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adc using 555 timer

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jeyes56

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Hi,

I would like to know if it is possible to convert an analog to digital signal using 555timer, i guess i can only generate 1bit but it is okay,,

this is just a simple circuit for us to understand how analog signal converts to a digital signal is our class,
 
The 555 circuit generates a pulse train with the pulse-width proportional to the input voltage.

A simple comparator (LM139) is an A/D with a one-bit static binary output. You can use three of the comparators with three evenly spaced threshold voltages (1V, 2V, and 3V, for example) and some simple logic to do a 2-bit A/D.
 
Hello,

If you are going to use a micro controller chip anyway then you dont really need a 555, you can use a comparator instead, or perhaps a comparator on the uC chip itself. The idea is to build a Delta Sigma A to D converter.
 
Hello,

If you are going to use a micro controller chip anyway then you dont really need a 555, you can use a comparator instead, or perhaps a comparator on the uC chip itself. The idea is to build a Delta Sigma A to D converter.

But all this is a bit 1970's :D

What's wrong with using a processor with in-built A2D?.
 
Hello Nigel,

Well for one, it sounded like he wanted something similar to that so i thought i'd mention this.

Second, there are advantages to using a SD converter. There's a little more to it than i care to get into here, but for example:
https://en.wikipedia.org/wiki/Delta-sigma_modulation#Why_delta-sigma_modulation.3F

Third, many uC chips only have 10 or 12 bit AD while sometimes higher resolution is needed but not much speed.

I've mostly used the built in ADC's in uC's myself but strongly considered SD converters for some apps. The SD converter is not yet ancient history.
 
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The op wants a simple circuit to demonstrate and understand A/D conversion. A built-in converter or the rather esoteric SD converter would not seem good candidates for that .;)
 
Well, the SD is a simple converter, in fact that's why it's used for various things.
 
Well, the SD is a simple converter, in fact that's why it's used for various things.
I've worked on the design of SD converters and they may appear simple, but the theory behind them is not. If you want to understand A/D converters that's not the place to start.

Edit: The SD is not used primarily because it's simple, it's used because it's capable of an accuracy exceeding 20 bits, which no other type of converter can do.
 
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It's simple and cheap, it's as simple as that. Look around on the web.
The theory isnt that hard either i dont know where you got that idea from.
 
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It's simple and cheap, it's as simple as that. Look around on the web.
The theory isnt that hard either i dont know where you got that idea from.
I have looked around the web. It's used primarily where you want low frequency, high accuracy conversion.

As far as theory (for example here), it may be simple to you but it certainly is more difficult to understand than other common converters such as flash or successive-approximation. My point is, it's not a good first example for someone trying to learn about A/D converters. ;)
 
Hi Carl,

Well although you may have a point there dont we have to consider that he was starting out with a 555 for an AD converter? Wouldnt that be a somewhat similar way? Or maybe you are saying that is too hard to understand too...in that case i would go for the simplest which is a voltage divider and set of comparators. But it appeared to me that he wanted to understand the way the 555 does it or similar, but then other people started suggesting other converters.

If it's the simplest possible converter than i would say a resistor divider and set of comparators, but that is gong to be nothing like how the 555 works for A to D.
 
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Hi Carl,

Well although you may have a point there dont we have to consider that he was starting out with a 555 for an AD converter? Wouldnt that be a somewhat similar way? Or maybe you are saying that is too hard to understand too...in that case i would go for the simplest which is a voltage divider and set of comparators. But it appeared to me that he wanted to understand the way the 555 does it or similar, but then other people started suggesting other converters.

If it's the simplest possible converter than i would say a resistor divider and set of comparators, but that is gong to be nothing like how the 555 works for A to D.
Well, I understand where you are coming from. It's certainly true that a SD converter is more like the 555 converter he mentioned (but still significantly different) than other types of converter architectures.

I was going by his statement "this is just a simple circuit for us to understand how analog signal converts to a digital signal is our class," so I was suggesting the simplest circuit I know of, a flash converter.

So I guess it's rather a matter of how you interpret that statement.:)
 
Hello again,


Yes and that is what it comes down to in many cases like this so it doesnt pay to be too critical about some posts :)
 
The 555 (or any comparator) can be set up to make a digital pulse width that varies with the reference voltage or a digital frequency that varies with the reference voltage.

I'm not sure if "analog to digital converter" is the best term to describe them though?
 
Hi MrRB,

In all of the material i have read they do consider them to be A to D converters, and yes that is a little strange that it takes a uC chip to work with it to actually produce any real usable results. So even though it may be a pulse width or pulse train there's still only one intended use, either convert to a 'word' or to transmit, both of which would be considered 'digital'.
 
I suppose that PW or PF modulation can be considered "digital" but I tend not to think of it as digital until it is converted into a series of digital binary words. The output of most commercial A/D converters are such binary words.
 
Hi Carl,

Yes, but think about it this way for a moment...

If you were to transmit that signal over some medium (such as two wire or fiber optic cable or even to make pits in a disc) when you looked at the signal with a scope you would proclaim, "It's digital".
 
Hi MrAl,

That brings up a sort of philosophical question. If say, a pulse is directly pulse-width modulated with an analog signal (without any discrete steps e.g. the width is an analog function) then is the information contained in the pulses in analog or digital format? Obviously any noise that affects the pulse-width will corrupt the signal, unlike a "pure" digital signal where pulse width and pulse amplitude noise do not affect the encoded data (as long as you can still distinguish a 1 from a 0).
 
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