100W Transistored Inverter 12VDC to 220VAC

This inverter circuit can be used for medium electronic devices such as emergency light, radio, battery charger etc. Be carefull during assembly this circuit because of high voltage on the output transformer.

100W Inverter PCB Diagram:

100W Inverter PCB Design Layout:

Source of the circuit: 100W Interver Circuit

9V Mini FM Transmitter

The following diagram is the circuit diagram of 9V Mini FM Transmitter.

Schematic diagram:

Components List:

R1,R3 = 100K
R2 = 10K
R4 = 470 ohm
C1,C4 = 470pF
C2,C3 = 4.7µF/16V
C5,C6 = 4.7pF
C7 = 4-40pF trimmer cap (optional, see text)
L1 = 1µH
Q1,Q2 = 2N2222, NPN transistor
Mic = Electret Microphone
B1 = 9 Volt battery

Circuit Notes:
Absolutely nothing crucial here. To get a bit of tuning out of the coil you could put a 4-40pF trimmer capacitor (optional) parallel over the 1 µH coil, L1.

C1/C4 and C5/C6 are ceramic capacitors, preferably NPO (low noise) types. C2/C3 are electrolytic or can be tantalum kinds.

In the event you determine to substitute transistors with some thing similar you already have, it perhaps necessary adjust the collector voltage of Q1 by changing the value of R2 or R3 (simply because you alter transistors, it changes this bias on the base of Q1). It ought to be about 1/2 the supply voltage (about four or 5v).

The antenna is nothing more than a piece of 12" wire or a piece of piano wire from 6" to 12".

To find the signal on your regular FM Radio dial, make certain there's a signal coming into the microphone, otherwise the circuit will not function. I use an old mechanical alarm clock (you know, with those two big bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm certain you get the concept... Or you can just lightly tap the microphone whilst looking for the location of the signal on your receiver.

The antenna is nothing more than a piece of 12" wire or a piece of piano wire from 6" to 12".

To find the signal on your standard FM Radio dial, make sure there is a signal coming into the microphone, otherwise the circuit won't work. I use an old mechanical alarm clock (you know, with those two large bells on it). I put this clock by the microphone which picks up the loud tick-tock. I'm sure you get the idea... Or you can just lightly tap the microphone while searching for the location of the signal on your receiver.

Source: http://www.sentex.ca/~mec1995/circ/fmt4.html
Design by Tony van Roon

Touch Activated Alarm

This is a touch activated alarm system. Your alarm system will be activated when someone touching the "trigger". You may use this circuit at your home door, your vehicle etc.

Parts list:

R1 = 100K R2 = 56K R3 = 10M R4 = 220K P1 = 100K D1 = 1N4004

T1 = 2N3904, or equivalent U1 = 555 Timer* C1 = 47μF/16V** C2 = 33μF/16V** Re1 = Relay***

Notes:

*The 555 can be a LM, NE, or MC(cmos) type, they're all pin-compatible.

**C1/C2's working voltage ought to be elevated to 25V in the event you decide to go with a 12V power source. Rule of thumb: the operating voltage of capacitors are at least double the supplied voltage, in other words, if the power source is 9 Volt, your capacitor(s) is a minimum of 18V. Transistor T1 could be any approximate substitute.

*** Use any appropriate relay for the project and if you're not tight on area, use any size. I've build this specific circuit to prevent students from fiddling using the security cameras in pc labs at the University I'm employed. I made sure the metal casing was not grounded. But as being the schematic shows you are able to essentially hook it as much as any type of metal surface. I utilized a 12-vdc power supply. Use any suitable relay to deal with your specifications. A 'RESET' switch (Normally Closed) can be added between the constructive and also the 'arrow-with-the-+'. The trigger (touch) wire is connected to pin 2 of the 555 and will trigger the relay, using the body resistance, when touched. It is apparent that the 'touching' component has to be clean and can make good contact using the trigger wire. This particular circuit might not be suitable for all applications. Just in case you wonder why pin 5 is not listed within the schematic diagram; it is not really required. In particular noisy circumstances a little ceramic capacitor is placed between pin 5 and ground. It will no harm to put one or leave it out.

Additional note: For those of you who didn't discover, there's an approximate 5-second delay build-in before activation of the relay to avoid false triggering, or perhaps a 'would-be' thief, and so on.

Circuit design by Tony van Roon.

Emergency Light and Alarm circuit

This is a simple and easy emergency light and alarm circuit. This circuit is permanently plugged into a mains socket and NI-CD batteries are trickle-charged. When a power outage occurs, the lamp automatically illuminates. Instead of illuminating a lamp, an alarm sounder can be chosen.

