1. It provides also, through R8, slow charge and discharge of C5, in order to change smoothly high-frequency attenuation. Q3 is used as a dc switch for the generator circuit. Q4 and Q5 are its drivers.
Notes:

    * Different operating delays can be chosen by changing R16 and/or C10 value.
    * 4060 ICs by some manufacturers are unable to oscillate at 3V supply. Motorola's MC14060 is therefore highly recommended for IC2.
    * If a fixed operating delay is desired, SW1 can be omitted and R14 and D1 anode can be hard wired to the proper pin of IC1.
    * Output volume can be increased lowering R9 value to about 47K. On the other hand it can be reduced increasing R9 value to about 150K.
    * If variable high-frequency attenuation is not needed, C5, C8, Q1 and R8 may be omitted.
    * If auto shut-down is not needed, omit R11, R12, R13, R14, Q3, Q4, Q5, C9, D1 and SW1, connecting pin #12 of IC2 to negative ground.
    * If only a straightforward white noise generator is required, omit also IC2, R15, R16 and C10 besides the above listed parts.
    * Current consumption is about 7mA and less than 600µA when in stand-by mode.
    * After shut-down, the circuit can be restarted opening SW2, then closing it again.

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

from  redcircuits.com

Salt-Taster by LM324

Detects the amount of salt contained in liquid foods
Three-level LED indicator

Parts:

R1________________470R   1/4W Resistor
R2,R5______________10K   1/4W Resistors
R3,R6_____________220K   1/4W Resistors
R4__________________5K   1/2W Trimmer Cermet
R7________________680R   1/4W Resistor
R8__________________2K2  1/4W Resistor
R9,R10,R11,R12,R13__1K   1/4W Resistors

C1________________100µF   25V Electrolytic Capacitor

D1,D2,D3______3 or 5mm. Red LEDs
D4____________3 or 5mm. Green LED
D5____________3 or 5mm. Yellow LED

IC1_______________LM324 Low Power Quad Op-amp

P1_________________SPST Pushbutton

Probes_________________ (See Text)

B1___________________9V PP3 Battery

Clip for PP3 Battery

Device purpose:

This circuit was designed to detect the approximate percentage of salt contained in a liquid. After careful setting it can be useful to persons needing a quick, rough indication of the salt content in liquid foods for diet purposes etc.
Circuit operation:

IC1A op-amp is wired as a DC differential amplifier and its output voltage increases as the DC resistance measured across the probes decreases. In fact, fresh water has a relatively high DC resistance value that will decrease proportionally as an increasing amount of salt is added.
IC1B, IC1C and IC1D are wired as comparators and drive D5, D4 and D3 in turn, as the voltage at their inverting inputs increases. Therefore, no LED will be on when the salt content of the liquid under test is very low, yellow LED D5 will illuminate when the salt content is low, green LED D4 will illuminate if the salt content is normal and red LED D3 will illuminate if the salt content is high.
D1 and D2 are always on, as their purpose is to provide two reference voltages, thus improving circuit precision. At D2 anode a stable 3.2V supply feeds the non-inverting inputs of the comparators by means of the reference resistor chain R8, R9 and R10. The 1.6V reference voltage available at D1 anode feeds the probes and the set-up trimmer R4.
One of these two red LEDs may be used as a pilot light to show when the device is on.
Probes:

It was found by experiment that a good and cheap probe can be made using a 6.3mm. mono jack plug. The two plug leads are connected to the circuit input by means of a two-wire cable (a piece of screened cable works fine).
The metal body of the jack is formed by two parts of different length, separated by a black plastic ring. You should try to cover the longest part with insulating tape in order to obtain an exposed metal surface of the same length of the tip part, i.e. about 8 to 10mm. starting from the black plastic ring.
In the prototype, three tablespoons of liquid were poured into a cylindrical plastic cap of 55mm. height and 27mm. diameter, then the metal part of the jack probe was immersed in the liquid.
Notes:

    * Wait at least 30 seconds to obtain a reliable reading.
    * Wash and wipe carefully the probe after each test.
    * To setup the circuit and to obtain a more precise reading, you can use a DC voltmeter in the 10V range connected across pin #1 of IC1A and negative supply.
    * Set R4 to obtain a zero reading on the voltmeter when the probe is immersed in fresh water.
    * You may change at will the threshold voltage levels at which the LEDs illuminate by trimming R4. Vary R8 value to change D4 range and R9 value to change D5 range.
    * P1 pushbutton can be substituted by a common SPST switch.

from:  redcircuits.com

solar battery charger with charging controller and regulator

Solar power is a good and clean source of electricity.But  before it is used in houses, it is first used to charge battery then the battery, with the help of inverter circuits, will power up household appliances like lights and TV sets.

During hot sunny days, solar panels can generate voltage above 14V dc or higher , enough to charge a 12V lead-acid battery. But during cloudy days, solar panels can generate voltages even less than 9V to 8V, which is very low enough to charger a 12V battery. In short, during this days, solar panels are useless.
The purpose of this project is to design a low cost (cheap) and simple solar battery charger that has a built in charging controller and regulator that can maximize the solar panels charging capacity and at the same time help the battery charging process continuous regardless the weather is sunny or cloudy.

The project uses a 555 timer IC to generates pulses of voltages at a specified duty cycle and frequency. This generated voltage will be feed to the input of bipolar junction  transistor and as a result generates an output voltage which is enough to charge the battery. This operation is similar to 3V charger project. The circuit also has comparator IC  that  monitors charger output voltage  and  controls the charger off when the battery is fully charge. The comparator also controls the output to more than 13.6V (15V) to ensure proper and continuous battery charging. The project also has an output regulator that limits the output voltage  acceptable to battery charging.The charger project also has a voltage output indicator and a diode to avoid battery charge draining.

from: electronician.blogspot.com

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