Frost Alarm

Frost Alarm

source: unknown

Notes:
The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents relay chatter when temperature is near the switching threshold of this circuit.

Capacitive Sensor

source: RED Free Circuit Designs

Special design for shop-windows animation

Useful for many types of touch controls

Parts:

R1,R2_____1M 1/4W Resistors
R3,R4____47K 1/4W Resistors

C1_______10΅F 25V Electrolytic Capacitor
C2______470pF 630V Ceramic or Polyester Capacitor

D1-D3____1N4002 100V 1A Diodes

Q1-Q3_____BC337 45V 800mA NPN Transistors

RL1_______Relay with SPDT 2A @ 220V switch
Coil Voltage 12V. Coil resistance 200-300 Ohm

J1________Two ways output socket

Sensor____Aluminium or copper thin sheet with the dimensions of a post-card,
glued at the rear of the same (approx. 15x10.5 cm.)

Thin screened cable

Circuit description:

The purpose of this circuit is to animate shop-windows by means of a capacitive sensor placed behind a post-card-like banner. The card is placed against the glass inside the shop-window, and the visitor can activate the relay placing his hand on the card, from the outside. Especially suited for toy-shops, the circuit can activate model trains, small electric racing cars, lights etc. Further applications are left at user's imagination. Adopt it to increase the impact of your shop-window on next Christmas season!

Q1, Q2 & Q3 form a high impedance super-Darlington that drives the relay, amplifying the 50Hz alternate mains-supply frequency induced in the sensor by the human body. C1 & D2, D3 ensure a clean relay's switching. Power supply can be any commercial wall plug-in transformer with rectifier and smoothing capacitor, capable of supplying the voltage and current necessary to power the relay you intend to use.

Note: For proper operation, circuit ground must be connected via a small value, high voltage-rating capacitor to one side of the mains supply socket. The "Live" side is the right one.

Heating System Thermostat

source: RED Free Circuit Designs

Controlled by indoor and outdoor temperature

Simple, high reliability design

Parts:

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_________470΅F 25V Electrolytic Capacitors
C3______________1΅F 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

Device purpose:

This circuit is intended to control a heating syste 616v219g m 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 output from the Relay contact 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's a bit old: but it's still doing its job very well and without problems of any kind.

Circuit operation:

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.

Notes:

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.

Touch Switch II

source: https://www.aaroncake.net/

A touch switch is a switch that is turned on and off by touching a wire contact, instead of flicking a lever like a regular switch. Touch switches have no mechanical parts to wear out, so they last a lot longer than regular switches. Touch switches can be used in places where regular switches would not last, such as wet or very dusty areas.

Schematic

Parts

Notes:

1. The contacts an be made with just two loops of wire close together, or two squares etched close together on a PC board.

2. When activated, the output of the circuit goes high for about one second. This pulse can be used to drive a relay, transistor, other logic, etc.

3. You can vary the length of the output pulse by using a smaller or larger capacitor for C1.

Voice activated switch

source: Motorola

This circuit uses an MC2830 to form a voice activated switch ( VOX ). A traditional VOX circuit is unable to distinguish between voice and noise in the incoming signal. In a noisy environment, the switch is often triggered by noise, or the activation sensitivity must be turned down. This circuit overcomes this weakness. The switch is activated by voice level above the noise and not activated by background noise. This is done by utilizing the differences in voice and noise waveforms. Voice waveforms generally have a wide range of variation in amplitude, whereas noise waveforms are more stable. The sensitivity of the voice activation depends on the value of R6. The voice activation sensitivity is reduced from 3.0dB to 8.0dB above the noise if R6 changes from 14k to 7.0k .

Rain Detector

source: https://www.aaroncake.net/

This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.

Schematic

Parts

Notes

1. The sensor is a small piece of PC board etched to the pattern showen in the schematic. The traces should be very close to each other, but never touching. A large spiral pattern would also work.

2. Make sure to use a loud buzzer.

Whistle Responder

source: RED Free Circuit Designs

Beeps when hears your whistle

A gadget suitable for key-holders, games etc.

