Circuit Designs

8/13/2019 Circuit Designs

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http://www.redcircuits.com/Hobby.htm

personal alarm

Circuit diagram:

Parts:R1____________330K 1/4W ResistorR2____________100R 1/4W Resistor

C1_____________10nF 63V Polyester or Ceramic CapacitorC2____________100F 25V Electrolytic Capacitor

Q1____________BC547 45V 100mA NPN TransistorQ2____________BC327 45V 800mA PNP Transistor

SW1____________Reed Switch and small magnet (See Notes)

SPKR___________8 Ohm Loudspeaker (See Notes)

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

Device purpose:

This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A smallmagnet is placed close to the reed switch and connected to the hand or the clothes of the personcarrying the bag by means of a tiny cord.If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens,the circuit starts oscillating and the loudspeaker emits a loud alarm sound.The device can be reverse connected, i.e. the box can be placed in a pocket and the cordconnected to the bag.This device can be very useful in signalling the opening of a door or window: place the box on
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the frame and the magnet on the movable part in a way that magnet and reed switch are veryclose when the door or window is closed.

Circuit operation:

A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a smallloudspeaker. Low part-count and 3V battery supply allow a very compact construction.

Notes:

The loudspeaker can be any type, its dimensions are limited only by the box that willenclose it.

An on-off switch is unnecessary because the stand-by current drawing is less than 20A. Current consumption when the alarm is sounding is about 100mA. If the circuit is used as anti-bag-snatching, SW1 can be replaced by a 3.5mm mono Jack

socket and the magnet by a 3.5mm. mono Jack plug having its internal leads shorted. The

Jack plug will be connected to the tiny cord etc. Do not supply this circuit at voltages exceeding 4.5V: it will not work and Q2 could bedamaged. In any case a 3V supply is the best compromise

Bells ring Generator

Three circuit options

Can be synchronized to Christmas tree flashing lights


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Circuit diagram:

Parts:R1,R3,R7,R9,R13_10K 1/4W ResistorsR2_______________1M5 1/4W ResistorR4______________27K 1/4W ResistorR5,R11__________47K 1/4W ResistorsR6,R12_________220K 1/4W ResistorsR8_______________2M2 1/4W ResistorR10_____________33K 1/4W Resistor

C1_______________22 25V Electrolytic CapacitorC2______________47F 25V Electrolytic CapacitorC3,C8___________10F 25V Electrolytic CapacitorsC4,C7___________10nF 63V Polyester CapacitorsC5,C6__________100nF 63V Polyester Capacitors

D1-D5_________1N4148 75V 150mA Diodes

IC1__________MC14106 or 40106 Hex Schmitt Inverter IC

Q1_____________BC337 45V 800mA NPN TransistorQ2,Q3,Q5_______BC238 25V 100mA NPN TransistorsQ4 ____________BC327 45V 800mA PNP Transistor

PH______________Photo resistor (any type) (see Notes)

P1______________SPST Pushbutton (see Notes)


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SW1_____________SPST Switch

SPKR____________8 Ohm Loudspeaker

B1______________3V Battery (two 1.5V AA or AAA cells in series etc.)

Parts added to optional modification:R14____________220K 1/4W ResistorR15______________1M 1/4W Resistor

C9_______________47 25V Electrolytic CapacitorC10______________1F 25V Electrolytic Capacitor

Device purpose:

This circuit generates a dual-tone bells ringing similar to most door-bell units. It can be used inmany applications other than door-bell. In the Notes below several options will be given in orderto suit different needs.

Circuit operation:

The circuit as shown in the diagram generates a "Ding-tone" when P1 is pressed and a "Dong-tone" when P1 is released. IC1D is the first-tone frequency generator and IC1F generates thesecond-tone.Q2, Q5 and related components act as shape and decay controls of the two tones, trying toimitate as close as possible the bells sound. Their outputs are mixed (R7 & R13), filtered (C5)and boosted by a simple class-A audio amplifier (Q3 & Q4) in order to drive the loudspeaker.The amplifier is switched-on by Q1 when P1 is pressed, then is switched-off some seconds afterP1 is released: this time-delay is fixed by C1 & R2. In this way the circuit will draw a negligiblecurrent when in stand-by mode.

Notes:

To obtain a "Ding-Dong" operation when pushing on P1, no matter when it is released, you mustmodify the circuit as shown in the frame placed at the low-right corner of the circuit diagram. D4must be removed. C10 & R15 set the time-delay separating first and second tone.

