Build  a light controlled screamer!

Here's a fun project to make with the 555 chip. It can be built as a stand alone circuit or you can put it inside a doll, toy or whatever! Here's how it works. When it's turned on, the 555 astable oscillators are activated. One will produce a high pitch squeal through the speaker and the other will blink the LED about twice per second. When you shield the photo cells from light, the frequency of the sound will decrease and the LED will blink slower. If you arrange the photo cells so that they are near the LED, some of the light from the LED will be reflected off whatever is shielding the photo cell. The photo cell will react to the light and raise the frequency while the LED is on, then go back to where  it was when the LED is off. See the video below for a demonstration. I encourage you to try building other circuits with the 555. It's a very versatile chip with many applications. Have fun and keep on making stuff! Questions? Email me at: makerdino@gmail.com

Click the images for full size. Schematic:   Parts list: 1- 10 ohm resistor 2 - 100 ohm resistor 1 - 1.2 K ohm resistor 1 - 7.5 K ohm resistor 1 - .01 mF Ceramic capacitor 1 - .047 mF Ceramic capacitor 1 - 100 mF Electrolytic capacitor 1 - LED 2 - LM555 8 pin DIP chips 3 - Photo cells 1 - Small speaker 1 - 9 volt battery 1 - 9 volt battery clip 1 - small perf board to mount components on Hook up wire Links: 555 Contest. This is the official site with contest rules. http://www.555contest.com/ ExpressPCB. This site offers a free download of a schematic and PCB design tool that's easy to use. See screenshot above. They also offer fabrication of PCBs. http://www.expresspcb.com/index.htm Rob Paisley's 555 timer circuit page. This has a TON of great info on the 555 including a few timing calculators to aid in component selection. http://home.cogeco.ca/~rpaisley4/LM555.html Doctronics. Another great website with a lot of cool info and circuits for the 555. http://www.doctronics.co.uk/555.htm Octopart. This site offers up a search engine similar to Google but it's especially for electronic component part numbers. http://octopart.com/

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