Monday, December 21, 2009

Playing with a 555 Timer Circuit

So I was bored yesterday and started going through my box of ICs. I came across a 555 timer chip, and an LED in my head went off:

Why not try to make some LEDs blink?? 

The original idea was to make a little blinking ornament or something. I still may, but I'm just happy I got it to work. Here's what I did.

I looked up the 555 timer datasheet and some example circuits. The Wikipedia article had some really good information as well. I learned that there are two modes which the timer can operate: monostable and astable. Monostable mode is a one-time pulse. Astable mode repeats that pulse indefinitely.

Armed with my new knowledge on monostable and astable operation, I realized that I needed an astable circuit, because who wants their decoration to blink once and quit? That's no fun. Anyway, I looked up some of the formulas, which would have been intimidating, had I not been tortured by introduced to all of these concepts during my university career.

In my net travels, I came across this excellent 555 resource. I learned that in order to get a duty cycle close to 50%, I need to choose R1 = 1k.

After I had everything all wired, I powerd it up and the LED lit up....but it didn't blink. This bothered me for a second, then I realized what was the culprit: the capacitor I used was a really large value. I switched it out for a 100uF and it blinked, still slowly, but blinked nonetheless. The duty cycle was at 50% because of my R1 resistor value. Then, I switched out the capacitor for an even smaller value (1uF). This blinked very rapidly - much faster than I would like, but at least I was learning how the timer worked.

I realize that by using the formula, I can more accurately pinpoint a frequency. This was just a preliminary exercise though. I definitely hope to get deeper into this chip later.