To obtain a one-tone-only generator, wire the circuit as in the optional modification, making thefollowing changes:

C9 = 100nF 63V Polyester Capacitor.Omit R9 to R13 & R15; C7, C8 & C10; D2, D4, D5 & Q5.Connect to negative supply pins 11 & 13 of IC1 and left open pins 10 & 12.


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An amusing application of this circuit wired as in the original schematic, is to use a photo-resistor in place of P1, then placing the unit near the flashing lamps of your Christmas tree. Asoft bell sound may be heard at switch-on and switch-off of the lamp chosen.

To obtain higher output power you may substitute R8, Q3 & Q4 with an audio amplifier IC likethe LM386 or LM380. In this case power supply must be raised to 6 - 12V but at the same timeR4 & R10 should be changed to adjust bell-tone frequencies.

Good tone frequencies are roughly 2000 and 1650Hz respectively. When in stand-by mode, current drawing of the circuit is 200A @ 3V supply: therefore SW1 can

be omitted.

Pulse-Generator & Signal-Tracer

Dual-purpose test-instrument

Very simple circuitry, 1.5V Battery-operated

Circuit diagram:

Parts:R1__________________1M 1/4W ResistorR2,R4_______________2K7 1/4W ResistorsR3________________150K 1/4W Resistor

C1__________________2n2 630V Ceramic or Polyester Capacitor (See Notes)C2,C3_______________4n7 63V Ceramic or Polyester Capacitors

D1_______________1N4148 75V 150mA Diode

Q1________________BC547 45V 100mA NPN TransistorQ2________________BC557 45V 100mA PNP Transistor

SW1________________SPST miniature Slider Switch (See Notes)

J1_________________Stereo switched 3mm. Jack socket (See Notes)

Probe______________Metal Probe 3 to 5 cm. long

Clip_______________Miniature Crocodile Clip


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B1_________________1.5V Battery (AA or AAA cell etc.)

Device purpose:

This simple circuit generates narrow pulses at about 700-800Hz frequency. The pulses,containing harmonics up to the MHz region, can be injected into audio or radio-frequency stagesof amplifiers, receivers and the like for testing purposes. A high-pitched tone can be heard fromthe speaker of the device under test when all is working properly. The clip must be connected tothe ground of the device under test, touching with the probe the different stages of the circuit,starting from the last stage and going up towards the first. When the tone is no longer heard, thedefective stage has been found.Connecting an earclip or headphone to J1, the circuit will automatically change into a two-stageamplifier and any audio signal coming from the device under test and picked-up by the probewill be heard through the headphones. The testing of a circuit should be made in the reversemanner, i.e. starting from the first stage and going down until the last stage. When nothing isheard, the defective stage has been found.

Circuit operation:

Q1 & Q2 form a complementary astable multivibrator, whose operating frequency is set mainly by R3, C2 & C3 values. Output pulses are taken at Q2 Collector and applied to the probe bymeans of decoupling capacitor C1. D1 provides a symmetrical shape for the output waveform.If an earclip or headphone jack is plugged into J1, the connection from Q2 Collector and C1 - C2is broken by the switch incorporated into J1: in this case the circuit becomes a two-stageamplifier.

Notes:

If you intend to use the circuit to test valve operated devices C1 must be a 630V type. Workingwith low voltage supply transistor devices the voltage of C1 can be lowered to 63 or 100V.

If instead of a short probe, you intend to connect the circuit to the device under test by meansof a piece of wire longer than a few centimeters, a small ceramic capacitor (470 to 1000pF)should be added in parallel to D1 to prevent unwanted RF oscillation.

Current drawing when in Pulse-Generator mode is about 60A and 1.2mA when in Signal-Tracermode operation. Therefore SW1 can be omitted, provided that the earclip or headphones are

unplugged when the circuit is unused. J1 is a stereo switched jack socket wired to obtain a series connection of the two earpiecesforming a stereo headphone. In this manner the circuit is loaded with a higher impedance andsensitivity will be improved.Therefore, the higher the load impedance the more sensitive the Signal-Tracer. In any case,common 32 Ohm impedance mini-headphones suitable for walkman sets will work fine.

A crystal (high impedance) earpiece is a good solution, provided you substitute J1 with a monoswitched jack socket.


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The entire circuit can be easily fitted into a pen-like enclosure, with the probe protruding like anib.

