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That's assuming that you can get exact values, 99% of the time that just is not going to happen. Why do you need this 1Hz oscillator? Are you making a clock or something?
The 1hz oscilator Colin post will work, it will also only be approximately a second and useless over any moderate length of time. If you need an actual time base of 1 second the easiest way to get it would to to use a small isolation transformer from the mains supply and run that through some logic, power companies have to keep very precise frequencies to match power, while there will always be some slight variation here or there the main frequency over time is quiet accurate, many old school clocks used synchronous motors powered from mains,.
Divide by 60 counters would work much better in this situation. All of the digital clock kits I've seen us a 32kHz crystal that then gets devided down to a 2Hz signal or a 1Hz signal. That would be better if the device had to be portable.
We didn't say you couldn't, we said that it will be vary hard if not imposible to find a resistor that will match your calculatios exactly. As a result the frequency will be off very slightly but that deviation will be noticed over time.
We didn't say you couldn't, we said that it will be vary hard if not imposible to find a resistor that will match your calculatios exactly. As a result the frequency will be off very slightly but that deviation will be noticed over time.
Notice they didn't say "with enough precision to keep accurate time", or anything like that. So basically, we have no idea what their exact requirements are.
So to me, the best answers, lacking further information, are those that gave the answer by giving circuits and component values. If you thought that you couldn't answer the question as posed, not knowing what precision was required, then the thing to do would have been to ask the simple question, "what kind of precision do you need?". But nobody asked that, did they?
By the way, the other best answer, rather than point to one of the hundreds of circuit sites out there in Web-land, would have been to post a link to the 555 datasheet, which, surprise! has the answers to all these questions and more.
Thanks for the schematic. That was exactly what I needed. It didn't have to be seconds exactly but within that time frame. One thing that still puzzles me is how those resistor and capacitor values match up with 1Hz according to f = 1/(.693 * C * (R1 + 2R2)). Also I noticed that your 5 pin is not connected to anything. According to wiki diagram it should be connected to 10uF capacitor. Is that wrong or what?
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