Circuit diagram:

Parts:

R1_____________22K 1/4W Resistor
R2_____________10K 1/4W Resistor
R3______________4M7 1/4W Resistor
R4,R8_________100K 1/4W Resistors
R5____________220R 1/4W Resistor
R6____________330K 1/4W Resistor
R7_____________47K 1/4W Resistor
R9______________2M2 1/4W Resistor
R10_____________1M5 1/4W Resistor

C1,C5__________47nF 63V Polyester or Ceramic Capacitors
C2,C3__________10nF 63V Polyester Capacitors
C4,C6___________1΅F 63V Electrolytic Capacitors

D1,D2________1N4148 75V 150mA Diodes

IC1____________4049 Hex Inverter IC

Q1____________BC337 45V 800mA NPN Transistor

MIC1_________Miniature electret microphone

BZ1__________Piezo sounder (incorporating 3KHz oscillator)

B1___________2.8 or 3V Battery (see notes)

Device purpose:

Some 15 years ago it was common to see small key-holders emitting an intermittent beep for a couple of seconds after its owner whistled. These devices contained a special purpose IC and therefore were not suited to home construction. The present circuit is designed around a general purpose hex-inverter CMos IC and, using miniature components and button clock-type batteries can be enclosed in a matchbox. It is primarily a gadget, but everyone will be able to find suitable applications.

Circuit operation:

This device beeps intermittently for approx. two seconds when a person in a range of about 10 meters emits a whistle.
The first two inverters contained in IC1 are used as audio amplifiers. IC1A amplifies consistently the signal picked-up by the small electret-microphone and IC1B acts as a band-pass filter, its frequency being centered at about 1.8KHz. The filter is required in order to select a specific frequency, the whistle's one, stopping other frequencies that would cause undesired beeper's operation. IC1C is wired as a Schmitt trigger, squaring the incoming audio signal. IC1D is a 2 second (approx.) monostable driving the astable formed by IC1E & IC1F. This oscillator generates a 3 to 5Hz square wave feeding Q1 and BZ1, thus providing intermittent beeper's operation.

Notes:

Power supply range: 2.6 to 3.6 Volts.

Standing current: 150΅A.

Depending on dimensions of your box, you can choose from a wide variety of battery types:

2 x 1.5 V batteries type: AA, AAA, AAAA, button clock-type, photo-camera type & others.

2 x 1.4 V mercury batteries, button clock-type.

1 x 3 V or 1 x 3.6 V Lithium cells.

Time Delay Relay II

source: https://www.aaroncake.net/

By [email protected]

When activated by pressing a button, this time delay relay will activate a load after a specified amount of time. This time is adjustable to whatever you want simply by changing the value of a resistor and/or capacitor. The current capacity of the circuit is only limited by what kind of relay you decide to use.

Schematic

Parts:

Notes:

1. Email [email protected] with comments, questions, etc.

2. To calculate the time delay, use the equation R1 * C1 * 0.85=T, where R1 is the value of R1 in Ohms, C1 is the value of C1 in uF, and T is the time delay in seconds.

3. S1 may be replaced with an NPN transistor so the circuit can be triggered by a computer, other circuits, etc.

4. Most any 6V relay will work for K1. If you use a large relay, you my need to add a transistor to the output of the circuit in order to drive the larger load.

Time Delay Relay

source: https://www.aaroncake.net/

A time delay relay is a relay that stays on for a certain amount of time once activated. This time delay relay is made up of a simple adjustable timer circuit which controls the actual relay. The time is adjustable from 0 to about 20 seconds with the parts specified. The current capacity of the circuit is only limited by what kind of relay you decide to use.

Schematic

Parts:

C1__________10uf 16V Electrolytic Capacitor
C2__________0.01uf Ceramic Disc Capacitor
R1__________1 Meg Pot
R2__________10 K 1/4 Watt Resistor
D1,D2_______1N914 Diodes
U1__________555 Timer IC
RELAY______9V Relay
S1__________Normally Open Push Button Switch
MISC_______Board, Wire, Socket For U1

Notes:

1. R1 adjusts the on time.

2. You can use a different capacitor for C1 to change the maximum on time.

3. S1 is used to activate the timing cycle. S1 can be replaced by a NPN transistor so that the circuit may be triggered by a computer, other circuit, etc.