LED or Lamp Flasher

Circuit diagram:

Parts:R1________1M 1/4W ResistorR2______100R 1/4W ResistorR3_______22R 1/4W Resistor

C1________1F 63V Electrolytic, Multilayer Ceramic or Polyester Capacitor

D1_______LED Any type and color

Q1____2N3906 40V 200mA PNP TransistorQ2____2N3904 40V 200mA NPN Transistor

SW1_____SPST Switch

B1________3V (Two 1.5V AA or AAA cells wired in series, etc.)

Notes:

Flashing frequency can be varied by changing R1 value in the 1M - 4M7 range. This circuit is very efficient when driving a small 3.2V incandescent lamp. In this case

omit the LED and R3, connecting the bulb across Q2 Collector and positive supply,further reducing parts counting.

Maximum current drawing of the bulb type used should not exceed 100mA. In order to facilitate oscillation when a bulb is driven, R2 value should be lowered to 82R

or 68R.


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LED or Lamp Pulser

Circuit diagram:

Parts:R1,R2___________4K7 1/4W ResistorsR3_____________22K 1/4W ResistorR4______________2M2 1/4W Resistor (See Notes)R5_____________10K 1/4W ResistorR6_____________47R 1/4W Resistor (See Notes)

C1______________1F 63V Polyester Capacitor

D1_____________5mm. Red LED (See Notes)

IC1__________LM358 Low Power Dual Op-amp

Q1___________BC337 45V 800mA NPN Transistor

Circuit operation:

This circuit operates a LED in pulsing mode, i.e. the LED goes from off state, lights upgradually, then dims gradually, etc.This operation mode is obtained by a triangular wave generator formed by two op-ampscontained in a very cheap 8 pin DIL case IC. Q1 ensures current buffering, in order to obtain a

better load drive.R4 & C1 are the timing components: using the values shown in the parts list, the total period isabout 4 seconds.

Notes:

The most satisfying results are obtained adopting for R4 a value ranging from 220K to4M7.

Adopting for R4 a value below 220K, the pulsing effect will be indistinguishable from anormal blinking effect.

The LED can be any type and color.


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Q1______BC337 45V 800mA NPN Transistor

P1______SPST Pushbutton

SW1_____DPDT Switch

SPKR____8 Ohm Loudspeaker

B1______6V Battery (4 AA 1.5V Cells in series)

Circuit operation:

This circuit is intended for children fun, and can be installed on bicycles, battery powered carsand motorcycles, but also on models and various games and toys. With SW1 positioned asshown in the circuit diagram, the typical dual-tone sound of Police or Fire-brigade cars isgenerated, by the oscillation of IC1A and IC1B gates. With SW1 set to the other position, the oldsiren sound increasing in frequency and then slowly decreasing is reproduced, by pushing on P1

that starts oscillation in IC1C and IC1D.The loudspeaker, driven by Q1, should be of reasonable dimensions and well encased, in order toobtain a more realistic and louder output. Tone and period of the sound oscillations can be varied

by changing the values of C1, C2, C5, C6 and/or associated resistors. No power switch isrequired: leave SW1 in the low position (old-type siren) and the circuit consumption will benegligible.

Variable DC Power Supply

Circuit diagram:


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Parts:P1____________500R Linear PotentiometerP2_____________10K Log. Potentiometer

R1,R2___________2K2 1/2W ResistorsR3____________330R 1/4W Resistor

R4____________150R 1/4W ResistorR5______________1R 5W Resistor

C1___________3300F 35V Electrolytic Capacitor (see Notes)C2______________1F 63V Polyester Capacitor

D1,D2________1N5402 200V 3A DiodesD3_____________5mm. Red LED

Q1____________BC182 50V 100mA NPN TransistorQ2____________BD139 80V 1.5A NPN Transistor

Q3____________BC212 50V 100mA PNP TransistorDevice purpose:

A Variable DC Power Supply is one of the most useful tools on the electronics hobbyist'sworkbench. 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 tosupply the circuits shown in this website. You can adapt it to your own requirements asexplained in the notes below.

Notes:

P1 sets the maximum output current you want to be delivered by the power supply at agiven output voltage.

P2 sets the output voltage and must be a logarithmic taper type, in order to obtain a morelinear 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 6800F, 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 circuitcan do the job.

The 2N3055 transistor (Q4) can be replaced with the slightly less powerful TIP3055 type.

