Saturday, 22 January 2011

555 Timer Hype-?

So if you have not noticed then engineering community is going nuts about the little 555 Timer IC. This is all because Jeri Ellsworth posted on twitter that she felt she should start a campaign to bring it back into popular use. In the space of a few days she has with the help of Chris Gammell placed a 555 contest website up with big companies asking to sponsor it. So what’s all the hype and why get so excited about such a little chip?

The 555 was originally designed by Hans R. Camenzind in 1970. The NE555 quickly became a massive seller and in 2003 it was estimated that more than one billion units are sold each year. The device its self contains very little, two comparators and a SR flip-flop and a bit of support circuit allow this device to perform a number of functions from generating square wave to detecting missing pluses or debouncing a switch input. The 555 has many uses but is now sadly over looked as old and impractical as a first choice.

The original NE555 which is still available was criticised as being current hungry and causing noise on supply rails due to its use of bipolar transistors. However a competitor using CMOS technology, the 7555, offers very low power usage and removed the horrid glitches seen on the 555. However despite the basic operation of the two devices being identical engineers have found a few minor differences in operation and its well worth investigating these when designing a circuit or wondering why your circuit is not working the same as one you have copied from the internet.

In its basic principles the 555 can work as a monostable or astable and achieves this by use of the designers selecting resistors and capacitors to connect to the outside of the device. Using simple RC calculation and an offset factor for the 555 it’s quick and easy to use.

Because the 555 has been around so long there are now vast amount of information and tutorials on the internet showing you how to use it. This is a list of the sites I have found that have good information and examples that you can work from.

This link will take you to DesignSpark and a little excel sheet the I put together at the request of Robotgrrl that helps you find a selection of R’s and C’s to fit your application: R-C Guide

Modern 21st century electronics is pushing back the use of the 555 chip. We are now able to purchase micros for under a dollar that are temperature stable and able to do so much more than a 555. However these micros hiding in tiny 8 pin packages have a disadvantage of needing programming and testing.

So why the hype for a 555 contest – well this little device has been around for a long time and as engineers we have a certain love for our hobby electronics roots and the days of building small projects from Radio Shack or Maplins. In the 80’s when I was building circuits you found 555 timers in tons of products, either that or a 741 op-amp! So Jeri like so many of us remembers the good old days and having a contest allows us to bring the little 555 timer back to the front of our minds and remind us that simple is sometimes better.

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