Door Alarm

source: RED Free Circuit Designs

Hangs up on the door-handle

Beeps when someone touches the door-handle from outside

Parts:

R1______________1M 1/4W Resistor
R2______________3K3 1 or 2W Resistor (See Notes)
R3_____________10K 1/2W Trimmer Cermet (See Notes)
R4_____________33K 1/4W Resistor
R5____________150K 1/4W Resistor
R6______________2K2 1/4W Resistor
R7_____________22K 1/4W Resistor
R8______________4K7 1/4W Resistor

C1,C2__________10nF 63V Ceramic or Polyester Capacitors
C3_____________10pF 63V Ceramic Capacitor
C4,C6_________100nF 63V Ceramic or Polyester Capacitors
C5______________2΅2 25V Electrolytic Capacitor
C7____________100΅F 25V Electrolytic Capacitor

D1,D2,D4_____1N4148 75V 150mA Diodes
D3_____________5 or 3mm. Red LED

Q1,Q2,Q3,Q5___BC547 45V 100mA NPN Transistors
Q4____________BC557 45V 100mA PNP Transistor

L1_________________ (See Notes)
L2_____________10mH miniature Inductor

Hook_______________ (See Notes)

BZ1___________Piezo sounder (incorporating 3KHz oscillator)

SW1,SW2________SPST miniature Slider Switches

B1_______________9V PP3 Battery

Clip for PP3 Battery

Device purpose:

This circuit emits a beep and/or illuminates a LED when someone touches the door-handle from outside. The alarm will sound until the circuit will be switched-off.
The entire circuit is enclosed in a small plastic or wooden box and should be hanged-up to the door-handle by means of a thick wire hook protruding from the top of the case.
A wide-range sensitivity control allows the use of the Door Alarm over a wide variety of door types, handles and locks. The device had proven reliable even when part of the lock comes in contact with the wall (bricks, stones, reinforced concrete), but doesn't work with all-metal doors.
The LED is very helpful at setup.

Circuit operation:

Q1 forms a free-running oscillator: its output bursts drive Q2 into saturation, so Q3 and the LED are off. When part of a human body comes in contact with a metal handle electrically connected to the wire hook, the body capacitance damps Q1 oscillations, Q2 biasing falls off and the transistor becomes non conducting. Therefore, current can flow into Q3 base and D3 illuminates. If SW1 is closed, a self-latching circuit formed by Q4 & Q5 is triggered and the beeper BZ1 is activated.
When the human body part leaves the handle, the LED switches-off but the beeper continues to sound, due to the self-latching behavior of Q4 & Q5. To stop the beeper action, the entire circuit must be switched-off opening SW2.
R3 is the sensitivity control, allowing to cope with a wide variety of door types, handles and locks.

Notes:

L1 is formed winding 20 to 30 turns of 0.4mm. diameter enameled copper wire on R2 body and soldering the coil ends to the resistor leads. You should fill R2 body completely with coil winding: the final turn's number can vary slightly, depending on different 1 or 2W resistor types actual length (mean dimensions for these components are 13-18mm. length and 5-6mm. diameter).

The hook is made from non-insulated wire 1 - 2mm. diameter (brass is well suited). Its length can vary from about 5 to 10cm. (not critical).

If the device is moved frequently to different doors, Trimmer R3 can be substituted by a common linear potentiometer fitted with outer knob for easy setup.

To setup the device hang-up the hook to the door-handle (with the door closed), open SW1 and switch-on the circuit. Adjust R3 until the LED illuminates, then turn slowly backwards the screwdriver (or the knob) until the LED is completely off. At this point, touching the door-handle with your hand the LED should illuminate, going off when the hand is withdrawn. Finally, close SW1 and the beeper will sound when the door-handle will be touched again, but won't stop until SW2 is opened.

In regular use, it is advisable to hang-up and power-on the device with SW1 open: when all is well settled, SW1 can be closed. This precautionary measure is necessary to avoid unwanted triggering of the beeper.

Light/Dark Detector

source: https://www.aaroncake.net/

This handy little circuit can tell the difference between darkness and light, making it very useful for switching on and off signs, porch lights or other things when it gets dark or light.