Q4 __________2N3055 60V 15A NPN Transistor

T1_____________220V Primary, 36V Center-tapped Secondary50VA Mains transformer (see Notes)

PL1____________Male Mains plug

SW1____________SPST Mains switch


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Jogging Timer

Circuit diagram:

Parts:R1_____________47K 1/4W ResistorR2_____________10M 1/4W ResistorR3______________1M 1/4W ResistorR4_____________12K 1/4W Resistor (see notes)

C1,C3__________10F 25V Electrolytic CapacitorsC2____________100nF 63V Polyester Capacitor

D1___________1N4148 75V 150mA Diode

IC1____________4093 Quad 2 input Schmitt NAND Gate ICIC2____________4060 14 stage ripple counter and oscillator ICIC3____________4017 Decade counter with 10 decoded outputs IC

Q1____________BC337 45V 800mA NPN Transistor

SW1___________1 pole 9 ways Rotary Switch (see notes)SW2___________SPST Slider Switch

BZ1___________Piezo sounder (incorporating 3KHz oscillator)

B1____________3V Battery (two 1.5V AA or AAA cells in series etc.)


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Device purpose:

This circuit was developed since a number of visitors of this website requested a timer capable ofemitting a beep after one, two, three minutes and so on, for jogging purposes.As shown in the Circuit diagram, SW1 is a 1 pole 9 ways Rotary Switch. Setting the switch in

position 1, the Piezo sounder emits three short beeps every minute. In position 2 the same thinghappens after a 2 minutes delay, and so on, reaching a maximum interval of 9 minutes in position9.

Notes:

Needing only one time set, rotary switch can be replaced by an hard-wired link. A DIP-Switch can be used in place of the rotary type. Please pay attention to use only one

switch at a time, or the device could be damaged. Varying R4 from 10K to 15K you can obtain more or less than three short beeps after the

preset time delay.

To obtain a one-second beep only, after the preset time delay, disconnect pin 9 of IC1Cfrom pin 9 of IC2 and connect it to pin 8 of IC1C.

Bicycle back Safety LightCircuit diagram:


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Parts:R1_____________10K 1/4W ResistorR2,R9,R10_____100K 1/4W ResistorsR3-R8,R11-R16__10R 1/4W ResistorsR17___________150R 1/4W Resistor

C1______________1F 63V Polyester CapacitorC2_____________10nF 63V Polyester CapacitorC3____________100F 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 efficiencyflashing LEDs arranged in a pseudo-rotating order. Due to low voltage, low drain batteryoperation and small size, the device is suitable for mounting on bicycles as a back light, or to puton 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 currentoperation 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 permanentlyon. This arrangement and the alternate flashing of the two series of LEDs provide a pseudo-rotating appearance.


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LED arrangement:

Notes:

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

Pulse-Generator & Signal-TracerCircuit diagram:

Parts:R1__________________1M 1/4W ResistorR2,R4_______________2K7 1/4W ResistorsR3________________150K 1/4W Resistor

C1__________________2n2 630V Ceramic or Polyester Capacitor (See Notes)C2,C3_______________4n7 63V Ceramic or Polyester Capacitors

D1_______________1N4148 75V 150mA Diode

Q1________________BC547 45V 100mA NPN TransistorQ2________________BC557 45V 100mA PNP Transistor

SW1________________SPST miniature Slider Switch (See Notes)

J1_________________Stereo switched 3mm. Jack socket (See Notes)


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Probe______________Metal Probe 3 to 5 cm. long

Clip_______________Miniature Crocodile Clip

B1_________________1.5V Battery (AA or AAA cell etc.)

Device purpose:

This simple circuit generates narrow pulses at about 700-800Hz frequency. The pulses,containing harmonics up to the MHz region, can be injected into audio or radio-frequency stagesof amplifiers, receivers and the like for testing purposes. A high-pitched tone can be heard fromthe speaker of the device under test when all is working properly. The clip must be connected tothe ground of the device under test, touching with the probe the different stages of the circuit,starting from the last stage and going up towards the first. When the tone is no longer heard, thedefective stage has been found.Connecting an earclip or headphone to J1, the circuit will automatically change into a two-stageamplifier and any audio signal coming from the device under test and picked-up by the probewill be heard through the headphones. The testing of a circuit should be made in the reversemanner, i.e. starting from the first stage and going down until the last stage. When nothing isheard, the defective stage has been found.

Circuit operation:

Q1 & Q2 form a complementary astable multivibrator, whose operating frequency is set mainly by R3, C2 & C3 values. Output pulses are taken at Q2 Collector and applied to the probe bymeans of decoupling capacitor C1. D1 provides a symmetrical shape for the output waveform.If an earclip or headphone jack is plugged into J1, the connection from Q2 Collector and C1 - C2is broken by the switch incorporated into J1: in this case the circuit becomes a two-stageamplifier.

