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Sunday, August 30, 2009

Sequential Turn Lights Driver

This device was designed on request and allows sequential operation of four Leds either to left or right direction, obtained by means of a 7555 CMos timer IC (IC1) wired as an astable multivibrator driving a Decade counter (IC2). This IC is set to count a sequence of four by connection of pin #10 to pin #15, but any sequence count in the 2-10 range can be set by choosing the appropriate pin connection. Obviously, LEDs, Transistors and their respective Base-limiting resistors must also be added or omitted accordingly.R1 is a variable resistor (Trimmer), used to set the desired speed of the LEDs. SW1 is a change-over switch that should already exist in your motorcycle, having a center-off position and Turn-left and Turn-right positions.D1, D3, D5 and D7 are the Turn-left LEDs; D2, D4, D6 and D8 are the Turn-right LEDs.

Sequential Turn Lights Driver

R1_____________500K 1/2W Trimmer Cermet or Carbon R2______________47K 1/4W Resistor
R3,R4____________1K 1/4W Resistors
R5,R6,R7,R8_____10K 1/4W Resistors
C1_______________1µF 63V Polyester or electrolytic capacitor C2_____________220µF 25V Electrolytic capacitor
D1-D8__________LEDs Yellow ultra-bright types
Q1,Q2,Q3,Q4___BC337 45V 800mA NPN Transistors
IC1____________7555 or TS555CN or TLC555CP CMos Timer IC
IC2____________4017 Decade counter with 10 decoded outputs IC SW1____________Vehicle Turn Lights switch (See Comments) Battery_________12V Vehicle battery

Sequential Turn Lights example

60W Bass Amplifier

This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure.The preamp is powered by the same 60V rails as the power amplifier, allowing to implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability.

60W Guitar Amplifier

R1__________________6K8 1W Resistor
R2,R4_____________470R 1/4W Resistors
R3__________________2K 1/2W Trimmer Cermet
R5,R6_______________4K7 1/2W Resistors

R7________________220R 1/2W Resistor
R8__________________2K2 1/2W Resistor
R9_________________50K 1/2W Trimmer Cermet

R10________________68K 1/4W Resistor
R11,R12______________R47 4W Wirewound Resistors C1,C2,C4,C5________47µF 63V Electrolytic Capacitors C3________________100µF 25V Electrolytic Capacitor C6_________________33pF 63V Ceramic Capacitor
C7_______________1000µF 50V Electrolytic Capacitor C8_______________2200µF 63V Electrolytic Capacitor (See Notes) D1_________________LED Any type and color
D2________Diode bridge 200V 6A
Q1,Q2____________BD139 80V 1.5A NPN Transistors

Q3_____________MJ11016 120V 30A NPN Darlington Transistor (See Notes) Q4_____________MJ11015 120V 30A PNP Darlington Transistor (See Notes) SW1_______________SPST Mains switch
F1__________________4A Fuse with socket
T1________________220V Primary, 48-50V Secondary 75 to 150VA Mains transformer (See Notes)
PL1_______________Male Mains plug
SPKR______________One or more speakers wired in series or in parallel Total resulting impedance: 8 or 4 Ohm Minimum power handling: 75W

Preamplifier circuit diagram:

Bass Preamp

Preamplifier parts:
P1_________________10K Linear Potentiometer P2_________________10K Log. Potentiometer
R1,R2______________68K 1/4W Resistors
R3________________680K 1/4W Resistor
R4________________220K 1/4W Resistor
R5_________________33K 1/4W Resistor

R6__________________2K2 1/4W Resistor
R7__________________5K6 1/4W Resistor

R8,R18____________330R 1/4W Resistors
R9_________________47K 1/4W Resistor
R10________________18K 1/4W Resistor
R11_________________4K7 1/4W Resistor

R12_________________1K 1/4W Resistor
R13_________________1K5 1/4W Resistor
R14,R15,R16_______100K 1/4W Resistors
R17________________10K 1/4W Resistor
C1,C4,C8,C9,C10____10µF 63V Electrolytic Capacitors C2_________________47µF 63V Electrolytic Capacitor C3_________________47pF 63V Ceramic Capacitor C5________________220nF 63V Polyester Capacitor C6________________470nF 63V Polyester Capacitor C7________________100nF 63V Polyester Capacitor C11_______________220µF 63V Electrolytic Capacitor Q1,Q3____________BC546 65V 100mA NPN Transistors Q2_______________BC556 65V 100mA PNP Transistor J1,J2___________6.3mm. Mono Jack sockets
SW1_______________SPST Switch

Technical data:

Sensitivity: 70mV input for 40W 8 Ohm output 63mV input for 60W 4 Ohm output Frequency response: 50Hz to 20KHz -0.5dB; -1.5dB @ 40Hz; -3.5dB @ 30Hz Total harmonic distortion @ 1KHz and 8 Ohm load: Below 0.1% up to 10W; 0.2% @ 30W Total harmonic distortion @ 10KHz and 8 Ohm load: Below 0.15% up to 10W; 0.3% @ 30W Total harmonic distortion @ 1KHz and 4 Ohm load: Below 0.18% up to 10W; 0.4% @ 60W Total harmonic distortion @ 10KHz and 4 Ohm load: Below 0.3% up to 10W; 0.6% @ 60W Bass control: Fully clockwise = +13.7dB @ 100Hz; -23dB @ 10KHz Center position = -4.5dB @ 100Hz Fully counterclockwise = -12.5dB @ 100Hz; +0.7dB @ 1KHz and 10KHz Low-cut switch: -1.5dB @ 300Hz; -2.5dB @ 200Hz; -4.4dB @ 100Hz; -10dB @ 50Hz


* The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice. * The Darlington transistor types listed could be too oversized for such a design. You can substitute them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4). * T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected. * SW1 switch inserts the Low-cut feature when open. * In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q2) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair. * R9 must be trimmed in order to measure about half the voltage supply across the positive lead of C7 and ground. A better setting can be done using an oscilloscope, in order to obtain a symmetrical clipping of the output wave form at maximum output power. * To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder. * Set the volume control to the minimum and Trimmer R3 to its minimum resistance. * Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA. * Wait about 15 minutes, watch if the current is varying and readjust if necessary.