Schematic

Parts:

Notes:

1. R1 Adjusts sensitivity

Phone line indicator

source: smartkit

   With this circuit you can monitor your telephone line. You are able to detect if any telephone in the same line is busy with the help of a LED. This circuit does not affect the telephone's line provider, so it's trouble free but you use it at your own risk.

    It connects in parallel with the telephone line. The bridge rectifier (D1...D4) at the input protects the circuit from reverse polarity. When none of the telephones of this line is used then the voltage across the line is about 50-60V. This voltage with the help of the bridge and R1/R2 voltage divider affects the gate of BF256B so it stays in non conductive mode. When a telephone is used the voltage across the line drops suddenly and Τ1 goes to conductive mode so the Led lights up, giving us the "in use indication".

    In Τ1 the current which flows through LED is about 10mΑ. The zener diode D5 prevents gate's voltage to excess 10V and C1 works like a filter for unwanted pulses. If your circuit doesn't work ok , you can replace R1 with another, but no more that a 220ΚΩ one.

    The circuit works ok with a 9V battery and you can put it into a plastic box.
Attention: 50V from the telephone line can become dangerous under some circumstances so take precautions when handling it.

PCB

         

Parts List

Black Light

source: unknown

This circuit is a simple ultraviolate light that can be powered by a 6 volt battery or power supply that is capable of supplying 1 or more amps.

Theoritical Diagramm

PARTS

Notes:

1. P1 changes brightness of the black light tube.

220 Volts Flashing Lamps

source: RED Free Circuit Designs

Especially designed for Christmas tree lamps

Replaces old thermally-activated switches

Parts:

R1___________100K 1/4W Resistor
R2,R5__________1K 1/4W Resistors
R3,R6________470R 1/4W Resistors
R4____________12K 1/4W Resistor

C1__________1000΅F 25V Electrolytic Capacitor

D1-D4_______1N4007 1000V 1A Diodes
D5__________P0102D 400V 800mA SCR

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

PL1__________Male Mains plug

SK1__________Female Mains socket

Device purpose:

This circuit is intended as a reliable replacement to thermally-activated switches used for Christmas tree lamp-flashing. The device formed by Q1, Q2 and related resistors triggers the SCR. Timing is provided by R1,R2 & C1. To change flashing frequency don't modify R1 and R2 values: set C1 value from 100 to 2200΅F instead.
Best performances are obtained with C1=470 or 1000΅F and R4=12K or 10K. Due to low consumption of normal 10 or 20 lamp series-loops intended for Christmas trees (60mA @ 220V typical for a 20 lamp series-loop), very small and cheap SCR devices can be used, e.g. C106D1 (400V 3.2A) or TICP106D (400V 2A), this last and the suggested P0102D devices having TO92 case.

Important Note:

For proper operation it's absolutely necessary to employ high Gate-sensitive SCRs.
If you are unable to find these devices you can use Triacs instead. In this case the circuit operates also with relatively powerful devices. A recommended Triac type is the ubiquitous TIC206M (600V 4A) but many others can work.
Note that in spite of the Triac, diode bridge D1-D4 is in any case necessary.

Nocturnal Animals Whisker

source: RED Free Circuit Designs

A low-rate flashing lamp drives away undesired visitors

Automatic on-off operation

Parts:

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_______47΅F 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 Lamp (see Notes)

SW1____________SPST Switch

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

Device purpose:

This circuit 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 at 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.

Circuit operation:

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 lamps. C2 prevents some brief instability when voltage at pin 4 of IC1 is very close to switching threshold.

Notes:

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's 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 lamp 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 lamps 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

Variable DC Power Supply

Voltage range: 0.7 - 24V

Current limiting range: 50mA - 2A

Circuit diagram:

Parts:

P1____________500R Linear Potentiometer

P2_____________10K Log. Potentiometer

R1,R2___________2K2 1/2W Resistors

R3____________330R 1/4W Resistor

R4____________150R 1/4W Resistor

R5______________1R  5W Resistor

C1___________3300µF 35V Electrolytic Capacitor (see Notes)

