Re: One shots, timers, etc
From: Terry Pinnell (terrypinDELETE_at_THESEdial.pipex.com)
Date: 01/28/05
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Date: Fri, 28 Jan 2005 15:21:14 +0000
vanagonvw@gmail.com wrote:
>I have a question about one-shots, multivibrators, and other like
>devices, if I may be permitted.
>
>I am a somewhat familiar with a number of one-shots and timer such as
>the hc123 and hc4538 for short pulses, and timing, but I am in need of
>something that can give me a timeout pulse for up to five minutes. When
>I look at the data sheets for these devices, I am not sure where I need
>to check to learn if the device is stable enough for a pulse that long,
>and if a simple R/C network can accomplish what I am hoping to provide.
>
>
>The question will be, how accurate? and I can only say that it must be
>as accurate as I can make it, and still make it affordable, so that is
>why I am wondering where on the datasheet I can find such information
>so I can understand my options.
>
>Are these kinds of chips going to be the right approach, or is there
>another way I should be accomplishing this long of a timeout with some
>degree of accuracy?
>
>I will need to select five timeouts, from one minute, through five
>minutes. I thought about using a dipswitch to choose between five
>different RC combinations. An idea for something more elegant would
>certainly be appreciated.
>Thanks for the space and the consideration.
>
>John
I'm afraid I'm going against the tide here. Unlike the professionals,
I think a 555 circuit with a 5-way rotary switch sounds fine!
You haven't been explicit about the accuracy, but the 555 itself is
capable of 1%. With a low-leakage electrolytic as timing capacitor,
and reasonably careful construction, you could expect close to that in
practice. Here's a circuit to do what you specified:
http://www.terrypin.dial.pipex.com/Images/555Mono+Reset.gif
-- Terry Pinnell Hobbyist, West Sussex, UK
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