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The circuit consists of a small PIC microcontroller, assembly program, and a few other parts to detect a switch closure from an open door, window, or manual push button and then dial the cell phone number, and transmit a steady tone to indicate the source of the call. The circuit uses the pulse dialing system to interrupt the line connection a number of times to indicate each digit.... [read more]

Apart from the obvious usage as a headphone amplifier, the circuit can be used for a range of applications where a wide bandwidth low power amplifier is needed. The circuit is based on an opamp, with its output current boosted by a pair of transistors.... [read more]

This handy circuit can be used as a speed controller for a 12V motor rated up to 5A (continuous) or as a dimmer for a 12V halogen or standard incandescent lamp rated up to 50W. It varies the power to the load (motor or lamp) using pulse width modulation (PWM) at a pulse frequency of around 220Hz.... [read more]

This circuit idea is certainly not new, but when it comes to making a trade-of between using a small, short-circuit proof transformer or a capacitive voltage divider (directly from 230 V mains voltage) as the power supply for a fan, it can come in very handy. If forced cooling is an afterthought and the available options are limited then perhaps there is no other choice. At low currents a capacitive divider requires less space than a small, short-circuit proof transformer.... [read more]

This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 800 turns of #30 - #35 magnet wire.... [read more]

This circuit of power supply, is very simple and easy to built, it can be assembled on a general-purpose PCB, finding its materials is very easy and cost-small. The output voltage is stabilized and is regulated in the region from 0V until + 15V dc, with biggest provided current 1 A. The regulation becomes with the P1. The Q1 is classic power transistor and it needs to be placed on a cool rib (Heatsink), when it works continuously in the region of biggest current it gets hot. The type of transformer is standard in the market.... [read more]