C2______________1µF 63V Polyester Capacitor

D1,D2________1N5402 200V 3A Diodes

D3_____________5mm. Red LED

Q1____________BC182 50V 100mA NPN Transistor

Q2____________BD139 80V 1.5A NPN Transistor

Q3____________BC212 50V 100mA PNP Transistor

Q4 __________2N3055 60V 15A NPN Transistor

T1_____________220V Primary, 36V Center-tapped Secondary 50VA Mains transformer (see Notes)

PL1____________Male Mains plug

SW1____________SPST Mains switch

Device purpose:

A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist's workbench. This circuit is not an absolute novelty, but it is simple, reliable, "rugged" and short-proof, featuring variable voltage up to 24V and variable current limiting up to 2A. Well suited to supply the circuits shown in this website. You can adapt it to your own requirements as explained in the notes below.

Notes:

• P1 sets the maximum output current you want to be delivered by the power supply at a given output voltage.
• P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a more linear scale voltage indication.
• You can choose the Transformer on the grounds of maximum voltage and current output needed.
  Best choices are: 36, 40 or 48V center-tapped and 50, 75, 80 or 100VA.
• Capacitor C1 can be 2200 to 6800µF, 35 to 50V.
• Q4 must be mounted on a good heatsink in order to withstand sustained output short-circuit.
  In some cases the rear panel of the metal box in which you will enclose the circuit can do the job.
• The 2N3055 transistor (Q4) can be replaced with the slightly less powerful TIP3055 type.
• Excellent quality-price ratio: enjoy!

Bicycle back Safety Light

Flashing 13 LED unit, 3V supply

Also suitable for jogger/walkers

Circuit diagram:

Parts:

R1_____________10K 1/4W Resistor

R2,R9,R10_____100K 1/4W Resistors

R3-R8,R11-R16__10R 1/4W Resistors

R17___________150R 1/4W Resistor

C1______________1µF 63V Polyester Capacitor

C2_____________10nF 63V Polyester Capacitor

C3____________100µF 25V Electrolytic Capacitor

D1-D13_____Red LEDs 5mm. or bigger, high efficiency

IC1,IC2________7555 or TS555CN CMos Timer IC

SW1____________SPST Slider Switch

B1_______________3V Battery (2 AA 1.5V Cells in series)

Device purpose:

This circuit has been designed to provide a clearly visible light, formed by 13 high efficiency flashing LEDs arranged in a pseudo-rotating order. Due to low voltage, low drain battery operation and small size, the device is suitable for mounting on bicycles as a back light, or to put on by jogger/walkers.

Circuit operation:

IC1 is a CMos version of the 555 IC wired as an astable multivibrator generating a 50% duty-cycle square wave at about 4Hz frequency. At 3V supply, 555 output (pin 3) sinking current operation is far better than sourcing, then LEDs D1-D6 are connected to the positive supply rail. In order to obtain an alternate flashing operation, a second 555 IC is provided, acting as a trigger plus inverter and driving LEDs D7-D12. D13 is permanently on.
The LEDs are arranged in a two series display as shown below, with a center LED permanently on. This arrangement and the alternate flashing of the two series of LEDs provide a pseudo-rotating appearance.

LED arrangement:

Notes:

• Flashing frequency can be varied changing C1 value.
• High efficiency LEDs are essential.

Push-bike Light

Automatic switch-on when it gets dark

6V or 3V battery operation

Circuit diagram:

Parts:

R1_____________Photo resistor (any type)

R2______________22K 1/2W Trimmer Cermet or Carbon type

R3_______________1K 1/4W Resistor

R4_______________2K7 1/4W Resistor

R5_____________330R 1/4W Resistor (See Notes)

R6_______________1R5 1W Resistor (See Notes)

D1____________1N4148 75V 150mA Diode

Q1_____________BC547 45V 200mA NPN Transistor

Q2_____________BD438 45V 4A PNP Transistor

LP1____________Filament Lamp(s) (See Notes)

SW1_____________SPST Toggle or Slider Switch

B1______________6V or 3V Battery (See Notes)

Comments:

This design was primarily intended to allow automatic switch-on of push-bike lights when it gets dark. Obviously, it can be used for any other purpose involving one or more lamps to be switched on and off depending of light intensity.
Power can be supplied by any type of battery suitable to be fitted in your bike and having a voltage in the 3 to 6 Volts range.
The Photo resistor R1 should be fitted into the box containing the complete circuit, but a hole should be made in a convenient side of the box to allow the light hitting the sensor.
Trim R2 until the desired switching threshold is reached. The setup will require some experimenting, but it should not be difficult.

