A few of the interesting and useful hobby electronic circuit diagrams already published in this blog have been selected and compiled here for quick reference and understanding.
Simple Touch Sensitive Switch Circuit
We all know about this little versatile chip which finds its way in almost all useful electronic circuits, yes our very own IC 555. The following circuit is no exception, it's a sensitive touch switch circuit using the IC 555.
Here the IC is configured as an monostable multivibrator, in this mode the IC activates its output momentarily by producing a logic high in response to a trigger at its input pin#2.
The momentary activation time period of the output depends on the value of C1 and the setting of VR1.
When the touch switch is touched pin#2 is pulled to a lower logic potential which may be less than 1/3 of Vcc.
This instantly reverts the output situation from low to high activating the connected relay driver stage.
This in turn switches ON the load attached with the relay contacts but only for the time until C1 gets fully discharged.
Simple Triac Dimmer Circuit
The circuit of a simple triac light dimmer shown below can be used for dimming incandescent lamps directly from AC mains.
The circuit is very easy to construct and uses very few components. The pot is used for controlling the load power or the intensity of the light. The circuit can be also used for controlling ceiling fan speeds.
Simple Audio Power Amplifier Circuit
The circuit illustrated here is probably the simplest form of an audio power amplifier.
Though the circuit is very crude by its specs yetis able to amplify an audio input up to a powerful 4 watts in a 8 Ohm speaker.
The transistor is a 2N3055 is used as a switch for inducing voltages in response to the input signals into one half winding of the transformer.
The back emf generated across the winding of the transformer is effectively dumped over the speaker generating the required amplifications. The transistor needs to be mounted on a suitable heatsink.
Simple Water Level Alarm Circuit
Just a couple of transistors are enough for implementing a simple water level alarm circuit and used for getting a warning signal when the water level inside a tank nears the overflowing level.
The two transistors are configured as a high gain, high sensitive switch, which also is capable of generating a tone when the shown terminals get bridged through the terminals coming in contact with the water inside the tank.
The water offers just about the right resistance value across the specified points of the circuit for initiating high pitched tone or the desired warning alarm.
Simple Temperature Detector Circuit
Parts List for the above simple transistor hobby circuit
R2 = 2K2,
D1 = 1N4148,
P1 = 300 Ohms,
T1 = BC547
LED = RED 5mm
100 Watt Transistor Based Inverter Circuit
The whole circuit mainly involves transistors and therefore becomes easier to construct and implement.
R1, R4 = 330 Ohms,R2, R3 = 39K,
R5, R6 = 100 Ohms, 1watt,
C1, C2 = 0.47uF,
D1, D2 = 1N5402
T1, T2 = BC547,
T3, T4 = TIP127,
T5, T6 = 2N3055,
100 Watt Transistor Power Amplifier Circuit
This circuit of a transistor power amplifier is outstanding with its performance and is able to provide a thumping 100 watts of pure music output.
As can be seen in the diagram it utilizes mainly transistors for the implementations and a handful of other inexpensive passive components like resistors and capacitors.
The required input is not more than 1 V, which gets amplified 200,000 times at the output.
Please refer the article below for the parts list:
Simple Automatic Emergency Lamp Circuit
This simple emergency lamp circuit uses very components and yet is able to provide some useful service.
The shown device is able to switch ON automatically when mains power fails, illuminating all the connected LEDs.As soon as power is restored, the LEDs shut off automatically and the connected starts charging through the built in power supply.
The circuit employs a transformerless power supply for initiating the explained automatic actions and also for trickle charging the connected battery.
Parts List for the above CIRCUIT DIAGRAM
R1 = 220K,
R2 = 10K,
D1, D2, D3 = 1N4007,
Z1 = 15V 1watt, zener diode,
C2 = 100uF/25V
LEDs = white, high bright type.
Automatic Day Night Light Switch Circuit
Thus the circuit can be used for switching ON the connected lights when night sets in and switch it OFF during day break. The threshold tripping point may be set by adjusting the 10K preset.
The capacitors are 100uF/25V, the transistors are ordinaryBC547, and the diodes are 1N4007.
Electronic Candle Circuit
This is a simple hobby project and exhibits all the properties of a conventional wax type candle.
Here the LED is used in place of the candle flame, which illuminates as soon as the mains power fails and shuts off automatically when the power is restored. So it also performs the function of an emergency lamp.
The connected battery is used for powering the candle”light and it is charged continuously when the unit is not being used and powered through the mains supply.
An interesting “puff off” feature is also included so tatthe “candle” light may be switched OFF whenever desired through a puff of airinto the attached mic which acts as the air vibration sensor.
