 OT: 555 timer... need a hand with Astable settings :), been a long time... |
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| Mueller |
 Oct 2 2006, 04:05 PM
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914 Freak!  Group: Members Posts: 17,155 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None 
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okay, so I have a device I want to turn on for 10 to 20 seconds via the output going to a relay, off to be a few seconds.
I just downloaded pspice student version to see if I can mimic the circuit which I am not sure if the student version can do so..... using a kit from Ramsey http://www.ramseyelectronics.com/downloads/manuals/UT5.pdf other res. I have on hand are 1M (variable), a couple of 100K and a bunch of 1K....for extra caps, 100uF is the max |
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| jsteele22 |
Oct 2 2006, 05:04 PM
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Senior Member Group: Members Posts: 727 Joined: 24-August 05 From: Colorado Springs, CO Member No.: 4,653 |
Hey Mike,
Here's a datasheet for the LM555; whenever I need a datasheet, I just look it up at digikey.com. This sheet has some formulas for choosing R and C values for astable operation on pp 7-8. As Tom found out, the outputs on this chip are kinda flaky : you have to buffer them somehow, or the circuit won't work right. That kit from Ramsey looks like a good way to go : by the time you hunt around for a the chip, a board, etc, you'll be up close to $10 anyway. And I'm sure they have more user-friendly directions. In the photo, you can see a transistor that they use to buffer the output; they claim 100 mA, which should be plenty to power a relay. Since the circuit is really all analog, it's gonna change its behavior with changing temperature. I would guess that the ratio of off to on time will stay pretty constant, but that the frequency will drift some. If you're just blinking lights or something, though, it shouldn't matter. Oops, can't attach the pdf file. try : LM555 |
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Posts in this topic
Mueller OT: 555 timer... need a hand with Astable settings :) Oct 2 2006, 04:05 PM
Tom Mueller,
If I remember right you find time in ... Oct 2 2006, 04:24 PM bd1308 thats why it may have helped to put the output int... Oct 2 2006, 04:47 PM
jkeyzer Hey Mike,
The 555 datasheet has a reference circu... Oct 2 2006, 04:58 PM Mueller google and ye shall find :)
555 timer calculator.... Oct 2 2006, 05:26 PM davep Some of the datasheets are flakey also. I forget w... Oct 2 2006, 06:46 PM |
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