Fridge door Alarm

This circuit, enclosed into a small box, is placed in the fridge near the lamp (if any) or the opening. With the door closed the interior of the fridge is in the dark, the photo resistor R2 presents a high resistance (>200K) thus clamping IC1 by holding pin 12 high. When a beam of light enters from the opening, or the fridge lamp illuminates, the photo resistor lowers its resistance (<2k),>

Fridge alarm circuit diagram


R1____________10K 1/4W Resistor
R2___________Photo resistor (any type)
R3,R4________100K 1/4W Resistors

C1____________10nF 63V Polyester Capacitor
C2___________100µF 25V Electrolytic Capacitor

D1,D2_______1N4148 75V 150mA Diodes

IC1___________4060 14 stage ripple counter and oscillator IC

Q1___________BC337 45V 800mA NPN Transistor

BZ1__________Piezo sounder (incorporating 3KHz oscillator)

SW1__________Miniature SPST slide Switch

B1___________3V Battery (2 AA 1.5V Cells in series)


* Connecting D1 to pin 2 of IC1 will halve the delay time.
* Delay time can be varied changing C1 and/or R3 values.
* Any photo resistor type should work.
* Quiescent current drawing is negligible, so SW1 can be omitted.
* Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
* Do not put this device in the freezer.

Plant Watering Watcher

This circuit is intended to signal when a plant needs water. A LED flashes at a low rate when the ground in the flower-pot is too dry, turning off when the moisture level is increasing. Adjusting R2 will allow the user to adapt the sensitivity of the circuit for different grounds, pots and probe types.

Plant Watcher circuit diagram


R1,R4________470K 1/4W Resistors
R2____________47K 1/2W Trimmer Cermet or Carbon
R3___________100K 1/4W Resistor
R5_____________3K3 1/4W Resistor
R6____________15K 1/4W Resistor
R7___________100R 1/4W Resistor

C1_____________1nF 63V Polyester Capacitor
C2___________330nF 63V Polyester Capacitor
C3,C4_________10µF 25V Electrolytic Capacitors

D1__________1N4148 75V 150mA Diode
D2_____________5mm. Red LED

IC1___________4093 Quad 2 input Schmitt NAND Gate IC

Q1___________BC557 45V 100mA PNP Transistor

P1,P2_______Probes (See Notes)

B1______________3V Battery (2xAA, N or AAA 1.5V Cells in series)

This little gadget encountered a long lasting success amongst electronics enthusiasts since its first appearance on this website in 1999. Nevertheless, in the correspondence exchanged during all these years with many amateurs, some suggestions and also criticism prompted me to revise thoroughly the circuit, making some improvements requiring the addition of four resistors, two capacitors and one transistor.
This resulted in a more stable and easy to setup device, featuring a more visible flashing indicator with no resort to ultra bright LED devices.
Extensive tests were also carried out with different flower-pots and probes. Although, as can be easily imagined, differences from various pots and probe types proved to be exceedingly high, typical resistance values across two 60mm long probes driven fully into the pot's ground about 50mm apart measured around 500 to 1000 Ohm with a high water content and about 3000 - 5000 Ohm when the ground was dry.

IC1A and related components R1 and C1 form a 2KHz square wave oscillator feeding one gate input of IC1B through the voltage divider R2/R3 made variable by adjusting the Trimmer R2. If the resistance across the probes is low (as when there is a sufficient quantity of water into the pot) C2 diverts the square wave to ground, IC1B is blocked and its output will go steady hight. IC1C inverts the high status to low, thus keeping IC1D blocked: the LED is off.
When the ground in the flower-pot is becoming too dry the resistance across the probes will increase and C2 will be no longer able to divert the square wave to ground. Therefore, IC1B output begins to transfer the 2kHz signal to IC1C which, in turn, passes it to the oscillator built around IC1D.
No longer disabled by a low level on its input, the IC1D oscillator slowly pulses Q1 base low causing the LED to flash, signalling the necessity to water the plant.
The short low pulse driving the base of Q1 is actually a burst of 2kHz pulses and therefore the LED flickers about 2,000 times per second - appearing to the human eye as if the LED was steadily on for the entire duration of the pulse.


* A square wave is used to avoid problems of probes oxidization.
* Probes are made with two pieces of bare, stiff lighting cable of 1mm diameter and should be about 60mm long.
* The probes should be driven fully in the pot's ground about 30 - 50mm apart. Please note that all parameters regarding probes material, dimensions and spacing are not critical.
* Current consumption: LED off = 150µA; LED on = 3mA for 0.1 sec. every about 2 sec. allowing the battery to last for years.
* The quiescent current consumption is so low that the use of a power on/off switch was considered unnecessary. In any case, to switch the circuit completely off, you can short the probes.

Ultra-simple Voltage Probe

This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building.When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate.Reversing polarities the Green LED will illuminate.Connecting the probes to an AC source both LEDs will go on.The bulb limits the LEDs current to 40mA @ 220V AC and its filament starts illuminating from about 30V, shining more brightly as voltage increases.Therefore, due to the bulb filament behavior, any voltage in the 1.8 to 230V range can be detected without changing component values.

Voltage Probe

D1________5 or 3mm. Red LED
D2________5 or 3mm. Green or Yellow LED
LP1_______220V 6W Filament Lamp Bulb

P1________Red Probe

P2________Black Probe


* A two colors LED (Red and Green) can be used in place of D1 & D2.

