Here’s a PC-based lighting system that lets you light up a candle using matchsticks by just pressing the ‘Enter’ key on the PC’s keyboard. It is especially useful when celebrating such occasions as birthdays and anniversaries.
The number of matchsticks required to light up the candle is placed on the candle (alongside its wick) as shown in the figure. The heating coil for igniting the matchsticks is kept near them.
The interface circuitry between the PC and the heating coil for the candle-matchsticks arrangement comprises an inverter, monostable and relay driver. Transistor BC548 (T1) acts as the inverter, IC 555 (IC1) is configured as the monostable circuit and transistor SL100 (T2) is the relay driver.
When you press ‘Enter’ key on the keyboard, the inverted output at the collector of transistor T1 goes low to trigger IC1 through its pin 2. Output pin 3 of the monostable goes high and transistor T2 conducts for around 50 seconds.
The conduction of transistor T2 energises relay RL1, which, in turn, connects the heating coil to 230V AC through the normally opened (N/O) contact. In place of the heating coil, you can also use an electric cigarrette lighter. The heating coil becomes red hot when connected across the 230V AC and ignites the matchsticks. The flames of the matchsticks light up the candle.
The program, written in ‘C’ language, is simple and easy to understand. The parallel-port D-type female connector normally available on the back of the PC is used for outputting the data to the interfacing circuitry. The address 378H of parallel-port LPT1 is used in the program. The parallel-port pin 2 corresponding to data bit D0 sends the control signal to energise the relay, which, in turn, connects the load to AC mains.
This circuit uses only one output of the PC’s parallel port to light up the candle, but it can be extended to light up up to eight diyas/candles in thiruvillaku (as called in South India) by using eight outputs with a slight change in the program and adding seven similar circuits.