555 timer IC design contest-- no strings

Chris Gammell from the blog The amp hour and Analog Life is running a 555 timer IC design contest. EDN’s Mike Demler wrote it up on his blog yesterday. So Mike or Chris asked me to do a mention on Anablog, and typical ex-mob-soldier cynic that I am, I wondered what nefarious use all the registration information was going to be put to.

I felt quite foolish when Chris wrote back explaining this was really a fun project, not a data-mining front for the NSA. Chris was patient with me and wrote a nice note:

• The contest is being run under the auspices (always liked that word) of…me. It’s hosted on my server and the domain is registered to my name. You should be able to check. As for registration, we’re not planning on harvesting any info. I don’t even plan on asking for anything other than an email to reach them at, they can give their mailing address to the prize givers if they win.
• I’m sorry for the contests you’ve experienced in the past. It’s apparent that you’ve had exposure to some of the true nature of some contests (yet another block of people into the “funnel”). However, as much as you can believe me (mostly what you can read about me online), it really is for fun. And from the perspectives of how most contests are run, the fact it is so different is what keeps us motivated (and the fun entries we’re expecting). So if you change your mind and are a hobbyist outside your day job, why not enter and try it out?

My apologies Chris, for not realizing there are other people in the world that think analog is fun. I will have to pass on doing a design entry, my experience with the 555 is that it is the hobbyist’s friend and the engineer’s nightmare. Indeed, having analog fun in my own curmudgeonly way, I wrote up a few 555 contests entries, several from personal experience. My contest submittals would be:

1)      Use a 555 timer for power-on-reset that you find out does not really work because the 555 is, at its heart, a digital chip, and then the entire design cannot be shipped and all the bosses hate you.

2)      Use the 555 with high-value resistors to learn that leakages change the oscillator period.

3)      Use the 555 as a one-shot that mysteriously latches up and never works if power is applied gradually.

4)      Us a 555 timer in a battery-powered product as a voltage sensor since the frequency varies with power supply voltage.

5)      Use a 555 with low-value capacitors so stray capacitance and board variance gives you an out-of-spec output frequency.

6)      Use the 555 timer as a temperature sensor, since its frequency goes all over the place depending on ambient temperature.

7)      Use a CMOS 555 to learn how input transients can latch and blow up the part.

OK, sorry for the snark– actually this is a lot of fun. I know it is the biggest selling chip in history, but man oh man, every time I saw one when I was a consultant, I knew I could fix some problem by designing it out. The only thing worse was the 74/54LS123. That was even more sensitive to glitches and false triggers. I should shout out to analog guru Robert Chao over at ALD who has done a pretty nice CMOS 555. Oh and EDN design ideas are constantly trying to get 555s to work. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13……… If you want a timer function that works, Linear Tech just came out with the TimerBlox.

Lets see what Bob Pease has to say about the pitfalls of 555s. Turns out someone asked Bob to contribute to the contest and he was not much kinder on the venerable 555. Pease commented:

• “I have almost NEVER used a 555. Maybe never? I use op-amps, LM324’s, LM311’s, LF356’s. I use 74HC04’s and 74C14’s but not 555’s. I’ve used ECL fast logic, and discrete transistors. But the 555 just does not do anything precise, or even semi-precise, that I need done. So that’s one thing I can “share” - my favorite circuit to use a 555, is: a blank piece of paper. Never touch the things. When I want to make a V-to-F converter, I use an LM301A. The patent number is 3,746,968. Most people can’t make a 0.02% linear VFC unless they pay $5 for a fancy sole-sourced IC. I rest my case.” Robert A. Pease, Engineer, Transtronix. .

Well you can tell what Bob and I think if 555 chips. I do know you can reverse bias the power and use them as effective clamp diodes. So please feel free to comment about what you think of the 555. Have you had as much problems with them as I have?