Saturday, August 29, 2009

Digital Remote Thermometer

This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained.Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter

Transmitter circuit diagram:

Thermometer transmitter

Transmitter parts:
R1,R3________100K 1/4W Resistors R2___________47R 1/4W Resistor R4____________5K 1/2W Trimmer Cermet R5___________12K 1/4W Resistor R6___________10K 1/4W Resistor R7____________6K8 1/4W Resistor R8,R9_________1K 1/4W Resistors C1___________220nF 63V Polyester Capacitor C2____________10nF 63V Polyester Capacitor C3_____________1µF 63V Polyester Capacitor C4,C6__________1nF 63V Polyester Capacitors C5_____________2n2 63V Polyester Capacitor C7,C8_________47nF 400V Polyester Capacitors C9__________1000µF 25V Electrolytic Capacitor D1__________1N4148 75V 150mA Diode D2,D3_______1N4002 100V 1A Diodes D4____________5mm. Red LED IC1___________LM35 Linear temperature sensor IC IC2__________LM331 Voltage-frequency converter IC IC3__________78L06 6V 100mA Voltage regulator IC Q1___________BC238 25V 100mA NPN Transistor Q2___________BD139 80V 1.5A NPN Transistor L1___________Primary (Connected to Q2 Collector): 100 turns Secondary: 10 turns Wire diameter: O.2mm. enameled Plastic former with ferrite core. Outer diameter: 4mm. T1___________220V Primary, 12+12V Secondary 3VA Mains transformer PL1__________Male Mains plug & cable Receiver circuit diagram:

Thermometer receiver

Receiver Parts:
R1__________100K 1/4W Resistor R2____________1K 1/4W Resistor R3,R4,R6-R8__12K 1/4W Resistors R5___________47K 1/4W Resistor R9-R15______470R 1/4W Resistors R16_________680R 1/4W Resistor C1,C2_________47nF 400V Polyester Capacitors C3,C7__________1nF 63V Polyester Capacitors C4____________10nF 63V Polyester Capacitor C5,C6,C10____220nF 63V Polyester Capacitors C8__________1000µF 25V Electrolytic Capacitor C9___________100pF 63V Ceramic Capacitor D1,D2,D5____1N4148 75V 150mA Diodes D4,D4_______1N4002 100V 1A Diodes D6-D8_______Common-cathode 7-segment LED mini-displays IC1__________4093 Quad 2 input Schmitt NAND Gate IC IC2__________4518 Dual BCD Up-Counter IC IC3__________78L12 12V 100mA Voltage regulator IC IC4__________4017 Decade Counter with 10 decoded outputs IC IC5__________4553 Three-digit BCD Counter IC IC6__________4511 BCD-to-7-Segment Latch/Decoder/Driver IC Q1___________BC239C 25V 100mA NPN Transistor Q2-Q4________BC327 45V 800mA PNP Transistors L1___________Primary (Connected to C1 & C2): 10 turns Secondary: 100 turns Wire diameter: O.2mm. enameled Plastic former with ferrite core. Outer diameter: 4mm. T1___________220V Primary, 12+12V Secondary 3VA Mains transformer PL1__________Male Mains plug & cable IC1 is a precision centigrade temperature sensor with a linear output of 10mV/°C driving IC2, a voltage-frequency converter. At its output pin (3), an input of 10mV is converted to 100Hz frequency pulses. Thus, for example, a temperature of 20°C is converted by IC1 to 200mV and then by IC2 to 2KHz. Q1 is the driver of the power output transistor Q2, coupled to the mains supply by L1 and C7, C8. Receiver circuit operation: The frequency pulses coming from mains supply and safely insulated by C1, C2 & L1 are amplified by Q1; diodes D1 and D2 limiting peaks at its input. Pulses are filtered by C5, squared by IC1B, divided by 10 in IC2B and sent for the final count to the clock input of IC5. IC4 is the time-base generator: it provides reset pulses for IC1B and IC5 and enables latches and gate-time of IC5 at 1Hz frequency. It is driven by a 5Hz square wave obtained from 50Hz mains frequency picked-up from T1 secondary, squared by IC1C and divided by 10 in IC2A. IC5 drives the displays' cathodes via Q2, Q3 & Q4 at a multiplexing rate frequency fixed by C7. It drives also the 3 displays' paralleled anodes via the BCD-to-7 segment decoder IC6. Summing up, input pulses from mains supply at, say, 2KHz frequency, are divided by 10 and displayed as 20.0°C.
Notes: * D6 is the Most Significant Digit and D8 is the Least Significant Digit. * R16 is connected to the Dot anode of D7 to illuminate permanently the decimal point. * Set the ferrite cores of both inductors for maximum output (best measured with an oscilloscope, but not critical). * Set trimmer R4 in the transmitter to obtain a frequency of 5KHz at pin 3 of IC2 with an input of 0.5Vcc at pin 7 (a digital frequency meter is required). * More simple setup: place a thermometer close to IC1 sensor, then set R4 to obtain the same reading of the thermometer in the receiver's display. * Keep the sensor (IC1) well away from heating sources (e.g. Mains Transformer T1). * Linearity is very good. * Warning! Both circuits are connected to 230Vac mains, then some parts in the circuit boards are subjected to lethal potential! Avoid touching the circuits when plugged and enclose them in plastic boxes.

Self-powered Fast Battery-Tester

This circuit runs a fast battery test without the need of power supply or expensive moving-coil voltmeters. It features two ranges: when SW1 is set as shown in the circuit diagram, the device can test 3V to 15V batteries. When SW1 is switched to the other position, only 1.5V cells can be tested.

