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Knowing that 555's behaviour varies according to temperature, I wondered:

In an astable configuration, is there some way to measure output frequency, compare it with some desired value, and use this to change the resistance in the config? (Basically a feedback loop)

This would be very useful, to create precision square wave generators.

I'm sorry if I couldn't explain myself correctly (the question sounds really bad when I read it but I'm struggling to express it correctly).

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    \$\begingroup\$ If you already had a precise way to measure the frequency you probably wouldn't need the 555 to begin with. Using a crystal oscillator, possibly with temperature control, is the way to get a precise square wave. \$\endgroup\$ – Elliot Alderson Jun 4 at 19:13
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    \$\begingroup\$ What analogsystemsrf is how we did thinks in the 1970s when there were no DDS chips yet. Now we would just get a DDS, the AD9850 is affordable and there are modules with that chip with an interface you can hook to a uC. Trying to use a 555 based oscillator and "stabilize" it simply isn't worth the effort. \$\endgroup\$ – Bimpelrekkie Jun 4 at 19:52
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    \$\begingroup\$ Also: if you want to learn about "precision square wave generators" then do some research into the subject. How many designs use a 555? ZERO. Says enough. The 555 is nice and very useful but not for anything precise. \$\endgroup\$ – Bimpelrekkie Jun 4 at 19:54
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    \$\begingroup\$ @Bimpelrekkie I've yet to find a use case where the NE555 is "nice and very useful". I keep coming across things that can be nicely explained by using a 555, but not a single application that wouldn't be easier to prototype at lower part and usually way better performance using the cheapest microcontrollers. But, alas, Iaka knows the 555, which is imho it's main strength: it's a nice introduction for many many people to analog electronics! \$\endgroup\$ – Marcus Müller Jun 4 at 20:09
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    \$\begingroup\$ @MarcusMüller Indeed I should have written "The 555 is nice and very useful for beginners to get started with electronics without any programming". The 555 is also nice to explain the basics of IC design (get the free ebook from: designinganalogchips.com ). Sure a uC is a better choice for a product but I see far too many people thinking that making a blinker with a uC is "real electronics" while they're basically just programming a uC. \$\endgroup\$ – Bimpelrekkie Jun 4 at 20:26
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In an astable configuration, is there some way to measure output frequency, compare it with some desired value, and use this to change the resistance in the config? (Basically a feedback loop)

Sure, thats relatively easy, but it requires that you have something to compare it to Ie. to check whether your output signal is actually let's say 100kHz, then you need a signal which you already know IS definitely 100kHz, and if you already have that then why create it in the first place using a 555 circuit?

All absolute measurements come from comparing the thing that you are measuring to a known standard. In the case of for instance multimeters measuring a voltage they will have inside them a voltage reference, which has a well known, well defined voltage across it which you can compare the voltage that you are measuring to.

In the case of a frequency counter it will have a well defined frequency standard inside it which generates a constant well defined frequency which you can compare the frequency that you are measuring to.

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  • \$\begingroup\$ But maybe you get a numerical value or some other output type when you measure the frequency and compare it with its desired value... For example, measuring the frequency using a microcontroller and comparing it that way. \$\endgroup\$ – Iaka Noe Sep 16 at 23:29
  • \$\begingroup\$ ????? You realy dont seem to understand the point i am trying to make. the only way to get a numerical value representing the frequency of the output of your 555 is to compare it to a known frequency. In the case of a microcontroller what you would use to compare the frequency to would be the clock frequency og the mcu. \$\endgroup\$ – Vinzent Sep 18 at 4:19
  • \$\begingroup\$ never denied that... Still not answering my question \$\endgroup\$ – Iaka Noe Sep 18 at 4:21
  • \$\begingroup\$ Okay then I don't understand your question."But maybe you get a numerical value or some other output type when you measure the frequency and compare it with its desired value..." How would you get a numerical value representing the frequency? well you could count the number of periods, but then you still need to divide the number of periods by the time you count them over, so in other words we are back to the fact that you still need an accurate source of timing, ie. a frequency standard, in order to measure a frequency.. I am not sure you understand what my answer is about. \$\endgroup\$ – Vinzent Sep 18 at 16:42
  • \$\begingroup\$ then give me some method to achieve that lol, in my example I would compare it with the timer of my uC but I was looking for some (maybe analog) method \$\endgroup\$ – Iaka Noe Sep 18 at 19:14

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