Simple Emergency Flashlight Circuit
As long as the input supply from the mains transformer is present the transistor remains switched OFF and so does the lamp. However the moment the mains power fails, the transistor conducts and switches ON the battery power to the bulb, instantly illuminating it brightly.The battery is trickle charged for so long as the mainspower remains connected to the circuit.
R2 = 1K,
D1 = 1N4007,
T1 = 8550,
Lamp = 3V flashlight bulb.
Transformer = 0-3V, 500 mA,
Battery = 3V, penlight 1.5 V cells (2nos. in series)
Music operated Dancing Light Circuit
This circuit may be used for transforming music into dancing light patterns.
The operation of the circuit is very simple, the music input is fed to the bases of the shown transistor array, each of them are configured to conduct at a specific voltage level in the incrementing order from the top to the bottom transistor.
Thus the uppermost transistor conducts with the input music is at the minimum volume level and the subsequent transistor starts to conduct in sequence as per the volume or the pitch of the music.
Each transistor is rigged with individual lamps which light up in response to the music levels in a “chasing” dancing light pattern.
All the base presets are = 10K,
All the collector resistors are 470 Ohms,
All the diodes are = 1N4148,
All NPN transistors are = BC547,
The single PNP transistor is = BC557,
All the triacs are = BT136,
The input capacitor = 0.22uF/25V non polar.
Simple Clap Switch Circuit
The interesting clap switch circuit shown here can be used in stairways and passages for illuminating the premise momentarily through clap sound. The circuit is basically a sound sensor circuit with an enclosed amplifier stage.
The clap sound or any similar sound is detected by the mic and converted into minute electrical pulses. These electrical pulses are suitably amplified by the subsequent transistor stage.
The Darlington stage shown at the output is the timer stage which switches in response to the above sound interaction and illuminate the connected LEDs for some period of time defined by the 220K resistor and the two39 K resistors.
After the time lapses the LEDs are switched off automatically and the circuit returns to its original state until the next clap sound is detected.
A Simple ELCB Circuit
Unlike usual configurations, here the ground to the circuit and the relay is acquired from the earthing line itself. Also since the input coil is also referenced to the common earthing ground, the entire functioning becomes compatible and accurate.
On sensing a possible current leakage at the input, the transistors come into action and switch the relays appropriately.
The two relay have their individual specific roles to play. One relay detects and switches OFF when there’s current leakage through an appliances body, while the other relay is wired up to sense the presence of a the earthing line and switches OFF the mains as soon a wrong or weak earthing line is detected.
R1 = 33K,
R2 = 4K7,
R3 = 10K,
R4 = 220 Ohms,
R5 = 1K,
R6 = 1M,
C1 = 0.22uF,
C2, C3, C4 = 100uF/25V
C5 = 105/400V
All diodes = 1N4007,
Relay = 12V, 400 Ohms
T1, T2 = BC547,
T3 = BC557,
L1 = output transformer as used in radio push pull amplifierstage
Simple LED Flasher
A very simple LED flasher circuit is illustrated in the diagram. The transistors and the corresponding parts are connected in the standard astable multivibrator mode, which forces the circuit to oscillate the moment power is applied.
The LEDs connected at the collector of the transistors start flashing alternately in wig wag manner. The LEDs shown in the diagram are connected in series and parallel, so that many numbers of LEDs can be accommodated in the configuration.
The pots P1 and P2 may be adjusted for getting different interesting flashing patterns with the LEDs.
P1,P2 = 100K pots,
T1, T2 = BC547,
Resistors connected with each LED series = 470 Ohms
LEDs are 5mm type, color as per choice.
Anything spoken into the mic of the presented circuit cab be clearly picked up and reproduced by any standard FM radio, within a range of 30meters of distance.
The circuit is very simple and just requires ther shown components to be assembled and connected with each other as depicted in the diagram.
The coil L1 consists of 5 turns of 1mm super enameled copper wire, having a diameter of around 0.6 cm.
R2 = 82K,
R3 = 1K,
C1 = 10pF,
C2, C3 = 27pF,
C4 = 0.001uF,
C5 = 0.22uF,
T1 = BC547
40 LED Emergency Light Circuit
The shown design of a 40 LED emergency light is driven using an ordinary transistor/transformer inverter circuit. The transistor and the respective winding of the transformer are configured as a high frequency oscillator stage.
The oscillations induce a high voltage across the winding of the transformer. The stepped-up voltage at the output is directly used to drive the LED which are all connected in series for getting the desired balance and the illumination.
VR1 = 47K,
C1, C2 = 1uF/25V
TR1 = 0-6V, 500mA,
Battery = 6V, 2AH,
LEDs = high bright white, 40 nos.
Simple Transistor Latch Circuit
If you are looking for a circuit which can be used to latch the output in response to an input signal, then this circuit can be used for the intended purpose very effectively and also very cheaply.