Battery Tester

R1______________2K2 1/4W Resistor R2______________3R3 1/4W Resistor R3_____________10R 1/4W Resistor R4______________4K7 1/4W Resistor R5_____________33K 1/4W Resistor R6,R7_________100K 1/4W Resistors R8____________220K 1/4W Resistor R9____________330K 1/4W Resistor R10___________500K Trimmer Cermet C1,C2__________10nF 63V Polyester Capacitors C3-C7_________100nF 63V Polyester Capacitors C8____________220µF 35V Electrolytic Capacitor D1,D7___________LEDs Red 5mm. (see Notes) D2-D6________1N4148 75V 150mA Diodes Q1___________2N3819 General purpose FET Q2,Q3_________BC337 45V 800mA NPN Transistors IC1,IC2________7555 or TS555CN CMos Timer ICs P1_____________SPST Pushbutton SW1____________DPDT Switch BUT____________Battery under test Holder or clips to connect the Battery under test to the circuit Testing 3V to 15V batteries: 1. Switch SW1 as shown in the circuit diagram. 2. Place the battery under test in a suitable holder or clip it to the circuit. 3. Wait some seconds in order to let C8 reach its full charge. 4. LED D1 illuminates at a constant intensity, independent of battery voltage. 5. If D1 illuminates very weakly or is completely off the battery is unusable. 6. If D1 has a good illumination, press P1 and keep an eye to LED D7. If D7 remains completely off, the battery is in a very good state. 7. If D7 illuminates brightly for a few seconds, the battery is weak. This condition is confirmed by a noticeable weakening in D1 brightness. 8. If D7 illuminates weakly for a few seconds but D1 maintain the same light intensity, the battery is still good but is not new. Testing 1.5V batteries: 1. Switch SW1 in the position opposite to that shown in the circuit diagram. 2. Place the battery under test in a suitable holder or clip it to the circuit. 3. Wait some seconds in order to let C8 reach its full charge. 4. LED D1 illuminates very weakly only in presence of a new battery, otherwise is off. 5. Press P1 and keep an eye to LED D7. If D7 remains fully off the battery can be in very good state. 6. If D7 illuminates brightly for a few seconds, the battery is weak. 7. If D7 illuminates weakly for a few seconds, the battery is still good but is not new. 8. If you are suspecting a 1.5V cell to be completely discharged, a better test can be made wiring two 1.5V batteries in series, then running the 3V test. Circuit operation: FET Q1 provides a constant current generator biasing LED D1 and Q2 Base. In this manner D1 illuminates at a constant intensity, independent of battery voltage from 3 to 15V and Q2 (when P1 is closed) applies a constant current load of about 120mA to the battery. IC1 is a square wave generator oscillating at about 3KHz. IC2 acts as an inverter and drives, together with IC1 but in anti-phase, Diodes D2-D6 and Capacitors C4-C7, obtaining a voltage multiplication. C8 is charged by this raised voltage and R8-R10 form a voltage divider biasing the Base of Q3. When P1 is open, a very light load is applied to the battery under test and Q3 Base is biased in order to maintain LED D7 in the off state. Closing P1, a 120mA load is applied to the battery under test. If the battery is not fully charged, its output voltage starts reducing: when this voltage falls 0.6V below the battery nominal voltage, Q3 Emitter becomes more negative than the Base, the transistor is hard biased and D7 illuminates. Obviously, this state of affairs will last a few seconds: the time spent by C8 to reduce its initial voltage to the new one, proportional to the voltage of the loaded battery. If the battery under test is in a good charging state, its output voltage will not fall under a 120mA loading current, so LED D7 will stay off. When testing 1.5V batteries, the circuit formed by Q1, Q2, D1, R1 & R2 does not work well at this supply voltage, so a 150mA load current is applied to the BUT by means of the 10 Ohm resistor R3 after switching SW1A. Q3 bias is also changed via SW1B. Notes: * To set-up this circuit apply a 6 to 7.5V voltage source to the input and trim R10 until LED D7 is completely off (without pushing on P1). * 1.5V test position needs no set-up. * CMos 555 ICs must be used for IC1 & IC2 because they are the only cheap devices able to oscillate at 1.5V supply or less.

Room Noise Detector

This circuit is intended to signal, through a flashing LED, the exceeding of a fixed threshold in room noise, chosen from three fixed levels, namely 50, 70 & 85 dB. Two Op-amps provide the necessary circuit gain for sounds picked-up by a miniature electret microphone to drive a LED. With SW1 in the first position the circuit is off. Second, third and fourth positions power the circuit and set the input sensitivity threshold to 85, 70 & 50 dB respectively.Current drawing is <1ma>

Noise Detector circuit diagram

R1____________10K 1/4W Resistor
R2,R3_________22K 1/4W Resistors
R4___________100K 1/4W Resistor
R5,R9,R10_____56K 1/4W Resistors
R6_____________5K6 1/4W Resistor
R7___________560R 1/4W Resistor
R8_____________2K2 1/4W Resistor
R11____________1K 1/4W Resistor

R12___________33K 1/4W Resistor
R13__________330R 1/4W Resistor
C1___________100nF 63V Polyester Capacitor
C2____________10µF 25V Electrolytic Capacitor
C3___________470µF 25V Electrolytic Capacitor
C4____________47µF 25V Electrolytic Capacitor
D1_____________5mm. Red LED

IC1__________LM358 Low Power Dual Op-amp
Q1___________BC327 45V 800mA PNP Transistor
MIC1_________Miniature electret microphone
SW1__________2 poles 4 ways rotary switch
B1___________9V PP3 Battery Clip for PP3 Battery


* Place the small box containing the circuit in the room where you intend to measure ambient noise. * The 50 dB setting is provided to monitor the noise in the bedroom at night. If the LED is steady on, or flashes bright often, then your bedroom is inadequate and too noisy for sleep. * The 70 dB setting is for living-rooms. If this level is often exceeded during the day, your apartment is rather uncomfortable. * If noise level is constantly over 85 dB, 8 hours a day, then you are living in a dangerous environment.

dB Example of sound sources

20 Quiet garden, electric-clock ticking, drizzling rain 30 Blast of wind, whisper @ 1 m. 40 Countryside areas, quiet apartment, wrinkling paper @ 1 m. 50 Residential areas, quiet streets, fridges, conversation @ 1 m. 55 Offices, air-conditioners 60 Alarm-clocks, radio & TV sets at normal volume 64 Washing machines, quiet typewriters 67 Hair-dryers, crowded restaurants 69 Dish-washers, floor-polishers 70 Loud conversation, noisy street, radio & TV sets at high volume 72 Vacuum cleaners 78 Telephone ring, mechanical workshop 80 Passing trucks, noisy hall or plant, shuffling @ 1 m. 90 Passing train, pneumatic hammer, car hooter @ 1 m. 95 Mega "disco", circular saw 100 Motorcycle without silencer

Battery-powered Night Lamp

This circuit is usable as a Night Lamp when a wall mains socket is not available to plug-in an ever running small neon lamp device. In order to ensure minimum battery consumption, one 1.5V cell is used, and a simple voltage doubler drives a pulsating ultra-bright LED: current drawing is less than 500µA.An optional Photo resistor will switch-off the circuit in daylight or when room lamps illuminate, allowing further current economy.This device will run for about 3 months continuously on an ordinary AA sized cell or for around 6 months on an alkaline type cell but, adding the Photo resistor circuitry, running time will be doubled or, very likely, triplicated.

