555 Timer Rapid Flashing

TI has a CMOS version of the 555 called the LMC555. Much lower power, astable operation up to 3 MHz, supply voltage can be 1.5V to 15V.  The data sheet has lots of application information, and diagrams showing frequency versus selections of R and C.

Sadly, the 555 (or 7555) is the only jellybean some people know.

Here is a theoretic run-down on some alternatives:

https://www.fairchildsemi.com/application-notes/AN/AN-118.pdf

This chip could do the osc and the gate at a similar price-point.

https://www.fairchildsemi.com/datasheets/MM/MM74HC132.pdf

If you use it you'll seem like a little bit less of a script-kiddie.

And, for the sake of the deity of your choosing, avoid 9-14 Hz.  These fqs can trigger epileptic seizure.

Thank you very much. I will definetly try with that circuit.

Here is the circuit I was originally trying that didn't seem to work:

The only thing I did differently was I used a 100K resistor for R2 instead of a 470K because I didn't have a 470K.

I didn't think that would make a huge different, but I'm not an expert on 555 timers because I've never used one before.

Thanks for all the good advice. I try again with the suggested circuit and see if it works.

Pin 3 is output and the LED looks backward. Also the LED should go to gnd.

Pin 3 is output

I think you'll find Pin3 is a digital output, so it should go low when in the OFF state.

http://www.555-timer-circuits.com/using-the-output.html

I see nothing wrong with your schematic.

What is the value of C1, and if it is an electrolytic did you have the - side to ground ?

It is worth adding a 1nF or similar across pin 5 to ground ... think of it as insurance.

For any digital circuit it is always a good idea to add a 470uF -1000uF capacitor PLUS a 100nF (0.1uF) across the supply rails close to the chip to stop the spikes causing unwanted issues.

Mark

The schematic I found on some website with a little bit of instructions but they didn't give a value for C1.

So I put in a 100uF capacitor (I don't think it was electrolytic) because that was what I had a easiest access.

So I put in a 100uF capacitor

100uF will be a polarised capacitor of some type.

Double check you have it the correct way, and if possible change it just in case it is leaky. 

If you do the calculation that was supplied earlier it runs at 0.0153Hz

http://www.daycounter.com/Calculators/NE555-Calculator.phtml

or from here http://web.udl.es/usuaris/p7806757/555-calculadora/555%20Calculator.htm

It is ON or Off for 32 secs.

so you can see how useful the 265 million hits are to resolving why it might not work the way you planned.

Mark

Thanks.

I did try the capacitor both ways but I may not have waited 32 seconds, so my problem might have been caused by impatience though I believe I left it for long enough.

I'll try again and see if it works once I have time.

I did try the capacitor both ways but I may not have waited 32 seconds

It is a long time when you think it should flash rapidly. ...

The lack of capacitor across Pin5 could also increase the time by a factor of 10...

If you try different values for R2 in the second link, swapping the 470k for 12k gets you a 0.9Hz flash.

You can always add a 12k across the 470 to try it ...it will check your circuit does work.

Mark