dinsdag 20 oktober 2009

Electronic components: The NE555 IC as a timer

Today we are going to build an astable flip-flop using the NE555 IC. IC stands for Integrated Circuit, which is miniaturized circuit (also called chip). The NE555 IC can be used as a timer. It will switch every X time, which makes it possible to do actions every X time. A flip-flop is a circuit that will switch states, in our example two LEDs which in turn go on and off. Astable means that will switch without external influences.

Let's talk a bit about ICs first. As said, IC stands for Integrated Circuit. You can use it by connecting the pins of the IC. You can figure out how to connect them by reading the datasheet. The following image is the NE555. An IC has a X number of pins, numbered anti-clockwise starting with the pin left of the notch or closed to a dot.




Note that the schematic symbol differs from the actual pin configuration as can been seen on the left.


For more information on what the pins mean see: http://en.wikipedia.org/wiki/555_timer_IC

The following circuit will put the NE555 to use in oscillator mode.
1 x 9V power supply
2 x 680 Ohm resistor (blue gray brown gold)
1 x 1 KOhm resistor (brown black red gold) 
1 x 10 KOhm resistor (brown black orange gold)
1 x Elco 35v 100 uF
1 x NE 555 IC
1 x red LED
1 x green LED


The Elco is a component which I will talk about later. For now it's enough to know it can store a certain amount of energy. The Elco will need to charge. While doing that, the red LED will be on. Upon the moment the energy stored in the Elco crosses 2/3 of the voltage put on pin 8 of the IC (in our case 6 V), the NE 555 will switch, discharging the Elco. This result in the green LED being lit. This continues until the voltage drops to 1/3 (3 volt in our case), in which case the charging starts and the red LED lights up again.






This is the end result, although I have to admit I blew a LED. Be careful when you are debugging the circuit, the Elco may contain voltages way more than  the LED can handle.

That's it for now. I'm on holiday for a few days, so expect new postings next week.

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