Night Lamp

R1,R2___________1M 1/4W Resistors R3_____________47K 1/4W Resistor (optional: see Notes) R4____________Photo resistor (any type, optional: see Notes) C1____________100nF 63V Polyester Capacitor C2____________220µF 25V Electrolytic Capacitor D1______________LED Red 10mm. Ultra-bright (see Notes) D2___________1N5819 40V 1A Schottky-barrier Diode (see Notes) IC1____________7555 or TS555CN CMos Timer IC B1_____________1.5V Battery (AA or AAA cell etc.) IC1 generates a square wave at about 4Hz frequency. C2 & D2 form a voltage doubler, necessary to raise the battery voltage to a peak value able to drive the LED.

Notes: * IC1 must be a CMos type: only these devices can safely operate at 1.5V supply or less. * If you are not needing Photo resistor operation, omit R3 & R4 and connect pin 4 of IC1 to positive supply. * Ordinary LEDs can be used, but light intensity will be poor. * An ordinary 1N4148 type diode can be used instead of the 1N5819 Schottky-barrier type diode, but LED intensity will be reduced due to the higher voltage drop. * Any Schottky-barrier type diode can be used in place of the 1N5819, e.g. the BAT46, rated @ 100V 150mA.

Infra-red Level Detector

This circuit is useful in liquids level or proximity detection. It operates detecting the distance from the target by reflection of an infra-red beam. It can safely detect the level of a liquid in a tank without any contact with the liquid itself. The device's range can be set from a couple of cm. to about 50 cm. by means of a trimmer.Range can vary, depending on infra-red transmitting and receiving LEDs used and is mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device's sensitivity.

Level Detector


R1_____________10K 1/4W Resistor
R2,R5,R6,R9_____1K 1/4W Resistors
R3_____________33R 1/4W Resistor
R4,R8___________1M 1/4W Resistors
R7_____________10K Trimmer Cermet
R10____________22K 1/4W Resistor

C1,C4___________1µF 63V Electrolytic or Polyester Capacitors
C2_____________47pF 63V Ceramic Capacitor
C3,C5,C6______100µF 25V Electrolytic Capacitors

D1_____________Infra-red LED
D2_____________Infra-red Photo Diode (see Notes)
D3,D4________1N4148 75V 150mA Diode
D5______________LED (Any color and size)
D6,D7________1N4002 100V 1A Diodes

Q1____________BC327 45V 800mA PNP Transistor

IC1_____________555 Timer IC
IC2___________LM358 Low Power Dual Op-amp
IC3____________7812 12V 1A Positive voltage regulator IC

RL1____________Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm

J1_____________Two ways output socket

IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the target on the same line, a couple of centimeters apart, on a short breadboard strip. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting input of the voltage comparator IC2B. This comparator switches on and off the LED and the optional relay via Q1, comparing its input voltage to the reference voltage at its non-inverting input set by the Trimmer R7.


* Power supply must be regulated (hence the use of IC3) for precise reference voltage. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
* Current drawing: LED off 40mA; LED and Relay on 70mA @ 12V DC supply.
* R10, C6, Q1, D6, D7, RL1 and J1 can be omitted if relay operation is not required.
* The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
* Avoid sun or artificial light hitting directly D1 & D2.
* Usually D1-D2 optimum distance lies in the range 1.5-3 cm.

Nocturnal Animals Whisker

This circuit has proved very useful in keeping away from a terrace or a porch some bats and other nocturnal animals. You can use it for similar or different purposes. The lamp illuminates for a 4-5 seconds delay and stays off about one minute and 15 seconds. The photo resistor allows automatic switch-on of the circuit at dusk and switch-off at dawn. Supposing an eight hours operation per night, the lamp stays on for a total of about 30 minutes, allowing great current economy.

Animals Whisker


R1____________100K 1/4W Resistor
R2______________2M2 1/4W Resistor
R3_____________10K 1/4W Resistor (see Notes)
R4______________4K7 1/4W Resistor
R5____________Photo resistor (any type, see Notes)

C1,C2,C3_______47µF 25V Electrolytic Capacitors

D1___________1N4148 75V 150mA Diode

IC1____________7555 or TS555CN CMos Timer IC

Q1____________BD681 100V 4A NPN Darlington Transistor

LP1____________6V 3W Bulb (see Notes)

SW1____________SPST Switch

B1_____________6V 1.2A Lead acid sealed rechargeable Battery (see Notes)

IC1 is wired as an astable multivibrator with on and off time-delays as explained before. R1 & C1 set the on time-delay, R2 & C1 set the off time-delay. As there is no critical parameter, you can set these delays at your wish. Q1 is the lamp driver and can feed rather big bulbs. C2 prevents some brief instability when voltage at pin 4 of IC1 is very close to switching threshold.


* Mount the photo resistor's sensitive surface at an angle of 90 degrees or more compared with the lamp, in order to avoid light interaction.
* Owing to the photo resistor type or to suit your own special needs, R3 can be varied to set the operating threshold.
* If you are not needing automatic on-off operation, omit R3 & R5 and connect pin 4 of IC1 to positive supply.
* The bulb can be any 6V type up to 10-12W, but a 3W one is a very good compromise.
* Batteries can be of the rechargeable type: lead acid sealed, NI-CD, NI-MH packages ranging from 3.6 to 12V, making sure that suitable bulbs are provided.
* Using 1.2 Ampere-hour batteries, you should probably recharge them once a week or less.
* Obviously you can feed permanently the circuit by means of a suitable mains power supply.

Friday, August 28, 2009

Live-line Detector

If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10.When remote from a live line, the unit stops counting, the LED resulting permanently off.

Live-line Detector

C1____________100nF 63V Polyester or Ceramic Capacitor D1_____________Red LED (any type) IC1____________4017 Decade counter with 10 decoded outputs IC P1_____________SPST Pushbutton B1_____________3V Battery (two 1.5V AA or AAA cells in series etc.) Sensing probe__3 to 15 cm. long, stiff insulated piece of wire Notes: * Sensitivity can be varied using a more or less long sensing probe. * Due to 3V operation, the LED's current limiting resistor can be omitted.

