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Time is set by potentiometer R2 which provides a range or 1 sec. To 100 seconds with timing capacitor C1 of 100uF. The output at pin 3 is normally low and the relay is held off.... [read more]

The circuit illustrates generating a single positive pulse which is delayed relative to the trigger input time.... [read more]

This circuit, enclosed in a small plastic box, can be placed into a bag or handbag. A small magnet is placed close to the reed switch and connected to the hand or the clothes of the person carrying the bag by means of a tiny cord. If the bag is snatched abruptly, the magnet looses its contact with the reed switch, SW1 opens, the circuit starts oscillating and the loudspeaker emits a loud alarm sound. A complementary transistor-pair is wired as a high efficiency oscillator, directly driving a small loudspeaker. Low part-count and 3V battery supply allow a very compact construction.... [read more]

The LED traffic Light circuit controls 6 LEDs (red, yellow and green) for both north/south directions and east/west directions. The timing sequence is generated using a CMOS 4017 decade counter and a 555 timer. Counter outputs 1 through 4 are wire ORed using 4 diodes so that the (Red - North/South) and (Green - East/West) LEDs will be on during the first four counts. The fifth count (pin 10) illuminates (Yellow - East/West) and (Red - North/South).... [read more]

This is a simple use of the PIC 16F84 about a diode tester.... [read more]

This amplifier can be directly connected to CD players, tuners and tape recorders. It is tested with several headphone models of different impedance: 32, 100, 245, 300, 600 & 2000 Ohm. Schematic shows left channel only. B1, SW1, J1 & C3 are common to both channels. R3 value was calculated for headphone impedance up to 300 Ohm. Using 600 Ohm loads or higher, change R3 value to 100K.... [read more]