Notes:

If you intend to use the circuit to test valve operated devices C1 must be a 630V type.Working with low voltage supply transistor devices the voltage of C1 can be lowered to63 or 100V.

If instead of a short probe, you intend to connect the circuit to the device under test bymeans of a piece of wire longer than a few centimeters, a small ceramic capacitor (470 to1000pF) should be added in parallel to D1 to prevent unwanted RF oscillation.

Current drawing when in Pulse-Generator mode is about 60A and 1.2mA when inSignal-Tracer mode operation. Therefore SW1 can be omitted, provided that the earclipor headphones are unplugged when the circuit is unused.

J1 is a stereo switched jack socket wired to obtain a series connection of the twoearpieces forming a stereo headphone. In this manner the circuit is loaded with a higherimpedance and sensitivity will be improved.Therefore, the higher the load impedance the more sensitive the Signal-Tracer. In any


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case, common 32 Ohm impedance mini-headphones suitable for walkman sets will workfine.

A crystal (high impedance) earpiece is a good solution, provided you substitute J1 with amono switched jack socket.

The entire circuit can be easily fitted into a pen-like enclosure, with the probe protruding

like a nib.

Circuit diagram:

Parts:R1,R2,R3,R10____10K 1/4W ResistorsR4,R5,R6_______100K 1/4W ResistorsR7,R8,R9________22K 1/4W Resistors

C1,C2,C3_______100nF 63V Polyester or Ceramic CapacitorsC4______________47F 25V Electrolytic Capacitor

D1,D3,D5_______5mm. Red LEDsD2,D4,D6_______5mm. Green LEDs

IC1___________4011 Quad 2 input NAND Gate ICIC2___________4016 or 4066 Quad bilateral switch IC

SW1,SW2,SW3___SPST Toggle or Slide SwitchesP1,P2_________SPST Pushbutton Switches

J1,J2,J3______1, 2 or 4mm. chassis sockets - or transistor socketor leads ended with crocodile clips

B1_______________9V PP3 Battery


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Clip for PP3 Battery

Circuit operation:

A three-phase wave form is derived from the 350Hz ring-of-three oscillator formed by IC1A,IC1B and IC1C, and applied to the device under test via the LEDs. The oscillator wave formenables each pair of device terminals to be forward, reverse and unbiased for one third of a cycle.Current flowing into the device will turn the appropriate Red LED on and current flowing outwill turn on the Green LED. Thus, the position of the Base lead and the polarity of a transistormay be deduced.IC2A, B and C are used to switch R7, R8 and R9 at once in parallel to R4, R5 and R6respectively, by pressing P2 Pushbutton. This operation allows higher current drive for the Baselead of the device under test and may be required when low-gain power transistors are tested.As in most cases the pin layout of TO3 metal encased power devices may be easily deduced, and

pin identification is mostly required by low power plastic encapsulated devices, IC2, R7, R8, R9,R10 and P2 can be omitted.

Testing procedure:

1. Connect randomly the pins of the transistor under test to J1, J2 and J3 sockets or clips.2. Close SW1, SW2 and SW3.3. Push on P1; if the transistor is in good health the response of the Identifier will be:4. Two terminals will show both LEDs illuminated, the remaining one will show a single

LED illuminated.5. If the LED illuminated is Red, the pin connected to the related connector will be the Base

of a NPN transistor.6. If the LED illuminated is Green, the pin connected to the related connector will be the

Base of a PNP transistor.7. Open the switch related to the single illuminated LED: the two terminals showing both

LEDs illuminated will change their state and a single LED per terminal will beilluminated. The LED which previously indicated the Base pin will turn-off.

8. If the transistor was previously identified as NPN, the pin connected to the nowilluminated Green LED will be the Emitter, whereas the pin connected to the Red LEDwill be the Collector.

9. If the transistor was previously identified as PNP, the pin connected to the nowilluminated Red LED will be the Emitter, whereas the pin connected to the Green LEDwill be the Collector.

This procedure will suffice for reliable pin identification of most transistor types.In some cases, mainly when low-gain high power transistors are tested, the LED could illuminatefaintly and reliable pin identification could be not so easy. Pushing both P1 and P2 will remedythis shortcoming.

Diode testing:

1. Connect randomly the diode pins to two of the three sockets or clips.


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2. Close SW1, SW2 and SW3.3. Push on P1: if the diode is in good health, only one Red LED and one Green LED will

illuminate.4. The Red LED will signal that the diode pin connected to its related terminal will be the

Anode, whereas the Green LED will signal that the diode pin connected to its related

terminal will be the Cathode.