Heating System Thermostat

This circuit is intended to control a heating system or central heating plan, keeping constant indoor temperature in spite of wide range changes in the outdoor one. Two sensors are needed: one placed outdoors, in order to sense the external temperature; the other placed on the water-pipe returning from heating system circuit, short before its input to the boiler. The Relay contact wiring must be connected to the boiler's start-stop control input.This circuit, though simple, has proven very reliable: in fact it was installed over 20 years ago at my parents' home. I know, it is a bit old: but it is still doing its job very well and without problems of any kind.

Heating System Thermostat


P1______________1K Linear Potentiometer

R1_____________10R 1/4W Resistor
R2______________1K 1/4W Resistor
R3______________3K3 @ 20°C n.t.c. Thermistor (see Notes)
R4______________2K2 @ 20°C n.t.c. Thermistor (see Notes)
R5_____________10K 1/2W Trimmer Cermet
R6______________3K3 1/4W Resistor
R7,R9___________4K7 1/4W Resistors
R8____________470K 1/4W Resistor
R10____________10K 1/4W Resistor

C1,C2_________470µF 25V Electrolytic Capacitors
C3______________1µF 63V Electrolytic Capacitor

D1,D2,D4_____1N4002 100V 1A Diodes
D3______________LED Red 3 or 5mm.

Q1____________BC557 45V 100mA PNP Transistor
Q2____________BC547 45V 100mA NPN Transistor
Q3____________BC337 45V 800mA NPN Transistor

RL1____________Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm

J1_____________Two ways output socket

SW1____________SPST Mains Switch

T1_____________220V Primary, 12 + 12V Secondary 3VA Mains transformer

PL1____________Male Mains plug &cable

When Q1 Base to ground voltage is less than half voltage supply (set by R7 & R9), a voltage is generated across R8 and the driver transistors Q2 & Q3 switch-on the Relay. When Q1 Base to ground voltage is more than half voltage supply, caused when one of the n.t.c. Thermistors lowers its value due to an increase in temperature, no voltage appears across R8 and the Relay is off.
C3 allows a clean switching of the Relay. P1 acts as main temperature control.


* R3 is the outdoor sensor, R4 the indoor sensor.
* If you are unable to find a 3K3 Thermistor for R3 you can use a 4K7 value instead. The different value can be easily compensated by means of Trimmer R5.
* R5 allows to set the heating system for outdoor temperatures ranging from about +10°C downwards. The higher R5's resistance the hotter the heating system and vice versa.
* The existing boiler thermostat should be set to its maximum value and not bypassed: it is necessary for safety's sake.
* This circuit can be dispensed with its differential feature and converted into a simple precision thermostat omitting R3.

Mains Remote-Alert

Pressing the pushbutton of the transmitter, a sound and/or light alert is activated in the receiver. The system uses no wiring or radio frequencies: the transmitted signal is conveyed into the mains supply line. It can be used at home, in any room from attic to cellar, simply plugging transmitter and receiver in the wall mains sockets. Transmission range can be very good, provided both units are connected to the mains supply within the control of the same light-meter.

Mains Remote-Alert Transmitter

Transmitter parts:

R1____________220K 1/4W Resistor
R2____________470R 1/2W Resistor
R3____________100K 1/4W Resistor
R4______________1K 1/4W Resistor

C1_____________10nF 400V Ceramic or Polyester Capacitor
C2____________330nF 400V Polyester Capacitor
C3______________1n5 63V Ceramic Capacitor (See Notes)
C4_____________10nF 63V Ceramic or Polyester Capacitor
C5____________100µF 25V Electrolytic Capacitor

D1,D2________1N4007 1000V 1A Diodes
D3_________BZX79C30 30V 500mW Zener Diode

Q1,Q2_________BC546 65V 100mA NPN Transistors

L1_______________IF Transformer for AM receivers, 445-470KHz

P1_____________SPST Mains suited Pushbutton

PL1____________Male Mains plug & cable

Receiver circuit diagram:

Mains Remote-Alert Receiver

Receiver parts:

R1____________220K 1/4W Resistor
R2____________470R 1/2W Resistor
R3____________150K 1/4W Resistor
R4______________2K2 1/4W Resistor
R5____________100K 1/4W Resistor
R6_____________47K 1/4W Resistor
R7______________2K2 1/4W Resistor (Optional)

C1____________100nF 400V Polyester Capacitor
C2____________330nF 400V Polyester Capacitor
C3______________1n5 63V Ceramic Capacitor (See Notes)
C4,C6_________330pF 63V Ceramic Capacitors
C5,C7_________100µF 25V Electrolytic Capacitors

D1,D2________1N4007 1000V 1A Diodes
D3_________BZX79C12 12V 500mW Zener Diode
D4,D5,D6_____1N4148 75V 150mA Diodes
D7_____________5mm. Red LED (Optional)

Q1,Q2_________BC547 45V 100mA NPN Transistors

L1_______________IF Transformer for AM receivers, 445-470KHz

BZ1___________Piezo sounder (incorporating 3KHz oscillator)

PL1____________Male Mains plug & cable

Transmitter circuit operation:

Q1 and Q2 are wired as a Darlington pair to obtain the highest possible output from a Hartley type oscillator running at about 135KHz frequency. The 230Vac mains is reduced to 30Vdc without the use of a transformer by means of C2 reactance, a two diode rectifier cell D1 & D2 and Zener diode D3.
The oscillator output is taken from L1 secondary winding and injected into the mains wiring by means of C1.

Receiver circuit operation:

The 135KHz sinewave generated by the transmitter is picked-up from mains wiring by C1 and selected by the tuned circuit L1-C3. Q1 greatly amplifies the incoming sinewave and converts it in a 12V-peak squarewave. D4 & D5 limit the input voltage at Q1 base to less than 1V-peak to avoid damaging of the transistor due to the high voltage transients frequently occurring on the mains line. D6 eliminates any negative component of the signal and Q2 drives the load. C7 is necessary to smooth the signal residues appearing across the load.
The 12Vdc supply for this unit is obtained as described above for the transmitter circuit.


