PWM Controller Circuit using SN75603 and SN75604

Here the circuit diagram of PWM Controller which uses complementary half-H peripheral drivers SN75603 and SN75604, with totem-pole outputs rated at 40 V and 2.0 A. These drivers effectively place the motor in a full-bridge configuration, which has the ability to provide bidirectional control.

USB Cellphone Charger

This is the schematic diagram of cellphone charger circuit which connecter to the USB as main power. Whit this circuit, you can charger your cell phone from USB port in your PC or notebook.

The majority of the cellphones battery is appraised 3.6 volts at 1000 to 1300 mah. These battery packs have 3 Nimh or Lithium cells having 1.2 volt rating. Generally the battery pack requires 4.5 volts and 300-500 mA current for quick charging. Anyway, low present charging is better to build the proficiency of the battery. The circuit depicted here gives 4.7 directed voltage and sufficient present for the moderate charging of the cellphone.

1.3-12V Small Variable Power Supply

This is a small variable power supply delivers adjustable output voltage of 1.3v-12v. The current output determined by R3. With current setting (see part list), it will deliver current output about 1A.

220V Light-Operated On/Off Switch

This schematic diagram is a light-operated, remote-controlled solidstate switch circuit to handle lamp. While in darkness, the resistance of Light Dependent Resistor (LDR) is extremely hight, it shoots up to megohm range. As a result, the triac isn't going to have gate drive and therefore it doesn't conduct.

Gold Detector Schematic

Here the very simple and easy build gold detector circuit. The circuit capable to sense gold or metal or coins from a distance of about 20cm, depending on the size of the object to detect.

The circuit oscillates at about 140kHz and a harmonic of this frequency is detected by an AM radio. You can simply tune the radio receiver until a squeal is detected.

Simple Intercom Circuit with Transistors

This is a 2-station simple intercom circuit build based on transistors part and using common 8R mini speakers. The speaker works as microphone and generate sound, so there is no need microphone for this intercom. The "press-to-talk" switches should have a spring-return so the intercom can never be left ON, push on switch can be used for this kind of task.

Interior Light Fader for Automobile

Here the circuit diagram of Interior Light Fader for Automobile. The circuit is build using low power operational amplifier LM324 which only need around 3mA of current, so it won't bother the battery supply if left connected for extended periods. This circuit is similar to the fading eyes circuit above and is used to slowly brighten and fade interior lights of older cars.

Dynamic Mic Amplifier (To Use Speaker as Microphone)

This is the circuit diagram of dynamic mic amplifier. This simple and easy built circuit can be used as a subtitute of an electret microphone. It will turn an ordinary mini speaker to become a pretty sensitive microphone.