Note:

Unfortunately, testing Darlington type transistors could lead to some trouble. In fact, the Base pin and the polarity of these transistor types will be correctly shown by the Pin Identifier in thesame way as common transistors, but Collector and Emitter pins will be displayed inverted; i.e. ifthe transistor was previously identified as NPN, the pin connected to the now illuminated GreenLED will be the Collector (NOT the Emitter), whereas the pin connected to the Red LED will bethe Emitter (NOT the Collector). On the other hand, if the transistor was previously identified asPNP, the pin connected to the now illuminated Red LED will be the Collector (NOT the

Emitter), whereas the pin connected to the Green LED will be the Emitter (NOT the Collector).This is due to the fact that Darlington power transistors usually incorporate on the same chip areverse-connected diode across Emitter and Collector.Doubts can be easily dissipated pushing on P2: Darlington transistors will cause all two LED

pairs related to Emitter and Collector pins to illuminate brightly. On the contrary, commontransistors will cause only a faint illumination of the remaining LEDs and, usually, a single LEDindicating the Collector pin will illuminate.

Halloween Flashing-eyes Badge

Two-LED-eyes follow the rhythm of music or speech3V Battery-operated device suitable for pins or badges

Circuit diagram:

Parts:R1______________10K 1/4W ResistorR2_______________1M 1/4W Resistor


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Blinking Arrow

17 LEDs in four groups bar-mode sequence

Suitable for shop-windows animation etc

Circuit diagram:

Parts:R1_____________500K 1/2W TrimmerR2______________22K 1/4W ResistorR3,R5,R7,R9_____10K 1/4W Resistors

R4,R6,R8,R10_____4K7 1/4W ResistorsR11,R12,R13____470R 1/4W ResistorsR14____________270R 1/4W Resistor

C1_______________47 25V Electrolytic CapacitorC2_____________220F 25V Electrolytic Capacitor

D1--D17________LEDs Any type and color (except blue and white, see Notes)

Q1,Q2,Q3,Q4___BC337 45V 800mA NPN Transistor


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IC1____________4093 Quad 2 input Schmitt NAND Gate ICIC2____________4520 Dual binary up-counter ICIC3____________4094 8-stage shift-and-store bus register IC

Comments:

A blinking arrow can be a very attractive gadget, suitable for many indication purposes. Thiscircuit provides a bar-mode sequencer driving 17 LEDs arranged in four groups in order to build-up a bright arrow. When the build-up of the arrow is completed, all LEDs stay on for some time,then off for the same time-delay and then the cycle restarts. Sequence speed can be set by R1.For those wishing to experiment, sequence timings can also be varied by connecting pin #5 ofIC1B to pin #5 of IC2 and pins #6, 8 and 9 of IC1 to pin #6 of IC2. Other pin combinations are

possibile by shifting the above named pins of IC1 to higher outputs of the counters contained inIC2, i.e. pins #6 and 11, pins #11 and 12 etc.The resulting effect of the original four groups of 17 LEDs arrangement is shown in the title

heading.

Notes:

Obviously, many different arrangements using more or less LEDs are possibile. At 12V supply the maximum number of LEDs per strip is that shown in the circuit

diagram, when red LED types are used. Yellow, green and orange types may require alower value of the limiting resistors or a lesser number of devices per strip.

Please note that the unused section of IC1 must have the inputs tied to negative groundwhereas the output must be left open, as shown at the bottom of the diagram.

One second Audible ClockCircuit diagram:

Parts:R1______________10K 1/4W ResistorR2_______________4K7 1/4W ResistorR3_____________100R 1/4W Resistor (Optional, see Notes)


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C1_______________1nF 63V Polyester or ceramic CapacitorC2______________10F 25V Electrolytic CapacitorC3_____________100nF 63V Polyester or ceramic Capacitor (Optional, seeNotes)

D1,D2,D3_____1N4148 75V 150mA DiodesD4______________LED (Optional, any shape and color, see Notes)D5___________1N4148 75V 150mA Diode (Optional, see Notes)

Q1____________BC337 45V 800mA NPN Transistor

IC1____________4024 7 stage ripple counter IC

BZ1___________Piezo sounder (incorporating 3KHz oscillator)

SPKR______________8 Ohm, 40 - 50mm diameter Loudspeaker (Optional, see Notes)

SW1____________SPST Toggle or Slide Switch (Optional, see Notes)

B1________________3 to 12V Battery (See Notes)

Comments:

This accurate one-pulse-per-second clock is made with a few common parts and driven from a50 or 60 Hertz mains supply but with no direct connection to it.A beep or metronome-like click and/or a visible flash, will beat the one-second time and can beuseful in many applications in which some sort of time-delay counting in seconds is desirable.The circuit is formed by a CMos 4024 counter/divider chip and 3 diodes, arranged to divide thefrequency of the input signal at pin #1 by 50 (or 60, see Notes).The input impedance at pin #1 is very hight, so simply touching the pin (or a short track or pieceof wire connected to it) is usually enough to provide the necessary input signal.