Notes:

• In this circuit, the maximum current and voltage delivered to the lamp(s) are limited mainly by R6 (that can't be omitted if a clean and reliable switching is expected).
  Therefore, the Ohm's Law must be used to calculate the best voltage and current values of the bulbs.
• For example: at 6V supply, one or more 6V bulbs having a total current drawing of 500mA can be used, but for a total current drawing of 1A, 4.5V bulbs must be chosen, as the voltage drop across R6 will become 1.5V. In this case, R6 should be a 2W type.
• At 3V supply, R6 value can be lowered to 1 or 0.5 Ohm and the operating voltage of the bulbs should be chosen accordingly, by applying the Ohm's Law.
  Example: Supply voltage = 3V, R6 = 1R, total current drawing 600mA. Choose 2.2V bulbs as the voltage drop caused by R6 will be 0.6V.
• At 3V supply, R5 value must be changed to 100R.
• Stand-by current is less than 500µA, provided R2 value after trimming is set at about 5K or higher: therefore, the power switch SW1 can be omitted. If R2 value is set below 5K the stand-by current will increase substantially.

Ultra-simple Voltage Probe

Detects 1.8 to 230 Volts DC or AC

Minimum parts counting

Circuit diagram:

Parts:

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

Device purpose:

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.

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

Room Noise Detector

One LED monitors three levels: 50, 70 & 85 dB

Useful to detect too noisy environments

Circuit diagram:

Parts:

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

Device purpose:

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 with LED off and 12-15mA when the LED is steady on.

Use:

• 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.

Dark-activated 230V Lamp

Compact circuitry using small-size parts only

Can be wired in parallel to existing switches

Circuit diagram:

Parts:

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

Comments:

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.

Notes:

• 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.

Clap Relay

Clap sensitive on-off Relay

3V Battery operated, small portable unit

Circuit diagram:

Parts:

R1,R6___________12K 1/4W Resistors

R2_______________1M 1/4W Resistor

R3,R9____________6K8 1/4W Resistors

R4_____________220K 1/4W Resistor

R5_______________2M2 1/4W Resistor

R7,R10_________100K 1/4W Resistors

R8______________22K 1/4W Resistor

C1,C3__________220nF 63V Polyester Capacitors

C2,C4,C5________22nF 63V Polyester Capacitors

C6______________47µF 25V Electrolytic Capacitor

D1,D2_________1N4148 75V 150mA Diodes

IC1_____________7555 or TS555CN CMos Timer IC

Q1_____________BC550C 45V 100mA Low noise High gain NPN Transistor

Q2,Q3__________BC328 30V 800mA PNP Transistors

MIC1___________Miniature electret microphone

SW1_____________SPST Switch

RL1_______________5V DIL Reed-Relay SPDT (See Notes)

B1________________3V Battery (2 x 1.5V AA, AAA Cells in series etc.)

Device purpose:

This circuit was intended to activate a relay by means of a hand clap. A further clap will turn-off the relay. An interesting and unusual feature of this project is the 3V battery operation.
The circuit's sensitivity was deliberately reduced, in order to avoid unpredictable operation. Therefore, a loud hand clap will be required to allow unfailing on-off switching.

Circuit operation:

Q1 acts as an audio amplifier. IC1 timer, wired as a monostable, provides a clean output signal and a reasonable time delay in order to allow proper switching of the following bistable circuit. A discrete-components circuit formed by Q2, Q3 and related parts was used for this purpose, in order to drive the Relay directly and to allow 3V supply operation.

Notes:

• A small DIL 5V reed-relay was used in spite of the 3V supply. Several devices of this type were tested and it was found that all of them were able to switch-on with a coil voltage value comprised in the 1.9 - 2.1V range. Coil resistance values varied from 140 to 250 Ohm.
• Stand-by current consumption of the circuit is less than 1mA. When the Relay is energized, current drain rises to about 20mA.