Comments on: LM555 Tick tick tick

By: Bill Compton

Bill Compton — Mon, 04 Jun 2007 22:21:07 +0000

Hi Jim. Photos i received. Thanks

By: dash

dash — Mon, 04 Jun 2007 04:34:38 +0000

i think it works great. I don’t have any ear phones though, so i used another led to replace the ear phone. It would be very cool if you could make it so one led blinks and then the other.

By: Lee

Lee — Fri, 01 Jun 2007 17:47:44 +0000

“1964…90 Volt battery…NE-2 neon bulb that formed a relaxation oscillator. It ran for two years”

You remind me of a “drive somebody crazy” device I always wanted to build after seeing it on an old magazine — several NE-2s and a 90V battery, blinking for years. It was cast inside a clear plastic block so there was NO WAY to turn it off!

By: Lee

Lee — Fri, 01 Jun 2007 17:47:06 +0000

You can use this circuit to figure out the value of the capacitor, if you know precisely the value of the resistor. Display the ticks on an oscilloscope and measure the time between ticks. 137 beats per minute is .44 seconds between ticks, a frequency of 2.28 Hz. Capacitance in farads C = 1.44/(R*Hz). So (if my resistor were exactly 27000 ohms) the capacitor labeled “20 mFd” actually was 23 microfarads.

.000023 = 1.44 / ( 27000 * 2.28)

By: Lee

Lee — Fri, 01 Jun 2007 17:46:08 +0000

“But why 137 beats per minute? Is this a cosmic joke?”

I’d like to say that constant was finely structured but actually I was aiming at 120 bpm, like an aroused heartbeat, with a deep red LED, like a valentine of constant undying LUUUUVVVV. She thought it was a bomb.

Mainly I liked the shiny blue capacitor and picked a resistor to get close. 555 spec sheets give a simple formula for calculating the period of this astable multivibrator T= .693(Ra + 2Rb)C .
The nominal component values I used were Ra=27000, Rb=0, C=.00002 .

By: Alan

Alan — Fri, 01 Jun 2007 10:52:12 +0000

I was just thinking that with a time delay this could be a profitable device for plumbers. Set it up to go off 5 months after you leave. Just hope the device isn’t spotted…

By: Rajah

Rajah — Fri, 01 Jun 2007 03:54:55 +0000

That’s a fun quickie project. I did something similar back in 1964 with a used 90 Volt battery for portable tube type radios, a megohm resistor, capacitor and an NE-2 neon bulb that formed a relaxation oscillator. It ran for two years, binking the neon bulb about once every two seconds, in my college dorm room before someone “borrowed” it. Thanks for reminding me.

By: Crudely Wrott

Crudely Wrott — Wed, 30 May 2007 21:27:33 +0000

“This device also simulates a faucet dripping. Hide it near a sink to frustrate a handyman.”

Hey! I’m a handyman! I get paid to come to your house and fix stuff, including drips. Do I look like I need further frustration?!! If I discover that you have fooled me with this silly contrivance . . . I’ll buy and fly!

But why 137 beats per minute? Is this a cosmic joke?

By: Jim Thompson

Jim Thompson — Wed, 30 May 2007 07:33:22 +0000

I love the versatility of the 555 timer, but when it comes to long-running low-power circuits, it doesn’t do nearly as well as the LM3909 oscillator. Add a capacitor, LED, and battery to the 3909 and you have an extremely simple LED blinker that will uses very little power. I made one such blinker, wired to a 1.5V alkaline battery, and gave it to my Dad to put on his office shelf. I chose a capacitor value for a blink every couple of seconds. Two years later, it was still blinking! I don’t know how long that one went before eventually giving up the ghost, but at two years I considered it a smashing success.

By: brandonu

brandonu — Tue, 29 May 2007 22:35:06 +0000

There is an artistic look to these free-form circuits that I love. A lot of the BEAM bots have the same kind of look to them. Nice job!