Audio Power Indicator

This is audio level indicator which can be used to measure the audio level output of your amplifier. Simply connect the output of your amplifier to the input of this circuit, then you will know the average value of your amplifier's power.

R1_____________220R  1/2W Resistor
R2,R5,R6,R8____100R  1/4W Resistors
R10,R12,R14____100R  1/4W Resistors
R3_____________220R  1/4W Resistor
R4,R7__________330R  1/2W Resistors
R9_____________560R  1/2W Resistor
R11____________820R  1/2W Resistor
R13______________1K2 1/2W Resistor

D1___________1N4004  400V 1A Diode
D2,D4,D6__BZX79C2V7  2.7V 500mW Zener Diodes
D3,D5,D7,D8,D9,D10   Red LEDs (Any dimension and shape) (See Notes)

Notes:

• The output power indicated by each LED must be doubled when 4 Ohms loads are driven.
• The circuit can be adapted to suit less powerful amplifiers by reducing the number of LEDs and related voltage dividers.
• LEDs of any dimension can be used, but rectangular shaped devices will be more suitable to be compacted in bars or columns.
• For a stereo amplifier, two identical circuits are required.

70 Watt MOSFET Audio Amplifier

This amplifier circuit will give you about 70W output power at 60v supply.
Please visit this page for detail information and characterization

20W Bridge Audio Amplifier based on TDA2005

This is 20W Bridge Audio Amplifier circuit based on the TDA2005 IC, a class B dual audio amplifier, specifically designed for car radio applications etc.
This circuit require Voltage input 18 VDC and will give you Output power - 20 W, 4 Ω

This is the amplifier kit:

This is the schematic:

To get the schematic diagram, component list and component layout, please download this file

8 LED Audio Level Meter

This is 8 LED audio level meter circuit diagram. Build based on 2 pieces of op-amp IC LM324. You should use 4 ICs for stereo audio level meter.
Here the schematic:

Running LED

This is the running LED circuit diagram. The LED will "running" (on) one by one. You can use this circuit for many purpose like motorcycle lamp, running character and much more.

Here the schematic diagram with IC timer 555:

And use this circuit use NAND logic:

Zone Alarm System

This is the circuit of alarm system with 5 independent zones. Suitable for a small office or home environment. It uses just 3 CMOS IC's and features a timed entry / exit zone, 4 immediate zones and a panic button. There are indicators for each zone a "system armed" indicator.

Zone 1 is a timed zone which must be used as the entry and exit point of the building. Zones 2 - 5 are immediate zones, which will trigger the alarm with no delay. Some RF immunity is provided for long wiring runs by the input capacitors, C1-C5. C7 and R14 also form a transient suppresser. The key switch acts as the Set/Unset and Reset switch. For good security this should be the metal type with a key.

Circuit works:
At switch on, C6 will charge via R11, this acts as the exit delay and is set to around 30 seconds. This can be altered by varying either C6 or R11. Once the timing period has elapsed, LED6 will light, meaning the system is armed. LED6 may be mounted externally (at the bell box for example) and provides visual indication that the system has set. Once set any contact that opens will trigger the alarm, including Zone 1. To prevent triggering the alarm on entry to the building, the concealed re-entry switch must be operated. This will discharge C6 and start the entry timer. The re-entry switch could be a concealed reed switch, located anywhere in a door frame, but invisible to the eye. The panic switch, when pressed, will trigger the alarm when set. Relay contacts RLA1 provide the latch, RLA2 operate the siren or buzzer.

Simple Electronic Buzzer

This is a simple electronic buzzer circuit diagram. Cheap and easy to build.
The 555 is used as astable multivibrator operating at about 1kHz and produces a shrill noise when switched on. The frequency can be adjusted by varying the 10K resistor. You may change the 10K resistor with variable resistor.

Variable Power Supply with L200

This is adjustable power supply schematic diagram with IC L200 for its power regulation.

Voltage output is controlled by 10K variable resistor. Output voltage range value will be about 3 to 15 volts, and current range is about 10mA minimum and 2 amp maximum. Reaching the current limit will reduce the output voltage to zero.