Welcome!

This simple circuit mixes two or more channels into one channel (e.g. stereo into mono). The circuit can mix as many or as few channels as you like and consume very little power. The mixer is shown with two inputs, but you can add as many as you want by just duplicating the "input sections" which are clearly visible on the schematic.... [read more]

While talking to a distant subscriber on telephone, quite often we feel frustrated when the voice of the distant subscriber is so faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive amplifier is presented here. It can be assembled and tested easily. There is no extra power source needed to power up the circuit, as it draws power from the telephone line itself. The amplifier will provide fairly good volume for the telephone conversation to be properly heard in a living room. A volume control is included to adjust the volume as desired.... [read more]

Turns-off your amplifier when idle for 15 minutes... [read more]

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]

If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10. When remote from a live line, the unit stops counting, the LED resulting permanently off.... [read more]

The circuit below uses two quad voltage comparators (LM339) to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 millivolts or about 22 milliwatts peak in an 8 ohm system.... [read more]