Another way to provide an input signal consists in a piece of wire wrapped several times aroundany convenient mains cable or transformer. No other connection is necessary.

Notes:

To allow precise circuit operation in places where the mains supply frequency is rated at60Hz, the circuit must be modified as follows: disconnect the Cathode of D1 from pin#11 of IC1 and connect it to pin #9. Add a further 1N4148 diode, connecting its Anode toR1 and the Cathode to pin #6 of IC1: that's all!

The circuit will work fine with battery voltages in the 3 -12V range. The visual display, formed by D4 and R3 is optional. Please note that R3 value shown in

the Parts list is suited to low battery voltages. If 9V or higher voltages are used, changeits value to 1K.

If a metronome-like click is needed, R2 and BZ1 must be omitted and substituted by thecircuit shown enclosed in dashed lines, right-side of the diagram.

Stand-by current drawing is negligible, so SW1 can be omitted.


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Electronic Candle Blow Out

Circuit diagram:

Parts:

R1______________10K 1/4W ResistorR2_______________1M 1/4W ResistorR3_______________1K 1/4W ResistorR4_______________4K7 1/4W Resistor (See Notes)R5______________10K 1/4W Resistor (See Notes)R6_____________100R 1/4W Resistor (See Notes)

C1_____________100pF 63V Ceramic CapacitorC2______________10F 25V Electrolytic CapacitorC3_____________100nF 63V Polyester or Ceramic Capacitor

D1___________1N4148 75V 150mA DiodeD2______________LED (Any suitable type)

Q1____________BC550C 45V 100mA Low noise High gain NPN TransistorQ2____________BC337 45V 800mA NPN TransistorQ3____________BC327 45V 800mA PNP Transistor

MIC1__________Miniature electret microphone

P1_____________SPST Pushbutton Switch

B1_______________3V Battery (2 x 1.5V AA, AAA Cells in series etc.)

Comments:

This design was developed by request of a correspondent having made a sort of LED candle andneeding to switch off the LED with a puff.This simple, easy to build gadget can be useful as a prop for Halloween and Christmas season,shows and the like.Q2 & Q3 form a self-latching pair that start operating when P1 is pushed: in this way the LED(or bulb) will illuminate steadily. When someone emits a strong puff in the vicinity of the small


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electret microphone, the resulting signal will be greatly amplified by Q1 and a rather long positive pulse (shaped by D1 and C2) will reset the self latching pair through the Emitter of Q2.The very low (and unusual) value of C1 acts as a simple high-pass filter, in order to prevent thatnormal speech or environmental noise shut off the device. Obviously, such a simple filter cannot

be very discriminating, therefore, not only a strong puff will reset the circuit but also a loud

shout, blow, clap or stroke.

Notes:

A small bulb can be used in place of the LED. In this case a 3 - 3.5V, 0.7W (200mA)incandescent bulb can be used satisfactorily. Therefore, D2, R5 and R6 must be omitted,the bulb wired in place of R5 and R4 value changed to 1K5.

Using a bulb instead of the LED, a 1.5V battery supply could also be used. A 1.5V, 0.3Aincandescent bulb will work, but R4 must be replaced by a 470 Ohm Trimmer, adjustedto allow a reliable circuit operation.

Please note that the circuit will draw a small current even when the LED or bulb are off.

This current is about 1.2mA for the LED version of the circuit, 1.5mA for the 3V bulbversion and 1mA for the 1.5V bulb version. Therefore, in some circumstances, theaddition of a power on-off switch could be necessary.