When power supply is restored, the lamp or the alarm is switched-off. A switch provides a "latch-up" function, in order to extend lamp or alarm operation even when power is restored.

Component parts list:

R1 = 220K
R2 = 470R
R3 = 390R
R4 = 1K5
R5 = 1R
R6 = 10K
R7 = 330K
R8 = 470R
R9 = 100R
C1 = 330nF/400V Polyester Capacitor
C2 = 10µF/63V Electrolytic Capacitor
C3 = 100nF/63V Polyester Capacitor
C4 = 10nF/63V Polyester Capacitor
D1-D5 = 1N4007
D6 = LED Green
D7 = 1N4148
Q1,Q3,Q4 = BC547
Q2,Q5 = BC327
SW1,SW2 = SPST Switches
SW3 = SPDT Switch
LP1 = 2.2V or 2.5V 250-300mA Torch Lamp Bulb
SPKR = 8 Ohm Loudspeaker
B1 = 2.5V Battery (two AA NI-CD rechargeable cells wired in series)
PL1 = Male Mains plug

Circuit Works:
Mains voltage is reduced to about 12V DC at C2's terminals, by means of the reactance of C1 and the diode bridge (D1-D4). This avoids the use of a mains transformer.

Trickle-charging current for the battery B1 is provided by the series resistor R3, D5 and the green LED D6 that also monitors the presence of mains supply and correct battery charging.
Q2 & Q3 form a self-latching pair that start operating when a power outage occurs. In this case, Q1 biasing becomes positive, so this transistor turns on the self latching pair.

If SW3 is set as shown in the circuit diagram, the lamp illuminates via SW2, which is normally closed; if set the other way, a square wave audio frequency generator formed by Q4, Q5 and related components is activated, driving the loudspeaker.

If SW1 is left open, when mains supply is restored the lamp or the alarm continue to operate. They can be disabled by opening the main on-off switch SW2.

If SW1 is closed, restoration of the mains power supply terminates lamp or alarm operation, by applying a positive bias to the Base of Q2.

Notes:

• Close SW2 after the circuit is plugged.
• 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.

Emergency Light and Alarm circuit source: http://www.redcircuits.com/Page45.htm

Amplifier Circuit based 4 Transistors

Above diagram very simple and easy to build class AB audio amplifier circuit which is working with 4 transistors. In class AB operation each output device performs more than half of the input signal cycle. Up to 78% effectiveness is possible with class AB designs and cross over distortion is minimized. The circuit shown here is appropriate for small radio receivers, audio players, intercom, phone etc.

Transistor Q1 with its connected parts is wired as a pre-amplifier stage. The audio input is coupled to the base of Q1 through resistor R1 and capacitor C1. Resistor R3 delivers collector to base bias for Q1 and C3 is an AC by pass capacitor for the collector resistor R4. Collector to base biasing is a great method of biasing for circuits like this because it provides enough negative feedback, prevents thermal runway and stabilizes the operating point. The second stage will be the driver stage for the push pull pair. Q2 with its connected parts carry out this job. This stage can also be collector to base biased, and its input is coupled towards the output from the pre-amplifier stage using capacitor C2. Resistor R8 limits the collector present of Q2.The third stage is the class AB push pull section comprising of transistors Q3 and Q4. Diodes D1 and D2 provides the bias voltage for the push pull stage. The output from the amplifier is coupled to the loud speaker through the capacitor C4. C5 and C6 are power supply filter capacitors.

Notes:

1. The circuit can be assembled on a vero board.
2. K1 may be an 8 ohm/5Wof loud speaker.
3. C6 must be grounded near towards the Q1 and C5 should be grounded near to the loud speaker ground. This reduces noise.
4. Use 5V DC power supply for powering the circuit.

EL34 Stereo Tube Amplifier 2x90 Watts

The following are step by step how to create a stereo tube amplifier using EL34 power tube. This stereo tube amplifier circuit is capable of producing an audio output of 90 watts for each channel.

Download EL34 Stereo Tube Amplifier 2x90 Watts step by step guide.
Download Link

220V Light Dimmer circuit

The following diagram is the schematic diagram of 220V Light Dimmer.

220V Light Dimmer diagram:

Parts List:
R1 = 10K
R2 = 2K2
R3 = 180K
Potentiometer 250K
C1 = 150nF/400V dipped polyester
C2 = 47nF/630V dipped polyester
C3 = 220nF/250V AC dipped polyester
Triac = 2N6075 or BT136-500D
Diac = HT-32
FUSE 2A or 3A

Download the 220V Light Dimmer circuit documentation here.

35W Power Amplifier Circuit using STK082

The following is the schematic diagram of 35W power audio amplifier. Built based on power-amp IC of STK082, this circuit will give great audio output for your home audio system.

Download the STK082 datasheet