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Firecrackers are normally ignited by using a matchstick or a candle. You have to run away quickly after igniting the fuse of the firecracker. This method of igniting firecracker is unsafe, because the danger of the firecracker bursting before you reach a safe distance is always there. The device described here uses remote control, usually used with TV receivers or CD players, to burst the fire-cracker. Thus the firecracker can be ignited from a safe distance using the circuit described below in conjunction with the remote control.... [read more]

This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to remain off. The conducting transistor can be turned off by grounding it's base through the push button which causes the collector voltage to rise and turn on the opposite transistor.... [read more]

This is the schematic for an FM transmitter with 3 to 3.5 W output power that can be used between 90 and 110 MHz. Although the stability isn't so bad, a PLL can be used on this circuit.... [read more]

The ckt is built around two 555 timer ICs. U1 and U2. U1 is wired as a variable duty cycle oscillator with a constant time period of around 0.1 second. Duty cycle can be varied from 0 to 100 per cent by R4 potentiometer. The output of U1 (pin 3) is connected to the rest input (pin 4) of U2.... [read more]

This circuit was designed to detect the approximate percentage of salt contained in a liquid. After careful setting it can be useful to persons needing a quick, rough indication of the salt content in liquid foods for diet purposes etc.... [read more]

This is a single zone alarm - with independently adjustable Exit, Entry and Siren Cut-Off timers. When the alarm is activated its Siren will sound once - for up to 20-minutes. Then it will switch off and remain off. If you wish - you can use a mains power supply. But the extremely low standby current makes battery power a realistic option.... [read more]