* Transmitter and receiver coils L1s must be tuned regulating their ferrite cores to obtain maximum output at C3 leads, either in transmitter and receiver.
* This setup is better done using an oscilloscope and placing the two units as far as possible to each other.
* The tuning of the coils at 135KHz frequency should be obtained with the ferrite core almost totally inserted in its slot, if 455KHz IF transformers are used for both L1s.
* Using IF transformers different from those specified, a change in both C3s value could be needed. The value of these capacitors may vary from 1 to 3.3nF but must be the same in transmitter and receiver.
* The load can be a beeper, a LED or both. Omitting the beeper and choosing the LED as the only load, its limiting resistor R7 should be reduced in value to about 1K, to increase device brightness. In this case, a 10mm. diameter LED type or greater, can also be useful .
* Warning! These units are connected to 230Vac mains, then some parts in the circuit boards are subjected to lethal potential! Avoid touching the circuits when plugged and enclose them in plastic boxes.

Cellular Phone calling Detector

This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashing LED.The device must be placed a few centimeters from the cellular phone, so its sensor coil L1 can detect the field emitted by the phone receiver during an incoming call.

Cellular Phone calling Detector

R1____________100K 1/4W Resistor R2______________3K9 1/4W Resistor R3______________1M 1/4W Resistor C1,C2_________100nF 63V Polyester Capacitors C3____________220µF 25V Electrolytic Capacitor D1______________LED Red 10mm. Ultra-bright (see Notes) D2___________1N5819 40V 1A Schottky-barrier Diode (see Notes) Q1____________BC547 45V 100mA NPN Transistor IC1____________7555 or TS555CN CMos Timer IC L1_____________Sensor coil (see Notes) B1_____________1.5V Battery (AA or AAA cell etc.) The signal detected by the sensor coil is amplified by transistor Q1 and drives the monostable input pin of IC1. The IC's output voltage is doubled by C2 & D2 in order to drive the high-efficiency ultra-bright LED at a suitable peak-voltage. Notes: * Stand-by current drawing is less than 200µA, therefore a power on/off switch is unnecessary. * Sensitivity of this circuit depends on the sensor coil type. * L1 can be made by winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Remove the coil from the former and wind it with insulating tape, thus obtaining a stand-alone coil. * A commercial 10mH miniature inductor, usually sold in the form of a tiny rectangular plastic box, can be used satisfactorily but with lower sensitivity. * IC1 must be a CMos type: only these devices can safely operate at 1.5V supply or less. * Any Schottky-barrier type diode can be used in place of the 1N5819: the BAT46 type is a very good choice.

AC Current Monitor

This circuit was designed on request, to remotely monitor when a couple of electric heaters have been left on. Its sensor must be placed in contact with the feeder to be able to monitor when the power cable is drawing current, thus causing the circuit to switch-on a LED.The circuit and its sensor coil can be placed very far from the actual load, provided an easy access to the power cable is available.Any type of high-current load or group of loads can be monitored, e.g. heaters, motors, washing machines, dish-washers, electric ovens etc., provided they dissipate a power comprised at least in the 0.5 - 1KW range.This design features three versions. The basic one illuminates a LED when the load is on. The second version activates a Relay when a pre-set current value flows into the power cable. The third version switches-on D7 when the load power is about 1KW, D6 when the load power is about 2KW and D5 when the load power is about 3KW.

AC Current Monitor

R1,R2,R8____________1K 1/4W Resistors R3,R4_____________220K 1/4W Resistors R5________________100R 1/4W Resistor (See Notes) R6_________________10K 1/2W Trimmer Cermet R7,R10______________1M 1/4W Resistors R9_________________22K 1/2W Resistor R11 to R17__________1K 1/4W Resistors C1,C3_____________100µF 25V Electrolytic Capacitors C2,C4_______________1µF 63V Electrolytic Capacitors D1________________5mm. Red LED D3,D4___________1N4002 100V 1A Diodes D2,D5,D6,D7_______LEDs (Any color and size) Q1_______________BC327 45V 800mA PNP Transistor IC1______________TL061 Low current BIFET Op-Amp (First version) IC1______________LM358 Low Power Dual Op-amp (Second version) IC1______________LM324 Low Power Quad Op-amp (Third version) L1________________10mH miniature Inductor (See Notes) RL1______________Relay with SPDT 2A @ 220V switch Coil Voltage 12V. Coil resistance 200-300 Ohm J1_______________Two ways output socket The basic circuit is shown top left in the drawing and must be used in all three versions. IC1 acts as a differential amplifier having a gain of 220. The small AC voltage picked-up by L1 is therefore amplified to a value capable of driving the LED D1. The second version is drawn bottom left, must be connected to the basic circuit and uses a dual op-amp: therefore IC1 will be labeled IC1A and its pin layout varies slightly. IC1B acts as a voltage comparator and its threshold voltage can be precisely set by means of trimmer R6. Q1 is the Relay driver and D2 illuminates when the Relay is on. You can use the Relay contacts to drive an alarm or a lamp when the AC load exceeds a pre-set value, e.g. 2KW. The third version is shown to the right of the drawing, must be connected to the basic circuit and uses a quad op-amp, therefore IC1 will be labeled IC1A and its pin layout varies slightly. IC1B, C and D are wired as comparators. They switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R11-R14.
Notes: * The pick-up coil L1 is a common 10mH miniature inductor, having the shape of a small rectangular plastic box of 10x7x4 mm. with radial leads. * This inductor must be placed tightly against one wire of the power cable, leaving the other wire some centimeters apart. * The sensitivity will be doubled if the inductor is placed tightly between the two wires as shown in the diagram, top left. On the contrary, do not place the inductor against paired wires as the signal tends to cancel and the circuit will not work. * The LED limiting resistor R5 should have a value comprised in the 100R - 1K range, depending on the output voltage obtained. * LED D1 and its limiting resistor R5 can be omitted in versions two and three of the circuit. * Versions one and three draw a small current, thus allowing possible 9V battery operation.

Temperature-controlled Fan

This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain.