This feed back voltage instantly latches the circuit and keeps the relay activated even after the trigger from the input is removed.Parts List
R1, R3 = 100k,
R2, R4 = 10K,
C1 = 1uF/25V
D1 = 1N4148,
T1 = BC547,
T2 = BC557
Relay = 12V, SPDT
This light exactly varies its length according to the pitch or the volume of the fed music signal.Parts list is provided in the diagram.
The circuit also incorporates an optional buzzer circuit which can be also included for getting a beeping sound in response to the flashing of the lamps.Parts List
R1, R2, R3 = 10K
T1 = D1351,
T2 = BC547,
T3 = BC557,
C1, C2 = 33uF.25V
L1 = Buzzer Coil
Simple Relay Motorbike Flasher Circuit
Just build it and wire it in your mo-bike for witnessing the intended functions...Parts List
R1 = 1K,
R2 = 4K7,
T1 = BC557,
C1 = 100uF/25V,
C2 = 1000uF/25V
Relay = 12V, 400 Ohms
D1 = 1N4007
VR1 = 100K,
D1, D2 = 1N4007,
C1, C2 = 100uF/25
T1, T3 = BC547,
T2 = BC557
Z1 = 3V/400mW
Transformer = 0-12V/500mA,
S1 = Bell Push
IC = UM66
Timer Circuit with Independent On and OFF Delay Adjust Facility
The circuit can be used for generating delays at a desired rate. The On time of the relay can be controlled by adjusting the Pot VR1 while the pot VR2 may be used to decide after how long the relay responds once theinput trigger is fed by the switch S1.
The parts list is enclosed inside the diagram.
Simple High and Low Mains Voltage Cut Off Circuit
Are you having problems with your input Mains supply? That’s common problem associated with our input mains AC line, where a high and a low voltage conditions are quite frequently encountered by us.
The simple circuit shown here can be built and installed in you house electrical board for getting a 24/7 safety from the possible dangerous AC voltage conditions.
The circuit keeps the relay and the wired appliances as long as the mains input stays within a safe tolerable level and switches the load OFF the moment a dangerous or unfavorable voltage condition is sensed by the circuit.
R1, R2 = 1K,
P1, P2 = 10K Preset,
T1, T2 = BC547B,
C1 = 100uF/25V,
D1 = 1N4007
RL1 = 12V, SPDT,
TR1 = 0-12V, 500mA
0 – 40 V, 0 – 4 Amp Continuously Variable Power Supply Circuit
This unique work bench circuit utilizes only a few inexpensive transistors and yet delivers some truly useful features.
The feature includes continuously variable voltage from zero to the maximum transformer voltage and current variable from zero to the maximum applied input level.
The output of this power supply is also over load protected. The pot P1 is used for setting the maximum current while the pot P2 is used for varying the output voltage level up to the desired levels.
R1 = 1K2,
R2 = 100 Ohms,
R3 = 470 Ohms,
R4 = Evaluate using Ohms law.
R5 = 1K8,
R6 = 4k7,
R7 = 68 Ohms,
R8 = 1k8,
T1 = 2N3055,
D1 = 1N4007,
D2, D3, D4, D5 = 1N5408,
C1, C2 = 2200uF/50V,
Tr1 = 0 – 35 Volts, 3 Amp
Simple Crystal Tester Circuit
When it comes to frequency generating circuits or rather precise oscillator circuits, crystals become a crucial part, especially because they play an important role for generating and maintaining accurate frequency rates of the particular circuit.
However these devices are prone to many defects and are normally difficult to check through conventional DMM units.
The shown circuit can be used for checking all types of crystals instantly. The circuit itself is a small transistor oscillator circuit which starts oscillating when a good crystal is introduced across the indicated points in the circuit.
If the crystal is a good one, the bulb lights up showing the relevant results and if there’s any defect in the attached crystal, the bulb remains switched OFF.
Simple Current Limiter Circuit Using two transistors
The proposed circuit is exactly meant for carrying out the discussed function. The lower transistor is the main output transistor which operates the output vulnerable load and by itself is unable to control the current through it.
The introduction of the upper transistor makes it sure that the base of the lower transistor is allowed to conduct as long as the current output is within the specified limits.
In case the current tends to cross the limits, the upper transistor conducts and switches OFF the lower transistor inhibiting any further passage of the exceeded current limit.
The threshold current may be fixed by R which is calculated with the shown formula.
The above discussion presented some of the most popular hobby circuits from this website, if you have any new ideas or suggestions regarding some of your own interesting hobby circuits for the newcomer, please drop a line in the comment box, I will be most happy to include it in this post. Happy Hobbying!