Infrared Switch

Infrared Switch circuit for common use, please visit this page for complete explanation.

This is a single channel (on / off) universal switch that may be used with any Infra Red remote control using 36-38kHz. (This is a very common remote handset frequency). In place of IR1 a TSOP1738 receiver may be used.

Any "button" of any remote control may be used to work this universal switch. The button must be pressed for about one and a half seconds (determined by R3 and C2) before the relay will operate. The circuit will remain in this state (latched) until reset. To reset, any button is pressed on the remote handset and held for a short duration.

For example, if you were watching TV, you could press and hold any button on the TV remote to trigger the circuit. In order not to change channel, you could press the button of the channel you are watching. You can connect anything to the relay, for example a lamp, but make sure that the relay contacts can handle the rated voltage and current.

Sound Effects Alarm Generator

This schematic in very simple and easy to made. The IC produces all the sound effects, the output at Pin 3 being amplified by the transistor. A 64 ohm loudspeaker can be substituted in place of the 56 ohm resistor and 8 ohm loudspeaker. The 2 pole 4 way switch controls the sound effects. Position 1 (as drawn) being a Police siren, position 2 is a fire engine sound, 3 is an ambulance and position 4 is a machine gun effect. The IC is manufactured by UMC and was available from Maplin electronics code UJ45Y. At the time of writing this has now been discontinued, but they have have limited stocks available.

NiCad Battery Charger

This simple and low cost battery charger uses a single transistor as a constant current source. The voltage across the pair of 1N4148 diodes biases the base of the BD140 medium power transistor. The base-emitter voltage of the transistor and the forward voltage drop across the diodes are relatively stable. The charging current is approximately 15mA or 45mA with the switch closed. This suits most 1.5V and 9V rechargeable batteries.

The transformer should have a secondary rating of 12V ac at 0.5amp

Low Cost Tone Control Circuit

This cheap tone control circuit provides a maximum cut and boost of around 10dB at 10K and 50Hz. Two potensiometer used to control the high frequency (treble) and low frequency (bass).

The first BC109C transistor (left hand side) is acting as a buffer. It provides the circuit with a high input impedance, around 250k has a voltage gain of slightly less than unity. As the Baxendall tone control circuit is a passive design, all audio frequencies are attenuated. The position of the controls and reactance of the capacitors alters the audio response. The last transistor provides a slight boost of about 3x. The output is designed to feed an amplifier with input impedance of 10k to 250k. Both tone controls should be linear type potentiometers.

Tweeter Crossover

This is tweeter (high frequency speaker) crossover which will filter the treble (high frequency) to be feed to tweeter. The bass (low frequency) cannot pass the tweeter speaker since there is low pass filter made of C1, C2 and R1 assembled before the tweeter.

Notes

• The tweeter can be a 2 to 3 inch, 4 to 8 Ohm one .
• R1 is used to adjust match the the tweeters output level to that of woofer.
• C1 and C2 are electrolytic capacitors.
• R1 should be rated more than 2 Watts.

Low Cost Mic Mixer

This is the schematics of a simple low cost mic mixer that can be assembled from the components in your junk box. This two channel mike mixer is designed for handling high impedance dynamic microphones. Transistor Q1 can be any general purpose pnp transistor like BC177 or BC558.

How ever better the transistor quality better the performance. Resistors R2 and R3 can be used for the level control of input signals.

Notes

• All capacitors are of ceramic type.
• Always use a battery two reduce noise .
• Avoid using power transistors as Q1. This is because power transistors have high leakage current and it adds to the noise which is not suitable for our purpose here

source: circuitstoday.com

12 Watt Audio Amplifier

This low cost amplifier is simple and give you good result. Here the op-amp used is uA 741 which produces the required gain.The four transistors are wired as complementary Darlington’s which produces the drive for the speaker.

The voltage drop across the resistors R2 and R3, are used as the input of the Darlington pairs . As the input current to the op-amp depends on the level of the signal op amp is amplifying the voltage drop across the resistors R2 and R3 will be proportional to the input signal. These voltage drops are given to the base of Darlington pairs. The amplification is stabilized as a result of the negative feedback from the junction of collectors of Q2 and Q4. The theory may seem little awkward for you. But its working good.cSuch a simple but stable circuit as this can produce a reasonable output of 12W on a 4 Ohm speaker.

2W Mono Audio Amplifier

This circuit diagram is very simple, very easy to build and will be great idea for newbie or student project.

The IC TDA7052 is a mono output amplifier coming in a 8-lead DI package (DIP). The device is mainly designed for battery-operated portable audio circuits. The features of TDA 7052 include ,no external components needed, no switch-on or switch-off click sounds, great overall stability, very low power consumption(quiescent current 4mA), low THD, no heatsinks required and short-circuit proof.

The gain of TDA 7052 is fixed internally at 40 dB. . To compensate the reduction of output power due to low voltage supply the TDA7052 uses the Bridge-Tied-Load principle
(BTL) which can provide an output of around 1 to 2 W Rms(THD = 10%) into an 8 Ohm load with a power supply of 6 V.

In the circuit the potentiometer can be used to control the volume. Capacitor C1 and C2 are meant for filtering the supply voltage if a battery eliminator is used as supply source. For operations using a battery C1 and C2 are no necessary.