Hobby & Models

Digital Step-Km Counter

Max. range: 9.950 meters with two digitsSlip it in pants' pocket for walking and jogging

One-IC two-tones Siren

Double tone Police soundSingle tone old ambulance sound

Personal Alarm

Small, portable, anti-bag-snatching unitAlso suitable for doors and windows control

Variable DC Power Supply

Voltage range: 0.7 - 24VCurrent limiting range: 50mA - 2A

LED or Lamp Flasher

Minimum parts counting - Improved version
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3V battery operation

Two-wire Lamp Flasher

Ideal to operate 3 to 24V DC existing on-circuit lamps

LED operation is also possible

LED or Lamp Pulser

Astonishing effect4.5V supply

Bicycle back Safety Light

Flashing 13 LED unit, 3V supplyAlso suitable for jogger/walkers

Jogging Timer

3V Battery poweredBeeps after a fixed minutes delay

Whistle Responder

Beeps when hears your whistleA gadget suitable for key-holders, games etc.

Pulse-Generator & Signal-Tracer

Dual-purpose test-instrumentVery simple circuitry, 1.5V Battery-operated

Magnetic-Radiation Remote-Control

Short-range 35KHz operation, single-channel unitsSimple circuitry, no outer antennas required

Capacitive Sensor

Special design for shop-windows animationUseful for many types of touch controls

Bells ring Generator
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Three circuit optionsCan be synchronized to Christmas tree flashing lights

Dancing LEDs

LED sequencer: follows the rhythm of music or speech9V Battery-operated portable unit

Fading LEDs

Two strips of LEDs fading in a complementary manner9V Battery-operated portable unit

LEDs or Lamps Sequencer

Very simple, versatile modular designNo limits to the number of modules used in the ring

Cuckoo-song Generator

Agreeable, very close sound imitationSuitable for sound effects, door-bells etc.

Brightness Control for small Lamps

Switch-mode driven 1.5V bulbs

Portable unit - 3V battery supply

Award winner!

Published on

ELECTRONICS WORLD

"Circuit Ideas"

June 2000 issue, page 458

230 Volts Flashing Lamps

Especially designed for Christmas tree lampsReplaces old thermally-activated switches

Dark-activated LED or Lamp Flasher

Simple photo-sensitive circuit
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3V battery supply

Two-LED Pilot Light

230 or 115 Vac mains operated

Very simple circuitry

E-B-C Transistor Pin Identifier

Tests transistors and diodes for polaritySimple circuitry - 9V Battery operation

Powerful Siren

Simple circuitry - No ICs12V Battery operation

1.5V LED Flasher Oscillator

Mimics the now discontinued LM3909 ICCan be adapted to a wide variety of applications

Halloween Flashing-eyes Badge

Two LED-eyes follow the rhythm of music or speech3V Battery-operated device suitable for pins or badges

Mains-operated Capacitive Sensor

Easily adjustable, high sensitivity circuitMinimum parts counting

Push-bike Light

Automatic switch-on when it gets dark6V or 3V battery operation

Fine Control SuperBright LED Pulser

Four timing controls - 12V supplySuitable for Halloween or Christmas props

Blinking Arrow


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17 LEDs in four groups bar-mode sequenceSuitable for shop-windows animation etc.

Programmable LED Flashers

LED goes to steady state after a preset number of flashesTwo simple, wide supply range operating circuits

Cricket Chirping Generator

Funny gadget for props and jokes5 - 12V Battery operation

One second Audible Clock

Accurate, finger-operated portable unit3 - 12V Battery supply

Electronic Candle Blow Out

LED or bulb switch off with a puffFunny gadget - 3V Battery supply

Dual-rail Variable DC Power Supply

Simple add-on for a single-rail supply

2.5V to 15V output

Rotating & Flashing 230V Lights

Three channels - Three operating modesCompletely ac-insulated circuit board

Long delay Timer

Suitable for battery-operated devicesFixed 35 minutes delay

Circuit Board Tester

Indicates the basic integrity of a printed boardSelf-powered - 3 to 30V range

Quick on-board Junction Tester


30/30

Acoustic check of transistor and diode junctionsAlso suitable as continuity tester

Flashing-LED Battery-status Indicator

Signals when an on-circuit battery is exhausted5V to 12V operating voltage

Cheap Transistor 'Beta' Meter

Measures the hfe of NPN and PNP transistorsRequires a digital or analog Multimeter

Simple Capacitance Meter

Operates in conjunction with a voltmeter1pF to 22F in six Ranges - 9V Battery supply

Simple Frequency Meter

10Hz - 200kHz in three rangesOperates in conjunction with a Digital Multimeter

Bar-mode Lights Sequencer

Can drive up to 15 LEDs or LED-clusters

Selectable Bar-length

Automatic fading lights

Suitable for 230V incandescent bulbsIdeal for Christmas decorations

Car Horn

Suitable for models and toys6-12V dc supply

Mini Touch Alert

Small portable gadget1.5 to 9V Battery supply
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