Long duration timers - Notes for beginners

[(*steve*)]

(*steve*) submitted a new resource:

Long duration timers - Notes for beginners - Tips for beginners on long duration timers.

One of the many things I've seen pop up time and time again is people's requirement for timers with periods of many minutes (or very low frequency oscillators). Often a 555 is mistakenly suggested.

1.0 Long period timers and low frequency oscillators

It is quite common to require a circuit to time long periods, or to supply a very low frequency signal.

The problem that many beginners don't realise is that the same techniques (RC oscillators of various descriptions) used for audio...

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[Arouse1973]

(*steve*) submitted a new resource:

Long duration timers - Notes for beginners - Tips for beginners on long duration timers.



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Steve
Audio up to 100KHz is that for bats?
Adam

 

[Harald Kapp]

Steve,
how about adding "555" somewhere in the title? I guess very many people will see the 555 as the prototype timer IC. Putting this number in the title will help them identify the thread as useful.

Harald

 

[mgrass]

(*steve*) submitted a new resource:

Long duration timers - Notes for beginners - Tips for beginners on long duration timers.



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The easiest way to do a long timer and most accurate is to use a uController. I use Arduino pro minis. just using millis() will give you a 24day timer. Add a loop counter to the program and you can go up from there. 10 times through the loop and you have 240 days. You could also use one of the timers and set up an interrupt to trigger. Much more accurate, more reliable, and easier to set for a certain "long time!"

 

[Gartmorn]

As good an excuse as any to invest in a microcontroller. They're so cheap now it's worth giving them a go even if you're a novice to the mysteries of programming like myself!

 

[(*steve*)]

Hahaha, in some cases a bare uC is cheaper than a 555

The intent of this was to address issues with RC circuits for long delays, but I'll agree that a uC solution may be well suited in many cases.

in addition to what has already been said, the uC can use an analog input to read the position of a pot and use that to vary the delay in a way that mimics an RC oscillator. And if you want to get fancy it can also drive a display to tell you what is happening.

 

[Paxee]

For a long-duration timer, you should consider the 4060 IC. It combines circuitry for an oscillator (using external R and C) with a 14-stage binary divider. For asymmetrical output
decoding several stages with some external gates should do the trick. And, being CMOS, its current drain is very low.

 

[(*steve*)]

after checking, I had mentioned both the uC and divider options.

 

[dorke]

Let me add here about the
"progress made regarding the good old 555"

There is the ICM755 CMOS version which is far better in any aspects including long duration timing signals.
It is available from several vendors like:
Intersil
NXP
Maxim
The best of the bunch (at least on "paper" should be the ALD7555

You should be able to get frequencies between 0.1Hz to 1Mhz
and time periods more than 10sec long.

Although, in general,
I would prefer the "digital synthesize of long time period interval signals".

 

[(*steve*)]

Very good comment. The CMOS devices address one of the concerns but not the other.

The input currents may be far lower, which allows lower charge and discharge rates, but this does not directly address leakage in the capacitor.

However it may allow the use of smaller, lower leakage capacitors. Even this doesn't eliminate the problem because the input impedance of CMOS may again become significant, and even leakage across the board may poke its ugly head in.

But sure, there are improvements to be had here.

 

[kooth]

For a long-duration timer, you should consider the 4060 IC. It combines circuitry for an oscillator (using external R and C) with a 14-stage binary divider. For asymmetrical output
decoding several stages with some external gates should do the trick. And, being CMOS, its current drain is very low.

I found this circuit and use it: It is awesome:

http://hackersbench.com/Projects/1Hz/​

I needed a countdown timer for a game -- it needed to count down from 30 seconds -- this works great and it's cheap to build!

 

[peterlonz]

"Notes for beginners" Not so sure this is an adequate set for the beginner.
I had to read all the comments, which I found rather more helpful, particularly the general view that a micro controller provides a low cost & optimal solution.
I would still like to know which mc meets those requirements.

 

[dorke]

@kooth ,
What " game"?
Is this a software game on a "platform" like PC or Smartphone etc. ?
If it is you can generate any timing you need via software.

Looks like there is no real requirement for accuracy,thus a crystal osc. solution isn't a must.

 

[dorke]

@peterlonz,
Some more points are:
1. Is there a need for a variable "time interval"'or is it fixed/small number of different intervals ?
2. What is the accuracy required ?
3. Is there any uC/uP in the system? If there is,using it is the cheapest way to go.

 

[Harald Kapp]

the general view that a micro controller provides a low cost & optimal solution.

What is optimal in one case is sub-optimal in another case. A microcontroller requires programming which some people may not be happy with.

I would still like to know which mc meets those requirements.

(Most) any microcontroller can do the timing. Which 'requirement' do you mean? Cost? Size? Ease of use? You have many parameters to play with and for any set of parameters you'll be able to find one or more fitting controller(s). As dorke states, using what's already there is the least expensive way to go.

 

[Pieter Kralt]

"Notes for beginners" Not so sure this is an adequate set for the beginner.
I had to read all the comments, which I found rather more helpful, particularly the general view that a micro controller provides a low cost & optimal solution.
I would still like to know which mc meets those requirements.

Some years ago (jan. 2011) elektor published an article comparing the 555 and an ATtiny25. The 555 should be (almost) obsolete. In a reaction on the forum (http://forum.elektor.com/viewtopic.php?f=180995&t=1697715) I compared the 555 with a PIC12F629 or a PIC12F675. Both the Atmel and the Microchip micros can replace a 555 in a lot of situations. (But not always!)

petrus bitbyter

 

[dorke]

The 555 is very much alive and kicking.

It still has a long way to go before being obsolete.
I think it will be around for as long as people are willing to use it,
that may be for decades...

 

[Pieter Kralt]

The 555 is very much alive and kicking.

It still has a long way to go before being obsolete.
I think it will be around for as long as people are willing to use it,
that may be for decades...

I fully agree and I told why in the elektor topic mentioned. But as that is in Dutch ...

petrus bitbyter