Temperature-controlled Fan


P1_____________22K Linear Potentiometer (See Notes)

R1_____________15K @ 20°C n.t.c. Thermistor (See Notes)
R2____________100K 1/4W Resistor
R3,R6__________10K 1/4W Resistors
R4,R5__________22K 1/4W Resistors
R7____________100R 1/4W Resistor
R8____________470R 1/4W Resistor
R9_____________33K 4W Resistor

C1_____________10nF 63V Polyester Capacitor

D1________BZX79C18 18V 500mW Zener Diode
D2_________TIC106D 400V 5A SCR
D3-D6_______1N4007 1000V 1A Diodes

Q1,Q2________BC327 45V 800mA PNP Transistors
Q3___________BC337 45V 800mA NPN Transistor

SK1__________Female Mains socket

PL1__________Male Mains plug & cable

R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4 generate a fixed two-thirds-supply "reference" voltage, P1-R1 generate a temperature-sensitive "variable" voltage, and Q1 is used as a bridge balance detector.
P1 is adjusted so that the "reference" and "variable" voltages are equal at a temperature just below the required trigger value, and under this condition Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1 temperature goes above this "balance" value the P1-R1 voltage falls below the "reference" value, so Q1 becomes forward biased, pulse-charging C1.
This occurs because the whole circuit is supplied by a 100Hz half-wave voltage obtained from mains supply by means of D3-D6 diode bridge without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1. Therefore the 18V supply of the circuit is not true DC but has a rather trapezoidal shape. C1 provides a variable phase-delay pulse-train related to temperature and synchronous with the mains supply "zero voltage" point of each half cycle, thus producing minimal switching RFI from the SCR. Q2 and Q3 form a trigger device, generating a short pulse suitable to drive the SCR.


* The circuit is designed for 230Vac operation. If your ac mains is rated at about 115V, you can change R9 value to 15K 2W. No other changes are required.
* Circuit operation can be reversed, i.e. the fan increases its speed as temperature decreases, by simply transposing R1 and P1 positions. This mode of operation is useful in controlling a hot air flux, e.g. using heaters.
* Thermistor value is not critical: I tried also 10K and 22K with good results.
* In this circuit, if R1 and Q1 are not mounted in the same environment, the precise trigger points are subject to slight variation with changes in Q1 temperature, due to the temperature dependence of its Base-Emitter junction characteristics. This circuit is thus not suitable for use in precision applications, unless Q1 and R1 operate at equal temperatures.
* The temperature / speed-increase ratio can be varied changing C1 value. The lower the C1 value the steeper the temperature / speed-increase ratio curve and vice-versa.
* Warning! The circuit is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Self-powered Door-bell Watcher

This very simple and self-powered device was conceived to allow a person to monitor if someone has rung his home door-bell when he was out.As most door-bells use 12Vac supply, the circuit must be simply connected to the two door-bell-coil leads.When the door-bell is activated, an ac voltage of about 10 - 16V is developed at its leads, so it is rectified by D1 and charges C1.

Door-bell Watcher

R1______________1K 1/4W Resistor R2____________220K 1/4W Resistor (Optional, see text) R3______________2K2 1/4W Resistor (Optional, see text) C1___________1000µF 25V Electrolytic Capacitor (See Notes) C2____________100nF 400V Polyester Capacitor (Optional, see text) D1__________1N4002 100V 1A Diode D2_____________5mm. Red LED P1_____________SPST Pushbutton BZ1___________Piezo sounder (incorporating 3KHz oscillator) (Optional, see text) Though this device was primarily intended to be used when a person leaves the house for a few hours or a week-end, a number of tests has proven that a minimum of 15 days "memory" can be guaranteed, even using cheap capacitor types. To know if the door-bell has rung, you must simply push P1: if the event occurred, LED D2 will illuminate and will fade slowly to the off-state in some seconds. This operation will reset the circuit also. The LED can be substituted or supported by a small Piezo sounder (incorporating 3KHz oscillator) A small number of door-bells powered by 230 or 115Vac can be found. In this case, R2, R3 and C2 must be added to the input of the basic circuit, allowing about 15Vac to develop across R3, the voltage-drop provided by C2 reactance. The mains supply operation facility, allows further development of the circuit purposes. In fact, almost any mains supplied apparatus can be monitored, e.g. household appliances, computers, radio and television sets, Hi-Fi systems, lamps etc., provided the circuit can be inserted after the main on-off switch. Notes: * The added high-voltage circuit formed by R2, R3 and C2 was designed for 230Vac operation. If your ac mains is rated at about 115V, you must change C2 value to 220nF 250V. No other changes are required. * In most cases, a 470µF 25V value for C1 would suffice. * Warning! If the circuit is connected to 230Vac mains, some parts in the circuit board can be subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Thursday, August 27, 2009

Dark-activated 230V Lamp

This device allows one or more lamps to illuminate at sunset and turn off at dawn.
Q1 and Q2 form a trigger device for the SCR, providing short pulses at 100Hz frequency. Pulse duration is set by R2 and C1.When the light hits R1, the photo resistor assumes a very low resistance value, almost shorting C1 and preventing circuit operation. When R1 is in the dark, its resistance value becomes very high thus enabling circuit operation.

Dark-activated Lamp


R1_____________Photo resistor (any type)
R2____________100K 1W Resistor
R3____________200K 1/2W Trimmer Cermet
R4,R7_________470R 1/4W Resistors
R5_____________12K 1/4W Resistor
R6______________1K 1/4W Resistor

C1_____________10nF 63V Polyester Capacitor

D1_________TIC106D 400V 5A SCR
D2-D5_______1N4007 1000V 1A Diodes

Q1___________BC327 45V 800mA PNP Transistor
Q2___________BC337 45V 800mA NPN Transistor

SK1__________Female Mains socket

PL1__________Male Mains plug & cable


* R3 allows fine setting of operating threshold and R2 value can be raised to 150K maximum.
* Several lamps wired in parallel can be connected to the circuit, provided total power dissipation of the load does not exceed about 300 - 500W.
* PL1 can be omitted and the input mains supply wires connected in parallel to any switch controlling lamps. In this case, if the switch is left open, the circuit will be able to drive the lamps; if the switch is closed, the lamps will illuminate and the circuit will be by-passed.
* Warning! The circuit is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential!. Avoid touching the circuit when plugged and enclose it in a plastic box.

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